Chemical availability and sediment toxicity of pyrethroid insecticides to Hyalella azteca: application to field sediment with unexpectedly low toxicity.

Tenax extraction is a simple, inexpensive approach to estimate the bioavailability of hydrophobic organic contaminants from sediment. In the present study, a single-point Tenax extraction was evaluated regarding its correlation with the acute toxicity to Hyalella azteca using field-collected sediments in California, USA. Pyrethroids were believed to be the primary contributor to the observed toxicity, and a significant correlation existed between the expected toxicity (given pyrethroid concentrations) and the mortality at most sampling sites. A small subset of sites, however, showed unexpectedly low toxicity to H. azteca despite high concentrations of pyrethroids. These samples were evaluated by Tenax extraction with the expectation that this procedure, which qualifies bioavailable instead of total pyrethroid concentration in sediment, would better explain the anomalously low toxicity. The term bioavailable toxic unit was proposed to link sediment toxicity with chemical availability, and the toxicity in the 17 selected sediments was better explained using Tenax extraction. The r2 value of the regression between sediment toxicity and toxic unit for the 17 sediments increased from 0.24 to 0.60 when the Tenax-extractable concentration was used in place of the total concentration. Results also showed that adsorption to sand particles might play a controlling role in pyrethroid bioavailability and, in turn, sediment toxicity to benthic invertebrates.