Toxicity of hexachlorobenzene to Hyalella azteca and Chironomus tentans in spiked sediment bioassays

Fourteen‐day, whole‐sediment toxicity tests using the amphipod Hyalella azteca and the midge Chironomus tentans were conducted on spiked sediment samples representing a range of hexachlorobenzene (HCB) concentrations. High rates of survival and growth relative to controls were observed in both test species. No observed effects concentrations (NOECs) were equal to the highest HCB concentration tested (42 mg/kg, normalized to 1% total organic carbon). Available literature on the aquatic toxicity of this hydrophobic chemical shows an absence of lethal and sublethal effects from exposure to HCB at or below water solubility concentrations, and toxicity from exposure to dissolved HCB in sediment porewater therefore would not be expected. Because whole‐sediment toxicity tests integrate exposure to HCB dissolved in porewater and adsorbed to particles, it was considered possible that exposure via sediment ingestion could cause toxicity; however, no such effect was observed in this study.