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with Palouse soil, one notices that only 0.14% of the total picloram adsorbed occurs on the clay fractions, while 5.22% is adsorbed in the case of parathion. Picloram can exist in various structural forms depending on pH and temperature (Cheung and Biggar, 1974). Its low total adsorption in general and, on clay in particular, may be attributed to the fact that most of it is in its anionic form. Previous results show that 99.7% was the anionic form based on pK, 3.4 and Palouse soil paste of pH 5.9, or 96.9% if the soil surface pH is assumed to be 4.9 due to suspension effects. Interactions with the negatively charged clay surface is highly unfavorable, leaving most of its interaction with the organic matter. Parathion has highly polar Pa+-O&and P=S bonds, as well as a conjugated ring and a polar -NOz group and is strongly adsorbed on the clay surface as well as on the organic matter. As shown in Table IV and system Ia, the iron oxide surfaces adsorbed 6.07% of the picloram. From structural considerations, the anionic picloram is capable of chelating with metal ions with its pyridinium nitrogen and the carboxyl group forming a five-membered ring. Parathion is adsorbed on iron oxides to a lesser extent. In systems IIa and IIIa parathion is reacting with different soils where it is adsorbed on both the organic matter and clay fraction. However, the adsorption by organic matter may predominate in many soils when it exceeds 1.0%. Yet, in soils relatively free of organic matter, when significant quantities of clay are present, the adsorption of parathion will still be significant. A simple flow method has been reported which facilitates the study of reaction rates of pesticides in soil. The relative adsorption constant k,, which is independent of the experimental conditions was found useful for comparison of reactions between different pesticides and soils. From the reported energies of activation, a dominance of physical interactions is suggested for the adsorption. The equilibrium adsorption results show that picloram interacts mainly with the organic fraction in soil and parathion with both the O.M. and clay fractions. Possible presence of the chemicals in the interlayer space of sodium montmorillonite has been demonstrated by X-ray analysis.
Woodrow et al.
The proposed procedure, aside from supplying a direct measure of the rate of adsorption important for the understanding of the movement of pesticides in soil, supplies activation parameters and insight into the mechanisms of soil-pesticide interactions. LITERATURE CITED Biggar, J. W., Cheung, M. W., Soil Sei. SOC. Am. Proc. 36, 863 (1973). Cheung, M. W., Biggar, J. W., J. Agric. Food Chem. 22,202 (1974). Cheung, M. W., Ph.D. Thesis, University of California, Davis, 1975. Davidson, J. M., Chang, R. K., Soil Sci. SOC. Am. Proc. 36, 257 (1972). Dowler, C. C., Forestier, W., Tschirley, F. H., Weed Sei. 16, 45 (1968). Frost, A. A., Pearson, P. G., “Kinetics and Mechanism”, Wiley, New York, N.Y., Chapter 5, 1963. Greenland, D. J., Quirk, J. P., Clays Clay Miner. 9, 484 (1961). Hamaker, J. W., Johnson, H., Martin, R. T., Redemann, C. T., Science 141, 363 (1963). Hygienic Guide Series, Am. Ind. Hyg. Assoc. J . 30(3), 308 (1969). Iwata, Y., Westlake, W. E., Gunther, F. A., Arch. Enoiron. Contam. Toxicol. 1(1), 84 (1973). Jackson, K. L., Soil Chemical Analysis-Advanced Course, University of Wisconsin, Madison, Wis., 1956, p p 31-58 and pp 101-140. Laning, E. R., Jr., Down Earth 19, 3 (1963). Lichtenstein, E. P., Schulz, K. R., J. Econ. Entomol. 57,618 (1964). Lynn, G. E., Doun Earth 20(4), 6 (1965). Robison, E. D., Proc. So. Weed Sei. SOC.20, 199 (1967). Saltzman, S., Mingelgrin, U., “Agrochemicals in Soil”, Banin, A., Ed., Springer Verlag, Berlin, 1978. Scifres, C. J., Burnside, 0. C., McCarty, M. K., Weed Sci. 17,486 (1969). Stewart, D. K. R., Chisholm, D., Ragab, M. T. H., Nature (London) 229, 47 (1971). Voerman, S . , Besemer, A. F. H., J . Agric. Food Chem. 18, 717 (1970). Weber, W. J., Jr., Gould, J. P., Adu. Chem. Ser. No. 60, 280-304 (1966). Yasuno, M., Hirakoso, S., Sasa, M., Uchida, M., Jpn. J. Exp. Med. 35(6), 545 (1966). Received for review April 10, 1978. Accepted August 7, 1978.
