Document 6RxveXvNpMmvn7Dr4bwG2XVm6

AR226-2671 RECYCLED 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 o f 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 Unpublished studies conducted by DuPont have indicated that APFO in air emissions is deposited as a particulate material on the ground surface.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 o f this testing is to subject natural soil columns, approximately six cm diameter by thirty five cm in length, to defined periods o f artificial rain. APFO will be dissolved in a small volume o f distilled/deionized water and applied to the top o f the soil column. At regular time intervals, artificial rain will be applied to the top o f 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 o f the Office o f Pesticide Programs in 1982. 1.1 Study Objectives There are two main objectives o f this study. The first objective is to evaluate the leaching behavior o f air deposited APFO/rainwater mobilized PFOA in silty clay or clayey silt. The second objective is to provide data for estimating the leaching potential o f PFOA, including determining and verifying the following parameters: retardation factor percent adsorbed/desorbed 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 o f Research Methods in Weed Science includes a revision o f 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 o f 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, ha 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 o f 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, i f permission from the site is obtained. The core acquisition procedure, as described by Weber and Peeper (1977) and Weber et al. (1986), w ill 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 o f 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, n in e sample tubes o f pre-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 o f 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 o f 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 o f 30 cm. Soil surrounding the sample tubes will be sampled on five cm intervals (0-5 cm, 5-10 cm, etc) to a depth o f 30 cm. Each o f 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 o f the pipe when removing the pipe from the ground. The top and bottoms o f the sample tubes will be marked on the outsides o f the sample tubes. The ends o f 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 o f 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 o f 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 o f the procedure in Weber and Peeper (1977) and Weber et al. (1986) will be documented in the report issued following the completion o f 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 CaCh solution made from deionized water. Figure 1 (in Appendix C) from Weber et al., 1986, shows a cross section o f 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 o f APFO, equivalent to application rates o f 0.05, 0.1, and 0.2 kg/hectare, will be dissolved in a small volume o f distilled or deionized water and applied to the surface o f three o f the soil columns. The fourth column will be used as a duplicate for the soil column in which the mid-concentration o f APFO 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 o f the column. A nonsorbing and nondegradable polar reference substance, such as sodium bromide, will also be applied to the tops o f the five soil columns to determine breakthrough point. Prior to initiation o f the leaching study, glass wool will be placed on the top surface o f the columns. Artificial rain (the 60 uM CaCl2 solution made from deionized water) will be applied to each o f the five columns, using an application rate o f approximately 1.6 cm/colunxn/day o f artificial rain. This application rate is slightly higher than the recommended rate o f 1.2 cm/column/day o f artificial rain but is the volume required to generate approximately 50 ml o f leachate per application, the minimum volume required for PFOA and tracer analysis. Leachate will be collected daily, 24 hours after the application o f 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 o f PFOA in the leachate has returned to a non-detectable amount or has leveled o ff 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: solution used for preconditioning the five columns solutions containing various amounts o f PFOA used to spike the four columns artificial rain applied to the five columns O leachate from the control column that was not spiked with PFOA leachate from the four columns that were spiked with varying concentrations o f PFOA 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 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 Cis 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 o f 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 o f concern, it is affected by any interfering substances in the sample to the same extent, as is the compound o f concern. 1.4 Data Analysis and Reporting After all o f the results o f the analysis o f 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 SoiIColumnStudy.doc APPENDIX A PESTICIDE ASSESSM ENT GUIDELINES SUBDIVISION N CHEMISTRY: ENVIRONMENTAL FATE (EPA-540/9-82-021) 07/07/04 WED 16:09 PAX 703 308 1850 .S. EPA.OPP.FEAD.GISB il002 EPA-540/9-82-021 O otober 1982 . Pesticide Assessment Guidelines Subdivision N Chemistry: Environmental Fate Prapared b y Staff o f Environmantai Fats Brandi Hazard Evaluation Division O ffice o f Pesticide Programs Guidelines Coordinator Robert K. Hitch Hazard Evaluation Division O ffice o f Pesticide Programs U.S. Environmental Protection Agency O ffice o f Pesticides and T o x ic Substances Washington, D .C . 20460 07/.07/04 WED 16; 00 FAX 703 308 1850 D.S, EPA.QPP.FEAD.GISB 64 Series 163 s MOBH i m ? STUDIES @003 I 1S3" 1 Leaching and adsorptlon/desorption studies. (a) Purpose, The movement of pesticide residues by n e w s of leaching through the soil profile or transport to and dispersion in the aquatic environment may cause contamination of food, result in loss of usable land and water resources to man due to contamina tion of groundwater supplies or cause habitat loss to wildlife' Therefore, laboratory studies are required to predicts (1) The leaching potential or pesticides and their degradates through the soil profile at terrestrial sites} and (2) The movement of pesticides and their degradates to and dispersion in aquatic sites (b) when required. Leaching or absorption/desorption data are required by 40 CFH 158 to support the registration of an end use product intended for domestic outdoor use, greenhouse use, terrestrial noncrap use, orchard crop use, field-vegetable'crop use, forestry use, aquatic use, and aquatic impact uses involving direct discharges of treated water into outdoor aquatic sites. Such data are also required to, support each application for registration of a manufacturing-use product which may legally be used to make such an end-use product. See, specifically, 40 8 $ 158*50 and 158.130 to determine whether these data must be submitted. Section 1I-A of this Subdivision contains an additional discussion of the "Fomulators' Exemption" and who must submit the required data as a general rule. (c> Test standards. leaching or absorption/descrption data submitted in response to 40 CSTt 158.130 should be derived from tests which comply with the general test standards in 160-4 and all of the following specific test standards: (1) Teat substance. Studies shall be conducted using each active ingredient in the product* . (1) If radioisotopic analytical techniques are- used (they are preferred), studies shall be conducted with the analytical grade of each active ingredient in the product; t (ii) If non-radioisotopic analytical, techniques are used, studies shall be conducted with the technical or purer'grade of each, active ingredient in the product. ' (2) Test procedure, (i) Analytical technique-selection. A laboratory study should be conducted to provide a quantitative estimate of pesticide mobility in soil or abaorption/desorption on sediments, . 