Assessment of toxicological interactions of benzene and its primary degradation products (catechol and phenol) using a lux‐modified bacterial bioassay

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Abstract
A bacterial bioassay has been developed to assess the relative toxicities of xenobiotics commonly found in contaminated soils, river waters, and ground waters. The assay utilized decline in luminescence of lux‐marked Pseudomonas fluorescens on exposure to xenobiotics. Pseudomonas fluorescens is a common bacterium in the terrestrial environment, providing environmental relevance to soil, river, and ground water systems. Three principal environmental contaminants associated with benzene degradation were exposed to the luminescence‐marked bacterial biosensor to assess their toxicity individually and in combination. Median effective concentration (EC50) values for decline in luminescence were determined for benzene, catechol, and phenol and were found to be 39.9, 0.77, and 458.6 mg/L, respectively. Catechol, a fungal and bacterial metabolite of benzene, was found to be significantly more toxic to the biosensor than was the parent compound benzene, showing that products of xenobiotic biodegradation may be more toxic than the parent compounds. Combinations of parent compounds and metabolites were found to be significantly more toxic to the bioassay than were the individual compounds themselves. Development of this bioassay has provided a rapid screening system suitable for assessing the toxicity of xenobiotics commonly found in contaminated soil, river, and ground‐water environments. The assay can be utilized over a wide pH range and is therefore more applicable to such environmental systems than bioluminescence‐based bioassays that utilize marine organisms and can only be applied over a limited pH and salinity range.