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AR226-2671 61 AR226-2671 SOIL COLUMN LEACHING STUDY FOR PFOA Date: August 2004 Project No.: 507423 18983990.04006 CORPORATE REMEDIATION GROUP An Alliance between DuPont and URS Diamond Barley Mill Plaza, Building 27 Wilmington, Delaware 19805 1.0 STUDY PURPOSE & PRINCIPLE A soil column leaching study for perfluorooctanoic acid (PFOA) was designed by DuPont to determine the vertical mobility or leaching of air deposited ammonium perfluorooctanoate (APFO)/rainwater mobilized PFOA through clayey silt and silty clay soil. This leaching study will begin in 3Q04. Unpublished studies conducted by DuPont have indicated that APFO in air emissions is deposited as a particulate material on the ground surface. These particulates are dissolved in rain water and carried through the soil column as PFOA. The principle of this testing is to subject natural soil columns, approximately six cm diameter by thirty five cm in length, to defined periods of artificial rain. APFO will be dissolved in a small volume ofdistilled/deionized water and applied to the top of the soil column. At regular time intervals, artificial rain will be applied to the top of the column and the leachate draining from the column will be collected and analyzed to determine PFOA concentration. In addition, after the leaching process is complete, soil samples from the column will be sampled from various depths within the column and analyzed for PFOA. The test method used for this soil leaching column study is derived from Pesticide Assessment Guidelines Subdivision N, Chemistry: Environmental Fate, Series 163: Mobility Studies (EPA-540/9-82-021; Appendix A) prepared by the Environmental Fate Branch, Hazard Evaluation Division of the Office of Pesticide Programs in 1982. 1.1 Study Objectives There are two main objectives of this study. The first objective is to evaluate the leaching behavior of air deposited APFO/rainwater mobilized PFOA in silty clay or clayey silt. The second objective is to provide data for estimating the leaching potential of PFOA, including determining and verifying the following parameters: Q retardation factor Q percent adsorbed/desorbed Q mass balance 1.2 Materials and Methods The protocol for this soil leaching column study is described in Research Methods in Weed Science (second Edition, 1977), Truelove, B. (eds.) in a paper by Weber, J. B. and Peeper, T. F. (see Appendix B). The paper by Weber and Peeper (1977) is a recommended reference in EPA-540-9-82-021. A 1986 edition of Research Methods in Weed Science includes a revision of the 1977 paper by Weber and Peeper. The same soil leaching column protocol is presented in the 1986 paper by Weber et al. along with very clear figures showing details of the setup that were not included in the 1977 paper. The Weber et al. (1986) paper is included as 08/24/04 Page 1 SoilColumnStudy.doc Appendix C and the figures referred to below are from this paper. In the following sections, the soil core acquisition and soil leaching study procedures are summarized. 1.2.1 Soil Core Acquisition There are two major types of soil columns used to investigate leaching behavior in soils, natural soil columns and hand-packed soil columns (Weber et al., 1986). For this study, natural soil cores will be used. The natural soil columns will be obtained from the Holocene floodplain at the Washington Works Site. Ideally, a location that has minimal PFOA impact to soil will be selected. Analytical data from the site and the results from air modeling conducted at and near the site will be used to determine potential coring locations. The exact sampling location will be determined following a field visit and the sampling location will be marked with flagging and surveyed. Soil column collection will be documented with notes and photographs, if permission from the site is obtained. The core acquisition procedure, as described by Weber and Peeper (1977) and Weber et al. (1986), will be utilized. However, the procedures may be modified as necessary based on actual field conditions. Any modifications to the soil core acquisition procedure in Weber and Peeper (1977) and Weber et al. (1986) will be documented in the report issued following the completion of this study. It is anticipated that nine soil cores will be collected from the sampling location, six for laboratory testing and the soil column leaching experiments and three for future use, if required. At the coring location, the surface conditions will be photographed and described in a field log. For soil core acquisition, nine sample tubes ofpre-cleaned, schedule 5 stainless steel sample tubes (approximately six cm diameter by 35 cm long) will be used. The bottom edge will be sharpened for ease of soil penetration. The stainless steel sample tubes will be driven 30 cm into the soil using either a driving block and a sledgehammer or the weight of a backhoe bucket. All nine sample tubes will be driven into the soil immediately adjacent to each other. The soil surrounding the sample tubes will be exposed and described to a depth of 30 cm. Soil surrounding the sample tubes will be sampled on five cm intervals (0-5 cm, 5-10 cm, etc) to a depth of 30 cm. Each of these samples will be homogenized in the field and each sample will be submitted for moisture content, total organic carbon (TOC), pH, clay content and texture analysis. Each sample tube will be removed with the soil core intact, taking care not to disturb the soil core in the bottom of the pipe when removing the pipe from the ground. The top and bottoms of the sample tubes will be marked on the outsides of the sample tubes. The ends of the sample tubes will be packed with glass wool, capped and sealed with tape to prevent disturbing the soil cores during shipment to the laboratory. The sample tubes will then be sealed in individual plastic bags and shipped to the laboratory in an upright position. In the laboratory, five of the nine soil cores will be prepared for use in the column study. Three soil cores will be stored in a cold room for future use, if necessary. The remaining soil core will be used to obtain soil samples that will be analyzed for background PFOA concentrations. Soil samples from this core will be 08/24/04 Page 2 SoilColumnStudy.doc collected from five-cm intervals the length of the column (0-5 cm, 5-10 cm, etc). Each five-cm interval sample will be homogenized and sampled for PFOA analysis. 1.2.2 Test System The soil leaching procedure described by Weber and Peeper (1977) and Weber et al. (1986) will be utilized for this study. However, this procedure may be modified if needed. Any modifications of the procedure in Weber and Peeper (1977) and Weber et al. (1986) will be documented in the report issued following the completion of the study. The five soil columns will be preconditioned by wetting the columns thoroughly and allowing them to drain overnight to field capacity. The wetting solution used will be a 60 uM CaCk solution made from deionized water. Figure 1 (in Appendix C) from Weber et al., 1986, shows a cross section of a natural soil core leaching system using a continuous saturated flow. This study will use the same setup but with saturated/unsaturated flow. Three different volumes ofAPFO, equivalent to application rates of 0.05, 0.1, and 0.2 kg/hectare, will be dissolved in a small volume of distilled or deionized water and applied to the surface of three of the soil columns. The fourth column will be used as a duplicate for the soil column in which the mid-concentration ofAPFO was applied. The applied APFO in solution will be allowed to equilibrate with the soil prior to beginning the leaching process. In the fifth column, no APFO will be applied to the surface of the column. A nonsorbing and nondegradable polar reference substance, such as sodium bromide, will also be applied to the tops of the five soil columns to determine breakthrough point. Prior to initiation of the leaching study, glass wool will be placed on the top surface of the columns. Artificial rain (the 60 uM CaClz solution made from deionized water) will be applied to each of the five columns, using an application rate of approximately 1.6 cm/column/day of artificial rain. This application rate is slightly higher than the recommended rate of 1.2 cm/column/day of artificial rain but is the volume required to generate approximately 50 ml ofleachate per application, the minimum volume required for PFOA and tracer analysis. Leachate will be collected daily, 24 hours after the application of the artificial rain and prior to the subsequent application. Leachate will be submitted to the laboratory once a week and analyzed on a batch basis. The column study will be considered complete when the. concentration of PFOA in the leachate has returned to a non-detectable amount or has leveled off to a constant concentration. After the final leachate sample has been collected from each column, the leaching apparatus will be disassembled and the soil columns will be removed from the column and divided into five-cm intervals (0-5 cm, 5-10 cm, etc.). The soil from each 5-cm interval will be homogenized and analyzed for PFOA. 08/24/04 Page 3 SoilColumnStudy.doc 1.3 Analytical Methods PFOA concentrations will be determined in the following media: Q solution used for preconditioning the five columns Q solutions containing various amounts of PFOA used to spike the four columns Q artificial rain applied to the five columns Q leachate from the control column that was not spiked with PFOA Q leachate from the four columns that were spiked with varying concentrations of PFOA Q soil samples (0-5 cm, 5-10 cm, etc.) from the five columns used in the leachate study after taking the last leachate sample from each column Q soil samples from one column (0-5 cm, 5-10 cm, etc.) not utilized in the column study In aqueous solutions, PFOA is extracted from water using Cig solid phase extraction (SPE) cartridges. Analysis is performed by liquid chromatographytandem mass spectrometry (LC/MS/MS) using selected reaction monitoring (SRM). Quantitation is accomplished via external standard calibration. For soil samples, the samples are mixed with methanol, sonicated, centrifuged and filtered. The methanol extracts are analyzed by LC/MS/MS. A known quantity of the labeled compound PFOA-di-13C is added to every sample and to the batch quality control samples prior to extraction. Because the isotopically labeled compound is chemically identical to the compound of concern, it is affected by any interfering substances in the sample to the same extent, as is the compound of concern. 1.4 Data Analysis and Reporting After all of the results of the analysis of PFOA in leachate and soil have been obtained, the data will be analyzed. Following data analysis, the testing procedures, test results and data interpretation will be documented in a report. 