2,4-D

CAS RN:94-75-7

Exposure Summary

2,4-D's production may result in its release to the environment through various waste streams; its use as a herbicide will result in its direct release to the environment. If released to air, a vapor pressure of 1.40X10-7 mm Hg at 25 deg C indicates 2,4-D will exist in both the vapor and particulate phases in the atmosphere. Vapor-phase 2,4-D 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 19 hrs. Particulate-phase 2,4-D will be removed from the atmosphere by wet and dry deposition. In aqueous media, phenoxy herbicides have ultraviolet maxima in the 280-290 nm range, suggesting that 2,4-D may be susceptible to direct photolysis. If released to soil, 2,4-D is expected to have very high to high mobility based upon a Koc range of 20 to 136. Volatilization from moist soil surfaces is not expected to be an important fate process based upon a Henry's Law constant of 9.75X10-8 atm-cu m/mole. 2,4-D is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Biodegradation is an important environmental fate process for 2,4-D in most soils, leading to various hydroxylic aromatic products. The rate of degradation is affected by the conditions, especially the concentrations of 2,4-D and water content temperature and the organic content of soil and the status of pre-exposure of the soil to 2,4-D or its salts or esters. If released into water, 2,4-D is not expected to adsorb to suspended solids and sediment based upon the Koc values. When released to water, 2,4-D will tend to biodegrade with the rate dependent upon level of nutrients present, temperature, availability of oxygen, and whether or not the water has a prior history of contamination by 2,4-D or other phenoxyacetic acids. Typical half-lives of 10 to >50 days have been reported with longer half-lives expected in oligotrophic waters and where a high concentration of 2,4-D is present. Volatilization from water surfaces is not expected to be an important fate process based upon the Henry's Law constant. An estimated BCF of 3 suggests the potential for bioconcentration in aquatic organisms is low. Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions (pH 5 to 9). Half-lives of 2-4 days were reported for 2,4-D photolysis in water solution irradiated at 356 nm. Occupational exposure to 2,4-D may occur through inhalation and dermal contact with this compound at workplaces where 2,4-D is produced or used. Monitoring data indicate that the general population may be exposed to 2,4-D via inhalation of ambient air, ingestion of food and drinking water, and dermal contact with consumer products containing 2,4-D. (SRC)
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