Document e7yvoXQQV45R8oq047wRVLEq

SOIL ADSORPTION TEST SUBSTANCE Identity:Perfluorooctanoiaccid,ammonium salt;may alsobe referredto as PFOA ammonium salt,Ammonium perfluorooctanoateP,FO, FC-116,FC-126,FC-169,orFC-143. (Octanoicacid, pentadecafluoro-a,mmonium saft,CAS # 3825-26-1) Remarks: The testsample isFC-143. lVspuritywas not sufficiently characterizedt,hough currentinformationindicatesitisa mixtureof96.5 100% testsubstance and 0 - 3.5% C6, C7, and Cg perfluoroanalogue compounds. The testsubstance used was 14C_Iabeled.This testingis being repeatedpe-rcurrentprocedures and best availablepractices. METHOD: Method: Adsorption-Desorptionstudy usingthe approach recommended by the U.S. EPA forpesticideregistration GLP (Y/N): No Year (study performed): 1978 Statisticamlethods: Statisticalnalysisand plottingof the data was done withtheMINITAB package of the3M TRAC computer service. Temperature: 16-190C Stock and testsolutionpreparation: Test solutionswere made by dilutinag stocksolutionof 14C-labeledammonium perfluorooctanoate. The type ofsolventused to make thestocksolutionisnot noted,nor isthe activitoyfthe 14C_Iabeledtestsubstance. Remarks field: ' The Brilslandy loam soilwas characterizedas having 57% sand, 360/osilt7,% clay,2.5% organicmatter,1.5% organiccarbon, withpH 6.5 and cationexchange capacityof 15.3 meq./l00 gms. Standard solutionsofthe 14C_Iabeledcompound were prepared inD.I. wateratconcentrationsof523 mg/L, 293 mg/L, 167 mg/L, 94 mg/L, 52 mg/L, and 5.2mg/L. Twenty-fivemi of each solutionwas shaken with duplicate5 gram samples ofthe soilina 50 ml polypropylenecentrifuge tubesfor24 hours on a wristshaker at room temperature(16-190C). Desorptionextractiownere performed withD.I.water afterthe adsorption phase ofthe experiment.The samples from the adsorptionand desorptionexperimentswere centrifugedindividualalty 5000 rpm for10 minutes,afterwhich,threealiquotsofeach supernatantsolutionwere preparedforscintillatcioounnting.From the raw countingdata,compound concentrationswere calculatedforallofthe supernatantsolutions. RESULTS K: 0.21(N=l) K.,: 14* The study reporthad indicateda K of0.38. This isthe coefficienotfC in the regressionequation,not the adsorptioncoefficienvtalue,based on bestfit.Taking a mean valueforK based on K=(x/m)/C.,K = 0.21.The K.Ocvalue based on the initialrleyportedorganiccarbon contentof 1.5% and the mean value forK (Koc= K x 100/1.5(% organiccarbon)becomes 14. CONCLUSIONS The studysubstance isexpected to exhibithighmobilityinthe kindofsoil tested. Submitter: 3M Company, EnvironmentalLaboratory,P.O. Box 33331, St.Paul,Minnesota,55133 DATA QUALITY ReliabilityK:limischranking3. This study lacksdetailon the stock solutionand thepurityofthe 14C_Iabeledtestsubstance. There was no analysisofthesoiltoverifythe amount remainingformass balance. Discrepanciesinthe organiccarbon contentare present.Use of Di water insteadofCaC12. Additionallys,ome calculationhsave questionable reliabiliAtdyd.itionaclomments by ProfessorStephen A. Boyd, Michigan StateUniversitya,lsoindicatethe reliabililteyvelofthisstudy. REFERENCES 3M TechnicalReport "Adsorptionof FC 95 and FC 143 on Soil."S.K. Welsh, Project9970612633 Fate ofFluorochemicals,Report No. 1,Feb. 27,1978 3M requestedexpertreviewby ProfessorStephen A. Boyd, Michigan StateUniversityM,ay 19, 1993. OTHER Last changed: 5/25/00 Attachedarecomments on the3M TechnicalReport "Adsorptionof FC 95 