08/24/04 Page 4 SoilColumnStudy.doc APPENDIX A PESTICIDE ASSESSMENT GUIDELINES SUBDIVISION N CHEMISTRY: ENVIRONMENTAL FATE (EPA-540/9-82.021) 07/07/04 TOP 18:09 PAX 703 308 1850 U.S. BPA.OPP.FEAD.GISB 12)002 EPA-540/9-82-021 October 1982 Pesticide Assessment Guidelines Subdivision N Chemistry: Environmenitai Fate Prepared by Staff of Environmental Fata Branch Hazard Evaluation Division Office of Pesticide Programs Guidelines Coordinator Robert K, Hitch Hazard Evaluation Division Office of Pesticida Programs U.S. Environmental Protection Agency Office of Pesticides and Toxie Substance Washington, D.C. 20480 07/.07/04 WED 16; 09 FAX 703 308 18SO U.S. EPA.OPP.FEAD.GISB 64 Series 163; MOSlliin? STUDIES 163-1 aeach^pq an4 adsorption/qaaorBtioa^ steadies. (a) Pusrpoae. "Eha laoveinaat of pesticide residues by aeana of laaching through the soil profile ox transport to and dispersion in teha aquatic eixrizoameni: wiy causa contaxainartion of food, result in loss of uaable land and water resources to man doe to con-fcaaiination of groundwat&r suppliesj of causa habitat loss to wildlife; Therefore, laboratory studies are z-aqoired to predict* (1) a&e leaching potential or pesticides and their degradatoes through the soil profile at tezreaferial sites t and (2) Tha wavewsnt of .pesticides and thair dagradates to and dispersion in aqpafcic sites* (b) when requirftd. le&ahing oz absesrpfiion/deeoi-pfclon data are required by 40 CFS 158 to support; the registration of an c;a<3use product intended fox' dcaeaUc outdoor u$e, greenhouse use, terrestrial noncrop use, orohard crop una, fi,6ld-'vegefcare"orop use* foreiatry use* aquatiio use, and aquatio impact uses involving diract diachargea of treated water- into outdoor aquatic sites* Such data are also rwyilred- to. support, each application foe registration of a Banufacturing"uae product whichi Bay legally be usad to make such aa end-use product:. See, specifically, 40 CfR 158*50 and 5 158*130 to dateraine whether these data ntust bo submitted. Section ZI-A of this Subdivision contal-ns an additional discussion of the "Fonnulators' axcaiption" and who must submit the ffequifed data as a general rule. (c> Test standards. leaching ox' absorption/desorption data submitted in response to 40 CTB. $ 158,130 should be derived, frctt testa which comply with the general test standards in 160--4 and all of the following specific test standards! (1) Teat aubstaace. Studies shall be conducted using' each active ingredient in the product* (i) If xadiolsotopic analytical tachniquss are- usad. (they are preferred), studies shall be conducted with the analytical grade of each active ingredient in the product; (ii) Xf non-radioiaotopic analytical, techniqnea are used* studies shall he conducted with the technical or purer grade of eagh. active ingredient in the product. ^ (2) Test grocaaaga. <i) Analytical technigue-selection, a laboratory study should be conducted to provide a quantitative estimate of pesticide mobility in soil or abaorption/deaorption on sediments* 12003 ,07/07/OjLJffip 16:09 PAX 703 308 1850 y.S. EPA.OPP.FEAD.GISB 1,, 0004 S5 (ii) amount of test substance* An aaiounf of test substance equal to the highest zeoooaended rate for a single application of the pefcicidal active iagradiisait should be added to fche soils/sediment utilized, in these studies. (iii) Soil selection. Bach study should include, at a miniiitua, four foils, finch as sand (agricultural), sandy loam, silt loam, clay, or clay-loam, each having a pB within the range of 4-8. if However, the pesticide is -toa ba limited to use with one specific soil type, them. the soils selected should include than specific j if soil type" In addition, the pesticide is intended fox an aquatic ! use oe for an aquatic impact we involving direct discharges of treated water into outdoor aquatic sites, batch equilibrium '(adsorpfcion/desorption) studiaa on one aquatic aadifflente obtained from or rapre!entativa of the proposed use area should be provided* (A) At least one of the soils selected, should have an organic matter contact less than or equal to one percent (gand or sandy loan preferred) (Bi Opa of the soils should be the soil used zdr 162-1 (aerobic soil etaboliam study). This soil preferably should be a, j aandy-loam soil. Ihia soil shall ba used to study leaching- of i pesticide degradatea. (iv) grepagateton of soil for Btuay^ofjaeatieide degrad&tes. if the test substance should be aged wider aerobic conditions for-30 daya or one naif-life (whichever is shorter) in tba soil selected in paragraph (o)(2)(iii)(B) of this section. The trea-ted soil should be maintained at a constant' temperature between 18 and 30c. The fcemperaturB ohoeen shall be the easae as that selected in the aerobic soil irotabolian study 162-1) that study is also required. The treated soil should be maintainad at a soil ntoistura content of 75 percent of 0,33 bar moisture content during the aging period* At the end of the aging period, either a portion of the i j aged soil containing the pesticide and ita degradatea or extracts J obt&ined. from the aged soil should be tasted by one of the methods i set forth belowi (A) The extract may ba tested on soil thin layer chrcnaato- : graphic (tifl) plates aa required by paragraph (c)(2)(v)(A) of this section; or (B) The portion of aged aoil nay be added to the prepared soil columns aa requi-cad by paragraph '(c) (2).(v)(B} of this section; or j 07/D7/04 WED 16;10 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB (C) Alternatively the mobility of individual degradates which have been dooonRfcratea independently to oacar in soil after tha aging parted speoifiad ia paragraph (o)(2)(v) o this section. (v) analysis methods. For terrestrial nono:i''op usea, orchard axojp va6a, -field-vegetable crop usaa, and forestry usies, the mobility of the teat aubatanca and ita degradatea ia aoil should be assessed either by soil thin layer ebroaiatogsaphy, soil colT.am, ov batch . equililuriua (adsotfption/desor.ption) procedures dascaribed below ia W, paragraphs (B), aad (C), rsaipeotivsly. Itoir domestic outdoor uses, gcaanboucie uaaa, aquatic uses, and aquatic impact usea, the mobility of tHe fteg-fc. substance and ita degradafcea in sail shall be asaeaaed only by the ba^oh equiliBriixn {adaorption/iissorptiQn) peocadura. Mhataver ps-ociedura ia gelected must be followed for all soilg atudiedo (a) Sojt.1 thin-layer chromatocg^phy (1'Ig) atmay. Soil I!LC studies to predict the ieachingr potential of peatiaides and theiz degradabea in soil should be perfoWtad as follows: TIC plates should h g^eparad wBiag tha soils described in paragraph {c)(2)(iii) of this saction^ to which both the tat substance (parent pesticide and degradates) are applieds ftpplioa-fcion of reference pesticide standards on each 'ELC plate in addition to the teate aubstanca is regu-Lrad, to assess the xela^ive mobility of tha test substance to that of other paaticides yhoae lehOfatQEy a&d field leaching behavior ia already fcnovna Tor eapsEiaicntal procediixea on soil and plate preparation, pefitieide application, plate developaent, pesticide visualization and Rt calcniiationat see reference <1)(ii) of paragraph (a) of this section. (B) Soil column gtiidvo Sail column studies to define the vertical distribution of the test substance and its degradatea in the soil profile should, be pecfozned as follows: The column(s) should be from 30 to 300 cm in height, consisting of soils described in 1631(e)(2)(iii), and should be elutead with a volume of water equal to [groundwatec rsahae^e values of] 20 inches {50*8 cm) tifflas the oross sectwnal area of this coliann. A distribution curve of the teat substance in tba column shall be determined by quantification of the test aubstanca and its degcadates in 6 en segmeats and in the elua.fcaa Par experifflental procedures on conducting- pa asraogirlapcholu(men) ostfutdhyi,g gseeecrteiofner^ences (1)(i), (iii), (iv) and (v) of (C) Batch equilibrium {aaaor&tiQn/desorpfcion) study* Adaorp" tion/desorption coefficiantg calculated from a batch aqullibriu.m study are used along with solubility data to predict the extent or depth of pasrticide leaching in tha diff<rent soil typea tested, and also the eatenfc of pesticide adsorption/deaorption on sediments when aquatic off aquatic iagaot. uses are proposed. 'Bha afcudy aboiLLd be conducted using the soils described in paragraph (c){2)<iii) of this section, plus oaa representative aauatio sediaient (if an _01/(7m_ TOD 16llfl_FAI 703 308 1850 U.S. EPA.OPP.FEAD.GISB 87 Ifaquatic or aquetio impact Qde involving direct discharge is proposed) "Eha test subatanoB inoluaing its dagradatsa iaantifisd, in and extracted from th aerobic soil aetabolism sifady { ia2-1> should, ba equilibrated, with fchs soils and aqaatio sadiaient aalactsd for this ataidy ah four coaosnteationa inaO.OiaiorsaCa ion solution. necaaaary, a an&ll amount of acstono off other solvent may be used to achieve sot-i^-ioo o goodly solubia; j?aaticides as: dAcfradatas foff exp^riinantal prociaduraa 00 condi.'-ating btech aquiiibrivm (adsorption/desorption) atuaieSi, iacluding calcula-kicn at Kd va-Luas see refesepcas (3)(i) tlu-oiagh (aii) and (4)(ii aad (ii) of jparageash (e) of this s^ifftla-a, (d) Reporfciaq aad a^aluation Q dafcao la addi-tion 'so tha applicable resportincr aaquleisitenfca apacisi&d ip. i60'3, the test report should contain VSaa follotfLng a^sci-fic iiafoeiaation; (1) S^oil fcKia jAyer ehgeaflatogg-agby {gs^c}a 'sh aobilitty of posticidea and teheif degeadatas ahoald he Kspairtad as nobility clasa 1 to 5ft coes-gagonding to s valuea o^ OoO to 009 [inanobila (olaqa 1}]* 0,10 to Oo34 Eicw '(claas! 2)],, 035 to 0<>e4 [intXfflediata (CKMW 3)], Oe65 to (1.39 taobile (olass <S)1, end 0,90 to 1Q [very ttobilB (olaas 5)3, ^"aagac'tivelyu Values of soil/wsitar a-alc.tionships (K^) ahould bQ zepoeted using appropziatQ Sf to S^Q/K^ aquations &eaaiple5 of calaulaeioQ^ usad in ctetaniiininig a^ valusi3 should be ' provided* .' . (2) Soil _t!oluian atgdy^ Valuiaa o aoil/ssateE'rala'cionahipa (K^) should bs rspayted fos the ^aafc autosfcaaca and its dagradatea using appropriate e<auat,iono Bxattplea of calcula-fcions used. to determining K^ vaiuaa should be pffavide4 (3) gatch attUiljbgiqai ^adSQj'Cltion/deaQgBtiQp) study* .Sdaorp" tioo/deeoirpfcion data to ba ffepoited should iaclude conceatirafclons of the taafc subatanca, iaolzidin? its deg^adatas, partitioned between soil and watee asa calculated aa Ka valaaa faroa ths concentrations if using apgropriat aqpatioaa Sos oalttulafciag smch valnfts the ?reundlich equation is uaed, euanples of calculations for 1/n and K values should be provided. (e) Sefegenoaag SD Th* following rafarences contain eaqasiriaental procedwaa w aoB4ueting inobility (leaching) studies s (i) Qrover ll 1972. ttebility of dioantfca, ticlorain and 2,4-0 in soil coluniaao Weed sci, 232l59~ie2a (This papor con^ares It leaching rataa using soil coluinna and aasorptioo paramatars for several aoil-sNSatioide combinations,. illustrates that theories relating adsorption and wyveiaaa.t can be verified with soil columns and the resulting data can be irelafcad 'to fiald Movements.] 07/07/04 TOP 16 ill PAX 703 308 18SO U.S. EPA.OPP.FEAD.GISB @007 68 (ii) Belling, C3 1,971 a festiaide mobility in soils* X chBottateograpliyo Soil Sci .goo. aimac., JTOO* Swwakws of 35s 732-737. thin-layer [iMs paper discusses the ugefclaesa o soil thin-layer ohromatography and details enfpetflioental parameters.3 (iii) Knooinsici, Sofo? C.KB Smickett,. and i7.0. ELsher. 1975. cofflpoanda in the enviroiaaents Bate of micxobicidal 3-isotaiaaolone and rates of disaigationo Jo Aqr^ good Chgnto 23il060-1068 modes (This pagar contaifla a prooedusa for a coLuzaa leaching study-I (I?} XiichbeasfcelBf SoS's S*R. Sctiula and loWa Puluesmann. and Sate of dyfonate in soils mOss leacihing and 1972. Mwenent Sa &iggo Foed Chea. 208831-838, [Botia (ac ' nanodnleraacdhioin-gtraccoenrdiattoinoanalyslls*oews wilols-o-egutszsadt,ioinn focffhisdiSatSue<Seygn'taittyhp^fiaadoiof-ldaebgeraUng in ta> poaitAona and bheix movemant in soils] dation products it (y) WbeSt >T.o, isattd 5'aS'. POdpsr, 1977. ae^bicide MoMUty in Soils. ?p 73-79 ^ ftese&eeh Mefchods in raised Sciancs. B> Second Edi-closio aubm-ti Prin-ting, "fouelonre (d). S tfeed Scij ftabuen, Alabama, (IMa soc pap^r grovidea a brieZ tout daaoriptive ne foe fcha study ss hezbicida leaching in analysis of aoil, and. ptfocedwee discuasaa the two wjca fcypsa of dolmms used fox these studies 0 (2) ttw following 3eEnces contain a^ppleiBBn'cal infoiinafcion, pertaining to mobility atwiiaat (i) Bailey, <a,Va, and JaXr Whites 197Qu of pesticides ia soils* i'gctoz' influencing the Residua Rgv. 32i29- 1 ' adsorption 92. [This and mwwsao.t is a good general rwiew discuaaing pitfalls to be aware I of in planning or inter^x-etation of leaching experiinen'ts.] ! (ii) Hamaker, JaW., and J.Ma "!"hofflpsott 1972. adaonifcion. l>p. I 49-143 j^ organic Chenioals in the Soil Bainakar <eds)<> Marcsl EnviraniRfen'fc Dakkez-i inc., 7ol< I C.A.I How ^ok I . Goring and ('[his ia a J*W* basic review o the tbaoicatical foundation of pesticide addesriovrepdtiocnonosntasnotsilsc,haanrdacatnereizxicnegllepnetstsicoiudrecesofiotz-adesqourapt-iboinon?a andIhethatables o data Bfty aid in initial range-finding..] (iii) Leistca, Ml., and WoA Dekkers. 1.976, computed, effects kinetics on pestioide movement in soils. J. Soil geio of adsorption 28:340-350 [This is a theoretical paper that may be useful for interpretation of leaching studies, ainoa it illustrates tha importance of rainfall pattern with respact to pesticide leaching.] 0710^04 WED 16:11 PAX 703 308 18SO U.S. EPA.OPP.PEAD.GISB ^ 68 (iv) Iittistra M,, J.J Smelt, and B. Zanvoort. 1975. Paraistaace and mobility of broBacil in orchard soils. Head Res.. ISs177-181, [This article ia raconuaended for those planning and interpreting pesticide leaching exparameatsi Zt reports that the leaching of a peaticida In field eKpesriaenta was substantially lower than pacsdicted by calculation froa results of soil-OTiC experiments.1 (v) Xiindsts'onin P.. To, L. BoerafflSt ARd ? Sfcockard* 1971- A theory on on the mass transport of previously distributed chemicals in a water saturated sorting porous medium; isothermal cases. Soil Sci. 112s291-300. [This papar presents a theoretical model fox predicting pesticide inoveBant from adsorption data and flow rates.] (vi) Oddson/ J.X., J. lieteey, and li.V. Weakso 1970o aradicted distribution ox organic ohaaical in eolation and adsorbed aa a function of position and tiai for various chaical and aoil properties' Soil Sci. SQC. anegii 344l2417. (This papea* .jprgaanta a theoretical"Biodel 'for the movainent of peaticidea in soila*] (vii) Van Qenuch-ten, Hoi!., P.Jc. wicenga, end G.A. 0'Connor. 