Soman

CAS RN: 96-64-0

Exposure Summary

Soman's production may result in its release to the environment through various waste streams; its use as a military nerve gas and chemical warfare agent will result in its direct release to the environment. If released to air, a vapor pressure of 0.41 mm Hg at 25 deg C indicates soman will exist solely as a vapor in the atmosphere. Vapor-phase soman 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 8 hours. The UV absorption spectrum of soman in cyclohexane solution exhibits little to no absorption above 290 nm; therefore, direct photolysis by sunlight in the environment is not expected to be an important fate process. Soman vapor has been observed to react with water vapor, probably through hydrolysis, suggesting that reaction of soman vapor with water vapor may be an important fate process in the atmosphere. If released to soil, soman is expected to have high mobility based upon an estimated Koc of 103. Volatilization from moist soil surfaces is expected to be an important fate process based upon an estimated Henry's Law constant of 4.7X10-6 atm-cu m/mole. Soman has been observed to volatilize from both wet and dry surfaces. Simulated rainfall events have shown that soman adsorbed to soil can desorb resulting in volatilization (off-gassing) to the atmosphere. Soman decomposes in soil via hydrolysis and is most stable in the medium pH range from 4 to 6. Soman has a hydrolysis half-life of about 60 hours at pH 6 and 25 deg C in water; extrapolation of hydrolysis rates to moist soil must be used with caution as susceptibility to hydrolysis in soil depends upon a variety of factors. However, hydrolysis is expected to be an important fate process in soil. The persistence of soman in soil may be expected for days-to-months depending upon soil type and conditions. Several species of bacteria, such as Alteromonas sp. and Flavobacterium sp., are capable of degrading G-type nerve agents, however data are not available to assess the environmental importance of soman biodegradation. If released into water, soman is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. Volatilization from water surfaces is expected based upon this compound's estimated Henry's Law constant. Estimated volatilization half-lives for a model river and model lake are 11 and 82 days, respectively. An estimated BCF of 7 suggests the potential for bioconcentration in aquatic organisms is low. Soman hydrolyzes in water at neutral or slightly acid pH and more rapidly under strong acid or alkaline conditions. The half-life of soman in water at pH 7, 20 deg C and 30 deg C has been reported as 82 and 22 hours, respectively; the half-life of soman in water at pH 7.6, 20 and 30 deg C has been reported as 41 and 9.6 hours, respectively. Occupational exposure to soman may occur through inhalation and dermal contact with this compound at workplaces where soman is produced or used. Exposure to soman occurs through vapor contact which is readily absorbable through not only the lungs and eyes but also the skin and intestinal tract. The general population will not be exposed to soman unless it is used as a weapon; exposure to soman, if used as a weapon, will be via inhalation of ambient air and dermal contact. (SRC)
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