and FC 143 on Soil. S.K.Welsh,Project9970612633 Fate of FluorochemicalsR,eport No. 1,Feb. 27, 1978"made by ProfessorStephenA. Boyd, Mchigan StateUniversityd,atedMay 19,1993. Review of TechnicalReportSummary Adsorptionof FC 95 and FC 143 inSoil Materialand Methods Should giverecoveriesof compounds -inblank (no-soile)xperiments.Statesthatpolypropylene sorbslessthanglasson polyethyleneb,ut doesn'tgive a numericalvalue. The largeheadspace(25 ml ina 50 tube)isundesirablea;ny lossesofthe'4C-labele,.g.,from volatilizatioornstickingto the tube,willinflattehe sorptioncoefficienstincethe method calculatetsheamount sorbedby differencbeetween the initiaalnd finalequilibriumsolution concentrationsA.lso the24 hour mixingperiodseems arbitrary.Were experimentsdone for differenpteriodsof time toestablisthhatequilibriumwas reachedwithin24 hours? Detailson the stocksolutioanre llcldng.What solventwas used and what isthe specific activitaynd mdiochemicalpurityof the"C-FC 95. The ideaof usinga cottonswab afterthedrainingstepisunusual.Hopefullythisdidn'tremove soilas wellas water. The - 20% orlessdecreasein soluteconcentratiodnue tosorptionisn't as high as I'dliketosee it.A 50% or greaterdecreasewould be better. This sectiongenerallylacksdetailthatwould normallybe requiredforpublication. Resultsand Discussion The linearitoyf theisothennhas been shown over theconcentratiornangeused. However, to demonstratethattheentireisothermislinear,thelinearitmyust extendtoequilibriumsolution concentrationtshatapproachthewatersolubilitoyf thecompound. Do you know thesolubility of FC95 or FC143: Ifnot,how were theinitiaslolutionconcentrationsselected? The sorptioncoefficien(tK)of FC 95 appearstobe about I as indicatedT.he organicmatter normalizedsorptioncoefficie(nYt.@.= K/f.) isK. = 1/0.025= 40, or logK. = 1.6. This isa soilsorptioncoefficienitntermediatbeetween benzene and toluene.Itwould be worthwhile to examine some additionasloilsto confirmthisK. value. Generally,theK. valuesshould convergewithina factorof 2 to3 fordifferenstoils.Thiswould increasemy confidenceinthe accuracy of theone measured value. I've spot checked the soilconcentrationosf FC-95 for both the sorptionand desorption experimentsand I getessentialltyhesame values.The calculationlsookgood. The K valuesforFC 143 islower thanFC 95 indicatintghatitprobablyhas a higherwater solubilityT.he hystersiisnthedesorptionisothermissurprisinga,nd has been over-interpreted. The sorptionisothermislinearindicatinag singlesorptiveprocess.Tle conclusionregarding "threedifferenbtindingmechanisms ...with strongerbindingathigherconcentrationasnd the converseatlower concentrationsi"svery speculativbeased on thesingleexperiment. Ifone examines column I "Amount Desorbed as a Percentof Amount Adsorbed' thevaluesrangefrom 26 to212 percent,so it'sprettyinconclusiveI.lere isa fairlgyood discussioonf hysteresiisn J. Environ.Qual. 12:325-330by Kosldnen and Cheng who observedthisphenomena for the weak acidpesticid2e,4,5-T. ne causesof hysteresiasre variedand complicatedand may includemicrobialdegradationof.thecompound duringdesorption,and changes inthe physical and/orchemicalpropertieosf thesou-solutiosnystem. For example,desorptionusingdistilled water (asisthecase here)could resultin soU dispersionso thata clearsupernatantsolution couldnot be obtained.This can cause quenchingofradioactivitiynsolutionand otherproblems leadingto error. The "materiablalance"as