1977 Mass transfer studies in sorbing media; XXX* experimental evaluation tdAb 2^A,5-T Spi.l^Sci._Sc<? .'uaag.v 4i;27a--285. [This paper peasants cctapariaons of model calculations and experiiaental it oatar ama, may be ucerul for planning or interpretation of leaching sxperiinents.] (3) Tha following raferenceg contain experiffiental proeadures for conducting adaorption/desorpteion attidieaii (i) Aharonson, a, and u. Kafltafi. 1975. Adsorption, mobi lity and gwc3istenca of thiabendazol and methyl 2-benzimidazolecar"' bamata in soile. J. agr. rood Cheat. 23s720-72A [The techniques iuid methoda used in this study are useful for both adsorption/d Qsor&tion and leaching studies.] (ii) by soils farmer, W.E'., and Yo Aochia 1974- picloraia sorption Soil Sci. 3oca Aaer. Proc. 38s4l8-423. [(tethoda of adaorption and. deeorption-can be found in this study<J (iii) cover,. R*,, and R.J Hance. 1S70. Effect of ratio of Boil to water on adsorption of linuron and atKazine. Soil Sci > 109(136-138. tThia paper presents information on the soil-water ratio to be used in laboratory studies of pesticide adsorption to soils. I (iv) Hamaker J.w.< C.a.I. (Soring, and CR. Youngaon. 196ri Sorptioa and leaohing of 4-afflino-35,6"trichloropiaolinie acid in soils" Advances in, Chemistry Series 60;23-37. [She techniques and ffiathods used in this study are standard except for the ti-ffle allowed for equilibration. 'lha data presented demonstrates the 07/07/04 WED 16:12 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB 70 ftwrt. u pH on adsorption ft in iooired apAcioa and the Lnvw And <dorplo(.] flaftionahip bcMn partition Qoelfflciene (v Kanca, R.J. 1.967. Th pgd o. attainment o{ aorption i-nvoiving hrbicidc. Haad n 7(29-36. qoAlibriA in aoa ayacaaa [lilia study Uluawacaa ;h< uao of cany* finding ftxswrlMnf to aquilibraeion fciaa foe Braniiiqful adiorption n<l dof9tion (xp<rtBWtt xpwrliwnu' and u o{ find an tachniquej niindLiah tw darpeion isothrm Are preMineod in Shis pap<sc.] il- (vi) Harvfty, U.S. 1974. Soil adsorption and volatility of Ala*taroBilUatlictdea. <Md Sei. 22i 120-124. t0i ot &boiy eion icofchefoa (or cha caJLculafclon of latent hue of adBoepe.l.on nd the affect o odaorption oft volatility of paaticidw &ra lUBtrated iA this paper*] (vii) Leistra. rt,, anpdesc.Aie<idoeEkixoavream*nt1i9n76a. oiClaom. puJt.edSoffil cSfceal. o adsorption Itinfttiea OR 28i340-150. Clhia id a siaulabion ot pesticide bohavior on 80il3 in &tr tiel-d by capuer.l (viii) texstri, it., and W.A. Doldeers. 1977. tfiae'fics of pft3ticidas In soil. J. Soae modal* (or Environ Sei. tha adaocptidn iMIth l2(2);a5-l03. [Thia continuation of the W6 pApc (ahov) 4J.euea the aultiiMch&nisa, niilcixate phanoaen& cespanaible {or the d&fifnfnces obaenrBd in rates of adsorption and ratea o dcaotpcion.1 (ix) lur^ay, 0.3,, ?.a. Santttliaann, and J.M. aavidaon- 1975. COBpacacive adsorption, deaeirption, and nobility oC dipeooetryo and ero--tEyn. iji soil. J. Aar* good chea. 23:S78~S82. (Tha corraUtion becwaen adsorption, sation exchange capacity, organic iAattr aad clay coaeeftt is -llustrated in thig paper, and adsorp tion/desoeption is comparad uith soil TLC experinents.] (n) Saltaaan, S , L. iU-iger, and B. Yacon. 1972. Adaorpeioi. [ daaorption of oayathion as aifeofd by soil organic natter, J. Agri. UI/ Pood Ch. 20; 1224.1226. [The importance of organic Bttter in absorp" '', cion o pestici.daa toy soil is dxacuasad in thia report.] (xi) savage, U.S., and R.D, Wauchope. 1.974. FXiiocaeturon ad- j I ao<pt.i.oi/<it3orption oqailibria in soil. weeds 22:106-110. [This papAr diseuases equationa used for compiitation of adsorption iaotheBwe and provides inforaation for tquation selection for quantitativ* depiction of acaorption and desorption.l <xii) wu, C.H>, t. auaaring, J.M. Oavidson, and ?.W. Sanfcclaann. 1 j 1975. SapropaadLda adaorptica, deaorption, and moveiaanfi in aoila. WMd Sci. 234S4457. '.Colusa leaching and soil Tic exyecinents conduetafl and rtjaorted her re correlatBd with adaorpcion/deaorpteion experiaenu*] 07/.07/04 TOP 16:12 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB 71, (aiii) (Reserved fors OBCD Guidelines for Tasting Cheaicala. 1, number 106 adsoypttion/Desorption.} Section (4) The following references contain, supplemental informa tion for developing protocol for adaorption/desorptioa studies: (1) . Sailay, G,V,, and JoL. White. 1970. factory influenc ing fche adsorption, <aorption, and moveaKsnt of pesticides in soils. Residue Rev. 32s 29-92. [This raview provides background information on th principlaa underlying the processes of adsorption and nobility of peatioidaa in soil 9] (ii) Weber, J*B. 1977. Soil Properties, Herbicide Sorption, and Model Soil ayatwn" fp- 59-72 in Research Methods in Weed Science- 2ad Sd* s. Weed Scio Soca B> Tnielove (ed) auburn Printing, Xno. Auawmf Ala* [This is a general review of experi mental methods for detecoination of aoil properties, herbicide adsorption, and construction of ainple model soil systems.] 163-2 Iiaboratoey volatility^atjadieg^ (a) Purpose. Volatilization can be a major mode for the move ment of pesticides from treated areas The vapors resulting from, Tolatilizatioa of soiaa pesticides can cause adverae effects to nan . via inhalation exposure at sites of application or biological effects in nontarget organisms at acme distance from the treated .site* The Agency ia particularly concerned about commercial green house applications involving intensive use of volatile pesticides, use patterns nih.ich .are characteristically involved with oonniodities having high economic value and high labor requirements? aach uses can result in significant inhalation eicposure to workers and appli cators*' ' ..'...-;.:" ' ' > " 's' (b) When required., ' (1) .Data-'from a laboratory volatility study are reguirad.by.40 ,.0?R 5, 158 on a case-by-oase basis to support the registra^ijsn of .each -ena-uae product intended for coannaroial greenhouse';, orchard* or fiald-yegatable crop usea that involve significant inbalation'-exposure* to''worker a. Data from such a study are also reo;uirad to support each application for registration of a fflanufao.turing-use' product which may legally be used to foiaaulate such an.and-uae product. See, specifically, 40 Cra 158.50, 158.130, "arid.'tha following discussion in 163.3-2 (b)(2) to determine whether these data nmat be submitted, section U-a, of this subdivision-contains an additional discussion of the "'fonnulatora' Exemption" and who oust subnii't the required data as a gnecal rule. ' > (2) ''"ha agency will evaluate the following information pro vided by the registration applicant to make att assessment of what constitutes a significant inhalation exposure to workers; 07/1>7/04 TOP 16;12 PAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB BlOll 72 (i) Vapor pressure at 25BC and water solubility of subdivision the 0); pes ticide active ingredient (H 63-9 and 63-8 Qf (ii) Soil adsorption coefficient intended (^) of the application test ait aubatanoa (S 163-1 uaing the soil froa a typical of this Subdivision); (iii) Soil characteristics, including noisfcare content, at the intended site of application; <iv) Method, rate, and intervals of pesticide application? (v) TeaperatuBef humidity, and air flow rates at the site of application? (vi) Ventilation sequences or practices for commercial green" hous applications? and (viil Inoillation toitioity of the pesticide ( 81-3 aAd 82-4 of Subdivision P). (3) 'line data regBi:s'Beot8 of this section nay also be satistied by data produced fronk a study that aeets tae test standards contained in 163-3 (fiald volatility studies). <a> response with tir specific Test standards. Laboratory volatility data aubiaitetsd i& tgoen4e0raOlS'Sf.ast 1a5t8aon2d6aaa-hdsouilnd be 1d6e0-r4iveadndfraolml otefstthsewfooiollhowcoinmgply test standards: (1) Test substance. and-uas product 'She teat substance shall be a typical (i) If tha applicant"a product is an end-uae formulation product, the is typical of test aubat&nce shall be a product whose the formulation category (e.g, wettabia powdery amalsiiiabia concentrate, wettabia powder) to which the product belongs. (ii) If the applicant's product is a inanufactwi&g-use product make an end-asa product for which which legally could volatility data are be used to requirad, the teat substance shall be a product includes that representative of the (Xf major formulation category which the manufacturing-use product is usually end-use product* end-uae products comprising two or more major formulated into formulation categories, a separate study must be perfomed with a typical end-uae product for each such category.) (2) Teat^proceaare. A laboratory study should be conducted to determine the actuiil rate or extent of pesticide volatilization conditions only for those pesticides frott soil under controlled with uses the agency considers pose a potentially significant .07/0.7/04 WED 16:13 PAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB 73 inhalation, exposure to workers. applicants may omit. the laboratory studies and prfoca a greenhouse and/or field study instead. (See . $ 163-3.) (1) Laboratory experimental conditions should represent, to the extent possible an envimnine&t whare the pesticide is interred 01: uae* (ii) "Eha rate of teat-substance application to soil should approximate the intended rate of field usage. (iii) the following factors should be addressed in designing a laboratory volatility study; (A) Properties of the pesticide such as vapor pressure, and watar solubility, whiob can influence the trapping medium and air sampling ratesr (B) propartioa relating? to the soil, such as adsorption to soil and soil texture, to avoid untoward reduction of the rato of volatility (e.g., sandy noil is praJi'erred) j (C) Environmental factors, 3uch as ai-r temperature, humidity, and movement, to avoid untoward dehyocration or flooding- of the soil, and to assure efficiency ox sampling. (iv) Mr samples should bs collected and analyzed for residues in the laboratory experimental aqiiipman-fc used. Monitoring' should be conducted continuously or at intervals which increase with time after tha start of the experiment. Monitoring should continue until the nature of the residue decline curve has been clearly established. (d) Reporting and evaluation, of dataj In addition to th basic reporting requirements specified in 160-5, the test report should include the following specific informations (1) Volatility data expressed as ug/cn^/hour; (2) Air concentrationa expressed aa ug/m3 or aig/a3? (3) vapor pressure expressed as torr (or the equivalent ex pressed in'other conventional units)? (4) Temperature and relative humidity; (5) A description of the soil used; and (6) & description of the laboratory test equipment used. ^^ _07^?7/04 WED 16:13 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB 74 (e) References. (1) the following references contain laboratory studies of pesticide volatility; information. in these payees could be useful for protocol development t (i) Kearnay, B.C., and. A. Kontaon. 1976* A simple system bo simultaneously measure volatilization and metabolism of pesticides troni soils J. Acrr. good Cheaa 24a 424-426. [& polyurethane foam Map and a potaaaiw* hydroxide trap were used to recover sequentially the parent compound and degradation product from air.] (ii) Spencer, WF< and M>M CXaith. 1974* E'acCorB affecting vapor lose of triflwalia. Eron soil. J. agr. Food Chaa. 22; 987-991. [The laboratory ufchod8 usad for detennining volatilizatloa of ohaoioala used in this study allow aieasuremenfc of effecta of several vaciablag. Ifae use of hexane as a trapping medium limitg the gas flow ratea and voluaas that can be used* I (iii.) Spencer tfaFx, 1'*D. Shoup, MM> Cliath, W.J. E^naar, and R. Baque. 1979 a Vapor pressure and relative volatility of ethyl and methyl paxathion* Jo Aqr Food Chain. 