Heterocyclic compounds: toxic effects using algae, daphnids, and the Salmonella/microsome test taking methodical quantitative aspects into account.

Heterocyclic aromatic hydrocarbons containing nitrogen, sulfur, or oxygen (NSO-HET), have been detected in air, soil, sewage sludge, marine environments, and freshwater sediments. Since toxicity data on this class of substances are scarce, the present study focuses on possible implications NSO-HET have for ecotoxicity (algae and daphnids) and mutagenicity (Salmonella/microsome test). A combination of bioassays and chemical-analytical quantification of the test compounds during toxicity assays should aid in determination of the hazard potential. Samples of the test concentrations of 14 NSO-HET were taken at the beginning and end of the bioassays; these samples were then quantified by high-performance liquid chromatography. The toxicity potential of the substances was evaluated and compared with the toxicity calculated with the nominal concentrations. Significantly different results were obtained primarily for volatile or highly hydrophobic NSO-HET. The concentration of heterocyclic hydrocarbons can change significantly during the algae and Daphnia test. The EC50 values (effective concentration value: the concentration of a chemical that is required to produce a 50% effect) calculated with the nominal concentrations underestimate the toxicity by a factor of up to 50. Prioritizing the tested compounds according to toxicity, the mutagenic and toxic compounds quinoline, 6-methylquinoline, and xanthene have to be listed first. The greatest ecotoxic potential on algae and daphnids was determined for dibenzothiophene followed by acridine. In the Daphnia magna immobilization test, benzofuran, dibenzofuran, 2-methylbenzofuran, and 2,3-dimethylbenzofuran and also carbazole are ecotoxicologically relevant with EC50 values below 10 mg/L. These substances are followed by indole with a high ecotoxic effect to daphnids and less effect to algae. Only minor toxic effects were observed for 2-methylpyridine and 2,4,6-trimethylpyridine.