DCPA (Dacthal) by Caroline Cox Mal Irritation (In Rabbits).3 Based on Are Being Used Even Though the Study Is Other EPA Data, the Acute Oral LD50 Ap- Inadequate

Home , Dicamba, Picloram

DCPA (Dacthal) By Caroline Cox mal irritation (in rabbits).3 Based on are being used even though the study is other EPA data, the acute oral LD50 ap- inadequate. A chronic feeding study of Dimethyl tetrachloroterephthalate, pears to be greater than 10,000 milli- dogs found no adverse effects,3 but a commonly known as dacthal, DCPA, grams per kilogram (mg/kg) of body subchronic (28 day) study found weight or chlorthal-dimethyl, is an herbicide weight in both rats and dogs.8 loss, decrease in liver weight and liver active ingredient used to control crab- degeneration at the only dose tested, 800 grasses, other annual grasses, and cer- Chronic Toxicity mg/kg/day.10 tain broad-leaved weeds in turf, home In a 1963 study, rats fed DCPA for Tests required for U.S. registration of flower gardens, nursery stock, and a two years had increased kidney weights dacthal found no teratogenic (causing number of fruit and vegetable crops.1 (in males), increased adrenal gland birth defects) or mutagenic (causing ge- First registered for use in the United weights (in females), excessive growth netic damage) effects,2 although a Rus- States in 1958, it is manufactured by of the thyroid, abnormalities of the liver, sian study of mouse bone marrow cells the Fermenta Plant Protection Com- and accumulation of iron in the spleen found that dacthal caused abnormalities pany and sold under the trade name (in females). The No Observable Effect in cell division.11 Valid tests of DCPA’s Dacthal.2 Estimated annual usage in Level (NOEL) for these symptoms was oncogenicity (ability to cause tumors) 1988 was between 3.2 and 4.7 million 50 mg/kg/day.2 EPA believes that the and reproductive toxicity had not been pounds. Only 37 percent of this is used test was not adequate to detect all of completed by 1988,2 although the two- on crops; the majority is used on turf the chronic effects of DCPA because a year rat study (above) found a variety sod farms, golf courses, home lawns, persistent lung infection was present in of tumors.9 and home gardens.3 Estimated use on both treated and untreated animals, re- golf courses in 1982 was 400,000 Contaminants and “Inert” (Secret) 4 Ingredients pounds. Figure 1 DCPA is a chlorinated benzoic acid2 DCPA and Its Contaminants DCPA is contaminated by two toxic (see Figure 1) in the same chemical impurities, 2,3,7,8-tetrachlorodibenzo-p- family as the herbicides dicamba and CO CH dioxin (2,3,7,8-TCDD) and chloramben.5 2 3 hexachlorobenzene (HCB).3 (See Figure Cl Cl 1.) Levels of 2,3,7,8-TCDD in DCPA are Mode of Action Cl Cl as high as 100 parts per trillion, while DCPA kills germinating seeds. Micro- HCB has been found at levels up to three CO CH scopic studies indicate that it does this 2 3 parts per thousand.3 Since both of these by disrupting microtubule formation in DCPA compounds are toxic, their presence in exposed cells and causing abnormal cell DCPA is of concern. division. Microtubules are slender cylin- O 2,3,7,8-TCDD is the most toxic mem- Cl Cl drical structures made of polymerized ber of the dioxin family of chlorinated proteins. They move chromosomes to organic (carbon-containing) compounds. Cl Cl newly forming daughter cells and con- O In animals, dioxins cause a variety of ad- trol the orientation of cell walls in plant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) verse health effects, including cancer, cells. Abnormal microtubules disrupt birth defects, atrophy of the thymus, cell wall formation, resulting in the for- liver damage, reduced functioning of the mation of large multinucleate cells when Cl immune system, reproductive failure, cell division is inhibited. They also dis- Cl Cl skin disfiguration, and weight loss12 (JPR rupt the process by which chromo- 9(4):32-36). somes replicate and divide.6,7 Cl Cl Many of these effects are found fol- Cl lowing exposure to minute amounts of Acute Toxicity Hexachlorobenzene (HCB) 2,3,7,8-TCDD. For example, both carci- Of the six acute toxicity tests required nogenic and reproductive effects have by the U.S. Environmental Protection been found at levels in animals of one Agency (EPA) for the registration of a sulting in a high mortality rate. In addi- part per trillion.13,14,15 Mortality, reduced pesticide, only one (a skin sensitization tion, the sample size of the test was growth, and lethargic behavior in rain- test in guinea pigs) had