27t273-278 [Polyuaretehane foaa traps aad GI-C detection largely spacific for the compounds of intexext ware used her<s. Specific detection avoids interference that may cause falsely high vapor Iwels in field tasting'] (2) Volatilization studies* req^ira asthoda for tetae trapping, extraction', cleanup, and guantitation of pesticides* A review of reported methods for laboratory investigations of pesticides in ai? can be found ins (i) Lawic, R.G. 1976. Sampling and Analysis of Airborne pesticides* Pp. 51~94 in Mr Bollution from Pesticides and agri cultural Processes* RE Lee (ed.)* CRC press* Inc. Cleveland, Ohio* (ii) [aesefved] S 163-3 Field volatility studies. (a) Piufpose* Volatilization can be a major mode for the move ment of pesticides from treated areas The vapors resulting frem volatilization of some pesticides can cause adverse effects to man via inhalation exposure at sites of application or biological effects in nontargat organisms at some distance from the treated site* The Agency is particularly concerned about commercial green house applications involving intensive use of volatile pesticides, use patterns which are characteristically involved with commodities having high economic value and high labor requirements; such uses can result ia significant inhalation exposure to workers and appli cators 07/07/04 TOP 16:13 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB 75 (b) Tjtoen reauired. Data fron a volatility study conducted and/a? in the field will be on-aite in a conoexcial gxeenhouae 40 CFR 158 on caae-by-caae basis only for those requited by pesticidea that tb Agency considers pee a potentially significant $ 163-2 (b)] and, based on the inhalation results ot exposure to workers [aee the laboratory study described i.n 1S3-2, that also aigaifleant rate of damonatrata, tn th opinion of the Agency, a x<m soil* See, apsoiflcally, 40 CKR S 158.30 and volatilization 5 158*130 to datenaiae Aethw these data must be wibnittad. additional discussion of Section the II-& of this Subdivision contains w and who oust submit the esquired data. &s a, "goCTnila.tora11 Exemption" general rul (c) 'gast standards. Fieldbve odleartiivleidtyfrdoantatessutbamwittheidchincoraeipsly ponse to 40 CTR 158.130 should tfisfc atandRxds in $ 160-4 and all o th following with the geaaral specific test standards: . (1) Test anbatanca. ale test subatanca shall be a typical and-usa sceoducto (i) Zf the applicant's product is foaanaeuniadt-iuosne. pisrotdyupcitc, atlheof ts subatanc; ahall be ft product whose the fommla-fcion category (ft9r wftttable powdw, enulaifiable ooncentx'atQ; granular product) to which the product bolonga^ (ii) Xz the applicant's produacnt iegnda-umseanpurofadcutcutrinrog-ruswehipchroduct that legally could be used to aalMi volatility data are required, the test aubatance shall be a product representative of the product. major fozmulation category which includes (If the end-use products th&t could be made that end-use the manufaisturing^uae product belong to two or oore major from formulation categories, a separate study must be performed for each such category,) plied (2to) a ^ssitset wprhoicehediusretay.pic(ia)l oTfhoeneteostf tshuebsataitnecse stohowuhldichbethaep product would b applied* ,y. (ii) the test aubatance should be applied to soil at the rate and by tae awthod stated in the label directions for the pesticida. (iii) The following factors should be addressed in designing a greenhouse or field volatility studys (A) Properties of the pesticide such as vapor-pressure and water solubility, which can influence the trapping medium and air sampling rates? (B> properties relating to the soil, auob as adsorption to soil and soil texture, to avoid untoward reduction oe the rate of volatility (a.g., sandy soil is preferred); @014 .07./07/04 WED 18:14 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB g,,,^ 76 (C> environmental factors, aaob aa air temperature, humidity, and Movement, to avoid untoward dehydration ox' flooding of the soil, and to assure efficiency of sampling. (iv) Air samples should be monitored foe residues at. treated sites t iatenrilg which increase with tima after pesticide appli cation* For example, tha following aohadula of sampling tines Blight be appropriate o? sotte situations! 6 and 12 hours, 1, 2, 4, 7 14 and 21 days- Sanpling should be continued until the nature of the dissipation curve haa been clearly established. (fl) Reporting and evaluation of data. 2n addition to infor mation meeting the basic reporting requirements specified in i 160-5, tha teat raport should include the following specific information; (1) Volatility data expressed as g/ha/day? (2) air concentrations expressed as vug/a3 as ng/a3; (3) Vapor px-sai3X expressed as torr (ox the equivalent expressed in other cowvanfcional units);: and (4) Metarologic conditions (teiaperature/ relative humidity, wind velocity and dicction< aad cloud cover) duri-ng the tiae of the field study. (e) aeferencea* (1) The following references contain aup- pleaental infonaation fox' developing a protocol to conduct field volatility studies; (i) Ciiath, M.Mt, W.Fo Spencer, H.J* Farmer, T*D. Shoup^ and R. <3rover 1980. Volatilization of s-ethyl MyH-dipropylth.l.ocarbainate froal watar and wet eoil during and after flood irrigation of an alfalfa field. J._ age. good chen. 288610-613. [This is a well-designed end wall-executed field study of volatilization with aiaiultanaous study of other flodea of dissipation of a pesticide.] <U} Harper, !,*&, &>Wo lAiite, <7r*, R.Ra Bruce, AW. Miomaa, and R.A* Leonard. 1976a Soil and iaiorocliate effects on triflu-calin volatilization* J Environ. Qual. 5;236-242. [Sthylene glycol vapor 'traps and non-specific QliC quantitation were used in this study. The influence of water in soil and thus rainfall during the study on volatilization of pesticide are illustrated as acre effects of wind, turbulence, and temperature.] (iii) Paraele, IrH., Efl. Lemon, and A.W. Taylor.. 1972. M4-arontaorological inaaaursaBent of pesticide vapor flua croia bars soil and corn under field conditions. Water, Air, and goiljpolluta " 1*433-451. [This study used hexylane glycol vapor traps and sampling periods adjusted to compensate for decrease in pesticide vapor .07/07/04 WED 18:14 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB ra^g Tl concnu*acion during ctr <iudy. fftleid* vapor flux (;< aoil wa eoleuXMud Ad fUtwd eo l<:xotocolo9iol iMwufu.] {iv) J0dcquit, C.J., O.Q. CXQby, X.W> ftoUurn, sf.H. Ssitrr, and ff.K ttoodxaw* 1975. oceotfifACf of txiflurjiin and le< phaeo- pfoduca In lr. J A<rr. rood ChM. 23i304-9a9 (Alhouqh efti* afcudf conownad with pbotalyia of plcid in jir, thr preowddf la thic s--pwx tor (Mur&iraMwc o( volfltiliaation off patici4 ftai oiL*l (3) Volatiliwicion uli rquir aachodj for tir trapping, witeacteiOB. olttiiup, md qojuic.lfcatlon of pttBtitfidef. A rvlaN of rapoEtad aaehodf for eiid invtigatioa* of p*Bfcicida In air <saa be eound iA: (A z^via, R.G, L7fi* SMpling md Anlyi of Ufbocna geateicideg. Vy, 51-94 ^ Air Pellution Cvou. 9fcj.cid4 and AgricuX- Ifcutfal grocasw. R.E. IM (wl<). ac Pra, inc. cXcv},and. Otiio. (i.i! [Saawved] / ./. f,' APPENDIX B HERBICIDE MOBILITY IN SOILS (WEBER AND PEEPER, 1977) CHAPTER 7 HERBICIDE MOBILITY IN SOILS JEKOME B. WEBER Department of Crop Science, North Carolina State University Raleigh, North Carolina 270)7 and TOM F. PEEPER Department of Agronomy, Oklahoma State University Stillwater, Oklahoma 74974 Pase INTRODUCTION......-.-------------.. .--.---__--._.-.-....---..-.-....-.--.--..-.-...--......74 DESCRIPTION OF METHODS---.-.-.-...--------.---------.----------.---...--..-74 APPARATUS, CHEMICALS, AND OTHER MATERIALS -....--------...----..-----.----74 NATURAL SOIL COLUMN METHOD..................................................................------74 HAND-PACKED SOIL COLUMN METHOD..---------.--.--....-...-.-..--.------..75 PREPARATION AND USE OF COLUMNS.----.-...---.--.-..---.------.-------------..------75 NATURAL SOIL COLUMNS....--......................................................................................75 HAND-PACKED SOIL COLUMNS.................................................................................75 Solid Columns--.....---.-----.-------.--.....--.------.---.------.-.--..__--------....75 Stacked-CvUnder Columns..--.....................------.--.....-.....--..--------......_.----..75 Split Columns__...----_.,,--....,,_------.------.------.----_-.__------76 APPLICATION OF HERBICIDE-..._-_----....-.------..,,_.._.___.-.-_--.76 PROCEDURES FOR NATURAL SOIL COLUMNS--...---..--.--..__----_--------.76 PREPARING THE COLUMNS---.--------..----...-------.--------------.--.--------.76 APPLICATION OF WATER......--.-.......----.---------------------.--..--.----------76 REMOVAL OF SOIL...--...------..--.-..------..-.-------------.-------._--77 PROCEDURES FOR HAND-PACKED SOIL COLUMNS--.....-.__-------...--.--_77 PREPARING THE COLUMNS----.......--......----._----.------...__.-----------77 APPLICATION OF WATER-.----------.....------..........._------......_--..__-.77 REMOVAL OF SOIL.....--.---...---------------.--.-..------.----.-------..----.77 LITERATURE CITED...----....---....---.-.--------.-.--.-----.--------------------..-.-..78 74 HERBICIDE INTRODUCTION The relative ease with which a herbicide moves vertically in soil is important in determining its efficacy, suitability for use as a placement selective herbicide, and potential for contaminating ground water or drainage effluent. Movement of a herbicide in soil is dependent on several factors, includ ing intensity and frequency of rainfall (19), soil properties (2,3,8,12,13,15,16,20), and herbicide properties (1,9,18,22). As researchers have continued to investigate the leaching of specific herbicides under conditions relating to specific soil or cropping situations, a proliferation of variations in equip ment and procedures has occurred. These variations have made it somewhat difficult to interpret the movement of herbi cides through soil (22). Several investigators have quantita tively described the movement of herbicides through soils using computer and conceptual models (4,7,14), and the mass-balance approach (2). Several methods for measuring relative herbicide mobility in soils have become generally accepted as standard state-of-the-art methods. They include the use of soil columns (4,5,8,9,13,18,19), soil thin-layer plates (10,11,12,22), and soil thick-layer trays (6,22). The soil thin-layer plate technique utilizes a soil matrixapplied to a glass plate as the supporting medium. Herbi cides are spotted onto the plate in a manner similar to that shown in Figure 1. One end of the plate is immersed in a small amount of water at the bottom of a closed glass cham ber. The herbicides move up the plate and are separated according to the principles of ascending chromatography (see Chapter 10). The technique is relativelyrapid and the results are comparable with those obtained in adsorption studies, al though of an inverse natuare; i.e., immobile herbicides are strongly adsorbed and do not ascend the plate, while highly mobile herbicides, which leach readily, are not adsorbed and move freely (12). The thin-layer plate technique also offers the advantage of allowing one to compare several herbicides at the same time under identical conditions. The thick-layer chromatography technique utilizes a shal low tray filled with soil and placed in a horizontal position (6). Herbicide is applied to the soil at one end of the trav and one end of a cloth wick is placed on the herbicide-treated soil, the other end of the wick is placed into a dish of water. Water ascends the wick and diffuses into the soil carrying the herbicide along. This technique has one distinct'ad vantage over the thin-layer plate technique in that the soil is deep enough to allow for a plant bioassay after the herbi cide leaching has been completed, as shown in Figure 2. Figure 2. Bioassay showing the movement of fiuomehuon sandy soil thick-layer chromatographic tray [Wu and' Santelm,,,,' The soil column technique is somewhat slows than u. thin-layer and thick-layer techniques but it does t ave seve features not present in the others: (a) soil colun ns may 1, used with field moist soils or soils at specific moii hire leve'' which is preferable to using dried soils; (b) natuni soil cor, may be obtained or surface soil and subsoil may be placed" columns simulating soils in their natural state; (c herbicin, leaching under saturated or unsaturated flow con< itions studied; (d) soil columns may be readily m^ disassembled be i permit the taking of serial samples for chemical and radio chemical analyses and plant .bioassay; and (e) herbicides be applied to soils in soil columns and allowed to m;i decompw. under near natural conditions before they are