presentedin thereportisa littlmeisleading.To obtaina material balanceyou shouldmeasure theamount of 14C_aCtiVitiyn soilat theend of theexperiment,and add itto themeasured solutionconcentrations. General Comments: The K, valuescalculatedhere use an organiccarbon contentof 2.2% whereas the valuestatedin theMaterialsand Methods is1.5%? The watersolubilitiaersecitedas 300 mg/L forFC 95 and > 20g/L forFC 143. Surelythe lattervalueiswrong. Ifthe solubilitiaerse trulythatdifferentt,henthe sorptiveproperties shouldbe vastlydifferentw,hich theyare not. IfFC 143 has a solubilitoyf > 20,000 mg/L, thenI would expectno sorption.This valuemust be erroneous. Recommendations: 1. ObtainingK, K. valueson additionasloils.DetermineifK,, isrelativelcyonstant. 2. Obtain a truemass balanceby measuring "IC-activitiyn soU and solutionphase. 3. Interpredtesorptiondatamore cautiously. 4. Get correctvalueofwater solubilitoyf FC 143. Form 6747 11 A TECHNICAL REPORT SUMMARY TO: TECHNICAL COMMUNICATIONS CENTER - 201-2CN tlmportat-itIfreportisprintvdobnoM sideOsfP&Per-,sendtwocopiestoTCC.) Division. EE & PC mopon itte To Fate of Fluorochemicals Adsorption of FC 95 and FC 143 on soil. rnbw 0222 ProlectNi-bje-r@r@ 9970612633 "OPOrt Numbw Autharist Stephen K. Welsh SY-LJ Nouftook neirwomm SECURITY #4067 3, #47704' 13 KEYWORDS: (Selecwtrns fmm 3M Thmuric Suam a#wr applicabluermli CURRENT OBJECTIVE: To obtain 3PACHEMICAL*oo, REGISTRY an indication of FC 95 and TC EMPIOYGO -M-b-o-rTsl-- 73S83 No. atPiili@-.Clud@ing -.rh@.t 14 Now ChemicalsR"Mnsd 13 ya [2 NO 143 mobility in sandy loam soil. EE & PC - Div. Fluorochemical Soil Adsorption Mobility aRlEePrO3tRMT'eAr1st3oSCToRnAiCpTa:n(yR2&0D0.-25w0ords)ThisabstracitnfomutioinsdistribubtyedtheTochnkalCommunic"ons Centerto As a part of the Fate of FluorochemicalsProject, an indication of mobility of FC 95 and FC 143 in sandy loam soil was *desired. Adsorption-desorption experiments (after Davids;n, 1976, and Hamaker.; 197S) along with water solubilitydata can provide such'information. The adsorption coeffi@entsfor FC 9S and FC 143 'weredetermined to be 0.99 and 0.38, respectively. For FC 9S adsorption and desorption could be described by a'single valued function while for FC 143, they could not. Based on these data, both compounds would be judged mobile in the sandy loam soil used in this study. InformatiLoinaison Initials: 2 CONCLUSIONS Adsorption coefficient for FC 95 and FC 143 were 0.99 and 0.38, 'respectively. For FC 9S, adsorption and desorption could be described by a single valued function while for FC 143, they could not. Considering adsorption coefficients, desorption characteristics and water solubilities, both compounds would be judged mobile in the sandy loam soil used in this study. INTRODUCTION As a part of the Fate of Fluorochemicals Project, an indication ofmobility of FC 9S and FC 143 in sandy loam'soil was de@sired. Adsorptiondesorption experiments (after Davidson, 1976, and Hamaker, 197S) along with water solubility data can provide this indicatign of mobility. This approach is used by the U. S. EPA in pesticide registration requirements. MATERIALS AND METHODS Duplicate S-g samples of air-dried Brill sandy loam soil (57% sahd, 36% silt, 7% clay, 2.S% organic matter, l.S% organic carbon, w?lthpH 6.S and C.E.C. of 15.3 meq./lOOg) were shaken with 2S ml of solution in SO ml.