been completed smaller than current EPA standards.9 bow trout was found in water contain- at the time DCPA’s registration standard EPA is requiring that the test be re- ing 38 parts per quadrillion of 2,3,7,8- was issued in 1988. The five missing tests peated. NOELs are used by EPA and TCDD.16 include oral toxicity or LD50* (in rats), other regulatory agencies to establish 2,3,7,8-TCDD persists in soil; esti- dermal toxicity (in rabbits), inhalation permissible exposure levels to pesti- mates of its half-life in soil range from 10 toxicity (in rats), eye irritation, and der- cides, and the results of this rat study to 30 years.17 It also concentrates in exposed animals, particularly in fish. In the rainbow trout study mentioned above, * The LD50 is the dose of a chemical that kills Caroline Cox is JPR’s editor. 50 percent of a population of test animals. bioconcentration factors in fish were cal-

JOURNAL OF PESTICIDE REFORM / FALL 1991 17 ingredients.1 Figure 2 Estimated Number of Cancers Human Exposure Caused by Exposure to DCPA's Contaminants3 DCPA residues have been found in the Total Diet Study conducted by the Pest control operators U.S. Food and Drug Administration. The treating lawns with DCPA study samples a “market basket” of 234 food items collected four times a year from different regions of the U.S. and Farmworkers treating crops tests for pesticide residues. The samples are analyzed for over 200 chemicals. In 1987, DCPA was found 20 times in the Children playing on 936 items sampled; it ranked twentieth treated lawns in frequency out of the 53 pesticides found in the survey. HCB was found 91 times and ranked sixth in frequency.22 Homeowners treating lawns EPA has established a Provisional Acceptable Daily Intake for DCPA of .5 mg/kg/day based on the inadequate two Consumers of treated TCDD year rat study discussed above.2 produce HCB Environmental Fate EPA’s “negligible risk” standard In 1988, nine of the ten environmental fate studies required by EPA for DCPA’s registration were incomplete.3 0.01 0.1 1 10 100 1000 Degradation of DCPA in soil is depen- Number of cancers per million people dent on both temperature and soil moisture. Half-lives in a recent study varied culated to be over 28,000. Similarly large estimated between three and six years.18 from 18 days at 30° C to 92 days at 10° bioconcentration factors have been cal- HCB bioconcentrates by a factor of 11 in C. Low soil moisture (10 percent) in- culated for carp and fathead minnows. chickens, over 6,000 in catfish, and creased DCPA’s half-life.23 Volatilization In cattle, 2,3,7,8-TCDD concentrations in 140,000 in seagull eggs.20,21 DCPA contains (evaporation) also increased with in- beef and milk fat are approximately five almost ten times as much HCB as the creasing temperature.24 times those found in the cattle feed.17 other three pesticides contaminated with Drift of DCPA onto parsley, daikon, HCB has been associated with arthri- HCB (chlorothalonil, picloram, and pen- dill, and kohlrabi (crops on which DCPA tis, osteoporosis of bones in the hands, tachlorophenol). A total of about 12,500 use is not registered) has been docu- liver damage (including the disease por- kilograms of HCB per year are released mented in California. A field study of phyria cutanea tarda), skin lesions, into the air in the United States as these DCPA drift to quantify this problem muscle weakness and short stature in pesticides are used.18 showed that DCPA volatilization contin- humans.18 HCB is concentrated in breast EPA estimated the carcinogenic risks ued up to 60 days after application. milk and high concentrations are passed associated with the 2,3,7,8-TCDD and About 10 percent of the DCPA was lost from mother to child during nursing. In HCB contaminants in DCPA. The results to the atmosphere in the first 21 days Turkey (where three to four thousand are as high as six hundred cancers per after application. Half-life in the soil in people consumed HCB contaminated million pest control operators exposed this study was 50 days.25 bread in 1955) all infants born to moth- to HCB while treating lawns with DCPA DCPA and its metabolites (breakdown ers with porphyria died. Mortality of and two hundred cancers per million products which EPA considers toxico- nursing babies was also high.18 In ani- children playing on DCPA-treated lawns.3 logically equivalent to DCPA3) have been mals, exposure to HCB causes similar (See Figure 2. For a discussion of the repeatedly found in groundwater and effects. In addition, HCB in animals problems with