Document O3QNBOvRybQOR7wpgv4kqwwmK

SOIL ADSORPTION TEST SUBSTANCE Identity: Perfluorooctanoic acid, ammonium salt; may also be referred to as PFOA ammonium salt, Ammonium perfluorooctanoate, PFO, FC-116, FC-126, FC-169, or FC-143. (Octanoic acid, pentadecafluoro-, ammonium salt, CAS # 3825-26-1) Remarks: The test sample is FC-143. It's purity was not sufficiently characterized, though current information indicates it is a mixture of 96.5 100% test substance and 0 - 3.5% C6, C7, and C9perfluoro analogue compounds. The test substance used was 14C-labeled. This testing is being repeated per current procedures and best available practices. METHOD:________________________________________________________ Method: Adsorption-Desorption study using the approach recommended by the U.S. EPA for pesticide registration GLP (Y/N): No Year (study performed): 1978 Statistical methods: Statistical analysis and plotting of the data was done with the MINITAB package of the 3M TRAC computer service. Temperature: 16-19C Stock and test solution preparation: Test solutions were made by diluting a stock solution of 14C-labeled ammonium perfluorooctanoate. The type of solvent used to make the stock solution is not noted, nor is the activity of the 14C-labeled test substance. Remarks field: The Brill sandy loam soil was characterized as having 57% sand, 36% silt, 7% clay, 2.5% organic matter, 1.5% organic carbon, with pH 6.5 and cation exchange capacity of 15.3 meq./100 gms. Standard solutions of the 14C-labeled compound were prepared in D.l. water at concentrations of 523 mg/L, 293 mg/L, 167 mg/L, 94 mg/L, 52 mg/L, and 5.2 mg/L. Twenty-five ml of each solution was shaken with duplicate 5 gram samples of the soil in a 50 ml polypropylene centrifuge tubes for 24 hours on a wrist shaker at room temperature (16-19C). Desorption extraction were performed with D.l. water after the adsorption phase of the experiment. The samples from the adsorption and desorption experiments were centrifuged individually at 5000 rpm for 10 minutes, after which, three aliquots of each supernatant solution were prepared for scintillation counting. From the raw counting data, compound concentrations were calculated for all of the supernatant solutions. 003614 RESULTS K: 0.21 (N=1) Koc: 14* * The study report had indicated a K of 0.38. This is the coefficient of C in the regression equation, not the adsorption coefficient value, based on best fit. Taking a mean value for K based on K=(x/m)/Ce, K = 0.21. The Koc value based on the initially reported organic carbon content of 1.5% and the mean value for K (Koc = K x 100/1.5(% organic carbon) becomes 14. CONCLUSIONS___________________________________________________ The study substance is expected to exhibit high mobility in the kind of soil tested. Submitter: 3M Company, Environmental Laboratory, P.O. Box 33331, St. Paul, Minnesota, 55133 DATA QUALITY___________________________________________________ Reliability: Klimisch ranking 3. This study lacks detail on the stock solution and the purity of the 14C-labeled test substance. There was no analysis of the soil to verify the amount remaining for mass balance. Discrepancies in the organic carbon content are present. Use of Dl water instead of CaCI2. Additionally, some calculations have questionable reliability. Additional comments by Professor Stephen A. Boyd, Michigan State University, also indicate the reliability level of this study. REFERENCES____________________________________________________ 3M Technical Report "Adsorption of FC 95 and FC 143 on Soil." S.K. Welsh, Project 9970612633 Fate of Fluorochemicals, Report No. 1, Feb. 27, 1978 3M requested expert review by Professor Stephen A. Boyd, Michigan State University, May 19, 1993. OTHER________________________________________________________ Last changed: 5/25/00 003615 r Attached are comments on the 3M Technical Report "Adsorption o f FC 95 and FC 143 on Soil. S.K. Welsh, Project 9970612633 Fate o f Fluorochemicals, Report No. 1, Feb. 27, 1978" made by Professor Stephen A Boyd, Michigan State University, dated May 19, 1993. 