*poly.propylene centrifuge tubes for 24 hours on a wrist action shaker at room temp. 0 (16-19 C). Polypropylene tubes were used because they were found in separate experiments (3M Tech Notebook #470673, "C. H. Schrandt) to absorb less FC 9S and FC 143 than glass or polyethylene tubes. Solutions were made by diluting a stock solution of each chemical. Concentrations of 14 C-labeled FC 95 were 282 mg/l., lS8 mg/l., 90 mg/l., Sl mg/.l.,28 mg/l., (100%. 56%, 32%, 18%, 10%, 1% of stock). Concentrations 14 of C'-labeled FC 143 were 523 mg/l. , 293 mg/l. , 167 mg/l. , 94 mg/l. , S2 mg/l and 5.2 mg/j. 3 After shaking the initial solutions as well as the three desorption extractions with deionized water, the samples were centrifuged at SOOO rpm :for10 min., and three aliquots of each supernatant solution were taken for scintillationcotmting. After the adsorption step, 22.5 ml of solution were recovered. Therefore, it was assumed that 2.5 ml of liquid remainedwith the soil in each step and this unt was accounted for in the desorption calculations (see Results and Discussion section). In the FC 9S experiment, the supernatant liquid was simply drained off at each step and the next 2S ml of liquid were @ut into the tubes. In the FC 143 experiment, the supernatant liquid remaining after the draining step was absorbed with a cotton swab before putting the next 25 ml of liquid into the tubes. The procedures for the FC 9S and FC 143 experiments were recorded in 3M Technical Notebook #40673, p. 49 and p. 51, respectively. From the raw counting data, disintegrations per minute (DPM) and FC 9S and FC 143 concentrations were calculated for all of the supernatant solutions. Statistical analysis and plotting of the data was done with the MINITAB package of the 3M TRAC computer service. RESULTS AND DISCUSSION FC 95 Adsorption data for FC 95 are presented in TABLE I and FIGURE 1. Comparing the regression equation of the adsorption isotherm (FIGURE 1) x/m a -0.29 + 0.99C with the Freundlich equation x/a = KC1/N, it could be seen that the adsorption coefficient, K, equaled 0.99 and the exponent,N, equaled one. The linear shape of the adsorption isotherms (N=l) indicated 4 that FC 95 adsorption on soil would be independent of concentration. The low adsorption coefficient (K=0.99) indicated that FC 95 would be m-obile, i.e., it would move readily with the ground water through this sandy loam soil. TABLE I A Initial FC 95 Conc., mg/l 282.2 158.0 90.0 51.0 28.0 2.8 FC 95 ADSORPTION DATA B Equil. Conc., C. mg/l. 233.9 134.2 76.9 42.0 22.1 2.0 c Removed y Soil @Zx ioo 17.1 is.1 14.6 17.8 21.1 27.0 D Total FC 95 In Initial Solln (A x 0.02S liters) 7.Osoo 3.9SOO 2.2506 1.27SO 0.7000 0.0700 E Total FC 95 in' Solln at Equil*.,mg (B x 0.02S liters) S.847.%O 3.35SOO 1.922SO I.OSOOO 0.55250 0.05000 FC 9S Adsorbed on Soil, x@m, ug/g (D-E) x 10 ullmj 5 Soil 240.8 119.0 6S.7 4S.3 29.5 3.8 Desorption data for FC 95 are shown in TABLE II and FIGURE 2. For comparison, desorption isotherms for the pesticide fluometuron are given in FIGURE 3. For clarity FC 95 desorption isotherms are not drawn in FIGURE 2. However, all of the data points lie very close to the adsorption isotherms indicating that adsorption and desorption could be described by a single-valued function with desorption coefficients, Ki, equaling the adsorption coefficient, K. 240 A 180 120 10 0 60 A A B A Regression Eqn.: Y -0.29 + 0.99 X R-Squared m 0.98S A = Actual Data Points' B - Predicted Y values 0 0 60 120 180 240 300 Equil. Conc., C, mg/l FI.GURE -1 FC 9S Adsorption Isotherm This, .along with the observation that approximately all of the adsorbed FC 95 was subsequently desorbed (TABLE ii, Column H) indicated that binding :forceswere weak and would be another indication of high mobility of FC 95. Material balance data for FC.95 are presented in TABLE III and these data indicate that all of the chemical was accounted for throughout the experiment. 