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MCPA(Chiptox,Dow MCP)Herbicide Profile 9/89 Page 3 of 6 study. - Metabolism. In a rat sti'%W, MCPA did not appear to be signifi'"Ifntly metabolized in vivo (82 and 38% were recovered in male and female rat urine, respectively) . Repeat dosing did not generally indicate bioaccumulation in any site except the kidney, primarily in male rats. Fat appeared to be the site for some MCPA sequestration. No additional metabolism studies are required. Special Neurotoxicity Testing. MCPA is structurally related to 2,4-D which is suspected of causing neuropathy in humans. Special neurotoxicity testing of 2,4-D is currently required. Because of this structural similarity to 2,4-D, the Agency is also requiring special neurotoxicity testing of MCPA. Toxicology Profile of Other MCPA Formulations. As stated previously from a toxicological standpoint one may expect the acid and sodium salt to be identical. The organic amines and esters may be significantly different and lacking data to show otherwise, may have different toxicological properties. The major exposure to these compounds is during application therefore acute toxicology data are ..� required on the various derivatives. The Agency has some acute testing on these derivatives and they fall in Toxicity Category III. Additional acute testing is required. Human Exposure. The greatest potential for direct human exposure comes during mixing and loading operations. Exposure would be minimized by wearing of protective equipment. The Agency is requiring protective eyewear for mixers, loaders, and home users of MCPA acid products. No specialized protective language other than those required in 40 CFR 156 is required for other MCPA derivative homeowner use r products. There have been no poisoning incidences with MCPA reported in California since 1974. Reentry data are not required since MCPA is generally in Toxicity Category III for acute studies. Environmental Characteristics. Preliminary data have shown that MCPA degrades under aerobic laboratory conditions with a half-life of less than a week to 50 days. Under aerobic conditions 89% of parent MCPA remained undegraded for 374 days. MCPA is stable to hydrolysis and to photolysis in soils. MCPA salts are highly stable in water. Available data are insufficient to fully assess the environmental fate of MCPA and its various derivatives. Groundwater Concerns. MCPA appears to be mobile from preliminary leaching studies. MCPA was found in well water in Missouri. Groundwater contamination appears to be associated with point sources. A special groundwater precautionary statement on labels is being imposed. Ecological Effects Based on available data, MCPA acid has been determined to be moderately toxic to avian species, slightly toxic to freshwater fish, practically nontoxic to freshwater invertebrates and estuarine and marine organisms. Additional ecological effects data are required on MCPA and its derivatives. The following data comes from acceptable - Acute LD50 377 mg/kg for Bobwhite quail - Dietary LC50 > 2000 ppm for mallard, bobwhite, and ring-necked pheasant .� - LC50 rainbow trout = 89 ppm - LC50 bluegill = 97 ppm - LC50 Daphnids > 180 ppm - LC50 Atlantic silverside = 179 ppm - LC50 Oyster Larvae = 155 ppm - Effects on Plants. The Agency has no data for toxicity to nontarget plants. A complete battery of tests are required using MCPA and all its derivatives. M - Potential Problems Related to Endangered Species. Because of MCPA's demonstrated toxicity to nontarget species and its intended use pattern, several endangered species could be put at risk from the application of MCPA acid and its derivatives. The Agency has proposed a comprehensive Endangered Species Protection program (Federal Register 54(126) July 3, 1989) . �+ - Nontarget Insects. MCPA acid and its sodium salt derivative are relatively nontoxic to honeybees. Data are required on the http://pmep.cce.comell.edu/profiles/herb-growthreg/fatty-alcohol-monuron/mcpa/herb-prof-mcpa.html 10/30/2003