003616 Review o f Technical Report Summary Adsorption o f FC 95 and FC 143 in Soil Material and Methods Should give recoveries o f compounds in blank (no-soil) experiments. States that polypropylene sorbs less than glass on polyethylene, but doesn't give a numerical value. The large headspace (25 ml in a 50 tube) is undesirable; any losses o f the 14C-label, e .g ., from volatilization or sticking to the tube, w ill inflate the sorption coefficient since the method calculates the amount sorbed by difference between the initial and final equilibrium solution concentrations. Also the 24 hour mixing period seems arbitrary. Were experiments done for different periods o f time to establish that equilibrium was reached within 24 hours? Details on the stock solution are lacking. What solvent was used and what is the specific activity and radiochemical purity o f the 14C-FC 95. The idea o f using a cotton swab after the draining step is unusual. Hopefully this didn't remove soil as well as water. The ~20% or less decrease in solute concentration due to sorption isn't as high as I'd like to see it. A 50% or greater decrease would be better. This section generally lacks detail that would normally be required for publication. Results and Discussion The linearity o f the isotherm has been shown over the concentration range used. However, to demonstrate that the entire isotherm is linear, the linearity must extend to equilibrium solution concentrations that approach the water solubility o f the compound. Do you know the solubility o f FC95 or FC143: If not, how were the initial solution concentrations selected? The sorption coefficient (K) o f FC 95 appears to be about 1 as indicated. The organic matter normalized sorption coefficient (K ^ = K/f^J is = 1/0.025 = 40, or log = 1.6. This is a soil sorption coefficient intermediate between benzene and toluene. It would be worthwhile to examine some additional soils to confirm this value. Generally, the K^, values should converge within a factor o f 2 to 3 for different soils. This would increase my confidence in the accuracy o f the one measured value. I've spot checked the soil concentrations o f FC-95 for both the sorption and desorption experiments and I get essentially the same values. The calculations look good. The K values for FC 143 is lower than FC 95 indicating that it probably has a higher water solubility. The hystersis in the desorption isotherm is surprising, and has been over-interpreted. The sorption isotherm is linear indicating a single sorptive process. The conclusion regarding "three different binding mechanisms ... with stronger binding at higher concentrations and the converse at lower concentrations" is very speculative based on the single experiment. If one examines column I "Amount Desorbed as a Percent o f Amount Adsorbed" the values range from 003617 26 to 212 percent, so it's pretty inconclusive. There is a fairly good discussion o f hysteresis in J. Environ. Qual. 12:325-330 by Koskinen and Cheng who observed this phenomena for the weak acid pesticide 2,4,5-T . The causes o f hysteresis are varied and complicated and may include microbial degradation o f the compound during desorption, and changes in the physical and/or chemical properties o f the soil-solution system. For example, desorption using distilled water (as is the case here) could result in soil dispersion so that a clear supernatant solution could not be obtained. This can cause quenching o f radioactivity in solution and other problems leading to error. The "material balance" as presented in the report is a little misleading. To obtain a material balance you should measure the amount o f 14C-activity in soil at the end o f the experiment, and add it to the measured solution concentrations. General Comments. The K^. values calculated here use an organic carbon content o f 2.2% whereas the value stated in the Materials and Methods is 1.596? The water solubilities are cited as 300 mg/L for FC 95 and > 20g/L for FC 143. Surely the latter value is wrong. If the solubilities are truly that different, then the sorptive properties should be vastly different, which they are not. If FC143 has a solubility o f > 2 0 ,0 0 0 mg/L, then I would expect no sorption. This value must be erroneous. Recommendations: 1. Obtaining K, values on additional soils. Determine if is relatively constant. 