07/07/04 WED 16:09 FAX 703 308 1850 O.S. EPA.OPP.FEAD,GISB @004 65 (iij n f test substance An of test substance equal to the highest recommended rate for a single application of the active ingredient should be added to the sorls/sediment utilized in these studies. . iiii) a-vii lection. Each study should include, at a minima, four soils, such as sand"'{agricultural), sandy lorn, silt loam, d a y , or clay-loam, each having a pH within the range of 4-8. However, if the pesticide is to be limited to use with one specific soil type, then the soils selected should include that specific soil type. In addition, if the pesticide is intended for an aquatic use or for an aquatic impact use involving direct discharges of treated water into outdoor aquatic sites, batch equilibrium (adsorption/desorption) studies on one aquatic sediment obtained from or representative of the proposed use area should be provided. (A) At least one of the soils selected should have an organic matter content less than or equal to one percent (sand or sandy loam preferred)* (B One of the soils should be the soil used for 162-1 (aerobic soil metabolism study). This soil preferably should be a sandy--loam soil. This soil shall ba used to study leaching o f pesticide dgradtes* (iv) Preparation of soil for Study of pesticide dgradtes. ijhe test substance should be aged under aerobic conditions for -30 days or one half-life (whichever is shorter) in the soil selected in paragraph (c)(2)(iii)(B) of this section. The treated soil should be maintained at a constant temperature between 18 and 30c. The temperature chosen shall be the same as that selected in the aerobic soil metabolism study 162-- 1) if that study is also required. The treated soil should be maintained at a soil moisture 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 aged soil containing the pesticide and its dgradtes or extracts obtained from the aged soil should be tasted by one of the methods set forth below: (A ) The extract may be tested o n soil thin layer chromato graphic (TIC) plates as required by paragraph (c)(2)(v) (A) of this section; or (B) The portion of aged soil may be added to the prepared soil columns as required by paragraph (c)(2)(v) (B) of this section; or 07/37/04 WED 16:10 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB @005 66 CC) Alternatively, the mobility of individual dgradtes which have been demonstrate independently to occur in soil after the aging period specified in paragraph (o)(2)<v) of this section. (v) analysis methods. For terrestrial noncrop usee, orchard crop uses, field-vegetable crop uses, and forestry uses, the mobility of the test substance and its dgradtes in soil should be assessed either by soil thin layer chromatography, soil column, or batch . equilibrium (adsorption/deeorption) procedures described below in . paragraphs CA), {B>, and (C), respectively. V ox domestic outdoor uses, greenhouse uses, aquatic uses, and aquatic impact uses, the mobility of the test, substance and its dgradtes in soil shall be assessed only by th batch equilibrium (adsorption/desorption) procedure. Whatever procedure is selected must be followed for all soils studied. ' . a ) Soil thin-layer chromatography (T&C) study. Soil t i studies to predict the leaching potential of pesticides and their dgradtes in soil should be performed as follows: M plates should be prepared using the soils described in paragraph (c) (2) (iii) of this section, to which both the test substance (parent pesticide and dgradtes) are applied. Application of reference pesticide standards on each TLC plat in addition to the test substance is required, to assess the relative mobility of the test substance to that of other pesticides whose laboratory and field leaching behavior is already known. For experimental procedures on soil and plate , preparation, pesticide application, plate development, pesticide visualisation, and Rf calculations, see reference of paragraph (e) of this section. (B) Soil column study. Soil column studies to define the vertical distribution of the test substance and its dgradtes in the soil profila should be performed as follows: The column(s) should be from 3 to 300 cm in height, consisting of soils described in 1631(e)(2)(iii), and should be eluted with a volume of water equal to [groundwater recharge values of] 20 inches (50.8 cm) times the cross sectional area of the column. A distribution curve of the test substance in the column shall be determined by quantification of the test substance and its dgradtes in 6 cm segments and in the eluats. For experimental procedures on conducting a soil column study, see references (1)(i), (iii), (iv) and (v) of paragraph (e) of this section. (C) Batch equilibrium (adsorption/desorption) study. Adsorp tion/desorption coefficients calculated from a batch equilibrium study are used along with solubility data to predict the extent or depth of pesticide leaching in the different soil types tested, .. and also the extent of pesticide adsorption/ desorption on sediments when aquatic or aquatic impact uses are proposed. The study should be conducted using the soils described in paragraph (c)(2)(iii) of this section, plus one representative aquatia sediment (if an 07/07/04 WED 16:10 FAI 703 308 1850 U.S. EPA.OPP,FED.GISB @006 .) 67 aquatic or aquatic impact use involving direct discharge is proposed) She teat substance including its degradatss identified in and extracted from the aerobic soil metabolism study { 132-1) should be equilibrated with the soils and aquatic sediment selected for hia study at four concentrations in a 0.01 5J o r a Ca ion solution. If necessaryr a small amount of acetone or other solvent may be used to achieve solution of poorly soluble pesticides or dagradates. for **! procedures on conducting batch equilibrium (adsorption/desorptiott) studies, including calculation of sd values see references (3)(i) through (til) and (4K13 and (ii) of paragraph <e) of this section. (d) aaaorfcittq and evaluation of data, la addition to the applicable reporting requirements specified in f 160-5 the test report should contain the following specific informations ! (1) soil fchln layer chromatography (T6CJL. She mobility of pesticides and their degradatas should he reported as mobility 1 to 5 corresponding to Sf values of 0,0 to 0.09 [immobile (class 1)] 0.10 to 0.34 [low (class i ) l * 0,35 to 0.64 [intermediate (class 3)1 0o6S to 0.39 [mobile (class 4)1 and 0,90 to 1,0 [very mobile (class 5)3, respectively values of soil/water relationships (Kd) should be reported using appropriate % to 5 ^ , / ^ equations. Examples of calculations used in determining Kg values should be provided, (2) Soil column study. Values of soil/water relationships (Kj ) should be reported for the test substance and its degradate using appropriate equation Examples of calculations used in determining Kg values should be provided, (3) ateh equilibrium (adsorption/^eacrption) study. Adaorption/desorption data to be reported should include concentrations of the test substance, including its degradatas, partitioned between soil and water and calculated as Kg values from the concentrations using appropriate aquations for calculating such values, if the yreundlieh equation is used examples of calculations for 1/n and K values should be provided. (e ) References, (1) The following references contain experi mental procedures for conducting mobility (leaching) studies! ' (i) Grover, a. 1972. Mobility of dicamfca, picloram and 2,4-D in soil columns. Weed sci. 23s159-162. [This paper compares iMnhittj rates using soil columns and adsorption parameters for several soil-pestioide combinations, It illustrates that theories relating adsorption and movement can be verified with soil columns and the resulting data can be related to field movements.) |; I I I 07/07/04 WED 16:11 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB @007 68 ,..; _ c.a_ 1 9 7 1 # Pesticide mobility in soils* 1 C^ L oftS-layer chromatography* soil Sci. goo- amar.^oo# 35^^732-737 ^ ^ s ^ r discusses the M M o soil thin-layer chromatography and details mapsrJnental parameters,] iiii) Krzaminaki, S-F# C-K= Brackett,, and J#0 U s h e r # 1975. .--Aht-iSal 3-isothiasolone compounds an the environments itneJaan [ffljis paper contains a procedure for a column leaching study#] (lv) Lichtenstein, K.R. Schula, and i#W# Puhremann- 197 2 . Movement and fate of dyfonate in soils under leaching and ___T,,,,,vMnfT conditions# or* her# Food C h m . 20 s831-833* [Both (^C Z f S a lyses used iTt h i s study with in tarn positions to allow illustration of different types of degra dation products and their movement in soils*] ,v) weber, 3 . B*, and 5?*F. Peeper. 1977. Herbicide Mobility soils. So. 73-78 in Research Methods in weed Sciatica B# teueioye (ad.) S* Weed Sei# soc. Second Bditioa* hoburn S ! Auburn, Alabama, [Shis paper provides a brxef but desorxptive analysis of procedures for the study of heroieide leaching in soil, and it discusses th e two major types of columns used for these studies. (2) The following references contain supplemental. Information pertaining to mobility studies Bailey, G , w ,, and J.S.# White, 1970# Factor influencing the 'adsorption and movement of pesticides in soils* gasidge 32:29~ 92. [This is a good general review discussing pitfalls to be aware of in planning or interpretation of leaching experiments] (il) Hamaker, JW*, and JM. Thompson# 1972 Adsorption fP* 49-143 in Organic Chemicals in the Soil Environment. Vol* I* C.A.I. Goring and ff.W# Hamaker (ads#)# Marcel Dekker, m e , Hew Xork# [This is a basic review of the theoretical foundation of pestxcxde adsoration on soils and an excellent source for equations and the derived constants characterizing pesticidesoil adsorption# The tables of data may aid in initial range-finding.] (iii) Leistra, M. and W.A# Dekkers# 1976, computed effects of ndsorution kinetics an pesticide movement in soils. J. Soil figi. 2 8 -340-350 , [This is a theoretical paper that may be useful for interpretation of leaching studies, since it illustrates the importance of rainfall pattern with respect to pesticide leaching,] I 07 07/04 WED 18:11 FAX 703 308 1850 .S. EPA.QPP.FEAD.GISB @008 89 (iv) Laistra, M., J.J. Smelt and R. Zanvoort. 