The research focus of this project is to evaluate behavior and ecotoxicological effects of synthetic pyrethroids in runoff on aquatic organisms. Synthetic pyrethroids are widely used insecticides in both urban and agricultural environments. The use of pyrethroids is likely to increase further as the use of some popular organophosphates is being restricted. Pyrethroids display high toxicity to a wide range of aquatic organisms including invertebrates, but also strong affinity to sediment and soil particles. In runoff or stream effluents, pyrethroids are expected to partition between the solid phases and the dissolved phase. Because only the dissolved chemical concentration is considered bioavailable, the actual toxicity of pyrethroids may be regulated by the level and properties of the suspended solids and dissolved organic matter (DOM) in runoff. However, current water quality programs require that the whole effluent is extracted and the total chemical concentration is determined. Such practices will likely result in erroneous estimation of toxicity.
With the support of this grant, we developed a solid phase microextraction (SPME) method that offers selective detection of the dissolved concentration. We further evaluated the application of this method for biomimetic sampling. This method has been used to study phase distribution of a number of pyrethroids in water systems containing suspended solids. We have demonstrated that in runoff effluents containing suspended solids at 100 mg L-1, a significant fraction of pyrethroids was associated with the solid phase and DOM. The freely dissolved concentration was inversely proportional to the content of suspended particulates and DOM. Using 14C-labelled compounds, we further found that bioaccumulation of pyrethroids decreased with increasing levels of suspended solids. Using EPA protocols, we also showed that the acute toxicity of pyrethroids in sediment suspensions decreased with increasing levels of suspended particulates and DOM. It appears that both the amount and properties of suspended solids and DOM affect the bioavailability and toxicity of pyrethroids. The inhibitory effect of suspended solids and DOM on bioavailability and toxicity should be considered in monitoring efforts as well as establishing water quality standards for pyrethroid compounds. During this project, we have closely collaborated with a range of stakeholders in carrying out this project. Our collaborators include nursery growers in Orange County and Ventura County, farm advisors, and regulatory agencies (e.g., SWRCB, Santa Ana RWQCB, CDPR). We have obtained extramural financial support from CDPR as well as from SWRCB.