Rationale for including metabolites in chemical toxicity bioassay

Toxicity and biodegradability are major factors affecting the fate and behavior of an organic contaminant in the environment. In this report, 2,4-dinitrotoluene (DNT), an important industrial chemical, was used as a model toxicant to demonstrate that toxicity and biodegradability are intimately related in determining a chemical's effect and impact on the total ecosystem. DNT was found to be aerobically stable, but could undergo anaerobic biotransformation with the formation of three metabolites. One of the metabolites, namely 2-nitroso-4-nitrotoluene, was extremely toxic to the six test bacterial isolates, while the other two aminonitro metabolites and the parent compound DNT were much less toxic or nontoxic to the bacterial cultures. It is suggested that the incorporation of some known metabolites into short-term bioassay procedures could increase the reliability of these tests in the impact assessment of toxic chemicals on the environment. In addition, the difference between toxicity data generated from short-term bioassay procedures and those from long-term toxicological studies was also delineated from a biochemical viewpoint.