1975. sistence and mobility of bromacil in orchard soils. Weed Res. 15-177-181, [This article is recommended for those interpreting pesticide leaching experiments, It reports that the leaching of a pesticide in field experiments was substantially lower than predicted' by calculation from results of soil-TLC experiments.] Per (v> liindstrom, F.T., 1 Boersma, and P. stockard. 1971- A theory on on the mass transport of previously distributed chemicals in a water saturated sorting porous medium? isothermal cases. B-vP sci. 112s291-300. [This paper presents a theoretical model for pesticide movement from adsorption data and flow rates.3 (Vi) Oddson, J.X. or. Letey, and L.V. Weeks. 1970. Predicted distribution of organic chemical in solution and adsorbed as a function of position and time for various chemical and soil properties. Soil sci. soc, amer. 34*412-417. [This paper presents a theoretical model for the movement of pesticides in soils.] . ! <vii) Van Genuchten, H.T., P.J- Wierenga. and G.A. O'Connor. 1977. Mass transfer studies in sorbing media? XXI* Experimental evaluation with 2,4,5-T, Soil Soi. See. Aaer, 41:278-285. [This paper presents comparisons of model calculations and experimental data, and it may be useful for planning or interpretation of leaching experiments*] (3) The following references contain experimental procedures for conducting adsorption/desorption studiess (i) Aharonson, , and u. Kafkafi. 1975. Adsorption, mobi lity and persistence of thiabendazole and methyl 2-benzimidazolecar- in soils- J. A g r Food Chem. 23s720-724. [The techniques and methods used in this study are useful for both adsorption/d asorption and leaching studies,] (ii) Parmer, W.F., and y. Aochi. 1974. picloram sorption by soils, soil Sci. Soc. Amer. Proc. 38:418-423. [Methods of adsorption and desorption can be found in this study.] (iii) Grover, R., and R.J. Haace. 1970. Effect of ratio of soil to water on adsorption of linuroii and atrazine. Soil Sci. 109?136-138. [This paper presents information on the soil-water ratio to be used in laboratory studies of pesticide adsorption to soils.] ' (iv) Hamaker, J.W., C.A.I. Goring, and C.R. youngson. 1966. Sorption and leaching of 4-aaino-3,5,6trichloropioolinic acid in soils. Advances in Chemistry Series 60?23-37. [The techniques and methods used in this study are standard except for the time allowed for equilibration. The data presented demonstrates the 07/07/04 WED 16:12 FAI 703 308 1850 .S. EPA.OPP.FEAD.GlSB 70 i o f pH on a d so rp tio n o t in io n ire d spncioa and th* I n w rtU tie n a h ip btM i p a rtitio n c o e ffic ie n t and adsorption. 3 (v) nance, R.J. 1-967. The spofld o' itMinmnnt oi miilihria in so* systems involving herbicides. wand Ron. 129-36. study iH*atn the us oi can, finding experiments to leehnlquflS foe adsorption and desorption experiments and us* of yraundlich isotherm* are presented In this papor.l tvi) Harvey, R*G- 197a. Soil adsorption and voUtiiity of dinitroaniUAeherbicide*. Wood Sol. 22*120-124. IBs* of absorp- ,<M1 < {or tha calculation of latent hiat of adsorption and the effect of adsorption on volatility- of pesticides are il lustrated in this paper] . (vii) Leistra, M., and W.A. oeKKer*. 197. Computed effects of adsorption Kinetics on pesticide movement in soils. J-.Soll Sci. 28*340-350. [Th*s is a simulation of pesticide behavior on soils in the field by computer.] ( v i l l i i e t e t r a , M., and W.A. 00Wears* 1977. Some models f o r th e a d so rp tio n K in e tic s o f p e s tic id e s in s o i l . J E_nviro.n. S o,-l. H e a l t h *B1i r2i(a2j s)o;3aS- '-v1-03. [i *Th"is c o n tin u a tio n o--f t--h e 1-9- 76* pr a~pe; ;r (above) d is c u s s e s th e m ultim echanism , m o ltira te phenomena re sp o n sib le f o r th e d iffe re n c e s observed in ra te s o f ad so rp tio n and r a te s of d e so rp tio n .] (ix> Murray, 0 .3 ., p.w. SantaIoann, and J.M . Davidson, 1975. Comparative adsorption, desorption, and m obility o f dipropetryn and prom *tryn i n s o i l . J . **r Pood ch ea. 23:S78-582. [The c o r r e la tio n between adsorption, c a tio n exchange cap acity , organic m a tte r, and clay content i s illu s tra te d in th is paper, and adsorp t i o n / d e so rp tio n i s compared v ith s o i l TIC experim ents.} (x) saltjaaan , 5 , L. iCiiger, and a . Varon. 1972. Adsorption.d e s o rp tio n o f p a ra th io n a s a ffe c te d by s o i l org an ic m a tte r. J . A gri. Pood Chet*. 20 sl224,t226. [The im portance o f o rg an ic m atter in absorp t i o n o f p e s tic id e s (by s o i l is d iscu ssed in t h i s re p o r t.] I (x i) savage, K .E., and R.D. wauehope. 1974. Fluooeturon ad s o r p tio n / d e so rp tio n e q u ilib r ia in s o l i . Weeds 225106-110. [T his paper discusses equations used fo r computation o f adsorption isotherm * and provides inform ation fo r equation se le c tio n fo r q u a n tita tiv e dep ictio n of adsorption and desorption,] (x ii) wu, C.H., W. au eh rin g , J.M. Davidson, and ?.W. Santelmann. jg g g , Napropataide a d so rp tio n , d e s o rp tio n , and movement in s o i l s . Head S e i . 23x454457, LColusa leach in g and s o il T ic experim ents conducted and rep o rted here sre c o rre la te d with adsorption/desorpfeion experim ents.] 07/.07/04 TOP 16:12 FAX 703 308 1850 .S. EPA.OPP.FED.GISB @010 r ?1. (xiii) (Reserved for: OECD Guidelines for Testing Chemicals* Section 1, Number 106* Adsorption/Desorptlon.J (4) The following references contain supplemental informa tion for developing a protocol for adsorption/desorption studies: (i) . Bailey# G.W., and J.L* White. 1970. Factors influenc ing the adsorption, desorption, and movement of pesticides in soils. Residue Rev. 32; 29-92. [This review provides background information on the principles underlying the processes of adsorption and nobility of pesticides in soil.] (ii) Weber, J.B. 1977. Soil Properties, Herbicide Sorption, and Model Soil Systems. Xp. 59-72 in Research Methods in Weed Science. 2nd Ed. S. weed Sci. Soc. B. T m e l o v e (ed). Auburn printing, Ino. Auburn, Ala. [This is a general review of experi mental methods for determination of soil properties, herbicide adsorption, and construction of simple model soil systems.] . 5 163-2 laboratory volatility studies. (a) Purpose. Volatilization can be a m a j o r mode for the move ment of pesticides from treated areas. The vapors resulting from, volatilization of some pesticides can cause adverse effects to man ... via inhalation exposure at sites of application or biological effects in nontarget organisms at some distance from the treated .site. The Agency is particularly concerned about commercial g r e e n 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 in significant-inhalation exposure to workers and appli cators*' ' (h) When required., (1) .-Data'-from a laboratory volatility study are required-by. 40 CFR 5, 150 on a case-by-case basis to support the registration of .each -end-use product intended for commercial greenhouse/, orchard,, or field-vegetable crop uses that , involve significant inhalation-exposure' to' workers. Data from such a study are also required to support each application for registration of a m&nufactairing-use- product which may legally be used to formulate such an.end-use product! See, specifically, 40 CFR 158.50, 158.130, "and. the following discussion in 163.3-2 (b)(2) to determine whether these data must be submitted, section IX-A of this subdivision-contains-an additional discussion of the "Formulators' Exemption" and who must submit the required data as a general rule. (2) The Agency will evaluate the following information pro vided by the registration applicant to make an assessment of what constitutes a significant inhalation exposure to workers: 07/1)7/04 WED 16:12 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB @011 72 S3 = " J S S S i X - _ 'S issrrs rs s s of this Subdivision); s= ? - ( H i ) Soil characteristics, i * d * * ^ i s t u r e content, at the intended site of application? <iv) Method, rate, and intervals of pesticide application) , (v) Temperature, humidity, and air flow rates at the site of a p p lic a tio n ; (vi) ventilation sequences or practices for commercial green house applications) and (vii) Inhalation toxicity of the pesticide ( 81-3 and 82 4 of Subdivision F)* 3 ) The data requirements of this section may also be satis- a* *-r -- ? f **" *" "a" aa c o n n e d in 163-3 (field volatility studa.es). ,,,v Teat standards. Laboratory volatility data submitted in to 40 CFR 158726 should be derived from tests which comply withthe general test standards in 160-4 and all of the following specific test standards* (1) Test substance. The test substance shall be a typical end-use product. ' (i) If the applicant's product is an end-use product, the test substance shall be a product whose fomulation is typical, of the formulation category (e.g., wettable powder, concentrate, wettable powder) to which the product belongs. (ii) If the applicant's product is a manufacturing-use product which leaallv could be used to make an end-use product for which .vSLiili?f<lata are required, the test substance shall representative of the major formulation category whxch xncludes that end-use product. (If the manufacturing-use product is usually formulated into end-use products comprising two or or 1 formulation categories, a separate study must be performed wxth a typical end-use product for each such category.) {2) Test procedure. A laboratory study should be conducted to determine theactuafrate or extent of pestxcide ^olatxliaation from soil under controlled conditions only for those Pesticides with uses the Agency considers pose a potentxally significant 07/0.7/04 WED 16:13 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB @012 inhalation, exposure to workers, applicants may omit the laboratory studies and perform a greenhouse and/or field study instead. (See . 