Dimethoate

CAS RN: 60-51-5

Exposure Summary

Dimethoate's production may result in its release to the environment through various waste streams; its use as a contact and systemic insecticide will result in its direct release to the environment. If released to air, a vapor pressure of 1.87X10-5 mm Hg at 25 deg C indicates dimethoate will exist in both the vapor and particulate phases in the atmosphere. Vapor-phase dimethoate will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 5 hours. Particulate-phase dimethoate will be removed from the atmosphere by wet or dry deposition. Due to a lack of absorbance of wavelengths of light above 290 nm, dimethoate is not expected to be susceptible to direct photolysis by sunlight. If released to soil, dimethoate is expected to have very high mobility based upon Koc values of 5.2-50. Volatilization of dimethoate from moist soil surfaces is not expected to be an important fate process given an estimated Henry's Law constant of 2.4X10-10 atm-cu m/mole. Microbially-mediated oxidative and hydrolytic degradation is the major degradation pathway in aerobic soil with a half-life of 2.2 days reported. Soil half-lives of 7 and 11 days were reported. However, a half-life of 122 days has also been measured in soil. If released into water, dimethoate is not expected to adsorb to suspended solids and sediment based upon the Koc values. Dimethoate may be subject to biodegradation in natural waters based on a half-life of 8 weeks for degradation in raw river water. Volatilization from water surfaces is not expected to be an important fate process based upon this compound's estimated Henry's Law constant. BCFs of 1.1-2.4 and 2.7-6 suggest bioconcentration in aquatic organisms is low. Dimethoate hydrolyzes very slowly in sterile buffered solutions at pHs 5 and 7 with half-lives of 156 and 68 days respectively, but hydrolyzes rapidly to desmethyl dimethoate and dimethylthiophosphoric acid with a half-life of 4.4 days at pH 9. Occupational exposure to dimethoate may occur through inhalation and dermal contact with this compound at workplaces where dimethoate is produced or used. Monitoring and use data indicate that the general population may be exposed to dimethoate via inhalation of ambient air, ingestion of food and contaminated drinking water, and dermal contact with this compound and other products containing dimethoate. (SRC)
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