6 A Equil. Conc. in Solution, C, mg/l. 233.900 134.200 76.900 42.000 22.100 2.000 TABLE II FC 9S DESORPTION ISOTIIERM DATA* B Equil. Conc. in First Desorption mg/l. 52.7000 30.3000 18.3000 9.6000 S.3000 0.6000 c Equil. Cone. in Second Desorption mg/l. 14.9000 9.0000 5.3000 2.9000 1.7000 0.2000 D Equil. Conc. in Third Desorption mg/l. 5.20000 2.80000 1.80000 1.00000 0.60000 0.10000 E Amount Adsorbed on Soil, x/m ug/g (Column F, TABLE I) 240.800 119.000 65.700 45.300 29.500 3.800 F Amount on Soil After First Desorption, ug/g 67.6000 19.4500 3.3000 13.2000 11.4000 1.7000 G Amount on Soil After Seco@d DeSOTption, ug/g 12.0000 -14.9000 -16.7000 2.0500 4.7000 0.9000 H Amount on Soil After Third Desorption, ug/g -9.1500 -25.8000 -23.9500 -2.0000 2.2500 0.4500 *Columns F, G, and H.were calculated in the same way as Column F,*TABLE I with correction for the amount of FC 95 in the 2.S ml of solution remaining from the.previous step in each case (See Materials and Wethods Section.) 10 zio.; 0.; W.E, 'CI a c Adso@Adrspotrpitoionn IIsso4therm 0+ --------- -- 60. ------ -- 120. ----- --------- 4 ---------- too. ?4u. )00. FIGURE 2 FC 9S DESORPTION DATA POINTS AND ADSORPTION ISOTHERM LO - S"'L'34'ZCS'-L*-C3L4"0C--4"34 C&" 3-CLIOC 0.1 seats C FLUDK"AM CL, saw" LO 10 CONC iaska loo. FIGURE 3 ADSORPTION A14D DESORPTION ISOTHERMS FOR FLUOMETURON ON COBB SAND. SOLID AND BROKEN LINES ARE BEST FIT FOR ADSORPTION AND DESORPTION. RESPECTIVELY. (From Davidson, 7 TABLE III FC 95 Material Balance* A Total Initial* FC 95 in Solution, mg. (Column D-;TABLE I)*. 7.05000 3.95000 2.25000 1.27500 0.7000 0.0700, B FC 95 in Solution at Equil., mg. (Column E, TABLE I) 5.84750 3.35500 1.99250 I.OSOO O.SS250 0.05000 c FC 95 on soil at Equil., mg. (A - B) 1.202SO 0.59500 0.32750 0.2250 0.14750 0.02000 D Amount Removed by First Desorption-,mg. 0.864500 0.497756 0.311000 0.159000 0.090500 0.011500 G Total Amount Desorbed by Three Desorptions, mg (D+E+F) 1.2483 0.7240 0.4473 .0.2350 0.1363 0.0178 E F Amount Removed'by Amou"ut Removed by Second Desgrgtion, mg.. Third Desorption, mg. 0.278000 0.171750 0.100000 O.OS5750 0.033500 0.004000 0.1057SO 0.054500 0.036250 0.020250 0.012250 0.0022SO H Amount Remaining on Soil After 3 Desorptions, mg. (C G) Amount Desorbed as Percent of Amount Aasorbed (G/C x 100). -0.457SO -0.12900 -0-1197S -0.01000 0.11250 0.002250 103.805 121.681 136.565 104.444 92.373 88.750 *Columns D, E, and F were obtained by first calculatingthe amount (mg) of FC-95 in 27.S ml (25 ml added plus 2.5 ml remaining from previous step) of solution in each respective step and then subtracting the amount (mg) in the 2.S ml of solution remaining from the previous step. 8 FC 143 Data for FC 143 are presented in TABLE IV and TABLE V and in FIGURE 4. The adsorption isotherm indicated FC 143 mobility similar to that of FC 95 with K=0.39 and N=l. Regression analyses were not performed on the desorption