quantitative risk assess- surface water. In EPA’s National Pesti- causes kidney damage, immune system ment, see JPR 8(1):7-12 and JPR 10(1):2- cide Survey, over 6 percent (about 6,000) suppression, neurologic effects, cleft pal- 7).) of the community water system wells ate, a reduction in the survival of nurs- The public has no information about contained DCPA metabolites as did over ing pups, and cancer.18 the identity of the “inert” ingredients 2 percent (about 264,000) of rural do- HCB residues have been found in the used in DCPA formulations or their tox- mestic wells. DCPA’s contaminant HCB blood of agricultural workers using icity, either alone or in combination with was found in 0.5 percent (about 470) ground spray equipment to apply DCPA. According to pesticide manufac- community water system wells. DCPA DCPA.19 Nineteen of twenty workers stud- turers, the identity of these ingredients metabolites were the most commonly ied had blood residues, and the concen- is a trade secret. EPA doesn't require detected pesticide residue in the survey. tration of HCB was correlated with the testing of “inert” ingredients and re- Since a larger percentage of community length of time the employees had worked quires only acute toxicity testing of the water system wells were contaminated with DCPA.19 formulated products (active plus “inert” by DCPA than were rural domestic wells, HCB is relatively resistant to degra- ingredients). A typical DCPA formulation, EPA believes that much of the contami- dation, and its half-life in soil has been Dacthal G-25, contains 50 percent secret nation may have come from urban rather

18 JOURNAL OF PESTICIDE REFORM / VOL. 11, NO. 3 Figure 3 Locations of DCPA-Contaminated Fish Samples29

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• • • • • • • •• • • • • • • • • • • • • than agricultural uses.26 EPA’s STORET in the results of toxicity tests, but from and chlordane, for example), residues water quality database indicated in 1988 changes in the factor used to calculate a of DCPA in fish are widespread. The that 19 percent of surface water samples margin of safety (from 1000 to 1,00) and U.S. Fish and Wildlife’s National Con- (386/1,995) and one percent of ground changes in assumptions used to calcu- taminant Biomonitoring Program ana- water samples (12/982) were contami- late the advisory levels.* lyzed fish samples from 112 stations nated with DCPA.8 The highest DCPA lev- in rivers throughout the U.S. as well els found in groundwater were 1,039 Effects on Nontarget Organisms as the Great Lakes. DCPA residues parts per billion (ppb) found in Suffolk Like residues of other persistent were found in 34 percent of the County, New York8 and 986 ppb found organochlorine pesticides (DDT, toxa- samples from 1978-79, 28 percent of in Malheur County, Oregon.27 phene, pentachlorophenol, dieldrin, the samples from 1980-81, and 45 per- EPA has calculated a lifetime health advisory level for DCPA in drinking wa- * Looking closely at the calculation of these This change, as well as the change in the as- ter of 4,000 micrograms per liter (equiva- health advisory levels is an interesting exer- sumed margin of safety (from 1000 to 100) re- lent to 4,000 ppb).8 This level is based cise. The first (draft) level set in 1982 calcu- sulted in an increase in the advisory level from on the toxic effects found in the inad- lated a “longer-term” advisory level, one that is 500 to 3500 ppb. The margin of safety is sup- based on the water consumption and body posed to compensate for the inadequate tests, equate two year rat study discussed weight of a child using the previously men- so it is ironic that only the margin of safety, above, although the study is being re- tioned inadequate two year rat study. In the and not the quality of the testing, were changed placed. Earlier guidance levels for DCPA 1987 revision, the longer-term level was based, between 1982 and 1987. In 1988, the levels were in drinking water, though much lower not on the two year rat study, but on a 28 day rounded off to the nearest 1000 ppb, resulting (5009 and 3500 ppb28), were based on rat study (also judged inadequate) and the two in another increase to 4,000 ppb. All of the year study was used to calculate a lifetime ad- changes have come, not from new information the same study. The increase in the advisory level. Lifetime levels are based on the about the toxicity of dacthal, but from new as- visory levels has come, not from changes water consumption and body weight of an adult. sumptions and calculations.