2. Obtain a true mass balance by measuring I4C-activity in soil and solution phase. 3. Interpret desorption data more cautiously. 4. Get correct value of water solubility o f FC 143. 003618 r, :Srr,,.A TECHNICAL REPORT SUMMARY ate 2/27/78 TO: TE C H N IC A L COM M UNICATIONS CENTER - 201-2CN (Important - I f report is printed on both tides o f paper, send two copies to TCC.) Division Project Report Title To EE PC Fate of Fluorochemicals Adsorption of FC 95 and FC 143 on soil Dept. Number 0222 Protect Number 9970612633 Report Number 1 A uthor! i) Stephen K. Welsh SfcuJ Notebook Rofranea Employ* N um btrlil 73583 No. of Paga* IncludingCovanhaat #40673, 47704 14 SECURITY ^ Open ( 2 Closed 3M CHEMICAL REGISTRY New Chemicals Reported Yes Q No KEYWORDS: (Select terms from 3M Thesaurus. Suggest other applicable terms.) CURRENT OBJECTIVE: To obtain an indication of FC 95 and C 143 mobility in sandy loam soil. EE 8 PC - Div. Fluorochemical Soil Adsorption Mobility REPORT ABSTRACT: (200-250 words) This abstract information is distributed by the Technical Communications Center ti alert 3M `ers to Company R&O. As a part of the Fate of Fluorochemicals Project, an indication of mobility of FC 95 and FC 143 in sandy loam soil was `desired. Adsorption-desorption experiments (after Davidson, 1976, and Hamaker, 1975) along with water solubility data can provide such information. The adsorption coeffients for FC 95 and FC 143 were determined to be 0.99 and 0.38, respectively. For FC 95 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. Information1 LL'iaaiiasvonn Initials: 003619 2 CONCLUSIONS Adsorption coefficient for FC 95 and FC 143 were 0.99 and 0.38, respectively. For FC 95, 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 of mobility of FC 95 and FC 143 in sandy loam soil was desired. Adsorption desorption experiments (after Davidson, 1976, and Hamaker, 1975) along with water solubility data can provide this indicatipn of mobility. This approach is used by the U. S. EPA in pesticide registration requirements. MATERIALS AND METHODS Duplicate 5-g samples of air-dried Brill sandy loam soil (57% sand, 36% silt, 7% clay, 2.5% organic matter, 1.5% organic carbon, with pH 6.5 and C.E.C. of 15.3 meq./lOOg) were shaken with 25 ml of solution in 50 m l . poly propylene centrifuge tubes for 24 hours on a wrist action shaker at room temp. (16-19C). Polypropylene tubes were used because they were found in separate experiments (3M Tech Notebook #470673, C. H. Schrandt) to absorb less FC 95 and FC 143 than glass or polyethylene tubes. Solutions were made by diluting a stock solution of each chemical. 14 Concentrations of C-labeled FC 95 were 282 mg/1., 158 mg/1., 90 mg/1., 51 mg/1., 28 mg/1., (100%, 56%, 32%, 18%, 10%, 1% of stock). Concentrations of *4C-labeled FC 143 were 523 mg/1., 293 mg/1., 167 mg/1., 94 mg/1., 52 mg/1., and 5.2 mg/1. 003620 3 After shaking the initial solutions as well as the three desorption extractions with deionized water, the samples were centrifuged at 5000 Tpm for 10 min., and three aliquots of each supernatant solution were taken for scintillation counting. After the adsorption step, 22.5 ml of solution were recovered. Therefore, it was assumed that 2.5 ml of liquid remained with the soil in each step and this amount was accounted for in the desorption calculations (see Results and Discussion section). In the FC 95 experiment, the supernatant liquid was simply drained off at each step and the next 25 ml of liquid were put 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 95 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 95 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 = -0.29 + 0.99C with the Freundlich equation x/m = KC*^N , it could be seen that the adsorption coefficient, K, equaled 0.99 and the exponent, N, 00362 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 mobile, i.e., it would move readily with the ground water through this sandy loam soil. TABLE I A Initial FC 95 Cone., mg/1 282.2 158.0 90.0 51.0 28.0 2.8 FC 95 ADSORPTION DATA B Equil. Cone., C, mg/1. 