Bioassay-directed identification of toxicants in sediments of Liaohe River, northeast China.

Contaminants accumulated in sediments may directly harm benthic organisms, however, the specific contaminants responsible for adverse effects have been poorly described. In this study, a bioassay-directed analysis combined with toxicity tests and chemistry analysis was conducted to determine the compounds eliciting the greatest toxicological effect in the sediments in Liaohe River, northeast China. A total of 24 sediment samples were examined to determine their acute toxicity to midge Chironomus tentans (C. tentans). Of these samples, 15 exhibited significant toxicity, with a mortality of 23%-93% (p < 0.05). Numerous contaminants, including 16 polycyclic aromatic hydrocarbons, 32 polychlorinated biphenyls, 20 organochlorine pesticides, 6 organophosphate pesticides, 8 pyrethroids, and 5 heavy metals were analyzed. On the basis of toxic unit (TU) analysis results, pyrethroids may contribute to the toxicity of 9 of the 15 toxic samples with concentrations of >1 TU. The significant correlation between the TUs of pyrethroids and the mortality of C. tentans (r2 = 0.74, p < 0.01) confirmed the major role of pyrethroids in toxicity. The selected sediment samples responding to piperonyl butoxide and low temperature with the increased toxicity exhibited the characteristics of pyrethroids. The bioassay-based screening framework provided strong evidence that pyrethroids were the primary cause of sediment toxicity in Liaohe River. Further studies should therefore be conducted to regulate this important class of pollutants.