Soil sorption of volatile and semivolatile organic compounds in a mixture

Studies were conducted to evaluate lipophilicity as a predictor of sorption for a mixture of organic compounds with high vapor pressures commonly present at hazardous waste sites. Sorption partition coefficients (K(p)) for the mixture of 16 volatile and semivolatile organic compounds were measured on a Captina silt loam (Typic Fragiudult) and a McLaurin sandy loam (Typic Paleudults) using a zero headspace extractor. The experimental K(p) was determined for acrylonitrile, furan, methyl ethyl ketone, tetrahydrofuran, benzene, toluene, p-xylene, chlorobenzene, chloroform, nitrobenzene, 1,2-dichlorobenzene, 1,2,3-trichloropropane, carbon tetrachloride, ethylene dibromide, 1,2,4,5-tetrachlorobenzene, and hexachlorobenzene on each of the two soils. The K(p) values were generally lower in the McLaurin sandy loam, which had a lower organic C content (0.66 ± 0.04%) than the Captina silt loam (organic C content = 1.49 ± 0.06%). Sorption was normalized to soil organic C content of the soil by converting K(p) for each compound and soil to K(oc). Weighted regression analyses of K(oc observed) for the compounds in the mixture on K(oc predicted) from the n-octanol/water partition coefficient (K(ow)) for individual compounds yielded a pooled, weighted regression of K(oc observed) = 1.084 + 0.457 K(oc predicted), n = 29, r = 0.88. Statistical analysis indicated that the slope of 0.457 ± 0.046 (estimated standard error) was significantly less than 1.00, indicating that soil sorption of nonionic organic compounds differed from that predicted for the same individual compounds based on K(ow). The results indicate that predictive equations for sorption of individual organic compounds can be applied to mixtures of volatile and semivolatile organic compounds in soils when log K(ow) are in a range from approximately 1 to 3; however, outside this range a correction factor may be needed.