Fate of Volatile and Semivolatile Organic Chemicals in Soils: Abiotic Versus Biotic Losses

Disappearance of 15 volatile and semivolatile organic compounds was determined in a mixture added to two different soil types, a Captina silt loam (Typic Fragiudult) and McLaurin sandy loam (Typic Paleudults), using experimental procedures to distinguish abiotic losses from biological degradation over a 7-d period. Losses due to volatilization were quantified and mass balances were calculated for each compound. Standard USEPA and National Institute of Occupational Health and Safety (NIOHS) methods were used for sample handling, storage, and analysis. The compounds (methyl ethyl ketone; tetrahydrofuran; chlorobenzene; benzene; chloroform; carbon tetrachloride; p-xylene; 1,2-dichlorobenzene; cis-1,4-dichloro-2-butene; 1,2,3-trichloropropane; 2-chloronaphthalene; ethylene dibromide; hexachlorobenzene; nitrobenzene; and toluene) were applied to the soil in a mixture such that the concentration of each chemical was 100 mg/kg soil (dry wt.). The headspace of the soil samples and matched sterile (autoclaved) controls, which were incubated in the dark at 20 °C in stoppered jars fitted with charcoal traps, was flushed daily to maintain aerobic conditions and to trap vapors. Apparent half-lives for the 15 organic compounds ranged from < 2 to 11.3 d and showed good agreement with published values in the few instances where they were available. Rapid disappearance due to abiotic factors was observed for all chemicals during the 7-d period. Although short-term spike and recovery analyses yielded consistently reproducible recovery for all compounds, careful attempts to account for all losses, including the use of ¹⁴C-toluene, were unsuccessful. Nonreversible sorption and preanalysis storage conditions were considered as contributors to this inability to achieve a mass balance. On the basis of these results, we strongly advise positive accounting for all test compounds and degradation products at the conclusion of studies involving volatile and semivolatile compounds.