Recent Advances in Sediment Toxicity Identification Evaluations Emphasizing Pyrethroid Pesticides

Abstract

Recent monitoring in California has indicated that sediment toxicity associated with pyrethroid pesticides is of concern in urban and agriculture-dominated watersheds. In some cases, waterbodies that are listed as impaired due to sediment toxicity may require development of Total Maximum Daily Load (TMDL) allocations to regulate chemicals of concern. This process will require identification of specific chemicals causing toxicity, and sediment toxicity identification evaluation procedures (TIEs) are one of the primary tools used in this process. This paper provides an overview of sediment TIE methods with an emphasis on those which have been demonstrated to be useful in resolving toxicity caused by pyrethroid pesticides. These include use of media for extracting non-polar organic chemicals from sediment and interstitial water and use of a carboxylesterase enzyme for hydrolyzing pyrethroids. Additional methods that have proven useful for identifying pyrethroid toxicity include addition of the metabolic inhibitor piperonyl butoxide, and manipulations of sample toxicity test temperatures. Methods are described for both solid-phase and interstitial water TIEs. In addition to discussing specific TIE methods, examples of studies that have successfully used the different procedures are cited. Results of two sediment TIE case studies which incorporate the majority of these methods are also provided to illustrate the utility of using a weight-of-evidence in the TIE approach. Results from the case study experiments conducted using samples from Westley Wasteway Creek (WWNCR) and an agriculture tailwater pond in the Salinas Valley (SV03) demonstrate that sediment toxicity at WWNCR was likely due to L-cyhalothrin and bifenthrin, and that toxicity at SV03 was likely due to L-cyhalothrin and cypermethrin. The results suggest that current solid-phase and interstitial water TIE methods are adequate for identifying toxicity caused by pyrethroid pesticides. Refinement of these methods will improve our ability to resolve causes of toxicity in sediments contaminated by complex chemical mixtures.