163-3.) (i) Laboratory experimental conditions should represent# to the extent possible, an environment where the pesticide is intended for use. (ii) the rata of test-substance application to soil should approximate the intended rate of field usage. (iil) The following factors should be addressed in designing a laboratory volatility study! . (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# such as adsorption to soil -and soil texture, to avoid untoward reduction Of the rate of > volatility (e.g., sandy soil is preferred): (G) Environmental factors# such as air temperature# humidity# and movement, to avoid untoward dehydration or flooding of the soil# and to assure efficiency of sampling. (iv) Air samples should he collected and analysed for residues in the laboratory experimental equipment used. Monitoring should be conducted continuously or at intervals which increase with time after the start of the experiment. Monitoring should continue until the nature of the residue decline curve has been clearly established. (d) Reporting and evaluation of data. In addition to the basic reporting requirements specified in 160-5, the test report should include the following specific informations (1) Volatility data expressed as ug/cm2/hour; (2) A ir c o n c e n t r a t i o n s e x p r e s s e d a s ug/m3 o r ntg/m3 j (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) A d e s c rip tio n o f th e la b o ra to ry t e s t equipm ent u sed . I 07/.07/04 WED 16:13 FAX 703 308 1850 U,S, EPA.OPP.FEAD.GISB 0013 74 t ,, \ References. (1) he following references contain laboratory studies of pesticide volatility; information in these papers could be useful for protocol development: (1) Kearney, i>c> and A Knutson. 1976 A sample system ^ to Measure volatilisation and metabolism of pesticides from soils- -t . a c t - Food Chem, 24a424-426. Ih polyurethane foam trap and a potassium hydroxide trap were used to recover sequentially parent compound and degradation product from air.] (ii) spencer, W.F. and K.M. Claith. 1974. Factors affecting vapor loss of trifluralin from soil. J. Agr. pood Cheaa. 22:987-991 [The laboratory methods used for determining volatilization of used in this study allow measurement of effects of several variables. The use of hexane as a trapping medium limits the gas flow rates and volumes that can be used.] (iii) Spencer, WoF- S.D Shoup, Si.M* Cliath, tf.tf. Farmer, and R. oaque. 1979. vapor pressure and relative volatility of ethyl and methyl parathion. J. Aar. Food Cham; 27:273-278. [Polyurethane foam traps and GLG detection largely specific for the compounds of were used here. Specific detection-avoids interference that may cause falsely high vapor levels in field testing-] (2) Volatilization studies require methods for the trapping, extraction', cleanup, and quantitation of pesticides. A review of reported methods for laboratory investigations of pesticides in air can be found ins . (i) Lewis, R.G. 1976- Sampling and Analysis of Airborne Pesticides. Pp. 51-94 in Air Pollution from Pesticides and Agri cultural Processes. R*E. Lae (ed-) CRC Press, Inc. Cleveland, Ohio* (ii) [Reserved] 163-3 Field volatility studies. (a ) Purpose. Volatilization can be a major mode for the move ment af pesticides from treated areas- The vapors resulting from of some pesticides can cause adverse effects to man via inhalation exposure at sites of application or biological effects in nontarget 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 in significant inhalation exposure to workers and appli cators l j : l .07/07/04 WED 16:13 FAX 703 308 1850 .s. EPA.OPP.FEAD.GISB 75 TiiiviAn required, Data from a volatility study conducted tb), on-sita in * eenhouse and/or in the field will be a caae-5-case basis only for those required by 40 CPR 5 considers*?* a potentially significant pesticides that the *163-3(1)] end, based on the 2S2T3 e^y * liSi^fratfof demonstrate, in the opinion^*- sLcific a i l y , 4 0 C F R 58.50 and - t f l S i S S r i t be submitted. Section ii1i8of3tbia Subdivision contains an additional discussion f the i J i s L t o r * S S p t i o n " and who must submit the required data as a genfiicali pul o .. Test standards Field volatility data submitted in res- . ' " x 1"'1to' should be derived ftc s x testa Which comply STatS 5 1 - . and sll of the - . specific test standards: { ]j mihatinea. The test substance shall be a typical end-use product (i) jf the applicant's product is an end-use product, the test i S m tance shall be a product hose formulation the formulation category wettable powder, emulsifiable concentrate, granular product) to whicn the product belongs. (ii) If the applicant's product is a manufacturing-use product that legally could be used to make an end-use product for which ... volatility data are required, the test substance shall ^ representative of the major formulation category which includes t h K end-use product. <If the end-use products that could b^ made X m the manufacturing-use product belong to two or more major formulation categories, a separate study must be performed for each such category) **- procedures. <i) The test substance should be ap plied to a fits Shich " typical of one of the sites to which the product would be applied (ii) The test substance should he applied to soil at the rate and by the method stated in the label directions for the pesticide. (ili) 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, suoh as adsorption to soil and soil texture, to avoid untoward reduction of the rate of volatility (e.g., sandy soil is preferred); ___ 07/07/04 WED 16:14 FAX 703 308 1850 U.S. EPA.OPP.FEAD.GISB @015 (C) Environmental factors, such as air tamperatura, humidity* and movement, to avoid untoward dehydration or flooding of the soil and to assure efficiency of samplinga {iv} Air "pi should he monitored for residues at treated sites at intervals which increase with time after pesticide appli cation* For example, the following schedule of sampling times might he appropriate for some situations; 6 and 12 hours, 1, 2, 4, 7, 14, and 21 days* Sampling should be continued until the nature of the dissipation curve has been clearly established. (d) no-porting and evaluation of data. In addition to infor mation nM*ing the basic reporting requirements specified in 160-5, the test report should include the following specific information: . (1) Volatility data expressed as g/ha/dayj (2) air concentrations expressed as ug/m3 or ng/m3j (3) vapor pressure expressed as torr (or the equivalent expressed in other conventional units) t and (4) Meterologie conditions (temperattire, relative humidity, wind velocity and direction, and cloud cover) during the time of the field study. (a) References. (1) The following references contain sup plemental information for developing a protocol to conduct field volatility studies; (i) Cliath, W.F. Spencer, W.J. Farmer, T,D. shoup, and R. Grover, 1980. Volatilisation of S-ethyl H,S-dipropylthlocarba- mate from water and wet soil during and after flood irrigation of an alfalfa field. J. agr. Food chem. 28:610-613* [This is a well-designed and well-executed field study of volatilization with simultaneous study of other modes of dissipation of a pesticide.] (ii) Harper, L.A., A.w. White, Jr., R.R. Bruce, A.w. Thomas, and R.A. Leonard. 1976. Soil and microclimate effects on trifluralin volatilization. J. Environ. Qual. 5:236-242. [Ethylene glycol vapor traps and non-specific GLC quantitation were used in this study. The influence off water in soil and thus rainfall during the study on volatilization of a pesticide are illustrated as are effects of wind, turbulence, and temperature.] (iii) Parmele, L.B., E.R. Lemon, and A.w. Taylor, 1972. Miorametaorologieal measurement of pesticide vapor flux from bare soil and c o m under field conditions. Water, Air, and soil Follut. ' li433-451. [This study used hexylene glycol vapor traps and sampling periods adjusted to compensate for decrease in pesticide vapor i  __ 07/07/04 WEB 16:14 FAX 703 308 1850 m .s. EPA.OPP.FEAD.GISB @016 ?7 concentracin dinrin? eh* study. P s s tie id s vapor flu x roa s o l w c a lenlatad and relatad to a ic r o e e tee c o lo g ic a l maaauxssiant*.] ( lv ) Soderqniat, C .J ., B.Q. CXOSby, X.W. (toilaneit, Jf.ll. Ssibar, and J .E . Woodrow. 