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Chapter 9 TRIFLURALIN AND ORYZALIN NO2 ~ /CH2 CH2 CH3 F3C - / \ - N \=< \CH2CH2CH3 NO2 NO2 ,: CH2CH2CH3 // \\ / NH2.O2 S - ( IN CH2CH2CH3 NO2 Trifluralin (a, a, ~-trifluoro-2 ,6-dinitro-N,N-dipropyl-~ toluidine; also known as Treflan) and oryzalin (3, 5-dinitro-N4, N4-dipropylsulfanilamide) are both members of a class of compounds known as dinitroanilines. Trifluralin is an orange crystalline solid that melts at 49C. It has a low solubility in water (0 .3 ppm) and a low vapor pressure (2 x 10 4 mm Hg at 30C). Oryzalin is a yellow-orange crystalline solid that melts at 141C. It has a much lower vapor pressure (less than 10 7 mm Hg at 30C) than trifluralin, but is slightly more soluble in water (2.5 ppm at 25C). Trifluralin is produced via a ser ies of reactions beginning with the reaction of hydrogen fluoride with E~chlorotoluene to produce 4-trifluoromethylchlorobenzene. The latter compound is then nitrated followed by reaction with di-N-propylamine, which replaces tbe chlorine to form trifluralin. me production of oryzalin begins with the nitration of E:chlorobenzenesulfonic acid, followed by the addition of chlorine to form 2,6-dinitro-E~chlorobenzenesulfonyl chlor ice, followed by the addition of ammonia and di-N-propylamine to yield oryzal in . 228

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PRODUCTION Eli I`illy and Co. {Elanco Products Division) is the sole U. S . producer of tr if luralin (Stanford Research Institute International, 1979 U.S. International Trade Commission, 1978~. The plant at Lafayette, End., has an estimated 23,000-metric ton capacity for production of trifluralin. Lilly owns the patent rights for oryzalin, but has contracted production to various other firms since receiving approval of oryzalin use in 1975. GAF Corporation made oryzalin for Lilly at Rensselaer, N.Y., from January 1975 to June 1976 (Chemical Week, 1979~. Proctor Chemical at Salisbury, N.C., produced oryzalin from January 1975 to January 1976. The U. S. International Trade Commission listed the Sodyeco Division of Martin Mar ietta Corporation, Sodyeco, N.C., as a producer of oryzalin in 1977 and 1978. Other processors and formulators of oryzalin for Lilly have included Bold Chemical of Tifton, Gal, Central Chemical of Hagerstown, Ark., and Helena Chemical of Helena, Ark. (Chemical Week, 1979~. Although no estimates of production capacity are available for these plants, the production of trifluralin in 1975 and 1978 is estimated at 12, 000 and 16, 000 metr ic tons, active ingredient, respectively. Oryzalin production in 1975 is estimated at 45 mete ic tons, active ingredient; 1978 production is estimated at 450 metric tons of active ingredient. 229

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U_ Trifluralin and oryzalin are both used almost exclusively as herbicides. Consumption estimates for each in 1978 are shown in Table 9-1. The Environmental Protection Agency {EPA} teas approved both trifluralin and oryzalin for use as herbicides; however, both compounds have been challenged on several occasions. Trifluralin was challenged on the grounds that it contained nitrosamine contaminants and that its use therefore posed an unacceptable carcinogenic risk. Risk-benefit studies initiated by EPA concluded that benefits of trifluralin outweigh any risks if nitrosamine contamination is kept below 1 ppm (Chemical Marketing Reporter, 19791. Subsequently, Lilly has produced trifluralin with a nitrosamine content of less than 1 ppm, and has continued to receive approval for its use as an herbicide. Oryzalin has been suspected of causing heart-related birth defects among children fathered by workers involved in its manufacture and of causing skin rashes in workers. However, EPA investigations did not disclose any adverse effects, and no regulatory action is planned (Chemical Marketing Reporter, 1980~. Nonetheless, Lilly is required to maintain ongoing teratological studies to support the continued registration of oryzalin (Pesticide and Tbxic Chemical News, 1980~. 230