233.9 134.2 76.9 42.0 22.1 2.0 C % Removed By Soil ( AzB x 100 ) A* -- {------17.1 15.1 14.6 17.8 21.1 27.0 D Total FC 95 In Initial Sol'n (A x 0.025 liters) 7.0500 3.9500 2.2500 1.2750 0.7000 0.0700 E Total FC 95 in Sol'n at Equil., mg (B x 0.025 liters) 5.84750 3.35500 1.92250 1.05000 0.55250 0.05000 F '* FC 95 Adsorbed on Soil, x/m, yg/g ,(D-E) x 103 yfc/mg . 1 5 p Soil J 240.8 119.0 65.7 45.3 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, K'> equaling the adsorption coefficient, r 003622 Adsorbed on Soil, x/m, yg/g. 5 Equil. Cone., C, mg/1 FIGURE 1 FC 95 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 forces were 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. 003623 6 A Equil. Cone, in Solution, C, mg/1. 233.900 134.200 76.900 42.000 22.100 2.000 TABLE II FC 95 DESORPTION ISOTHERM DATA* B Equil. Cone, in First Desorption mg/1. C Equil. Cone, in Second Desorption mg/1. 52.7000 30.3000 18.3000 9.6000 5.3000 0.6000 14.9000 9.0000 5.3000 2.9000 1.7000 0.2000 D Equil. Cone, in Third Desorption mg/1. 5.20000 2.80000 1.80000 1.00000 0.60000 0.10000 E Amount Adsorbed on Soil, x/m yg/g (Column F, TABLE I) 240.800 119.000 65.700 45.300 29.500 3.800 F Amount on Soil After First Desorption, yg/g 67.6000 19.4500 3.3000 13.2000 11.4000 1.7000 G. Amount on Soil After Second Desorption, yg/g 12.0000 -14.9000 -16.7000 2.0500 4.7000 0.9000 H Amount on Soil After Third Desorption, yg/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 2.5 ml of^ solution remaining from the previous step in each case (See Materials and Methods Section.) a -ro. - -- -- --------- ------------ 1*0. 4M. * 0 . 1 0 0 . 50(1. FIGURE 2 FC 95 DESORPTION DATA POINTS AND ADSORPTION ISOTHERM SOumoN CONC 003624 FIGURE 3 ADSORPTION AND 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 II, 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 1.0500 0.55250 0.05000 C FC 95 on soil at Equil., mg. (A - B) 1.20250 0.59500 0.32750 0.2250 0.14750 0.02000 D Amount Removed by First Desorption, m g . 0.864500 0.497750 0.311000 0.159000 0.090500 0.011500 E F Amount Removed by Amount Removed by Second Desorption, m g .. Thirdf Desorption, m g . 0.278000 0.171750 0.100000 0.055750 0.033500 0.004000 0.105750 0.054500 0.036250 0.020250 0.012250 0.002250 G Total Amount Desorbed by Three Desorptions, mg (D+E+F) 1.2483 0.7240 0.4473 0.2350 0.1363 0.0178 H Amount Remaining on Soil After 3 Desorp tions, mg. (C - G) -0.45750 -0.12900 -0.11975 -0.01000 0.11250 0.002250 I Amount Desorbed as Percent of Amount Adsorbed (G/C x 100). 103.805 121.681 136.565 104.444 92.373 88.750 Columns D, E, and F were obtained by first calculating the amount (mg) of FC-95 in 27.5 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 th 2.5 ml of solution remaining from the previous step. 003625 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=0.38 and N=l. Regression analyses were not performed on the desorp tion isotherms, however, the graphed data (FIGURE 4) indicated that adsorption and desorption could not be described by a single-valued function. That is, the K' and N 1 values for desorption would not be the same as K and N for adsorption. Subjective evaluation would indicate that the desorption coefficient K*, would be much smaller than the adsorption coefficient, K, at solution concentrations greater than about 25 mg/1, since the slope of the adsorption isotherm was much greater than the slopes of the desorption isotherms in t this range. At solution concentrations less than 25 mg/1., 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 quite 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. 003626 9 TABLE IV FC 143 Adsorption Data A Initial FC 143 Cone., mg/1. 522.5 292.6 167.2 94.1 52.3 5.2 B Equil. Cone., C, mg/1. 485.8 279.1 160.3 92.2 49.9 5.1 C Z Removed By Soil ( A y - x 100) A> ' 7.0 st4.6 4.1 2.0 4.5 1.9 D Total FC 143 in Initial Sol'n, mg (A x 0.025 liters) E Total FC 143 in Sol'n at Equil., mg (B x 0.025 liters) F FG 143 Adsorbed on Soil, x/ yg/g (D-E) X 103 C . 5 e SoilJ 13.0625 7.3150 4.1800 2.3525 1.3075 0.1300 12.1450 6.9775 4.0075 2.3050 1.2475 0.1275 183.5 67.5 34.5 9.5 12.0 0.5 C03S7 10 TABLE V FC 143 Desorption Isotherm Data* AB CD Equil. Cone, in Solution, C, mg/l Equil. Cone. in first Desorption Solution, mg/1. (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 EF Equil. Cone. Equil. Cone. in Second Desorp- in Third Desorption tion Solution, mg/1. solution, mg/1. 