1975. oecarranee o t r if lu r a iin and lea pheeo- Products ln a i r . J . km. Food Chao. 23i304-309* (Although cha atudy vas eonowrned v i ti pfcotolyeia o p e s tic id a s ln a i r , thara ara proceduraa ln th l* papar Cor ataasuraneat o v o la t iliz a t io n o a p esticid a roe aoil*] (2 ) V o la tliz a tio n tudlee racjuire nectaoda o r the trapping, e x tr a e tio n , cleanup, and q a a n tita tio n ot p e e tic id a e . A review o f re p o rta d eathde fox i e l d in v ea tig a tio n * o p ea ticid a* in a ir can be ound in ( i ) Lav i a , R.G, 1976. Saapling and Analyaia o Airbome PflBfeiCidea. Sp, 51-94 ln Air Pelluttion (ron P esticid a and A grieu llt u r a l Procesase. R.E. le a ( e d . ) . CSC P ress, In c. Cleveland, Ohl o . ( i i ) (Reservad] i I / /'. i,' APPENDIX B HERBICIDE MOBILITY IN SOILS (WEBER AND PEEPER, 1977) CHAPTER 7 HERBICIDE MOBILITY IN SOILS Jerome B. W eber Department o f Crop Science, North Carolina State University Raleigh, North Carolina 27607 and Tom F. Peeper Department of Agronomy, Oklahoma State University Stillwater, Oklahoma 74974 Page INTRODUCTION.......................................................................................... DESCRIPTION OF METHODS....................................................................... APPARATUS, CHEMICALS, AND OTHER MATERIALS..................................................._.74 NATURAL SOIL COLUMN METHOD...... ............. !_____ _ ._________ __________74 HAND-PACKED SOIL COLUMN METHOD.......... ....................................................... .75 PREPARATION AND USE OF COLUMNS................................................. NATURAL SOIL COLUMNS...... ................................................................... HAND-PACKED SOIL COLUMNS........................................................ Solid Columns........................................................................ Stacked-Cylinder Columns---------------------------------------------------- Split Columns---------------------------------------------------------------------------------------76 APPLICATION OF HERBICIDE______ :_____ ___________________________________ .76 PROCEDURES FOR NATURAL SOIL COLUMNS_____________________ PREPARING THE COLUMNS............................................................................. APPLICATION OF WATER...---------------------------------------------------------------------- 76 REMOVAL OF SOIL___________________ 77 PROCEDURES FOR HAND-PACKED SOIL COLUMNS________________ PREPARING THE COLUMNS___ ______________________ APPLICATION OF WATER_______________________________________________ 77 REMOVAL OF SOIL........... ............... 77 LITERATURE C IT E D .............................................................................................. 74 74 75 75 .75 75 75 76 76 77 77 78 74 HERBICIDE MOBILITY INTRODUCTION . "^ e ,relalive 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 (1 9 ), 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 (2 2 ). Several investigators have quantita tively described the m ovement 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 ,2 2 ). The soil thin-layer plate technique utilizes a soil matrix applied 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 relatively rapid 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 (1 2 ). 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. _ The soil column technique is somewhat slower than tl, thin-layer and thick-layer techniques but it does kave sev features not present in the others: (a) soil columns may used with field moist soils or soils at specific moi: ture level* which is preferable to using dried soils; (b ) natural soil con may be obtained or surface soil and subsoil may be placed columns simulating soils in their natural state; (c) herbicii leaching under saturated or unsaturated flow com iitions nu be studied; (d ) soil columns may be readily disassembled^ permit the taking of serial samples for chemical and radii, chemical analyses and pliant .bioassay; and (e) herbicides nu be applied to soils in soil columns and allowed to decompo* under near natural conditions before they are lei ched, the providing data on both parent herbicides and netabolite (2 1 ). This chapter describes methods for measuring the rel.tive mobilities of herbicides in soils using soil coll rains. DESCRIPTION OF METHODS _ Basically, there are two major types of colum ns used i investigate the leaching behavior of herbicides in soils: natural soil columns, and (b ) hand-packed soil columi,., Three types of hand-packed soil columns are used, depends; upon the kind of soil assays to be performed after the lead ing is completed. They include: (a) solid columns (in son;' cases holes or slots are cut into the columns to aic in remm ing the soil or to allow for bioassays to be carriec out whr. leaching is com pleted), (b) stacked-cylinder colLimns, arc (c) split columns. Figure 3 illustrates these varioji;s kinds r< soil columns. APPARATUS, CHEMICALS, AND O' 'HER MATERIALS N atural Soil C olum n M ethod (A motorized, truck-mounted, column-driving init woulii be useful if available.) Columns (7 to 30-cm diam by 30-cm long zalvanizrc steel pipes) Hardwood driving block Sledge hammer Shovel Plastic bags Marking pen Cardboard box I HERBICIDE MOBILITY 75 Filter paper disks Glass wool Buret, 500 to 1000-ml Erlenmeyer flask, 1-L Funnels (same diam as columns) Brass screen (same diam as columns) Teflon-lined tubing Plastic tape Deionized water nd-Packeu So il C o lu m n M ethod 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 N atural So il C olum ns 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 Reeve (1 7 ). This technique provides a column withina-column and reduces boundary-now errors resulting from water and herbicide 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. , H and-Packed So il C olum ns 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 A. B. 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 Stacked-cylinder columns are prepared from desired lengths of plastic pipe with pipe cap attached. The pipe is We 3. Major types of soil leaching columns: A. Natural soil f. "sing a solid column. The scheme demonstrates the set-up " tor saturated flow studies (B, C, and D are hand-packed soil B. Simulated soil profile, where surface soil and subsoil added to the column in the position in which they occur in natural state. The scheme demonstrates the set-up used for aturated flow studies. C. Stacked-cylinder soil column. After ,|ln8> the cylinders may be separated and assayed indepenB. Split soil column. After leaching, the column may be ?d vertically to provide two continuous half columns, one oioassay and another for chemical or radiochemical assay. Figure 4. Soil leaching columns, with split column feature, in 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 earth, place i a plastic b a g and stand it upright in a cardboard bn / transport back to the laboratory. If longer columns are sired, it will generally be necessary to use a pipie with a i Jineter smaller than the recommended minimum of 23 * If columns of iesser diameter are employed, it is sugg*.!1' that the divided-bottom technique of McNeal and Reeve r,- be used. ' ` In preparing the column for leaching, remove the nli bag and place a small mat of glass wool and a brass J r on the bottom of the column. For many studies i is desini i to establish the columns at moisture levels ar proxim,*;'1' field capacity. This may be accomplished mo t easily !' standing the columns in deionized water and applying a J ' 'me 6) f SUCHOn t0 ^ t0P f th CIumn (s* B Fit , Figure 5. Cucumber bioassay of split soil leacbing column. The herbicide applied to the upper column was immobile and was re tained m the upper 4 cm of the soil column, thus only cucumber seedlings m 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. . TO VACUUM NNEL APEO TO (fOLUMN then sawed into 5-cm sections and reassembled by placing the sections together with silicone sealer and tape (see Figure 3 .0 .). 