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Table 9-1 Consumption of Trifluralin and Oryzalin Percent of Product Conta in ing compound Tr if luralin 103 Metric Ton. of Active Ingredient Cotton 21. 2 . 7 Deciduous fruits/nuts 1 0 .05 Peanuts 1 0.1 Soybeans 7 4 9 7 Sugar beets 1 0.05 Vegetables 2 0.3 Other f ield crops 1 0 .14 Industr ial/co~ercia 1 0.1 Total 100 13.1 OrYzalin Cotton 10 0.05 Deciduous fruits/nuts ~ 10 0.05 Soybeans 60 0.27 Industrial/commercial 20 0. 09 Total 100 0 .45 Stanford Research institute, 1979 231

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EXPOSURE The principal routes of exposure to trifluralin and oryzalin are the following: workers are exposed dur ing n~anufactur ing process ; agricultural workers are exposed while applying~the substances to crops; and the general public is exposed through releases of the compounds into air and water during manufacturing processes, through drift, volatilization, and runoff as a result of application, and via contaminated food crops. Because more trifluralin is used than oryzalin, and because much more data about trifluralin exist, this chapter focuses on exposure to trifluralin. Trifluralin is produced at a single site in Lafayette, Ind. (population, 45,000~; thus, exposure of the public to trifluralin during its manufacture is of only local importance. Although no data are available on trifluralin plant discharges, small quantities are known to be discharged into the Wabash River as waste from the manufacturing processes. m e treatment procedure involves activated sludge, followed by settling, and then filtration through activated carbon (Specie and Hamelink, 19791. Parts per trillion (ppt) concentrations of trifluralin have been measured in the water downstream from the plant. However, the tissues of fish captured in these waters contain concentrations of trifluralin several thousand times greater than those in the water (Specie and Hamelink, 1979~. 232

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The most likely source from which the general public is exposed to trifluralin is the herbicide's application to soils to control grass and broadleaf weeds. This is practiced primarily in the North Central and South Central States, especially in Illinois, Iowa, and Mississippi (Helling, 1976~. ~ Trifluralin is not an especially persistent chemical. m ere have been some studies of the persistence of trifluralin in soil under actual field conditions (Golab et al., 1979; Golab and Amundsen, 1975; Probst et al., 1967) These studies show that trifluralin concentrations decreased from 10% to 15t of their original value 1 year after application. Trifluralin is lost through volatilization as well as through degradation. At this rate of loss, trifluralin does not tend to accumulate in soils receiving repeated applications. Although the rate of volatilization of trifluralin depends to a great extent on the method of its application, such dissipation provides a signif icant potential exposure route for persons living downwind of treated f ields . If trifluralin is applied to the soil surface, up to 90% of the compound may be volatilized within 2-3 days of application . If it is incorporated into the soil, volatilization losses can be as little as 3% or 4% in 90 days (Taylor, 1978~. In an experiment in which trifluralin was sprayed onto soil and then tilled into the soil, White et al. t1977} measured ~ maximum concentration of 16.5 Ug/m 3 20 cm above the soil during application. The maximum concentration was 3.4 ~g/m 3 20 cm above the soil on the second day 233

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after the compound was tilled into the soil, decreasing to 100 ng/m 3 after the 35th day. They estimated total volatilization losses to be at 22.41 during the growing season (120 days) and vapor losses during spraying to be at 3.58. Exposure of persons living downwind of sprayed fields is somewhat reduced because trifluralin is subject to fairly rapid photochemical decomposition. Measurements of trifluralin degradation in air indicate a balf-life of 20 minutes under midday summer sunlight conditions. Woodrow et al. {1978} observed that the half-life increased to 193 minutes in the fall. Trifluralin is stable in the dark. Although relatively immobile in soil, trifluralin may be transported long distances from its initial source of application via runoff into streams and rivers. Indeed, trifluralin has been detected at levels of up to 0.2 ~g/1 in the Cape Fear River, N.C. Trifluralin concentrations tended to correlate with periods of greatest runoff and soil erosion on agricultural lands adjacent to tributaries of that waterway {Horder, 19771. Although there is probably minimal direct exposure.of humans via this route, the tendency of trifluralin to accumulate in fish must not be overlooked (Specie and Hamelink, 19791. Humans may also be exposed to trifluralin through food crops treated with the herbicide. However, analyses of residues in a wide variety of tolerant crops indicate that trifluralin is not 234

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incorporated into the leaves, seeds, or fruits (measurement sensitivity, 5-10 ppb). In treated root crops, such as onions and garlic, trifluralin residues are found only in the outer shell, which is usually discarded before consumption. me exception is carrots ~ : 31% of the total residue of 0.65 ppm was found~in the interior of the carrot proper--69% was concentrated in the peel (Protest et al., 1967) 235 .

