CAS RN:77-47-4

Exposure Summary

Hexachlorocyclopentadiene's production and use as an intermediate in the production of pesticides, resins, dyes, and pharmaceuticals may result in its release to the environment through various waste streams. It has previously been used as a biocide. If released to air a vapor pressure of 0.060 mm Hg at 25 deg C indicates that hexachlorocyclopentadiene will exist solely as a vapor in the ambient atmosphere. Vapor-phase hexachlorocyclopentadiene 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 29 days. Hexachlorocyclopentadiene absorbs light greater than 290 nm and direct photolysis is an important degradation pathway. Hexachlorocyclopentadiene adsorbed onto silica gel, underwent 46.0% photomineralization when irradiated with UV light (>290 nm) for 17 hours. If released to soil, an average Koc value of 4,265 indicates that hexachlorocyclopentadiene is expected to have low mobility in soil. Volatilization from moist soil surfaces is expected to be an important environmental fate process based on a Henry's Law constant of 0.027 atm-cu m/mole; however, adsorption to soil may attenuate volatilization. Volatilization losses of 0.84-1.60% from moist sand, 0.35-0.67% from moist loam, and 0.15-0.285% from moist humus were observed over a two hour period in a laboratory study, carried out at 25 deg C. Hexachlorocyclopentadiene is susceptible to direct photolysis, hydrolysis and biodegradation on soil surfaces with losses of over 90% in unsterilized soil subjected to natural sunlight over a 7 day period. If released to water, hexachlorocyclopentadiene is expected to adsorb to suspended solids and sediment in the water column based on the average Koc value. Volatilization from water surfaces is expected to be an important fate process based upon this compound's Henry's Law constant; however, adsorption may attenuate volatilization from water. Estimated volatilization half-lives for a model river and model lake are 2 hours and 7 days, respectively if adsorption is neglected. The volatilization half-life from a model pond is estimated as 37 days if adsorption is considered. Hexachlorocyclopentadiene photodegrades rapidly in sunlit surface waters with a photodegradation half-life on the order of several minutes to over an hour. Hydrolytic half-lives ranging from several hours to 2-3 weeks are expected for hexachlorocyclopentadiene under environmental conditions. BCF values on the range of 100-1354 measured in fish, suggest bioconcentration in aquatic organisms is very high. Occupational exposure to hexachlorocyclopentadiene may occur through inhalation and dermal contact with this compound at workplaces where hexachlorocyclopentadiene is produced or used. (SRC)
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