Toxicity reduction evaluation of PCB-contaminated soils

The ultimate goal of bioremediation is to complete biodegrade environmental toxic substances. However, pollutants can undergo partial biodegradation or biotransformation producing more toxic byproducts than the parent compound. In this manuscript, two aquatic ecotoxicological analysis, Tetrahymena pyriformis and Microtox™, were used to assess the toxicity of a bioremediation process that uses a surfactant solution to extract PCBs from soil and two genetically engineered microorganisms to degrade the PCBs. Approximately 50% of PCBs and 90% of surfactants were degraded in the bioremediation process and there was no increase in the toxicity. The relative toxicity of the major metabolites formed by aerobic PCB degradation (chlorobenzoic acids) was studied using both an acute and chronic Tetrahymena assay. Log K_ow and pK_a were used as descriptors for the development of QSARs. Results showed that neutralized chlorobenzoic acids are less toxic than non-neutralized and chlorine substituents at meta and para position render benzoic acids more toxic than benzoic acids with chlorines at ortho position.