isotherms, however, the graphed data (FIGURE 4) indicated that adsorption and desorption could not be described by a single-valued function'. That is, the KI and N' values for desorption would not be the same as K and N :for adsorption. Subjective evaluationwould indicate that.the desorption coefficients would be much smaller than the adsorption coefficient, K, at solution concentrations greater than about 25 mg/l, since the slope of the adsorption isotherm was much greater than the slopes of the desorption isotherms in this range. At solution concentrations less than 25 mg/l., the desorption coefficients would appear to be much greater than the adsorption coefficient. From this it would appear that two or three different binding mechanisms. were involved with stronger binding occuring at the higher concentrations and the converse at lower concentrations. While this may indicate a tendency for FC 143 to be immobile at high concentrations, it would be quiti@mobile in any situations involving low concentrations. Material balance data for FC 143 are presented in TABLE VI. While the two concentrations resulting in 212%and 201% desorption (last column in TABLE VI) were erratic, in general, the data indicated that all of the FC 143 was accounted for throughout the experiment-. 9 TABLE IV PC 143 Adsorption Data A InitialPC 143 Conc. . 1%/l- B Equil. Conc., -C, mg/l. 522.5 292.6 167.2 94.1 52.3 5.2 485.8 279.1 160.3 92.2 49.9 5.1 c z Removed By Soil A -B x 100). A 7.0 4.6 4.1 2.0 4.5 1.9 D E Total PC 143 Total PC 143 in in Initial Sol'n, Sol'n at Equil., M& mg _(A x 0.025 literg) (B x 0.025 liters) 13.0625 7 3150 4:1800 2.3525 1.3075 0.1300 12.1450 6.9775 .4.0075 2.3050 1.2475 0.1275 F FG 143 Adsorbed on Soil, xim. ug./g (D-t) X-10 . UL/ma 5 v sojlj 183.5 67.5 34.5 9.5 12.0 0.5 10 TABLE V FC 143 Desorption Isotherm Data* A B Equil. Conc. in Solution, C, mx/l Equil. Conc. in first Desorption Solution, mit/l. (Column B Table IV) 485.800 279.100 160.300 92.200 49.900 5.100 47.6000 28.8000 17.2000 10.7000 6.1000 0.6000 c Equil. Conc. in Second Desorption Solution, mg/l. 6.80000 4.80000 3.40000 2.00000 0.80000 O.ioooo D Equil. Conc. in Third Desorption solution, MR/l-. 3.50000 2.90000 2.00000 0.50000 0.20000 0.01000 E F Amount Adsorbed Amount on Soil on Soil, x/m, After First besorp- ug4g ug/st (Column F, TABLE -IV) tion 183.500 67.500 34.500 9.500 12.000 0.500 164.600 50.850 20.050 --;3.250 3.400 -0.250 Amount on Soil After Second Desorpux/it tion 151.000 38.650 9.950 -8.900 2.050 -0.500 Amount on Soil Af ter Third Desorpult/it tion 135.150 25.100 0.650 -10-650 1.350 -0'.505 *Columns F, G, and R were calculated in the same way as Column P, TABLE IV with correction for the amount of FC 143 in'the 2.5 ml of solution remaining from the previous step in each case (See Materials and Methods Section). 200 iso B 100 so 0 qloo, A c 0 D -B D /1 E 0 A 0 2A B A c y -16.3 0.38' X R-SQUARED =.0.936 -50 0 100 200 300 Equil. Conc., C, mg/l 400 Soo FIGURE 4 FC 143 ADSORPTION AND DESORPTION ISOTHERMS Solid line is best fit adsorption isotherm. Dotted lines are estkmated desorption isotherms. A's are adsorption isotherm data points. B. Co Dp Es and F are desorption data points for the respective concentrations. GENERAL COMMENTS The FC-95 and FC 143 adsorption coefficients from these experiments may be converted to the analogous constants based on soil organic carbon conten; K , with the equation K oc oc = 100 K/(% organic carbon) giving* a K oc of 45 for FC 95 and 17 for FC 143 (2.2% organic carbon for this soil). Comparing these values to those in TABLE VII, it can be seen that FC 95 and FC 143 are at the low end of the spectrum, again indicating high mobility of these compounds. 