Physicochemical properties as predictors of organic chemical effects on soil microbial respiration

Structure‐activity analysis was used to evaluate the effects of 19 hazardous organic chemicals on microbial respiration in two slightly acidic soils (a Captina silt loam from Roane County Tennessee, and a McLaurin sandy loam from Stone County, Mississippi), both low in organic car bon and typical of the southeastern United States. Single additions of individual chemicals were applied at 1,000 μg/g (dry weight) soil, which was moistened to 80% base saturation and incubated in the dark at 20°C. CO₂ efflux from the soils was monitored at 24‐h intervals over a 6‐d period The chemicals included in the study were the following: acrylonitrile, furan, methyl ethyl ketone tetrahydrofuran, benzene, toluene, 1,2‐dichloroethane, p‐xylene, chlorobenzene, chloroform nitrobenzene, trans‐1,4‐dichloro‐2‐butene, cis‐1,4‐dichloro‐2‐butene, 1,2‐dichlorobenzene, 1,2,3 trichloropropane, carbon tetrachloride, 1,2‐dibromoethane (ethylene dibromide), 1,2,4,5 tetrachlorobenzene and hexachlorobenzene. Seventeen of the chemicals caused temporary depressions in CO₂ efflux in at least one soil, bu treatments were not significantly different from controls by the sixth day for most of these com pounds, indicating the ability of the microbial community to recover from chemically induced toxicity at this concentration. Acrylonitrile, nitrobenzene, and the 1,4‐dichloro‐2‐butenes causec sustained depressions, whereas methyl ethyl ketone and benzene increased respiration. The octanol/water partition coefficient (K_OW) and molecular connectivity (¹x) gave good correlations with effects on soil respiration for a subset of benzene and the six alkyl‐ and chloro substituted derivatives (i.e., toluene, p‐xylene, chlorobenzene, 1,2‐dichlorobenzene, 1,2,4,5‐tetra chlorobenzene and hexachlorobenzene).