Soil Sorption of Volatile and Semivolatile Organic Compounds in a Mixture

Abstract

Abstract Studies were conducted to evaluate lipophilicity as a predictor 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.