leiched, (hi providing data on both parent herbicides and netabolitc (21). This chapter describes methods for measuring the rel.. live mobilities of herbicides in soils using soil coll mns. DESCRIPTION OF METHODS Basically, there are two major types of columns used i investigate the leaching behavior of herbicides in soils: (; natural soil columns, and (b) hand-packed soi colimii., Three types of hand-packed soil columns are used, dependin; upon the kind of soil assays to be performed after the lead. ing is completed. They include; (a) solid columrs (in son" cases holes or slots are cut into the columns to aic in renioi ing the soil or to allow for bioassays to be carriet out whe: leaching is completed), (b) stacked-cylinder coi imns, an. (c) split columns. Figure 3 illustrates these vario is kinds r' soil columns. APPARATUS, CHEMICALS, AND O^HER MATERIALS' Figure 1. Application of herbicides to soil thin-layer chromatoeraphy plates (courtesy of Dr. C. S. Helling, U.S. Department of Agriculture, Beltsville, MD). NATURAL SOIL COLUMN METHOD (A motorized, truck-mounted, column-driving be useful if available.) Columns (7 to 30-cm diam by 30-cm long steel pipes) Hardwood driving block Sledge hammer Shovel Plastic bags Marking pen Cardboard box mit woulii ^alvaniw : HERBICIDE MOBILITY 75 Filter paper disks Glass wool JBuret,500 to 1000-ml Erienmeyer flask, 1-L Funnels (same diam as columns) Brass screen (same diam as columns) Teflon-lined tubing Plastic tape Deionized water LND-PACKEU SOIL COLUMN METHOD jColumns[9.5-cm (inside diam) by 30-cm lengths of polyi vinylchloride (PVC plastic) pipe, threaded and capped j on one end] |Soil sieve, 2-mm 1,2-cm drill bit Tubing connector Marking pen Silicone sealer Vortex-type mixer Teflon-lined tubing Buret, 500 to 1000-ml Filter paper disks Quartz sand Deionized water Spatula Plastic tape Glass wool Saw PREPARATION AND USE OF COLUMNS FLASK BURET WATER HEAD FILTER PAPER- NATURAL SOIL CORE C-GALVANIZED STEEL PIPE, 14 GUAGE ^surface 50)1 -PLEXIGLASS TUBING /GLASS WOOL., FUNNEL TAPED - Y TO COLUMN BRASS SCREEN STOPCOCK subsoil A. -FILTER PAPER- -PLEXIGLASS CYLINDERS s -PLASTIC TAPE- BE IZ S TO. GLASS WOOL BRASS SCREEN B. /LONGITUDINAL CUT -PLASTIC PIPE NATURAL SOIL COLUMNS Seven to 30-cm diam, 14-gauge galvanized steel pipe is cut into sections 30 cm long. A 1,5-cm steel rim is welded to the top of each column for reinforcement. The bottom is sharpened for ease of soil penetration. A brass screen is cut to fit flush with the bottom of the column (see A of Figure 3). If columns of less than 23 cm diam are employed, it would be desirable to use the divided-bottom technique of McNeal and Eeeve (17). This technique provides a column withina-column and reduces boundary-flow errors resulting from water and lierbicide moving down the walls. The soil must be removed from this column and transferred to plastic bags for chemical analysis or to small pots for plant bioassay. HAND-PACKED Soil- COLUMNS Each of the following columns is fitted with a plastic pipe cap (see Figure 4). A 1.2-cm hole is drilled in the center of the cap and the hole fitted with the female half of a tub ing connector packed with glass wool (see Figure 5). Solid Columns Solid columns, 30 to 40 cm long are cut from plastic pipe and threaded on one end. Since the soil must be removed from the columns for bioassay or chemical analysis, the col umns should not be longer than 40 cm (see Figure 3.B.). Stacked-Cylinder Columns SoltiaKc-ak-ecdu--cuyyliilnuduecri ccuoiluuimnnnss are prepared fnrom daeessiirreeda lie--n.--gtthi-s- o-rf p--lia.-s.-ti"ic- p_i-p_e w-.itih- p- ipe cap at,.tach1 edl . mThe pipe is S c. D. '"TO 3. Mafor types of soil leaching columns: A. Natural soil p using a solid column. The scheme demonstrates the set-up " for saturated flow studies (B, C, and D are hand-packed soil mnns). B, Simulated soil profile, where surface soil and subsoil i added to the column in the position in which they occur in natural state. The scheme demonstrates the set-up used for tturated flow studies. C. Stacked-cylinder soil column. After ^"ing, the cylinders may be separated and assayed indepen,'y. D. Split soil column. After leaching, the column may be 'oed vertically to provide two continuous half columns, one "loassay and another for chemical or radiochcmical assay. Figure 4. Soil leaching columns, with split column feature, hi position for herbicide leaching. Note white silicone sealer at joints and tape used to hold column halves together. 76 HERBICIDE MOBILITY Carefully remove the soil column from the eartii, place j( a plastic bag, and stand it upright in a cardboard box i transport back to the laboratory. If longer columns are ii sired, it will generally bs necessary to use a pipe with a d ameter smaller than the recommended minimurh of 23 , If columns of iesser diameter are employed, it is suggey' that the divided-bottom technique of McNeal and Reeve lf- be used. In preparing the column for leaching, remov' the ply,.;. hag and place a small mat of glass wool and a ?rass scr(' on the bottom of the column. For many studies i isdesh-al' to establish the columns at moisture levels a] woximatii" field capacity. This may be accomplished mo t easily i',' standing the columns in deionized water and app ring a sm' amount of suction to the top of the column (see 8 SSj'Slk we 6). ; " '"''-' Figure 5. Cucumber bioassay of split soil leaching column. The herbicide applied to the upper column was immobile and was re tained in the upper 4 cm of the soil column, thus only cucumber seedlings in the upper 4 cm were affected. The herbicide applied to the center soil column was very mobile and leached readily through the soil and out of the column. Herbicide which was retained by the soil was uniformly phytotoxic to the cucumber seedlings. The herbicide applied to the lower soil column was very mobile in the soil and leached readily, but was present at such high concentrations that it completely killed the seedlings throughout the length of the column. , ^ n n /'' TO VAJCUUM / \ ' '-FUNNEL ' APED TO (OLUMN then sawed into 5-cm sections and reassembled by placing the sectior.s together with silicone sealer and tape (see Figure 3.C.). Split Columns Split columns are prepared from desired lengths of plastic pipe, capped on one end. The columns are cut longitudinally, reassembled using silicone sealer, and reinforced by wrapping with tape (see Figures 4 and 5). APPLICATION OF HERBICIDE When possible, herbicide should be applied to the soil in s. manner analogous to that employed in the field. Herbicide may be mixed with water and applied to the surface or it may be incorporated into the top 2.0-cm of soil. In either case, the appliedherbicide should be equilibrated with the soil for several hours before the leaching process is initiated. When "C-tagged herbicides are employed, mix formu lated, non-radioactive herbicide and "C-tagged herbicide to provide approximately 5 to 10 jitCi of activity with the desired application rate per soil column. PROCEDURE FOR NATURAL SOIL COLUMNS PREPARING THE COLUMNS Select a representative site for obtaining the soil sample. Examine and describe surface cover conditions. Record the kind of crop and stage of growth, and any surface litter or mulch cover. Describe the surface soil conditions, freshly cultivated, cloddy, cracked, or crusted. Drive the 30-cm long steel column approximately 25 cm into the soil using the driving block and sledge hammer. Remove the soil from around the pipe to allow for easy removal of the column with out disturbing the soil at the bottom of the core. At the same time, collect soil samples in plastic bags, from various depths for soil moisture determinations. Examine and describe the soil profile at this time. Determine texture and soil structure and note any conditions that might influence water intake. SOIL wmfmfn-^ai 1----rn----'^PLATE TT --VORTEX 0 MIXER B B , t t ' jn BUCKET OF \ f WATER scafv. OKaua ] i 1 \S ^ -'-== A. B. Figure 6. Preparation of hand-packed soi [ leaching (olumns: A jnifonn packing of column by addition of small increr lents of soil nd use of vortex-type mixer, B. prewetting of soil coi umn by usr f subim'gation and gentle suction. APPLICATION OF WATER For saturated flow studies, use plastic tape to connect .: unnel to the bottom of the column and attach x piece <ii 'eflon-lined tubing and a stopcock to regulate 1 ow out of he column. (See A of Figure 3.) Place a glass wool mat 01 disk of filter paper on the surface of the soil i nd use an Srienmeyer flask filled with deionized water to naintain ;i 'onstant head of water at the soil surface. For unsaturated flow studies, tape a funnel to ihe bottom f the column as shown in B of Figure 3. Place a d sk of filter Mper on the soil surface and use a buret to regula ie the rate f flow of deionized water through the column. (A morr ccurate flow rate can be achieved by use of a nicropump nd time clock arrangement.) The amount and fn quency of vatering should be commensurate with the rainfill or uriation pattern for the area. Water may be applied to the columns by adding a specific mount (usually 2 to 4 cm) per day fo r a specifici [ time peiod (usually 30 to 45 days). At the end of thi" leachinp HERBICIDE MOBILITY od the columns should be allowed to drain and dry out a day or two before the soil is removed from the columns. 10 IMOVAL OP SOIL Some soils may be removed from the columns by pushing entire soil core out of the column with a wooden plunger ing a diameter slightly smaller than the column interior. h other soils, a sample must be removed from the soil |imn by use of a soil sampling tube (see Chapter 6) or ji a long handled scoop. The soil column should be di ed into 5-cm sections. Each section should be placed a plastic bag, thoroughly mixed, a sample taken and ked for chemical or radiochemical assay, and the. re nder placed into small pots for herbicide bioassay. ; PROCEDURES FOR HAND-PACKED SOIL COLUMNS ^ 14 12 - 77 ^"'~ '15 SPARING THE COLUMNS .Soil in these studies may be established at a specific soil jsture level by adding an appropriate amount of water to sample, mixing, and storing overnight in a plastic bag pre the soil is put into the columns. If it is desired to es- |ish columns at soil moisture levels approximating Beld scity, this may be accomplished by placing the columns in imized water and applying gentle suction to the top of the tmn (see B of Figure 6)'. |If a natural soil profile is unobtainable, a simulated soil pie can be a close approximation of the natural soil profile urring in the field. In using the method, soils collected n various depths are arranged in the proper sequence in \soil column, as shown in B of Figure 3, Three types of imns which may be employed are shown in Figure 3. The [1column, B, necessitates the removal of the soil from the tain for bioassay or chemcial analysis. The stacked cylin- ', column, C, allows for ease of separation of the various 'depths and analysis of the herbicide in each cylinder of isoil column. The split column, D, provides a continuous : column for herbicide analysis. The recently developed t soil column and bioassay system shown in Figure 7 is h a practical and simple system to measure herbicide (and fcr pesticide) leaching and bioactivity in soil. 'The sample of soil from each depth should bs sieved lugh a 2-mm screen, mixed, and uniformly packed into the columns. The soil should be used in field moist condition brought to a specified moisture level, as described pre- isly. Uniform packing can be accomplished by adding ill increments of soil to a column held in firm contact with trtex-type mixer set at a speed which has previously been id to result in the desired soil bulk density (see A of Fig.6). Uniform packing and consistent soil moisture levels required for obtaining reproducible results from leaching imns (23). When it is desired to compare herbicide movement (ugh a uniform mixture of soil, it is necessary to use n (ogeneous soil column. This technique permits compari! to be made between homogeneous soil samples taken '> various soil depths, and homogeneous soil samples repnting different soil types. The method is generally useful . pmparing the surface portion of cultivated soils down to j plow layer. In cultivated soils- the surface has been sub- tially disturbed and mixed by land preparation operations thus no longer has the characteristics of a virgin soil. soil is sieved, mixed, and uniformly packed into the soil inn a.s previou.slv described. 