Rates of Transformation of Trifluralin and Parathion Vapors in Air James E. Woodrow, Donald G. Crosby, Terry Mast, Kenneth W. Moilanen, and James N. Seiber* The herbicide trifluralin (cu,cu,cu-trifluoro-2,6-dinitro-N,N-dipropyl-~-toluidine) and the insecticide parathion (0,O-diethyl 0-p-nitrophenyl phosphorothioate) were released separately to the atmosphere as emulsifiable concentrate sprays. Their vapors were sampled downwind by high-volume air samplers filled with XAD-4 macroreticular resin as the trapping medium. Analysis of the air samples indicated rapid photochemical conversion of trifluralin vapor to a dealkylated product (2,6-dinitro-N-propyla,a,a-trifluoro-p-toluidine) and parathion vapor to paraoxon (0,O-diethyl o-p-nitrophenyl phosphate). Half-lives for conversion were estimated as 20 min and 2 min for trifluralin and parathion, respectively, under comparable midday summer sunlight conditions. The half-life for trifluralin conversion increased to 193 min when the season changed from summer to fall. Trifluralin was stable in the dark; however, parathion showed some conversion to paraoxon on a summer night (131-min half-life). Results from laboratory experiments conducted under simulated sunlight conditions were consistent with the field results. Rates of photochemical conversion in the laboratory were significantly increased when 1-3 ppm ozone was added to the reaction flask. While it has long been known that pesticides may enter the atmosphere during and after application, the role of Department of Environmental Toxicology, University of California, Davis, California 95616. 0021-8561/78/1426-1312$01.00/0
chemical reactions in the dissipation of airborne pesticide residues has only recently been investigated. For example, chemical conversion takes place when the vapor of aldrin, dieldrin, or DDT is exposed to simulated sunlight (Crosby and Moilanen, 1974; Moilanen and Crosby, 1973), and 0 1978 American Chemical Society
Transformation Rates of Pesticide Vapors in Air
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Analysis. After each field experiment, the samples were under both laboratory and field irradiation of trifluralin packed immediately in dry ice, transferred to the labo(Soderquist et al., 1975) and parathion vapors (Woodrow ratory and stored at -10 "C until analyzed. The XAD-4 et al., 1977). The formation of epoxidized (aldrin), hyair samples were eluted with 100 and 200 mL of ethyl droxylated (DDT), dealkylated (trifluralin), and oxon acetate, for 30 and 60 g of XAD-4, respectively, on a rotary (parathion) products suggested photooxidation as a prishaker for 1 h. The ethyl acetate was then decanted and mary reaction mechanism in irradiated atmospheres. This filtered using additional portions (25 mL) of ethyl acetate is not surprising since many pesticides undergo such a to rinse the flasks. reaction on surfaces and in solution (Crosby, 1973). Analysis for parathion and paraoxon (0,O-diethyl 0We were, however, surprised by the rapid rate with p-nitrophenyl phosphate) was carried out by gas chrowhich some photooxidations occurred in the air under field matography (GLC) using a Varian Model 2100 gas conditions. The conversion of parathion to paraoxon, for chromatograph equipped with a rubidium sulfate alkali example, was estimated from analysis of vapors downwind flame ionization detector (AFID) at 210 "C and a 1.8 m from a treated orchard to occur with a half-life of only 1-10 X 2 mm (i.d.) glass column containing 10% DC-200 on min (Woodrow et al., 1977). In the present study we have 100/120 mesh Chromosorb W a t 200 "C. Trifluralin, attempted to establish a method for estimating more including the sample containing lindane, was analyzed with accurately the rate of photooxidation of pesticide residues a Varian Model 1700 gas chromatograph equipped with in the field atmosphere and to correlate the field results a tritium foil electron capture (EC) detector at 210 "C and with those obtained under controlled conditions in a a 1.8 m X 3 mm (0.d.) glass column containing 3% OV-17 laboratory photoreactor. The latter was particularly useful on 80/100 mesh Chromosorb G a t 180 "C. After analysis for investigating the role of atmospheric oxidant, such as for trifluralin, a 50-mL aliquot of the XAD-4 extract was ozone, in the course and rate of reaction. The test concentrated to 0.5 mL and 20-pL aliquots were injected chemicals were the insecticide parathion (0,O-diethyl onto a 25 cm x 4 mm (0.d.) Vydac reverse phase column 0-p-nitrophenyl phosphorothioate) and the herbicide (pC-18) (Applied Science Corp., State College, Pa.) at room trifluralin (a,cu,cu-trifluoro-2,6-dinitro-N,N-dipropyl-p-temperature. The column was eluted with 70% methanol toluidine). in water using high-pressure liquid chromatography (LC) and an ultraviolet detector a t 254 nm (Laboratory Data MATERIALS AND METHODS Control, Riviera Beach, Fla.). The elution volume for each compound was determined using standards. The fractions Materials. Parathion 4EC (PaCoast Chemical Co., suspected to contain trifluralin products I (2,g-dinitroSacramento, Calif.), Treflan EC (44.5% trifluralin; Elanco N-propyl-a,a,a-trifluoro-p-toluidine) and I1 (2,6-dinitroProducts Co., Indianapolis, Ind.), and lindane (20% w/w; a,a,a-trifluoro-p-toluidine) were analyzed using the same Cooke Laboratory Products, Pic0 Rivera, Calif.) were gas chromatographic conditions as for trifluralin. Fractions obtained from commercial sources. Analytical standards suspected to contain I11 (2-ethyl-7-nitro-l-propyl-5-triwere obtained from the Environmental Protection Agency, fluoromethylbenzimidazole) and IV (2-ethyl-7-nitro-5Beltsville, Md. Solvents were distilled twice from comtrifluoromethylbenzimidazole) were analyzed using a mercial grades except for ethylene glycol (EG) which was Varian Model 2100 gas chromatograph equipped with an purified from reagent grade solvent (Mallinckrodt AFID a t 210 "C and a 1.8 m X 2 mm (i.d.) glass column Chemical Works, St. Louis, Mo.) by the procedure of filled with 3% OV-17 on SO/lOO mesh Chromosorb G at Sherma and Shafik (1975). Amberlite XAD-4 (Rohm and 180 "C. Quantitation was done by comparing peak heights Haas, Philadelphia, Pa.), 20/50 mesh, was cleaned before with those of standard injections. Field background levels, use by rinsing with 0.02 M hydrochloric acid and water, obtained by sampling air prior to release of the pesticides, followed by Soxhlet extraction with acetone. were below the limit of detectability of