JOURNAL OF PESTICIDE REFORM / FALL 1991 19 cent of the samples from 1984 (See residue in recent groundwater surveys dibenzo-p-dioxin and 2,3,7,8-tetrachloro- Figure 3).29 Highest concentrations and are often detected in surface wa- dibenzofuran in rainbow trout. Environmen- tal Toxicology and Chemistry 27:47-62. were found in the lower Rio Grande ter. DCPA is transported by air cur- 17. U.S. Environmental Protection Agency. Of- (Texas) where agricultural use of rents over long distances. Fish col- fice of Health and Environmental Assess- DCPA has been widespread. HCB, lected from sample locations through- ment. 1988. Estimating exposures to 2,3,7,8- which contaminates DCPA, was de- out the United States are frequently TCDD. External review draft. Washington, tected in 19 percent of the 1984 contaminated by DCPA, with high con- D.C. ■ 18. U.S. Department of Health and Human Ser- samples. Fish from four out of five riv- centrations in agricultural areas. vices. Agency for Toxic Substances and ers in the heavily agricultural San References Disease Registry. 1990. Toxicological pro- Joaquin Valley in California also con- file for hexachlorobenzene. Washington, D.C. tained DCPA residues.30 1. Diamond Shamrock Corporation. Agricul- 19. Burns, J.E. et al. 1974. Hexachlorobenzene tural Chemicals Division. 1980. Dacthal G- exposure from contaminated DCPA in veg- In Great Lakes fish, DCPA residues 25 herbicide label. Cleveland, OH. etable spraymen. 1974. Arch. Environ. are even more common. In a 1980-81 2. U.S. Environmental Protection Agency. Of- Health. 29:192-194. survey, DCPA was detected in 73 per- fice of Pesticides and Toxic Substances. 20. Dobson, S. and P. Howe. 1986. Evaluation cent of the samples, while HCB was Office of Pesticide Programs. 1988. Pesti- of the environmental impact of hexachloro- cide fact sheet (DCPA). Washington, D.C. benzene. IARC Scientific Publications 77:203- found at all eight of the sites where 3. U.S. Environmental Protection Agency. Of- 31 209. collections were made. At Siskiwit fice of Pesticides and Toxic Substances. 21. Bro-Rasmussen, F. 1986. Lake, on Isle Royale in Lake Superior, 1988. Guidance for the reregistration of pes- Hexachlorobenzene: An ecotoxicological DCPA residues were found in both lake ticide products containing dimethyl profile of an organochlorine compound. trout and whitefish. Because of the tetrachloroterephthalate (DCPA) as the ac- IARC Sci. Publ. 77:231-243. tive ingredient. Washington, D.C. (June). 22. U.S. Food and Drug Administration Pesti- lake’s remote location in a national 4. Kriner, Richard. 1985. Final report on the cide Program. 1988. Residues in foods-1987. park where no pesticides have been results of a national survey of pesticide us- J. Assoc. Anal. Chem. 711(6): 156A-174A. used since some DDT applications age on golf courses in the U.S. conducted in 23. Choi, J. 1987. Effect of temperature, mois- were made in the 1960s, the authors July-September 1982. Washington, D.C.: ture, and soil texture on DCPA degrada- American Association of Retired Persons of this study believe that the presence tion. PhD dissertation. University of Illinois and U.S. EPA. at Urbana-Champaign. Abstract. of DCPA indicates that the herbicide 5. Witt, J.M. 1988. Grouping pesticides by 24. Nash, R.G. and T.J. Gish. 1989. Halogenated has been transported over long dis- structure. In Witt, J.M. and C.J. Adams pesticide volatilization and dissipation from tances from the sites where it was ap- (eds.). Chemistry, biochemistry, and toxicol- soil under controlled conditions. Chemo- ogy of pesticides. Proceedings of an Oregon sphere 18(11/12): 2353-2362. plied and then deposited in Lake State University Extension Service 32 25. Ross, L.J. et al. 1990. Volatilization, off-site Siskiwit. DCPA’s volatility increases Shortcourse. Corvallis, OR: OSU Extension deposition, and dissipation of DCPA in the this kind of long distance transport. Service. field. J. Environ. Qual. 19:715-722. Mussels growing in intertidal areas 6. Vaughan, M.A. and K.C. Vaughn. 