30 -' hf Figure 7. Herbicide soil leaching column and bioassay system. Two column halves (14) are joined together with silicone sealer ( I01* nng ^ aad a ""P " f111"!6! cap (12). Quartz sand is added to the bottom of the column on top of the screen (20). Surface soil (0 to 10 cm), and subsoil (10 to 20-cm and 20 to 30-cm samples) are added to the column to their respective sidcwall marks (15). (The molded marks also prevent herbicide movement down the sidewalk.) Herbicide is applied and the column leached with water applied at 1-cro increments (19). After 30 days of leaching, the column halves are separated, the side rails (28) at tached to one of the column halves and the end caps (24) snapped in place at each end. The cohnnn half is laid in a horizontal position. End plates (27) are installed to keep the soil in place. Soil dividers (29) are inserted into Ihe roil at 2-cm increments. Seeds of sensitive plants are planted in between each soil divider to bioassay for the herbicide at each depth. Insect boxes (25) are used to bioassay for insecticides when they are leached. APPLICATION OF WATEH The set-up for saturated or unsaturated flow studies or for adding specific amounts of water daily is the same as de scribed for natural ;.oil columns (see earlier section). REMOVAL OF SOIL Soil is removed from the solid column in the same manner as described for tlie natural soil column method. The stacked-cylinder soil column is disassembled by removing the tape at the joints, end cutting cross-sectionallv through the .soil core with a thin-bladed knife or sawing through with a piece of taut wire. Soil from each cylinder should be placed into a plastic bag. m:\ed, a sample removed and marked for 78 HERBICIDE MOBILITY chemical or rndiochemical assay, and the remainder returned to the cylinder for bioassay. Removal of soil from the split column is accomplished by removing the tape from the joint and cutting the column in two longitudinally. Soil samples may be rejinovedf, one of the half columns and used for chemuial or rad chemical assay. The other column half may be used f,,' bioassay of the herbicide as shown in Figure 5. LITERATURE CITED 1. Bayer, D. E. 1967. Effect of surfactants on leaching of substituted urea herbicides in soil. Weeds 15:249-252. 2. Best, J. A. and J. B. Weber. 1974. Disappearance of s-triazines as affected by soil pH using a balance-sheet approach. Weed Sci. 22;364-373. 3. Chapman, T., P. A. Gabbott, and J. M. Osgerby. 1970. Technique for measuring relative movement of herbicides in soil under leaching conditions. Pestic. Sci. 1:56-58. 4. Davidson, J. M, and P. W. Santelmann. 1968. Displace ment of fluometuron and diuron through saturated glass beads and soil. Weed Sci. 16:544-548. 5. Eshel, Y. and G. F. Warren. 1967. A simplified method for determining phytotoxicity, leaching, and adsorption of herbicides in soil Weeds 15:115-118. 6. Gerber, H. R., P. Ziegler, and P. Dubach. 1970. Leach ing as a tool in the evaluation of herbicides. Proc. Br. Weed Control Conf. 10; 118-125. 7. Gillett, J. W., J. Hill, A. W. Jarvinen, and W. P. Schoor. 1974. A conceptual model for the movement of pesti cides through the environment. Environ. Prot. Agency (U.S.), Ecol. Res. Serv. 660/3-74-024, 79 pp. 8. Guenzi, W. D. and W. E. Beard. 1967. Movement and persistence of DDT and lindane in soil columns. Soil Sci. Soc. Am. Proc. 31:644-647. 9. Harris, C. I. 1967. Movement of herbicides in soil. Weeds 15:214-216. 10. Helling, C. S. 1971. Pesticide mobility in soils. I. Parameters of soil thin-layer chromatographv. Soil Sci. Soc. Am. Proc. 35:732-737. 11. Helling, C. S. 1971. Pesticide mobility in soils. II. Applications of soil thin-layer chromatography. Soil Sci. Soc. Am. Proc. 35:737-743. 12. Helling, C. S. 1971. Pesticide mobility in soils. III. Influence of soil properties. Soil Sci. Soc. Am. Proc. 35:743-748. 13. Lambert, S. M., P. E. Porter, and R. H. Schieferstein. 1965. Movement and sorption of chemicals applied . the soil. Weeds 13:185-190. 14. Leistra, M. 1973. Quantitative description of pestit,,. persistence and mobility in soil. Meded. Fac. La,,, bouwwet. Rijksuniv. Gent 38:769-774. 15. Linscott, J. J., 0. C. Burnside, and T. L. -avy. 19fr Phytotoxicity and movement of amiben d irivatives soil. Weed Sci. 17:170-174. 16. Logan, A. V., N. R. Odell, and V. H. Freed, 1953. TI, use of C11 in a study of the leaching rate of isoprop. N-phenyl carbamate. Weeds 2:24-26. 17. McNeal, B. L. and R. C. Reeve. 1964. E: imination, boundary-flow errors in laboratory -- hydraauulliicc i ------vi| cooonndduucctus vh measurements. Soil Sci. Soc. Am. Proc. 28 713-714. 18. Peeper, T. F. 1975. Fate and behavior in the environ ment of selected thiadiazole and s-triazim herbicidn Ph.D. Thesis, Crop Science Dept, North C irolina Stair University, Raleigh, NC. 19. Unchurch, R. P. and W. C. Pierce. 1957. he leachin; ofmonuron from Lakeland sand soil. I. lie effect 01 amount, intensity, and frequency of simuls ted rainfall Weeds 5:321-330. 20. Upchurch, R. P. and W. C. Pierce. 1958. ^ leachiii; of monuron from Lakeland sand soil. II. 1 effect o: soil temperature, organic matter, soil m< listure, am: amount of herbicide. Weeds 6:24-33. 21. Weber, J. B. 1972. Model soil systems, her! licide learfi. ing, and sorption. Pages 145-160, m R. E Willdnson ed. Research methods in weed science. Sou them Weec Science Society, POP Enterprises, Inc., AAtt]laita, GA. 22. Wu, C. H. and P. W. Santelmann. 1975. Comparison of different soil leaching techniques with fou herbicides. Weed Sci. 23:508-511. 23. Yaron, B., E. Bresler, and J. Shalhevet. 1966JA. method for uniform packing of soil columns. Soil Skl. 101:205- 209. APPENDIX C HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS (WEBER etal., 1986) Chapter IX HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS Jerome B. Weber and Len R. Swain Department of Crop Science, North Carolina State University Raleigh. North Carolina 27695-7627 and Harry J. Strek E.I. DuPont de Nemours & Co., Inc. Wilmington, Delaware 19898 and Jose L. Sartori Universidade Estadual Paulists Jaboticabal, Brazil ! PAGE ; INTRODUCTION................................................................................. 190 ; DESCRIPTION OF METHODS ................................................................... 191 \ ^jil^ APPARATUS, CHEMICALS. AND OTHER Natural Soil Column Method MATERIALS ........................................... 191 191 Hand-Packed Soil Column ...........................................................:;'. 191 "tw PREPARATION AND USE OF CMOLeUtMhNoS d..................................................... ^.... 192 ! Natural Soil Columns ....................................................... 192 I Hand-Packed Soil Colu.m..n.s................................................................. 192 ................................................................ ! APPLICATION OF HERBICIDE ................................................................... 192 | PROCEDURE FOR NATURAL SOIL COLUMNS 193 ! Preparing the .................................................. 193 | Application of Columns.................................................................... 194 i Removal of SoiWl aandteHrer.b.i.c.i.d.e..A.s.s..a.y......................................................... 194 PROCEDURES FOR HAND-PACKED SOIL C..O.L.U..M..N.S............................................. 195 Preparing the ........................................... 195 Application of CWaotelur mns.................................................................... 195 ! Removal of Soil and .H.e.r.b.i.c.id.e..A..s.s.a.y....................................................... 196 ; EXAMPLE AND METHOD OF COMPUTING..R.E..S.U.L.T..S............................................ Constructing ...........................................191966 ' Applying Column...................................................................... 196 ApplicatioHn eofrWbaitceirdaend..S..a.m..p.l.in..g............................................................. 196 ; Effect of Herbicide ........................................................ 198 Effect of Soil Type Type................................................................... 198 , 1 Effect of Column ........................................................................ 198 Size..................................................................... LITERATURE CITED ............................................................................. 200 1SQ 190 RESEARCH METHODS IN WEED SCIENC : INTRODUCTION The relative ease with which a herbicide moves vertically in soil is important in determining its efficac /. suitability for use as a selective herbicide, and potential for contaminating ground water or draina( a effluent. Movement of a herbicide in soil is dependent on several factors, including chemical properties i >f the herbicide (5,17,18), soil properties (1.8,13.16). and intensity and frequency of applied water (12.17 I. The mobility of a given group of herbicides is generally inverse to their adsorptivity by soil as measured n Chapter 8 of this manual. Cationic herbicides, such as paraquat and diquat, are the least mobile because i f their strong ionic bonding to the cation exchange complex of soil colloids. Water insoluble nonion c herbicides, such as trifluralin. are very immobile in the liquid state due to low solubility, but may be mobi e in the vapor state due to moderate to high vapor pressure. Herbicides with basic properties, such as the itriazines prometryn, prometon, and propazine are moderate to low in mobility and their mobility s dependent upon the pH of the soils. Higher mobility occurs under neutral or alkaline conditions than und >r acidic conditions. Acidic herbicides, such as picloram, bromacll, 2,4-D, and dicamba, and highly wati>r soluble nonionic herbicides such as fenuron are highly mobile in soils because of this low adsorptivity 1o soil colloids. Mobility of a herbicide in soils is thus dependent upon: (a) ionizability, (b) water solubility, (:) vapor pressure, and (d) lipophilic nature of each compound. Chemical properties of soils that influem e herbicide mobility include the kinds and amounts of each soil constituent (humic matter, type and amoui it of clay minerals, amount of iron and aluminum hydrous oxides) present, soil pH, soil permeability, porosit f. and structure. Drying a soil may also delay the movement of a herbicide into the soil. In general, herbicide s move faster and in greater amounts through coarse textured, sandy soils which are low in humic matti ir than they do through loamy soils containing moderate to high amounts of humic matter. The intensity and frequency of applied water, whether it be from natural rainfall or by irrigation, great y affects herbicide movement and distribution in the soil. Large amounts of water (51 cm) applied continuously, under saturated-flow conditions over a short period of time (3 h) can move as much as 81 & of a relatively mobile herbicide, like tebuthiuron, completely through a soil column and out into tre leachate (17). Application of the same total amount of water but in small amounts (1.2 cm/day), und< r unsaturated-flow conditions, over a long period of time (40 days) can result in as little as 2.5% of the sarr e herbicide ending up in the leachate. The relative mobility of selected herbicides has been determined by using: (a) soil leaching columr s (4.5,10.12,13.14.15.16.17), (b) soil thin-layer chromatographic plates (2,6,7,8.9,18), and (c) soil thici layer chromatographic trays (3.18). The soil thin-layer plate technique utilizes a fine silty soil matrix applied to a glass plate as the supporting medium. Herbicides are spotted onto the soil matrix in a manner similar to that done whe i using routine silica gel coated TLC plates. One end of the plate is immersed in a small amount of water c t the bottom of a closed glass chamber. The herbicides move up the plate and are separated and identifie 1 according to the principles of ascending chromatography (see Chapter 11). The technique is relatively rap! d and the results are comparable with those obtained in adsorption studies, although of an inverse nature ; i.e., immobile herbicides are strongly adsorbed and do not ascend the plate, while highly mobile herbicide s are not adsorbed and move freely. The thin-layer plate technique also offers the advantage of allowing on a to compare several herbicides at the same time under identical conditions. The soil thick-layer chromatographic technique utilizes a shallow tray filled with soil and placed in 3 horizontal position with the herbicide-treated end at a slightly higher elevation than the other end (15'o slope) (3). Herbicide