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ANALYTIC METHODS Methods to analyze trifluralin in a variety of vegetables, plant tissues, soil, water, oily crops, wheat grain and straw, and mint and mint hay are described in the Pesticide Analytical Manual of the Food and Drug Administration (1973~. Trifluralin is extracted from crops by blending it with methanol and subsequent extraction from the solvent into dichloromethane. After evaporation of the dichloromethane, the extract is dissolved in hexane, cleaned up on a column of Florisil, and analyzed by electron-capture gas chromatography (EC-GC). GC columns (1.83 m) packed with 3% XE-60 or 5t SE-30 on Chromosorb W are used at approximately 180C with the carrier gas flowing at 90 ml/minute. The retention time (tR, for trifluralin is 3 to 4 minutes. The analytic procedure is modified as required for aqueous or oily samples. Recoveries of approximately 80% or more can be expected, and the sensitivity ranges from 5 to 10 ppb. Samples containing residues of benzene hexachloride, ethion, and/or zineb require additional cleaning. The interfering compounds are separated by thin-layer chromatography (TEC). Ihe trifluralin- is then scraped from the plate, elated, and assayed by EC-GC. The procedure used at North Carolina State University (T.J. Sheets, North Carolina State University, personal communication, 1980) to determine trifluralin residues in soils requires a 4-hour Soxhlet extraction of the oven-dried sample with benzene-isopropyl alcohol (1:2~. The extract is evaporated just to dryness, dissolved in hexane, cleaned on a Florisil column and subsequently analyzed 236

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by EC-GC. Glans columns {1.83 m long 0.635 cm outside diameter) packed with 4% SE-30 plus 61 QF-1 or with 51 Carbowax 20M on Gas Chrom Q are opera ted at 155C with a Me flow of 80 to 100 ml/minutes. Under these conditions, the tR for trifluralin is approximately 2.0 minutes. Recently reported analytic methods have focused mainly on GC techniques, coupled with various types of detectors including mass spectrometers. Payne et al. (1974) developed a procedure to analyze trifluralin, diphenamid, and paraguat in admixture in soil, sediment, and water. The procedure permits simultaneous GC assays of trifluralin and diphenamid, without cleanup, by employing a Couison electrolytic conductivity detector. Paraquat is determined calorimetrically. m e 1.83 m long glass GC column (0.635 cm outside diameter) was packed with 10% DC-200 on Gas Chrom Q. Recoveries of trifluralin spiked into water at concentrations of O .05 to 10 ppb were 82% to 91%; those from soil spiked at 0 . OS and 1.0 ppm were 861 and 941. Smith (1974 ~ used acetonitr ire-water (9 :1) and ultrasonication to extract residues of four herbicides, including trifluralin, from three types of soil. ffl e addition of excessive amounts of water and saturated sodium sulfate solution to the extract facilitated subsequent partitioning of the herbicide residues into hexane. me hexane extract was then concentrated and assayed by EC-GC. The GC system consisted of ~ 1.5 m long glans column (6 ~ outside diameter), packed with 10% OV-1 on Q~romosorb G-HP operated at 237

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ml/minute, tR's for dichlorobenil, trifluralin, dinitramine, and triallate were approximately 1.0, 2.9 , 4 . 5 , and 5.0 minutes, respectively. Recoveries of all four compounds spiked into the three types of soil at 0.05 and 0.5 ppm levels were 92% or more. Lawrence (1976) examined the separation characteristics of Several GC liquid phases (i.e., 31 OV-1, 4% SE-30-6. SP-2401, 10% DC-200, and 5% DEGS on Chromosorb W HP) for 12 pesticides, including trifluralin, by using the Coulson detector. Sensitivities (50% scale) for trifluralin at a tR of approximately 3 minutes on OV-1 at 175C were reported as 6 ng and 3 ng for the nitrogen and chlorine modes, respectively. Later, Lawrence et al. (1977) reported a confirmatory procedure for pesticides that contain nitrogen dioxide (NOW. ate pesticide residue in ~ m] of benzene was shaken with 0.5 ml of aqueous chromous chloride to convert the NO2 groups to NH2. me solution was made basic and the product extracted with benzene for analysis by GO with a Coulson detector (nitrogen mode). The products were found to be approximately as sensitive as the parents and had tR values of 0.4 to 0.9 minutes relative to the parent compound on the SE-30/SP-2401 column. The procedure was used to confirm trifluralin residues in extracts of potato spiked at levels of 0.5 to 1.0 ppm. Woodrow et al. (1978 ~ used EC-GC to study the behavior of trifluralin vapors released into the atmosphere as emulsifiable concentrate sprays. The experiment wan conducted with a 1.8 m long glass column (3 mm, internal diameter), packed with 3% OV- 17 238