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 bv wrapping with tape (see Figures 4 and 5 ). ' APPLICATION OF HERBICIDE When possible, herbicide should be applied to the soil in a manner analogous to that employed in the field. Herbicide may be mixed with water and applied to the surface or F may be incorporated into the top 2.0-cm of soil. In either case, the applied herbicide should be equilibrated with the soil for several hours before the leaching process is initiated. When 14C-tagged herbicides are employed, mix formu lated, non-radioactive herbicide and 14C-tagged herbicide to provide approximately 5 to 10 fiCi of activity with the desired application rate per soil column. PROCEDURE FOR NATURAL SOIL COLUMNS P reparing t h e C olum ns 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, freshlv cultivated, cloddy, cracked, or crusted. Drive the 30-em 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. PLATE -VORTEX MIXER 3UCKET OF WATER A. 8. aoRunfngdisfuuourrbesmiem6op.gfaacPtvkioroiernnptgeaaxron-atfdtyicopgoneelunmomtfliexnHesbrau;yncBdtai-.odpnpda.rcietkiwoednettosiofniglsmloeafalclshoiniilncgrceoiln("uojiirleuannmtsnbosyf: A soil use A pplica tion of W ater For saturated flow studies, use plastic tape to connect tunnel to the bottom of the column and attach ,, ppiieeccee <r. leflon-lined tubing and a stopcock to regulate fo w out of the cohimn (See A of Figure 3.) Place a glass ool mat or a disk of filter paper on the surface of the soil and use Erlenmeyer flask filled with deionized water to maintain a constant head of water at the soil surface. f ? or ^saturated flow studies, tape a funnel to Ihe bottom of the column as shown in B of Figure 3. Place a d isk of filter paper on the soil surface and use a buret to regulate the rate ot flow of deionized water through the column. (A more accurate flow rate can be achieved by use of a nicropumn and time clock arrangement.) The amount and fnquency of watering should be commensurate with the rainfill or irri gation pattern for the area. Water may be applied to the columns by addins a specific amount (usually 2 to 4 cm) per day for a specific,i the pe riod (usually .30 to 45 days). At the end of th f leaching I I J 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. m 77 moval o f 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 ii 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 bioassav. i PROCEDURES FOR HAND-PACKED SOIL COLUMNS 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 field acity, this may be accomplished by placing the columns in jmized water and applying gentle suction to the top of the imn (see B of Figure 6)" If a natural soil profile is unobtainable, a simulated soil [lie can be a close approximation of the natural soil profile 1 luring in the field. In using the method, soils collected a 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 S column, B, necessitates the removal of the soil from the Imn for bioassay or chemcial analysis. The stacked cylinicolumn, C, allows for ease of separation of the various depths and analysis of the herbicide in each cylinder of soil column. The split column, D, provides a continuous column for herbicide analysis. The recently developed soil column and bioassay system shown in Figure 7 is i a practical and simple system to measure herbicide (and :r pesticide) leaching and bioactivity in soil. [The sample of soil from each depth should be sieved iugh 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 tty- Uniform packing can be accomplished by adding II increments of soil to a column held in firm contact with irtex-type mixer set at a speed which has previously been )d to result in the desired soil bulk density (see A of Fig6 ). Uniform packing and consistent soil moisture levels required for obtaining reproducible results from leaching imns (2 3 ). When it is desired to compare herbicide movement (ugh a uniform mixture of soil, it is necessary to use a logeneous soil column. This technique permits compari ! to be made between homogeneous soil samples taken !>various soil depths, and homogeneous soil samples rep uting different soil types. The method is generally useful . emparing the surface portion of cultivated soils down to i plow layer. In cultivated soils, the surface has been subtially 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 mn as previously described. Figure i . Herbicide soil leaching column and bioassay system. Two column halves (14) are joined together with silicone sealer | : 4J j ? i.p i 11! and ? a p on funnel 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 s f erri?ded i a ,the column to their respective sidewall Iw m `-A^ e,,m.olded mad" , also prevent herbicide movement w!H, J Herbicide is applied and the column leached with water applied at I-em increments (19). After 30 days of the 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 co.umn half is laid in a horizontal Plates (27) are installed to keep the soil in place. L`l d - d e r s ,1?9) are inserted into fhe 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. Applica tion o f W ater set-up for saturated or unsaturated flow studies or for adding specific amounts of water daily is the same as de scribed for natural soil columns (see earlier section). R em oval o f Soil Soil is removed from the solid column in the same manner as described for the natural soil column method. The stacked-cylinder soil column is disassembled by removing the tape at the joints, and cutting cross-sectionally through the soil coie 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. mixed, a sample removed and marked for HERBICIDE MOBILITY chemical or radiochemical 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 rmoved f one of the half columns and used for chemidal or r , chemical assay. The other column half may b used f bioassay of the herbicide as shown in Figure 5. ! "r LITERATURE CITED 1. Bayer, D. E. 1967. Effect of surfactants on leaching of substituted urea herbicides in soil. W eeds 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. W eed 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. W eed Control Conf. 10:118-125. 7. Gillett, J. W ., J. Hill, A. W. Jarvinen, ami W. P. Schoor. 1974. A conceptual model for the movement of pesti cides through the environment. Environ. Prot. Agencv (U .S .), Ecol. Res. Serv. 660/3-74-024, 79 pp. ' 8. Guenzi, W. D. and W. E. Beard. 1967. Movement and persistence of D D T 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-laver chromatography. Soil Sci. Soc. Am. Proc. 35:732-737. ' 11. Helling, C. S. 1971. Pesticide mobility in soils. II. Applications o f 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 chem icas ann!;B,i the soil. W eeds 13:185-190. ^d 14. Leistra, M. 1973. Quantitative description of pesK, persistence and mobility in soil. Meded. Fac. La bouwwet. Rijksuniv. Gent 38:769-774. 15. Linscott, J. J., O. C. Burnside, and T. L. Lavy. jg,.. Phytotoxicity and movement of amiben d irivative* soil. W eed Sci. 17:170-174. 16 Logan, A. V., N. R. Odell, and V. H. Freed, 1953. f l use of CH in a study 0f the leaching rate of isonmn. N-phenyl carbamate. W eeds 2:24-26. ep 17 McNeal, B. L. and R. C. Reeve. 1984. Elimination boundary-flow errors in laboratory hydraulic conductive measurements. Soil Sci. Soc. Am. Proc. 28:713-714 18. Peeper, T. F. 1975. Fate and behavior in the envir0, ment of selected thiadiazole and s-triazin herbicide Ph.D. Thesis, Crop Science Dept., North Cirolina Sh, University, Raleigh, NC. " 19. Upchurch, R. P. and W . C. Pierce. 1957. The leach,, of monuron from Lakeland sand soil. I. The effect fj amount, intensity, and frequency of simulated rainfall Weeds 5:321-330. 20. Upchurch, R. P. and W. C. Pierce. 1958. 1"he leach, of monuron from Lakeland sand soil. II. 1 he effect o- soil temperature, organic matter, soil moisture, an,amount of herbicide. Weeds 6:24-33. 21 Weber, J. B. 1972. Model soil systems, herbicide leach ing, and sorption. Pages 145-160, in R. E Wilkinson ed. Research methods in weed science, Son them Ween Science Society, POP Enterprises, Inc., AtJaita, GA 22 Wu, C. H. and P. W. Santelmann. 1975. Comparison of different soil leaching techniques with fou herbicides W eed Sci. 23:508-511. 23. Yaron, B., E. Bresler, and J. Shalhevet. 19661. A method for uniform packing of soil columns. Soil Sjji. 101:205 209. I APPENDIX C HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS (WEBER et. a!., 1986) Chapter IX HERBICIDE MOBILITY IN SOIL LEACHING CO LU M N S 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.l. DuPont de Nemours & Co., Inc. - , Wilmington, Delaware 19898 and Jose L. Sartori Universidade Estadual Paulists Jaboticabal, Brazil PAGE IN TR O D U CTIO N ........................................................................................................................................... .. DESCRIPTION OF M E T H O D S ............ ..................................................................................................... .. APPARATUS. CHEMICALS. AND OTHER MATERIALS.................................................. ................... . 191 Natural Soil Column M e th o d ............................................................................................. . Hand-Packed Soil Column M e th o d ......................................................................... 191 PREPARATION AND USE OF C O L U M N S .................................................... " i l " . ! " " ! . " ! . . ! . " ! 