is applied to the soil at one end of the tray and one end of a cloth wick is placed on th a herbicide-treated soil, the other end of wick is placed into a dish of water. Water ascends the wick an 1 diffuses into the soil carrying the herbicide along down the slope. After the soil has been wetted to the en 1 of the tray. the soil is seeded with a plant species which is sensitive to the herbicide. The resulting injury t > the bioassay plants is an indicator of herbicide movement. A much wider variety of soil textures can b i examined using the soil thick-layer technique, as compared with the soil thin-layer technique. Bot i techniques are carried out under saturated-flow conditions. The soil column technique, the method to be described herein, consists of filling a column with sol, preconditioning with water, mixing herbicide with the surface soil. applying a given quantity of walei, allowing the soil to drain freely, and then determining the herbicide distribution in the soil column and i i the leachate. Herbicide analyses may be done by radioassay, chemical assay, and/or plant bioassay, a i described in other sections of this book. The technique has great flexibility, allowing one to compare: (f I relative mobility of many different herbicides through an unlimited number of soil types, (b) herbicid i HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS 191 mobility under saturated-flow conditions versus unsaturated-flow conditions, (c) herbicide mobility through moist versus air-dried soils, (d) herbicide mobility in reduced-tillage systems versus conventionally tilled systems, (e) herbicide mobility through undisturbed soil cores versus hand-packed soil columns, and (f) herbicide degradation product mobility through herbicide-treated, aged soil columns. DESCRIPTION OF METHODS Basically, there are two major types of columns used to investigate the leaching behavior of herbicides in soils: (a) natural soil columns, and (b) hand-packed soil columns. Two types of hand-packed soil columns are used. depending upon the kind of soil assays to be performed after the leaching is completed. They include: (a) stacked cylinder columns, and (b) split columns. Figures 1 to 4 illustrate these various kinds of soil columns. APPARATUS. CHEMICALS. AND OTHER MATERIALS Natural Soil Column Method (A motorized, truck-mounted, column-driving unit would be useful if available.), Columns (5 to 10 cm diameter by 35-cm long sharpened galvanized steel pipes) Hardwood driving block Sledge hammer Shovel Plastic bags Marking pen Cardboard box Glass wool ,_ ; Quartz sand Erienmeyer flasks, 4-L Erienmeyer flasks, 250-ml Funnels (same diameter as columns) Brass screen Silicone sealer Plastic tape Deionized water Rubber stopper Glass tubing Plastic tubing NaCI AgNOa Soil sieve. 4-mm opening 1.0-cm diameter drill bit Tubing connector. 1-cm Marking pen Silicone sealer Vortex-type mixer Hand-Packed Soil Column Method 192 RESEARCH METHODS IN WEED SCIENCE Plastic tubing Quartz sand Deionized water Spatula Plastic tape Saw PVC plastic pipe, 5- to 10-cm diameter PVC cap 1 -L buret {for saturated/unsaturated-flow) or 4-L flask with stopcock (for saturated-flow) NaCI AgNOa Erienmeyer flask, 250-ml Glass wool PREPARATION AND USE OF COLUMNS Natural Soil Columns Five to 10-cm diameter, 14-gauge galvanized steel pipe is cut into sections 35 cm long (Figure 1). T ie bottom is sharpened for ease of soil penetration. To eliminate water flowing down the interior wails of t ie column, it would be desirable to use the divided-bottom technique of McNeal and Reeve (11). T) is technique provides a column within-a-column and only water moving down the center of the column is collected. This reduces boundary-flow errors resulting from water and herbicide moving down the walls. In many cases, however, natural channels in soil cores would probably contribute as much to herbici Ie movement as herbicide movement down the walls so the technique may not provide any clearer picture of herbicide movement and distribution than catching all of the water passing through the column. The s >il must be removed from this column and transferred to plastic bags for chemical analysis or to small pots 1or plant bioassay. Hand-Packed Soil Columns Each of the following columns is fitted with a plastic pipe cap (Figures 2 and 3). A 1-cm hole is drilled in the center of the cap and the hole fitted with a tubing connector to which plastic tubing is attached. A 250-ml Erienmeyer flask is placed beneath each column to catch the leachate. Stacked-Cyt/nder Columns. Stacked-cylinder columns are prepared from 5- to 10-cm diamet plastic PVC pipe which has been cut into 5-cm sections (Figure 2). The 5-cm sections are fastened togeth with silicone sealer and plastic tape such that a 2- to 5-mm ridge of silicons sealer extends into the interii of the column at each section. The siticone sealer eliminates water and herbicide movement down the wal of the columns. The plastic PVC cap is also attached with silicone sealer to allow for easy separation at tl termination of the study. Split Columns. Split columns are prepared from desired lengths of plastic pipe (generally 40 err), capped on one end (Figure 3). The columns are cut longitudinally down the pipe to the cap and the n transversely. It is reassembled using silicone sealer, and reinforced by wrapping with tape. The ridges i >f silicone sealer are applied at 5-cm increments to the interior columns sections before the sections ai e joined together. The plastic PVC cap may be attached with PVC glue and left in place after column separation (Figure 3B). APPLICATION OF HERBICIDE When possible, herbicide should be applied to the soil in a manner analogous to that employed in th field. Herbicide may be mixed with water and applied to the surface or it may be incorporated into the to) 2.0-cm of soil. In either case, the applied herbicide should be equilibrated with the soil for several hour s before the leaching process is initiated. HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS 193 FLASK DEIONIZED WATER QUARTZ SAND BRASS SCREEN PLASTIC TUBING NATURAL SOIL CORE GALVANIZED STEEL PIPE SILICONE SEALER SHARPENED EDGES FUNNEL Figure 1. Cross-section of natural soil core, solid column, leaching system. Apparatus is set up for a continuous saturated-flow study. After leaching, soil must be removed from column for herbicide assay. When ^C-tagged herbicides are employed, mix formulated, non-radioactive herbicide and ^C-tagged herbicide together to provide approximately 5 to 10 /jQi of ^C-activity at the desired application rate per soil column. It is also desirable at this time to add 2 ml of 1 M NaCI to the top of the soil column and to test the leachate with a few drops of 1 M AgNOa at 100 ml increments to determine the Cl~ ion breakthrough point. The Cl~ ion breakthrough point is useful for evaluating the relative mobility of herbicides with C!" ion to verify the performance of each column and to check the reproducibility between replicate columns. Glass wool is added to the top of the column to maintain the integrity of the surface. PROCEDURE FOR NATURAL SOIL COLUMNS Preparing the Columns Select a representative site for obtaining the soil sample. Examine and describe surface cover conditions. Record the kind of crop and stage of growth, and any surface litter or mulch cover. Describe the surface conditions, freshly cultivated, cloddy, cracked, or crusted. Drive the 35-cm long steel column approximately 30 cm into the soil using the driving block and sledge hammer. Remove the soil from around the pipe to allow for easy removal of the column without disturbing the soil at the bottom of the core. At the same time collect soil samples in plastic bags, from various depths for soil moisture determinations. Examine and describe the soil profile at this time. Determine texture and soil structure and note any conditions that might influence water intake. Carefully remove the soil column from the earth, place it in a plastic bag and stand it upright in a cardboard box for transport back to the laboratory. In preparing the column for leaching, remove the plastic bag and place the column into a funnel filled with quartz sand fitted with a brass screen (Figure 1). Apply silicone sealer along the joint where the column and funnel meet. Allow to harden and tape securely with tape. For most studies it is desirable to precondition the columns by wetting the column thoroughly and allowing to drain overnight to field capacity. This may bfr accomplished most easily by standing the columns in deionized water as shown in Figure 4B and allowing to drain free. 194 RESEARCH METHODS IN WEED SCIEN BURET PLASTIC CYLINDER GLASS WOOL SILICONS RIDGE SOIL SILICONE SEALER PLASTIC CAP QUARTZ SAND PLASTIC TUBING FLASK LEACHATE Figure 2. Cross-section of hand-packed soil column using stackedcylinders. Apparatus is set up for incremental additions of water in saturated/unsaturated-flow studies (A). Cylinders are fastened together with silicone sealer and plastic tape. After leaching, cylinders are bioassayed independently according to soil depth (B). Application of Water For saturated-flow studies arrange the soil column as shown in Figure 1. Using the flask of deioniied water and stopper arrangement shown, a small head (2 cm) of water can be maintained over the cours i of the leaching period (generally 50.8 cm of water applied over a 2 to 4 h period). Place a small mat of g ass wool on the top of the column and a 250-ml Erienmeyer flask under the funnel to catch the leachate be1 ore initiating the leaching cycle. For saturated/unsaturated-flow studies, arrange the column as shown in Figure 2A. Place a ma glass wool on the soil surface, and a 250-ml Erienmeyer flask under the column. Using a buret, a[ deionized water in an amount equivalent to the desired rainfall rate (generally 1.2 cm/column/day); allow the water to leach through the column and collect in the leachate flask. For a 10 cm diami column, a 1.2 cm/day addition of applied water will result in approximately 100 ml/day of leach; For continuous, unsaturated-flow studies, arrange the column as shown in Figure 3A. Place a ma glass wool on the soil surface and a 250-ml Erienmeyer flask under the column. Using the stopcock . ind flask of water apparatus shown, adjust the flow of water such that water drips onto the glass wool mat with no head of water. Removal of Soil and Herbicide Assay Some soils may be removed from the column by pushing the entire core out of the column wit i a wooden plunger having a diameter slightly smaller than the column interior. With other soils, a sample must be removed from the soil column by use of a soil sampling tube or with a long handled scoop. The foil column should be divided into 5-cm sections. Each section should be placed into a plastic bag, thoroug ily mixed, a sample taken and marked for chemical or radiochemical assay, and the remainder placed i ito small pots for herbicide bioassay. HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS 195 FLASK------r~'-7 A' DEIONIZED WATER ------^ 'Jf STOPCOCK --------0 PLASTIC PIPE GLASS WOOL SILICONE RIDGES SOIL PLASTIC CAP QUARTZ SAND CONNECTOR PLASTIC TUBING FLASK LEACHATE Figure 3. Cross-section of hand-packed soil column using a split-column system, apparatus is set up for unsaturated-flow studies (A). After leaching, column may be divided longitudinally to provide two con tinuous half-columns, one for chemical or radiochemical assay and one for plant bioassay (B). PROCEDURES FOR HAND-PACKED SOIL COLUMNS Preparing the Columns Soil in these studies may be utilized in a field-moist or air-dried condition. A field-moist condition is preferred if the soil contains significant amounts of organic matter or expanding-type clay minerals which generally shrink and contract greatly when dried. It is generally desirable to precondition the column before initiating leaching by saturating the soil and allowing the column to drain to field capacity. This may be accomplished by placing the column in deionized water as shown in Figure 4B. Soil from each 5-cm depth should be sieved through a 4-mm screen, mixed, and uniformly packed into the soil columns if it is desirable to establish a "simulated" soil profile. It is generally satisfactory to take soil from the plow layer (0 to 15 cm depth) and from the 15 to 30 cm suboil zone, but more commonly soil is taken from the 0 to 15 cm depth and used throughout the 0 to 30 cm of soil in the column. Uniform packing can be accomplished by adding small increments of soil to a column held in firm contact with a vortex-type mixer as shown in Figure 4A. The mixer should be set at a speed which has previously been found to result in the desired soil bulk density (generally 1.6 g/cm3 for a sandy soil). Uniform packing and consistent soil moisture levels are required for obtaining reproducible results from leaching columns (19). Application of Water The set-up for saturated-flow, saturated/unsaturated-flow or continuous, unsaturated-flow studies is the same as described for natural soil columns (see earlier section). 