1990. DCPA 26. U.S. Environmental Protection Agency. Of- of the central California coast also con- causes cell plate disruption in wheat roots. fice of Water. Office of Pesticides and Toxic Annals of Botany 65:379-388. tain DCPA residues. A 1982-83 survey Substances. 1990. National survey of pesti- 7. Corbett, J.R., K. Wright, and A.C. Baillie. cides in drinking water wells. Phase 1 re- found DCPA in mussels from eight out 1984. The biochemical mode of action of port. Washington, D.C. (November). of the twelve sites sampled, including pesticides. Second edition. London: Aca- 27 Malheur County Groundwater Management a site (Bodega Head) thought to be demic Press. Committee. 1991. Northern Malheur County 8. U.S. Environmental Protection Agency. Of- groundwater management action plan. relatively uncontaminated with pesti- fice of Drinking Water. 1988. DCPA (Dacthal) 33 Ontario, OR. (June). cides and PCBs. health advisory. Washington, D.C. (June). 28. U.S. Environmental Protection Agency. Of- 9. U.S. Environmental Protection Agency. Of- fice of Drinking Water. 1987. DCPA (Dacthal) Summary fice of Drinking Water. Health Effects health advisory. Washington, D.C. (August). DCPA is a moderately persistent Branch. 1982. Health effects guidance for 29. Schmitt, C.J., J.L. Zajicek, and P.H. Peter- dacthal. Draft. Washington, D.C. (July). organochlorine herbicide that kills man. 1990. National Contaminant 10. U.S. Environmental Protection Agency. Of- Biomonitoring Program: Residues of or- plants by inhibiting cell division. It has fice of Pesticide Programs. 1984. Dacthal ganochlorine chemicals in U.S. freshwater been registered for use in the United “tox one-liner.” Unpublished document. fish, 1976-1984. Arch. Environ. Contam. States since 1958, but most of the re- 11. Kurinnyi, A.I., et al. 1982. Implementation Toxicol. 19:748-781. quired testing is incomplete or invalid. of a program of cytogenetic study of pesti- 30. Saiki, M.K. and C.J. Schmidtt. 1986. Organo- cides: Preliminary evaluation of cytogenetic chlorine chemical residues in bluegills and Chronic exposure to DCPA has activity and potential mutagenic hazard of common carp from the irrigated San caused adverse effects in the adrenal 24 pesticides. Tsitologiya i Genetika Joaquin Valley floor, California. Arch. glands, kidneys, livers, thyroids and 16(1):50-53. Environ. Contam. Toxicol. 15:357-366. spleens of laboratory animals. DCPA 12. Silbergeld, E.K. and T.A. Gasiewicz. 1989. 31. DeVault, D.S. 1985. Contaminants in fish Commentary: Dioxins and the Ah receptor. is contaminated with two compounds, from Great Lakes harbors and tributary Amer. J. of Industrial Med. 16:455-474. mouths. Arch. Environ. Contam. Toxicol. 2,3,7,8-TCDD and hexachlorobenzene, 13. Murray, F.J. et al. 1979. Three-generation 14:587-594. that are toxic (including carcinogenic- reproduction study of rats given 2,3,7,8- 32. Swackhamer, D.L. and R.A. Hites. 1988. Oc- ity and reproductive abnormalities) at tetrachlorodibenzo-p-dioxin in the diet. Tox. currence and bioaccumulation of organo- low doses. Both compounds bioac- Appl. Pharm. 50:241. chlorine compounds in fishes from Siskiwit 14. Nisbet, I. and M. Paxton. 1982. Statistical Lake, Isle Royale, Lake Superior. Environ. cumulate in animals. The chronic tox- aspects of three-generation studies of the Sci. Technol. 22:543-548. icity of commercial DCPA products reproductive toxicity of TCDD and 2,4,5-T. 33. Martin, M. and W. Castle. 1984. Petrowatch: cannot be assessed because the “in- Am. Statistician 36(3):290. Petroleum hydrocarbons, synthetic organic ert” ingredients have not been tested. 15. U.S. Environmental Protection Agency. compounds, and heavy metals in mussels 1980. Dioxins (600-2-80-197). Washington, Most Americans are unknowingly from the Monterey Bay area of Central Cali- D.C. fornia. Marine Pollution Bulletin 15(7):259- exposed to DCPA. It's metabolites are 16. Mehrle, P.M. et al. 1987. Toxicity and 266. the most commonly detected pesticide bioconcentration of 2,3,7,8-tetrachloro-

20 JOURNAL OF PESTICIDE REFORM / VOL. 11, NO. 3