6.80000 4.80000 3.40000 2.00000 0.80000 O.lOOpO * t G 3.50000 2.90000 2.00000 0.50000 0.20000 0.01000 H Amount Adsorbed Amount on Soil on Soil, x/m, After First Desorp- UR/8 Pg/g________ tion (Column F. TABLE IV) Amount on Soil After Second Desorp- Pr/ r tio n Amount on Soil After Third Desoxp- pr/ r tio n 183.500 67.500 34.500 9.500 12.000 0.500 164.600 50.850 20.050 -3.250 3.400 -0.250 151.000 38.650 9.950 -8.900 2.050 -0.500 135.150 25.100 0.650 -10.650 1.350 -0.505 Columns F, G, ;and H were calculated in the same way as Column F, 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). 003628 Adsorbed on Soil, x/m, yg/g. 11 Equil. Cone., C, mg/1 FIGURE 4 FC 143 ADSORPTION AND DESORPTION ISOTHERMS Solid line is best fit adsorption isotherm. Dotted lines are estimated desorption isotherms. A's are adsorption isotherm data points. B, C, D, E, 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 contend K , with the equation K = 100 K/(% organic carbon) giving a K of 45 for FC 95 and 17 for FC 143 (2.2% organic carbon for this Wv 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. 003629 12 TABLE VI FC 143 MATERIAL BALANCE* A Total FC 143 Initially in Solution mg. (Column D, Table IV) 13.0625 7.3150 4.1800 2.3525 1.3075 0.1300 D Amount Removed by First Desorption, mg. 0.09450 0.08325 0.07225 0.06375 0.04300 0.00375 G Total Amount De sorbed by Three Desorptions, mg (D+E+F')________ 0.2418 0.2120 0.1693 0.1008 0.0535 0.0050 B FC 143 in Solution at Equil., mg. (Column E, TABLE IV) C FC 143 on Soil at Equil., mg. (A - B) 12.1450 6.9775 4.0075 2.3050 1.2475 0.1275 0.9175 0.3375 0.1725 0.0475 0.0600 0.0025 E *F Amount Removed by Amount Removed by Second Desorption, m g . Third Desorption, m g . 0.06800 0.06100 0.05050 0.02825 0.00675 0.00125 0.079250 0.066750 0.046500 0.008750 0.003500 0.000025 H Amount Remaining on Soil After 3 Desorp tions, mg. (C - G )___________ I Amount Desorbed as percent of Amount Ad sorbed (G/C x 100) 0.676750 0.125500 0.003250 -0.053250 0.006750 -0.002525 26.349 62.815 98.116 212.105 88.750 201.000 *Columns D, E, and F were obtained by first calculating the amount (mg) of FC 143 in 27.5 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 2.5 ml of solution remaining from the previous step. 003630 13 TABLE VII Comparison of Adsorption Coefficients for a Selected Group of Pesticides (Hamaker and Thompson", 1972) Chemical KQc (mobile) (immobile) Chloramben 12.8 (FC 1 4 3 .................. 17) 2,4-D 32 (FC 95 - ................ 45) Propham 51 Bromacil 71 Monuron 83 Simazine 135 Propazine 152 Dichlobenil 164 Atrazine 172 Chloropropham 245 Prometone 300 Ametryn 380 Diuron Prometryne 485 513 t Chloroxuron Paraquat 4,986FH<fZ 7. 20,000 DDT 243,000 The small amounts adsorbed and ease of desorption is consistent with the relatively high water solubility of FC 95 (300 mg/1) and Fc 143 ( > 2 0 g/1.) and with the chemical nature of the molecules - organic salts which ionize in aqueous solution: 8F17S03 K FC 95 C7F 15C02 NH< FC 143 003631 14 / Terms DPM - Disintegrations per minute C - Concentration of chemical in solution at equilibrium x/m - Concentration of chemical adsorbed on soil at equilibrium - Coefficient of determination K - Adsorption coefficient K' - Desorption coefficient N - Exponential term in FreundlichEquation N 1 - Exponential term for desorption equation Kq C - Adsorption coefficient based on soil organic carbon content References Davidson, J. M . , et. al., 1975, Use of Soil Parameters for Describing Pesticide Movement Through Soils, U. S. EPA, EPA-660/2-75-009. Davidson, J. M., 1976, "Vertical Movement and Distribution of Organics in Soils," presented at Symposium on Nonbiological Transport and Transformation of Pollutants on -Land and Water, at National Bureau of Standards, Gaithersburg, MD., May 11-13, 1976. Hamaker, J. W. and J. M. Thompson, 1972. "Adsorption" in Organic Chemicals in the Soil Environment. C. A. I. Goring and J. W. Hamaker- (eds.). Marcel Dekker, Inc., N. Y. Hamaker, J. W., 1975, "Interpretation of Soil Leaching Experiments," in Chemicals, Human Health and the Environment, A Collection of Dow Scienti fic Papers, Vol. 1, Dow Chemical USA, Midland, Mich. 48640 003632