196 RESEARCH METHODS IN WEED SCIENCE COLUMN SOIL QUARTZ SAND BUCKET OF WATER VORTEX MIXER Figure 4. Preparation of hand-packed soil leaching columns: A. Uniform packing of column by addition of small increments of soil and use of Vortex-type mixes; B. Prewetting of soil column by use of subirrigation. Removal of Soil and Herbicide Assay The stacked-cylinder soil column is disassembled by removing the tape at the joints, and cutting cro; ssectionally through the soil core with a thin-bladed knife or sawing through with a piece of taut wire. S oil from each cylinder should be placed into a plastic bag, mixed, a sample removed and marked for chernii al or radiochemical assay, and the remainder returned to the cylinder for bioassay (see Figure 28). Bioassay standards should be included to determine the approximate herbicide concentrations in each soil cylindi T. Removal of soil from the split column is accomplished by removing the tape from the joint and cutti ig the column in two longitudinally. Soil samples may be removed from one of the column sections and us id for chemical or radiochemical assay. The other section may be used for a bioassay of the herbicide as shown in Figure 3B. Bioassay standards should be included. EXAMPLE AND METHOD OF COMPUTING RESULTS Constructing Column Construct a hand-packed soil column system using a split column with a 10-cm diameter and 40-cm length, as described previously and shown in Figure 3A. Place quartz sand in PVC cap portion of t ie column to a depth of 5 cm followed by approximately 3600 g of sandy loam soil to a depth of 30 cm ai id bulk density of 1.5 g/cm3 (3600 g/2355 cm3) as shown in Figure 4A. Place soil column in bucket of water overnight to precondition as shown in Figure 4B. Remove column from water and allow to drain free. Applying herbicide Mix 5/^Ci of "C-labeled atrazine (0.3 mg of ^C-atrazine with sp act. = 25.0/^Ci/mg) with formulated atrazine (4.16 mg of 80WP atrazine) to achieve a rate of 4.5 kg ai/ha (based on soil surface area of colun in of 78.5 cm2) in 5 ml of water and apply with a pipet in a cross hatch pattern to the soil surface. Add 2 ml of 1M NaCI to the top of the soil column. Application of Water and Sampling Set up apparatus shown in Figure 3A to provide for a continuous unsaturated-flow study. Apply water in a continuous drop fashion until 4-L have passed through the soil column. Sample each 100 ml if HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS 197 leachate and test for Cl' ion by adding several drops of 1 M AgNOa (watch for a white, cloudy precipiate of AgCI). Record the volume of leachate when Cl ion is first detected (normally detected in the first 400 to 600 ml of leachate). Radioassay each 200 ml of leachate by placing 1 ml of leachate into 10 ml of liquid scintillation cocktail (16.5 g 2,4-diphenyloxazole (PPO). 0.5 g 1,4-bis [2-(4-methyl-S-phenyloxazoyll benzene (POPOP), 1-L Triton X-100. and 2-L toluene] and" placing into a liquid scintillation spectro- photometer. Record cumulative volume (or weight) of leachate and cumulative amount of atrazine (% of applied) for each 200 ml volume of leachate until all applied water has passed through the column. See Table 1 for example of ^C-activity (atrazine) distribution in leachate. Allow column to drain overnight, then remove plastic tape and siiicone sealer. Split soil column by pulling a taut wire down the longitudinal slot. Lay column sections side by side on a table. Remove approximately 40 to 50 g of soil from each 0 to 5 cm section, place into separate plastic bags, mark bags, and knead and mix each sample thoroughly. Remove a 10 g sample from each 0 to 5 cm zone and determine soil moisture content as described in Chapter 8. Remove 10 subsamples (1 g each) from each bag, place into separate 50 ml beakers and dry at HOC overnight. Mix each dried sample thoroughly, and remove a 1 g sample for ^C determination by placing into a Harvey Biological Oxidizer (OX-300) programmed to burn at a temperature of 900 C for 4 minutes and trap the ^COz in liquid scintillation cocktail containing Harvey No. 161 CO; trapping solution. Counting efficiencies wilt range from 70 to 80%. Convert disintegration/min/g to % of re activity applied and record as shown in Table 2. The soil samples can also be extracted with methanol and the extracts separated by TLC to obtain the amount of atrazine parent and metabolites present. Radiochemical chromatographic methods are described in another section of this manual. Table 2 illustrates the "C-activity (atrazine) distribution in the soil after leaching a 30-cm Norfolk soil column continuously with 50.8 cm of water under unsaturated-flow conditions. The total amount Table 1. ^C-activity distribution in leachate from Norfolk sand treated with "C-atrazine and leached continuously with 50.8 cm (4-L) of water under unsaturated-flow conditions Cumulative volume of leachate (ml) 0 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 Total 'CF ion first detected. Cumulative ^C-activity (% of applied) 0 0.00' 0.06 0.48 0.87 1.27 1.58 1.89 2.40 3.08 3.84 4.49 5.13 5.99 6.83 7.54 8.18 8.82 9.94 9.94 198 RESEARCH METHODS IN WEED SCIEN Table 2. "C-activity distribution in Norfolk sand treated with ^C-atrazine and leached continuously with 50.8 cm (4-L) of water under unsaturated-flow conditions Soil depth (cm) 0 - 5 5 . 10 10 15 15 20 20 25 25 30 Total "C-activity {% of applied) 12.0 11.5 14.8 15.2 11.4 7.5 72.4 recovered (% of applied in leachate + % of applied in soil) in this case amounts to 9.94 4- 72.4 = 82.3^ will normally range from 70 to 105% 5 to 10%. Effect of Herbicide Type Herbicides move through soils differently depending on the chemical properties of both the herbici les and the soil. Table 3 shows the distribution of three herbicides with high (bromaci!), moderate (atrazi ne) and low (diuron) mobility through a Lakeland sand when leached with 36 cm of water, at 1.2 cm/day for 30 days, under unsaturated-flow conditions. The acidic, highly water soluble bromacil is much mare mobile than the less soluble atrazine and diuron. Effect of Soil Type Soil humic matter content, clay type and content, soil pH, and other factors greatly affect the mobi ity of herbicides through different soil types. Some herbicides bind to both organic (humus) and inorganic (clay) soil colloids, while others bind to one of the soil colloids and not to the other. Table 4 shows the distribution of a relatively mobile herbicide, tebuthiuron. through three different soil types. Movement of the herbicides was controlled primarily by the humic matter content and the clay content of the so Is. Effect of Column Size Many different diameter leaching columns have been used to measure the relative mobility of herbicides through soils. They have ranged in size from as small as soda straws to as large as field sti ed Table 3. ^C-labeled herbicide (bromacil, atrazine, diuron) distribution in Lakeland soil treated with '^C-herbicide and leached with 1.2 cm/day for 30 days (36 cm of total water applied) under unsaturatedflow conditions [Weber and Whitacre (17)] Soil depth (eni 0 - 5 5 - 10 10 - 15 15 - 20 20 - 25 25 - 30 Total Bromacil . 7.3 13.2 18.5 20.4 17.0 10.4 86.8 "C-herbicide Atrazine -.-..(% of applied) - 72.2 26.3 16.9 0.8 0.0 0.0 114.2 Diuron 107.3 0.3 0,0 0.0 0.0 0.0 107.6 HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS 199 Table 4. ^C-activity distribution in three soils treated with ^C-tebuthiuron and leached with 1.2 cm/day for 40 days (48 cm total) under unsaturated-flow conditions [Weber and Whitacre (17)] Soil depth |cm) 0 - 5 5 - 10 10 - 15 15 - 20 20 25 25 30 Total Portsmouth sandy loam 47.9 19.0 12.1 6.7 3.4 1.1 90.1 Rains silt loam (% of applied). . 50.9 11.4 8.5 5.0 2.6 1.0 79.4 Davidson clay 2.4 4.3 6.7 7.6 9.2 10.2 40.4 lysimeters. Table 5 shows the relative distribution of the very mobile herbicide picloram through a 30-cm long column of Norfolk sandy loam (Typic Paleudult; fine-loamy, siliceous, thermic. 0.2% HM 0.5% OM, 2% clay) using columns with diameters of 2.5, 5.0, and 10.0 cm and leaching continuously with 50 cm of water under saturated-flow conditions. No differences in picloram distribution in the soils or total recovered in the iaachate occurred between columns with diameters of 5.0 or 10.0 cm. The soil distri bution of picloram and the % recovered in the leachate of the 2.5 cm diameter column was significantly different from the two larger columns. More consistent results would probably be obtained if leaching columns of 5.0 to 10.0 cm in diameter or larger were used. The larger columns also provide more soil for chemical, radiological, and biological assays. Table 5. Effect of column diameter on ^C-picloram distribution in Norfolk sandy loam and in leachate when leached continuously under saturated-flow conditions with 50 cm of water (30 cm soil profiles) Column diameter (cm)1 Soil depth (cm) 0 5 5 10 10 - 15 15 20 20 25 25 30 Total Lsd (0.5) =0.2 (columns). 0.3 (depth) Total in leachate Lad (.05) = 3.0 (columns) Total accounted for 2.5 1.5 2.2 2.7 3.2 3.5 3.9 17.0 5.0 % of applied) 0.6 1.2 1.6 2.0 2.4 2.7 10.5 10.0 0.7 1.1 1.5 1.9 2.2 2.6 10.0 87.3 90.3 89.2 104.3 100.8 99.2 'Column's contained 245, 975, and 3900 of soil, respectively. 200 RESEARCH METHODS IN WEED SCIE LITERATURE CITED 1. Best, J. A. and J. B. Weber. 1974. Disappearance of s-triazines as affected by soil pH us! balance-sheet approach. Weed Scl. 22:364-373. 2. Change, S. S. and J. F. Stritzke. 1977. Sorption. movement, and dissipation of tebuthiuron in: foils Weed Sci. 25:184.187. 3. Gerber, H. R., P. Ziegler, and P. Dubach. 1970. Leaching as a tool in the evaluation of herbicides. Proc. Br. Weed Control Conf. 10:118-125. 4. Guenzi, W. 0. and W. E. Beard. 1967. Movement and persistence of DOT and lindane ir soil columns. Soil Sci. Soc. Am. Proc. 31:644-647. 5. Harris, C. I. 1967. Movement of herbicides in soil. Weeds 15:214-216. 6. Helling. C. S. 1971. Pesticide mobility in soils. 1. Parameters of soil thin-layer chromatography Soil Sci. Soc. Am. Proc. 35:732-373. 7. Helling, C. S. 1971. Pesticide mobility in soils. II. Applications of soil thin-layer chromatogn phy. Soil Sci. Soc. Am. Proc. 35:732-737. 8. Helling, C. S. 1971. Pesticide mobility in soils. III. Influence of soil properties. Soil Sci. Soc. Am. Proc. 35:743-748. 9. Helling. C. S. and B. C. Turner. 1968. Pesticide mobility: Determination by soil thin-layer chr )matography. Science 162:562-563. 10. Lambert, S. M., P. E. Porter, and R. H. Schieferstein. 1965. Movement and sorption of chert icals applied to the soil. Weeds 13:185-190. 11. McNeal, B. L. and R. C. Reeve. 1964. Elimination of boundary-flow errors in laboratory hydiaulic conductivity measurements. Soil Sci. Soc. Am. Proc. 28:713-714. 12. Upchurch, R. P. and W. C. Pierce. 1957. The leaching of monuron from Lakeland sand soil. I The effect of amount, intensity, and frequency of simulated rainfall. Weeds 5:321-330. 13. Upchurch, R. P. and W. C. Pierce. 1958. The leaching of monuron from Lakeland sand soil. II. The effect of soil temperature, organic matter, soil moisture, and amount of herbicide. Weeds 6:2' -33. 14. Weber. J. B. 1972. Model soil systems, herbicide leaching, and sorption. Pages 145-160//? ^. E. Wilkinson (ed.) Research Methods in Weed Science. South. Weed Sci. Soc.. POP Enterprises; Inc., Atlanta, GA. 15. Weber, J. B. and T. F. Peeper. 1977. Herbicide mobility in soils. Pages 73-78 in B. Truelove (ed.) Research Methods in Weed Science (2nd Edition). South. Weed Sci. Soc., Auburn Printing, Inc., Auburn, AL. 16. Weber, J. B. and T. F. Peeper. 1982. Mobility and distribution of buthidazole and metabolites ir four leached soils. Weed Sci. 30:585-588. 17. Weber, J. B. and D. M. Whitacre. 1982. Mobility of herbicides in soil columns under saturated and unsaturated-flow conditions. Weed Sci. 30:579-584. 18. Wu, C. H. and P. W. Santelmann. 1975. Comparison of different soil leaching techniques with four herbicides. Weed Sci. 23:508-511. 19. Yaron, B., E. Bresler, and J. Shalhevet. 1966. A method for uniform packing of soil columns Soil Sci. 101:205-209.