Stormwater-related transport of the insecticides bifenthrin, fipronil, imidacloprid, and chlorpyrifos into a tidal wetland, San Francisco Bay, California

The authors sampled creeks that enter Suisun Marsh in San Francisco Bay for contaminants including imidacloprid during a large storm event. Freshwater enters the marsh from both urban and agricultural creeks, so it receives compounds from a variety of sources. Suisun Marsh provides essential habitat for several threatened fish species, so its health is of particular concern. The sampling was conducted during a winter storm, so these results do not address most agricultural applications that occur during the summer. The storm sampled was the first major event of the season, so it flushed a high sediment load and accompanying contaminants towards the bay. Sample water was analyzed for contaminants as well as used for 96 hour toxicity testing with Hyalella azteca and Chironomous dilutus that evaluated for dead and impaired invertebrates. H. azteca were paralyzed in 4 of 10 creek water samples, and C. dilutus were impaired in 6 of 10 samples. Based on additional testing, the authors determined that the toxicity to H. azteca likely resulted from pyrethroids, and the C. dilutus toxicity was attributable to fipronil. Imidacloprid, though detected, was considered an unlikely contributor to the invertebrate toxicity because the detection levels were below those that harm the species. Imidacloprid was detected in 4 of the 5 creek samples at concentrations ranging from 13.5 to 1462 ng/L (most samples were below 70 ng/L).

Authors: 
Weston, D.P., D. Chen, and M.J. Lydy
Journal: 
Science of the Total Environment
Year published: 
2015