The contribution of pyrethroid pesticides to sediment toxicity in four urban creeks in California, USA

As part of a statewide assessment of pyrethroid pesticides and sediment toxicity in urban creeks, sites throughout California were screened, and thirty were chosen to evaluate the potential of pyrethroids to contribute to biological impacts. Sediment samples from four sites containing varied concentrations of pyrethroids were investigated using toxicity identification evaluations (TIEs) to determine causes of toxicity. Treatments were conducted on both whole sediment and interstitial water to determine the role of pyrethroids in the observed toxicity to the amphipod Hyalella azteca, and to evaluate TIE method performance. Whole sediment treatments included the addition of binding resins for organics and metals, and specific treatments designed to alter pyrethroid toxicity, including the addition of carboxylesterase enzyme, the addition of piperonyl butoxide (a pyrethroid synergist), and the testing of sediments at two temperatures. Interstitial water TIEs included solid-phase extraction (SPE) columns to reduce and return toxicity caused by organics and metals, as well as the treatments specific to pyrethroids. Resin and SPE column treatments characterized the causes of toxicity as organic compounds. Results of pyrethroid-specific treatments in whole sediment were variable, but similar treatments in interstitial water demonstrated pyrethroids were contributing to toxicity. Measured pyrethroid concentrations in whole sediment and interstitial water SPE extracts were high enough to have contributed to toxicity. Using both whole sediment and interstitial water TIEs and chemical analysis provided multiple lines of evidence that pyrethroids contributed to toxicity.