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REFERENCES Production, Uses, Exposure Chemical Marketing Reporter . 1979. P. 4 in September 3, 1979 issue. Schnell Publishing Company, New York. Chemical Marketing Reporter. adver se e f feats . 217 {11) :3, 32. 1980. EPA herbicide probe finds no Chemical Week. 1979. Union seeks ban on Eli Lilly herbicide. 125(20):28. Golab, T., and M. E. Amundson. 1975. Degradation of trifluralin, oryzal in and isopropyl in in soil . 3: 258-261 . Environ . Qua 1. Sa f . Suppl . Golab, T., W. A. Althaus , and H. L. Wooten . 1979 . Fate of [14C] tr if luralin in soil . J . Agr ic . Food Chem. 27: 163-179 . Hell ing, C. S. 1976. Dinitroaniline herbicides in soils. J. Environ. Qual. 5: 1-lS . 263 \

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Horden, W. 1977. A Report on the Ose of the Macroreticular Resin XAD-2 to Isolate Pesticides from the Cape Fear River. University of Nor th Carolina, Chapel Hill, N.C. Pesticide and Toxic Chemical News. 1980. EPA requires more oryzalin toxicity studies; no FIFRA action taken. 8 (16) :33-34. Probst, G.W., T. Golab, R.J. Herberg, F.H. Holzer, S.J. Parka, C.C. Van der Schans, and J.B. Tepe. 1967. Fate of trifluralin in soils and plants. J. Agric. Food Chem. 15: 592-599. Spacie, A., and J.L. Hamelink. 1979. Dynamics of trifluralin accumulation in river fishes. Environ. Sci. Technol. 13: 817-822. SRI International. 1979. 1979 Directory of Chemical Producers: United States of America. Stanford Research Institute International, Menlo Park, Calif. 1122 pp. Taylor, A.W. 1978. Post-application volatilization of pesticides under f ield conditions. J. Air Pollut. Control. ASSOC. 28: 922-927. U. S . International Trade Commission. 1978. Synthetic Organic Chemicals . Un ited States Production and Sales, 1977. ISI]C Publication 920. U.S. Government Printing Office, Washington, D.C. 417 pp. 264

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Wnite, A.W., Jr., L.A. Harper, R.A. Leonard, and J.W. Turnbull. 1977. Trifluralin volatilization losses from a soybean field. Environ. Qual . 6: 105-110 . Woodrow, J.E., D.G. Crosby, T. Mast, X.W. Moilanen, and J.N Seiber. 1978. Rates of transformation of trifluralin and . parathion vapors in air. J. Agric. Food Cbem. 26:1312-1316. 265 J.

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Analytic Methods Downer, G.B., M. Mall, and D.N.B. Mallen. 1976. Determination of benefin and trifluralin residues by quantitative gas-liquid chromatography/mass spectrometry. J. Agric. Food Chem. 24:1223-1225. ~ Food and Drug Administration. 1973. Pesticide Analytical Manual. Heck, H.d'A., R.L. Dyer, A.C. Scott, and M. Anbar. 1977. Determination and disposition of trifluralin in the rat: Separation by sequential high-pressure liquid chromatography and quantitation by field ionization mass spectrometry. J. Agric. Food Chem. 25: 901-908. Lawrence, J.F. 1976. Gas chromatographic separation of herbicides of major interest in Canada, with electrolytic conductivity detection in the nitrogen and chlorine modes. J. Chromatogr. 121: 85-87. Lawrence, J.F., D. Lewis, and H.A. McLeod. 1977. Confirmation of some NO2- containing pesticides by chemical reduction and gas chromatography with electrolytic conductivity detection. J. Agr ic. Food Chem. 25 :1359-1361. Payne, W.R. , Jr. , J.D. Pope, Jr. , and J.E. Benner. 1974. An integrated method for trif luralin , diphenamid, and paraguat in soil and runoff from agricultural land. J. Agric. Food Chem. 22:79-82. 266

