Malathion

CAS RN: 121-75-5

Exposure Summary

Malathion's production may result in its release to the environment through various waste streams; its use as an insecticide and an acaricide will result in its direct release to the environment. If released to air, a vapor pressure of 3.97X10-5 mm Hg at 30 deg C indicates malathion will exist in both the vapor and particulate phases in the atmosphere. Vapor-phase malathion 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 malathion will be removed from the atmosphere by wet and dry deposition. Malathion contains chromophores that absorb at wavelengths >290 nm and, therefore, may be susceptible to direct photolysis by sunlight. If released to soil, malathion is expected to have low to no mobility based upon Koc values of 927-17,620. Volatilization from moist soil surfaces is not expected to be an important fate process based upon a Henry's Law constant of 4.89X10-9 atm-cu m/mole. Malathion is not expected to volatilize from dry soil surfaces based upon its vapor pressure. The degradation half-life of malathion in five different soils was 1.33-4.14 days. Malathion was degraded 81-94% in 10 days in various non sterile loam soils. If released into water, malathion is expected to adsorb to suspended solids and sediment based upon the Koc values. The degradation half-life of malathion in different types of water was 1.03-3.93 days. Photodegradation may compete with hydrolysis and biodegradation based on a study finding a photolysis half-life of 533 minutes. Volatilization from water surfaces is not expected to be an important fate process based upon this compound's reported Henry's Law constant. Malathion did not bioconcentrate in topmouth gudgeon or pinfish suggesting bioconcentration in aquatic organisms is low. Hydrolysis is the main route of malathion degradation in water with pH >7.0; at pH <7.0, the rate of hydrolysis is slow relative to the rate of biodegradation. Occupational exposure to malathion may occur through inhalation and dermal contact with this compound at workplaces where malathion is produced or used. Monitoring data indicate that the general population may be exposed to malathion via inhalation of ambient air, ingestion of food and drinking water, and dermal contact with consumer products containing malathion. (SRC)
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