12 TABLE VI FC-143 MATERIAL BALANCE* A Total FC 143 Initially in Solution mg. _(Column D, Table IV) 13.062S 7.31SO 4.1800 2.3S2S 1.307S 0.1300 D Amount Removed by First De;!orption,mg. 0.09450 0.0832S 0.07225 0.0637S 0.04300 0.0037S G Total Amount Desorbed by Thiee Desorptions, mg .LD+E+F)- 0.2418 0.2120 0.1693 0.1008 O.'053S 0.0050 B FC 143 in Solution at Equil.',mg. (Column E, TABLE IV) 12.14SO 6.9775 4.007S 2.3050 1.247S 0.1275 E Amount Removed by Second Desorption, mg. 0.06800 0.06100 0.05050 0.0282S 0.0067S 0.0012S H Amount Remaining on Soil After 3 Desorptions, mg. (C - G 0.676750 0.125SOO 0.003250 -0-OS32SO 0.006750 -0.002525 c FC 143 on Soil at Equil., mg. (A - B) 0.917S 0.337S 0.1725 0.047S 0.0600 0.002S F Amount Removed by Third Desorption, mg. 0.0792SO 0.066750 0.046500 0.0087SO 0.003SOO 0.000025 I Amount Desorbed as percent of Amount Adsorbed (G/C x 100) 26.349 62.815 98.116 212.10S 88.7SO 201.000 *Columns D, E, and F were obtained by first calculating the amount (mg) of FC 243 in 27.5 ml (25 ml added plus 2.S ml remaining from previous step) of solution in each respective step and then subtracting the amount (mg) in the 2.5 ml of solution remaining from the.previous step. 13 TABLE VII Comparison of Adsorption Coefficients for a Selected Group of Pesticides (liamakerand Thompson7-i 9-27-) Chemical KOC (mobile) Chloramben 12.8 (PC 143 - - - - - - - - - 17) 2,4-D 32 (PC 95 :- - - - - - - - - -45) Propham si Bromacil 71 Monuron 83 Simazine 135 Propazine IS2 Dichlobenil 164 Atrazine 172 Chloropropham 245 Prometone 300 Ametryn 380 Diuron 485 Prometr)rne 513 .Chlo-roxuron Paraquat 4 986 F t4 20:000 (immobile) DDT 243,000 The small amounts adsorbed and ease of desorption is consistent with'the relativelyhigh water solubilityof PC 95 (300 mg/1) and FC 143 (>20 g/i.) and with the chemical nature of the molecules organic salfs which ionize in aqueous solution: + c 8 F IIS03 K PC 9S + C7 F isC02-NH4 PC 143 14 Terms DPM - Disintegrations per minute C - Concentrationof chemical in solution at equilibrium x/m - Concentration of chemical adsorbed on soil at equilibrium R2 - Coefficient of determination K - Adsorption coefficient KI - Desorption coefficient N Exponential term in Freundlich Equation N' - Exponential term for desorption equation Koc - Adsorption coefficient based on soil organic carbon content References Davidson,,J. M., et. al., 197S, Use of Soil Parameters for Describing Pesticide Movement Through Soils, U. S. EPA, EPA---6-6072-7S-009. Davidson, J. M., 1976, "Vertical Movement and Distributionof Organics in Soils," presented at Symposium on Nonbiological Transport and Transformation of Pollutants on -Landand Water, at National Bureau of Standards-,Gaithersburg,,MD., May 11-13, 19 6. Hamaker, J. W. and J. M. Thompson, 1972. "AdsorptioiPin Organic Chemicals in the Soil Environment. C. A. 1. Goring and J. W. Hamaker (eds.).Marcel Dekker, Inc., N. Y. Hamaker, J. W., 1975, "Interpretationof Soil Leaching Experiments," in Chemicals Human Health and the Environment, A Collection of Dow Scientific Papers, Vol. 1, Dow Chemical USA, Midland, Mich. 48640