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Smith, A.E. 1974. A aulti-residue extraction procedure for the gas chromatographic deteraination of the herbicides dichlobenil, dinitramine, triallate and trifluralin in ~oila. J. Chromatogr. 97:103-106. Soderquist, C.J., D.G. Crosby, X.W. Hollanen, J.N. Seiber, and, J.E. Wocdrow. 1975. Occurrence of trifluralin and its pt~otoproducts in air. J. Agric. Food Chem. 23: 304-309. Woodrow, J.E., D.G. Crosby, T. Mest, K.W. Mailanen, and J. N. Seiber. 1978. Rates of transformation of trifluralin and parathion vapors in air. J. Agric. Food Cbem. 26:1312-1316. 267

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Health Effects Andersen, K.J., E.G. Leightly, and H.T. Takahashi. 1972. Evaluation of herbicides for possible mutagenic properties. J Agric. Food Chem. 20:649-656. Bartels, P.G., and J.L. Hilton. 1973. Comparison of trifluralin, oryzalin, pronamide, propt~am and colchicine treatments on microtubules. Pestic . 8iochem. Physiol. 3: 462-472 . Bartsch, H., C. Mala~reille, and R. Montesa no. 1976. The predictive value of tissue-mediated mutagenicity assays to assess the carcinogenic risk of chemicals. Pp. 467-491 in R. Montesano, H. Bar tech, and L. Tomatis, eds. Screening Tests in Chemical Carcinagenesis. (IARC Scientific Publication No. 12), International Agency for Research on Cancer, Lyon. Beck, S.L. 1977. Postnatal detection of prenatal exposure to herbicides in mice, using normally occurring var. iations in skeletal development. Teratology 15: 15A (Abstract). Bond, D.J., and L. McMillan. 1979. Meiotic aneuploidy: Its origins and induction following chemical treatment in Sordaria brevicollis. Environ. Healtb PersPect. 31:67-74. Brusick, D.J., and V.W. Mayer. 1973. New developments in mutagenicity screening techniques with yeast. Environ. Health Perspect. 6:83-96. 268

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Chaisson, C.~. 1978. Summary of evidence on mutagenic potential of Treflan. Toxicology Branch, Office of Pesticide Programs, Environmental Protection Agency, Washington, D.C. Caisson, C.F., and T.D. Burkhalter. 1978. Mutagenicity considerations: Treflan. Toxicology and Plant Studies Branch, Off ice of Pesticide Programs, Environmental Protection Agecy, Washington, D.C. Couch, J.A., J.T. Winstead, D.J. Hansen, and L.R. Goodman. 1978. Vertebral dysplasia in young fish exposed to the herbicide trifluralin. Contribution No. 346, Gulf Breeze Environmental Research Laboratory, Environmental Protection Agency, Gulf Breeze, Fla. Environmental Protection Agency. 1979 . Tr if luralin (Treflan Position Document. Office of Pesticide Programs, Special Pesticide Review Division, Washington, D.C., August 29, 1979. Epste in , S . S ., E. Arnold, J. Andrea , W. Bass, and Y. Bishop. 1972. Detection of chemical mutagens by the dominant lethal assay in the mouse. roxicol. Appl. Pharmacol. 23: 288-325. Griffith~, A.J.F. 1979. Neurospore prototroph selection System for studying aneuploid production. Environ. Bealth Perepect. 31: 75-80 . 269

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Jackson, W.T., and D.A. Stetler . 1973. Regulation of mitosis. IV. An in vitro and ultrestructura1 study of effects of trifluralin. Can. J. Bot. 51:1513-1518. Kruger, F.W. 1973. Metabolism of nitrosamines in vivo. II. On the methylation of nucleic acids by aliphatic di-N-alkyl-nitrosamines in viva caused by ~-oxidation: me increased formation of 7-methylquanine after application of 8-hydroxypropyI-propyl-nitrosamine compared to that after application of di-n-propyl-nitrosamine. Z. Rrebeforech. Elin. Onkol. 79:90-97. Kuroki, T., C. Drevon, and R. Montesano. 1977. Microsome- medisted mutagenesis in V79 Chinese hamster cells by various nitrosamines. Cancer Res. 37:1044-1050. Matsuoka, A., H. Hayashi, and H. Ishidate, Jr. 1979. Chromosomal aberration test. on 29 chemicals combined with S9 mix in vitro. Mutat. Res. 66: 277-290 . Mauer, I. 1979. Treflan: Rebuttable Presumption Against Registration Document: Mutagenicity Risk Assessment. Toxicology Branch, Office of Pesiticide Programs, Enviornmental Protection Agency, Washington, D.C. 270