192 Natural Soil C olum ns...................................................................................................................... .... Hand-Packed Soil Colum ns.................................................................................... j 92 APPLICATION OF H ER B IC ID E.................................................................................................................. .. PROCEDURE FOR NATURAL SOIL C O L U M N S ..................................................................................... .. Preparing the Columns............................................................................................................... . 193 Application of W a te r........................................................................................................................ .. Removal of Soil and Herbicide A s s a y ........................................................... j94 PROCEDURES FOR HAND-PACKED SOIL C O L U M N S ................................. 195 Preparing the Columns................................................................................................................. ^99 Application of W a te r................................................................................. 1 99 Removal of Soil and Herbicide A ssa y ............................................... -jgg EXAMPLE AND METHOD OF COMPUTING RESUL T S ...................... . . . . . . . . 196 Constructing Column..................................................................................................................... .. 196 Applying Herbicide......................................................................................................................... ' .j9q Application of Water and S am p ling ..................................................................................... . . . , . ! 196 Effect of Herbicide Type..................................................................................................... 1 9g Effect of Soil Type . . . . ................................................................................................. 198 Effect of Column S ize .........................................................................................................! . 198 LITERATURE CITED 200 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 drain effluent. Movement of a herbicide in soil is dependent on several factors, including chemical properties of the herbicide (5,17,18), soil properties (1,8,13,16), and intensity and frequency of applied water (12 171 The mobility of a given group of herbicides is generally inverse to their adsorptivity by soil as measured Chapter 8 of this manual. Cationic herbicides, such as paraquat and diquat, are the least mobile because <if 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 is dependent upon the pH of the soils. Higher mobility occurs under neutral or alkaline conditions than und<ir acidic conditions. Acidic herbicides, such as picloram, bromacil. 2.4-D. and dicamba, and highly wat ir I,H nT ,M C?rIb,C!de! *" ?h.8.,anuron ara hish,y mobi,e in soils because of this low adsorptivity i o 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 o f soils that influent 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 t and structure. Drying a soil may also delay the movement of a herbicide into the soil. In general, herbicidi s move faster and in greater amounts through coarse textured, sandy soils which are low in humic m attlr 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 v affects herbicide movement and distribution in the soil. Large amounts o f 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 t ie leachate (17). Application of the same total amount of water but in small amounts (1.2 cm/day), undur unsaturated-fiow conditions, over a long period of time (40 days) can result in as little as 2.5% of the same herbicide ending up in the leachate. 14 5Ti o ^ w ,!> Cted, harbl,cides has been determined by using: (a) soil leaching columrs (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 tha supporting medium. Herbicides are spotted onto the soil matrix in a manner similar to that done when using routine silica gel coated TLC plates. One end of the plate is immersed in a small amount of watert the bottom of a closed glass chamber. The herbicides move up the plate and are separated and identified according to the principles of ascending chromatography (see Chapter 11). The technique is relatively rapi J 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 herbicides 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 a honzonta! Position with the herbicide-treated end at a slightly higher elevation than the other end (15% 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 i 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 ba examined using the soil thick-layer technique, as compared with the soil thin-layer technique. Bot j techniques are carried out under saturated-flow conditions. The soil column technique, the method to be described herein, consists of filling a column with soi preconditioning with water, mixing herbicide with the surface soil, applying a given quantity of watei. allowing the soil to dram freely, and then determining the herbicide distribution in the soil column and in the leachate. Herbicide analyses may be done by radioassay, chemical assay, and/or plant bioassay, at i ! ! 0d "1L ? ? er ect,ons l th,s b? k-.The technique has great flexibility, allowing one to compare: (a) relative mobility of many different herbicides through an unlimited number of soil types, (b) herbicide 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 o f 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. CHEM ICALS. AN D OTHER M ATERIALS 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 Erlenmeyer flasks, 250-ml Funnels (same diameter as columns) Brass screen Silicone sealer Plastic tape Deionized water Rubber stopper Glass tubing Plastic tubing NaCI AgNOj 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 Plastic tubing Quartz sand Deionized water Spatula Plastic tape Saw PV C plastic pipe. S- to 10-cm diameter PV C cap RESEARCH METHODS IN WEED SCIENCE 1-L buret {for saturated/unsaturated-fiowj or 4-L flask with stopcock (for saturated-flow} Nad AgNOa Erlenmeyer flask. 250-ml Glass wool PREPARATION A N D U SE O F CO LUM NS " Natural Soil Columns Five to 10-cm diameter, 14-gauge galvanized steel pipe is cut into sections 35 cm long Figure 11 t L c o iu Z 'h i SO" penetration- To eliminate water flowing down the interior walls i f I e column, it would be desirable to use the divided-bottom technique of McNeal and Reeve <111 This S S "/ TM TM S' * Ct IU'n" Wi,hi " " " l" m " -'V TM . . r n J t a , d oflm tte center o f t t o 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 cg n trib C IH s m u ^ h to Z h 5 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 oil J 2 bioas^ T tH,S C ,Umn 8nd transferred t0 p,astic baps for chem*cal analysis or to small fr nmiu-racKeo ooit columns Each of the following columns is fitted with a plastic pipe cap {Figures 2 and 3 A hi,, i, a n j 250 f tHe P ? nd th8 h le f'tted With a tubin9 connector to which plastic tubing is attached 250-ml Erlenmeyer flask is placed beneath each column to catch the leachate . f * * c * e * C ylider Columns. Stacked-cylinder columns are prepared from 5- to 10-cm d ia m e tt plastic PVC pipe which has been cut into 5-cm sections (Figure 2). The 5-cm sections are fastened tnneth, with silicone sealer and plastic tape such that a 2- to 5-mm ridge of silicone sealer e xte n d s into th * f 2 * CO!Umn ataach section. The silicone sealer eliminates water and S J TM unmoTt; her r pvccaplsa,soattaohedw ith^ Split Columns. Split columns are prepared from desired lengths of plastic pipe (generallv 40 r.ni) capped on one end (Figure 3). The columns are cut longitudinally down the pipe to the cap and then z :zt:<; z . z T 5" * , -sii" *........ ...... '* " * < '* w ,.Pp;,,8p: r , . i e pvc c,p m ,v "mohod -- pvc * ' - p '- APPLICATION OF HERBICIDE HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS FLASK DEIONIZED WATER G U SS WOOL 193 NATURAL SOIL CORE GALVANIZED STEEL PIPE QUARTZ SAND BRASS SCREEN PUSTIC TUBING SILICONE SEALER SHARPENED EDGES FUNNEL FUSK LEACHATE Figure 1. Cross-section of natural soil core, solid colum n, leaching system. Apparatus is set up for a continuous saturated-flow study. After leaching, soil must be removed from column for herbicide assay. When 14C-tagged herbicides are employed, mix formulated, non-radioactive herbicide and ,4C-tagged herbicide together to provide approximately 5 to 10 pCi of 14C-activity at the desired application rate per soil column. It is also desirable at this time to add 2 ml of 1M NaCI to the top of the soil column and to test the leachate with a few drops of 1M AgN Oa at 100 ml increments to determine the C l- ion breakthrough point. The Cl* ion breakthrough point is useful for evaluating the relative mobility of herbicides with C F 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. PR O CED U R E FO R N ATURAL SOIL C O LU M N S 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 her 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 SCIENCE - BURET PLASTIC CYLINOER GLASS WOOL SILICONE RIDGE SOIL SILICONE SEALER PLASTIC CAP QUARTZ SAND PLASTIC TUBING FLASK LEACHATE B. Figure 2. Cross-section of hand-packed soil colum n 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 deionised water and stopper arrangement shown, a small head (2 cm) of water can be maintained over the cours, of the leaching period {generally 50.8 cm of water applied over a 2 to 4 h period). Place a small mat of glass wool on the top of the column and a 250-mi Erlenmeyer flask under the funnel to catch the leachate be! ore initiating the leaching cycle. For saturated/unsaturated-flow studies, arrange the column as shown in Figure 2A. Place a m a : of glass wool on the soil surface, and a 250-ml Erlenmeyer flask under the column. Using a buret ai ply deionized water in an amount equivalent to the desired rainfall rate (generally 1.2 cm/column/day) iirnd allow the water to leach through the column and collect in the leachate flask. For a 10 cm diamt iter column, a 1.2 cm/day addition of applied water will result in approximately 100 ml/day of leachnte. For continuous, unsaturated-ftow studies, arrange the column as shown in Figure 3A. Place a ma tof glass wool on the soil surface and a 250-ml Erlenmeyer flask under the column. Using the stopcock iind flask of water apparatus shown, adjust the flow of water such that water drips onto the glass wool mat Removal of Soil and Herbicide Assay Some soils may be removed from the column by pushing the entire core out of the column wiinth a wooden plunger having a diameter slightly smaller than the column interior. With other soils, a sarr pie must be removed from the soil column by use of a soil sampling tube or with a long handled scoop. The coil column should be divided into 5-cm sections. Each section should be placed into a plastic bag. thoroughV mixed, a sample taken and marked small pots for herbicide bioassay. for chemical or radiochemical assay, and the remainder placed iihto HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS FLASK A. DEIONIZED WATER STOPCOCK PLASTIC PIPE GLASS WOOL SILICONE RIDGES SOIL A 195 PLASTIC CAP QUARTZ SAND CONNECTOR PLASTIC TUBING FLASK LEACHATE A Figure 3. Cross-section of hand-packed soil column using a split-column system, apparatus is set up for un.saturated-fiow studies (A). A fter 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). PR O CED U R ES FO R H AN D -PACKED SOIL C O LU M N S 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 1.5 g/cm 3 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 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 i l K der S?H columnJ s disassemb!ed by moving the tape at the joints, and cutting croessectionally 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, mixed, a sample removed and marked for ciem l"a. or radiochemical assay, and the remainder returned to the cylinder for bioassay (see Figure 2B). Bioassay standards should be included to determine the approximate herbicide concentrations in each soil cylinder. 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. neroicide as EX A M P LE AN D M ETHOD O F COMPUTING RESULTS Constructing Column Construct a hand-packed soil column system using a split column with a 10-cm diameter and 40-c m length, as described previously and shown in Figure 3A. Place quartz sand in PV C cap portion of tite co umn to a depth of 5 cm followed by approximately 3600 g of sandy loam soil to a depth of 30 cm and bulk density of 1.5 g/cm (3600 0/2365 cm3) as shown in Figure 4 A. 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 atrarinB V S f " V i S S ? atra?ine i0,3 mfl of "C-atrazine with sp act. = 25.0/rCi/mg) with formulated atrazme (4.16 mg of 80WP atrazme) to achieve a rate of 4.5 kg ai/ha (based on soil surface area of colun in . - m *?*1! . !" 5. m of wf ter end apply with a pipet in a cross hatch pattern to the soil surface. Add 2 ml o* 1" 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 wat sr in a continuous drop fashion until 4-L have passed through the soil column. Sample each 100 ml jof HERBICIDE MOBILITY IN SOIL LEACHING COLUMNS 197 leachate and test for C l' ion by adding several drops of 1M A g N 0 3 (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-methyI-S-phenyloxazoyl] 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 14C-activity (atrazine) distribution in leachate. Allow column to drain overnight, then remove plastic tape arid silicone 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 110 C overnight. Mix each dried sample thoroughly, and remove a 1-g sample for 14G 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 14C 0 2 in liquid scintillation cocktail containing Harvey No. 161 C 0 2 trapping solution. Counting efficiencies will range from 70 to 80%. Convert disintegration/min/g to % of r e activity applied and record as shown in Table 2. The soil samples can also be extracted with methanol and the extracts separated by T L C to obtain the amount of atrazine parent and metabolites present. Radio chemical chromatographic methods are described in another section of this manual. Table 2 illustrates the ,4C-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. 14C-activity distribution in leachate from Norfolk sand treated with 14C-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 1CI ion first detected. Cumulative 14C-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 9.941 198 & RESEARCH METHODS IN WEED SCIEN C E Table 2. "(-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 ,4C-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 + 72.4 = 82.34 .It 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 Ibromacil). moderate (atrazme) 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 more mobile than the less soluble atrazine and diuron. Effect of Soil Type Soil humic matter conte- nt-, c--lay typ--e----a--n---d- --con. wte. n. . t, , soil pH,, , aannud vouthi oeir lfaavcitvoirbs ygireeaautlyyaanffeeucit mtheemmoowbii nlityy 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 Effect of Column Size . 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 sired Table 3. 14C-labeled herbicide (bromacil, atrazine, diuron) distribution in Lakeland soil treated with 14C-herbicide and leached with 1.2 cm/day for 30 days (36 cm of total water applied) under unsaturatedflow conditions [Weber and Whitacre (17)J Soil depth (cm) 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 14C-herbicide Atrazine i% of applied) 72.2 25.3 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 Table 4. 14C-aetivity distribution in three soils treated with 14C-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 (%o f 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 40.4 199 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 Rachats 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 sdil for chemical, radiological, and biological assays. Table 5. Effect of column diameter on 14C-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 2.5 5.0 10.0 (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 Lsd (.05) = 3.0 (columns) Total accounted for 4% of applied) 1.5 2.2 2.7 3.2 3.5 3.9 17.0 0.6 1.2 1.6 2.0 2.4 2.7 10.5 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 'Columns contained 245, 975, and 3900 of soil, respectively. 200 RESEARCH METHODS IN WEED SCIENCE LITERATURE CITED 1. Best, J . A . and J . 8. Weber. 1974. Disappearance of s-triazines as affected by soil pH us ng a balance-sheet approach. Weed Sci. 22:364-373. 2. Change, S. S. and J. F. Stritzke. 1977. Sorption, movement, and dissipation of tebuthiuron in oils. Weed Sci. 25:184-187. 3. Gerber, H. R., P. Ziegler, and P. Dubach. 1970. Leaching as a tool in the evaluation of herbic ides Proc. Br. Weed Control Conf. 10:118-125. 4. Guenzi, W. D. and W. E. Beard. 1967. Movement and persistence of DDT 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. I. Parameters of soil thin-layer chromatography Soil Sci. Soc. Am. Proc. 35:732-373. r 7. Helling, C. S. 1971. Pesticide mobility in soils. II. Applications of soil thin-layer chromatogruphy. Soil Sci. Soc. Am. Proc. 35:732-737. T 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 chrLma tography. Science 162:562-563. 10. Lambert, S. M., P. E. Porter, and R. H. Schieferstein. 1965. Movement and sorption of chenicals applied to the soil. Weeds 13:185-190. 1 1 . 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. 1 2 . 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 moriuron from Lakeland sand soil. IIl Tmhee effect of soil temperature, organic matter, soil moisture, and amount of herbicide. Weeds 6:2' -3 3 . 14. Weber, J. B. 1972. Model soil systems, herbicide leaching, and sorption. Pages 145-160/ FI E Wilkinson (ed.) Atlanta, GA. Research Methods in Weed Science. South. Weed Sci. Soc.. POP Enterprises* Inc., 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 Printino Auburn, AL. Inc., 16. Weber, J . B. and T. F. Peeper. 1982. Mobility and distribution of buthidazole and metabolites leached soils. Weed Sci. 30:585-588. four 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.