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Mauer, I. 1978. Treflan: Summary of Scientif ic Evidence. Toxicology Branch, Off ice of Pesticide Programs, Environmental Protection Agency, Washington, D.C. McCann, J., E. Choi, E. Yamasaki, and B.N. A - es. 1975. Detection of carcinogens as mutagens in the Selmonella/microsome test: Assay of 300 chemicals. 72: S13 5-5139 . Proc. ~tl. Acad. Sci. U.S.A. Montesano, R., and H. Bartscb. 1976. N-n i trove compounds: Res. 32: 179-228 . Murnik, M. R. 1978. Mutagenic and carcinogenic Possible environmental hazards. Mutate Mutagenicity of the herbicide trifluralin in Drosophila melanogaster. Mutat. Res. 53: 23S-236 {Abstract No. 149) . Naka jims, T., A. Tanaka, and R. Tojyo. 1974. me effects of metabolic activation with rat liver preparations on the mutagenicity of several N-nitrosamines on a streptomycin-dependent strain of Escherichia colt. 26: 361-366. Mutat. Res. Nehez, M., A. Paldy, A. Selypes, M. Koro';falvi, I. Lorinczi, and G. Berencsi. 1979. The mutagenic effect of trifluralin~containing herbic ide on mouse bone marrow In viva. Ecotoxicol. Environ . Saf . 3: 454-4S7 . 271

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Nelson, J.O., P.C. Kearney, J.R. Plimmer, and R.E. Henzer. 1977. Metabolism of trifluralin, profluralin, and fluchloralin by rat liver microsomes. Pestic. Biochem. Physiol. 7:73-82. Olejos, E.J., and H.H. Cornish. 1976. Mutagenicity of dialkyl- nitrosamines: Metabolites and derivatives. Toxicol. Appl. Pharmacol. 37 :109-110 (Abstract No. 43) . Propping, P., G. Rohrborn, and W. Buselmaier. 1972. Comparative investigations on the chemical induction of point mutations and dominant lethal mutations in mice. Mo1. Gen. Genet. 117:197-209. Russell, L.B. 1977. Validation of the in vivo somatic mutation method in the mouse as 8 pre screen for germinal point mutations. Arch. Toxicol . 38: 75-85 . Sawamura, S., and W.T. Jackson. 1968. Cytological studies ~n vivo of picloram, pyriclor, trifluralin, 2,3,6-TBA, 2,3,5,6-TBA and nitralin. Cytologia 33: 545-554. Seiler, J.P. 1972. Mutagenicity of benzimidazole and benzimidazole derivatives. I. Forward and re~rerse mutations in Salmonella typhimurium caused by benzimidazole and some of its derivatives. Mutat. Res. 15: 273-276. &ntein, P. 1977. Trifluralin, an inhibitor of the achromatic apparatus which damages the chromosomes. Arch. Anat. Microsc. Morphol. Exp. 66:263-277. 272

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Shirasu, Y., M. Moriya, K. Kato, A. Furohashi, and T. Kada. 1976. Mutagenicity Screening of pesticides in the microbial system. Mutat. Res. 40:19-30. Simmon, V.F., A.D. Mitchell, and T.A. Jorgenson. 1977. Evaluation of selected pesticides as chemical mutagens. ~ In visor and ~ in vitro. studies . Prepared by Stanford Research Institute, Menlo Park , Calif ., for the Environmental Protection Agency, Health Effects Research Laboratory, Research Triangle Park, N.C. Report No. EPA-600/1-77-028. Available from National Technical Information Service, Spr ingf ield, Va ., as PB-268 647. 251 pp. Yahag i , T ., M. Nagao , Y. Se ino , T. Ma tsush ima , T. Sug imura , and M. Okada . 1917 . Mutagen ic ities of N-n itrosamines on salmonella . Mutat. Res. 48: 121-130. Yoder, J., M. Watson, and W.W. Benson. 1973. Lymphocyte chromosome analysis of agricultural workers during extensive occupational exposure to pesticides. Mutat. Res . 21: 335-340 . 273 .