Effects of pyrethroid insecticides in urban runoff on Chinook salmon, steelhead trout, and their invertebrate prey

Abstract

Pyrethroid insecticides can affect salmonids either indirectly through toxicity to their prey or directly by toxicity to the fish themselves. In support of a study on pyrethroid impacts to Chinook salmon and steelhead trout in the American River (Sacramento, California, USA), 96-h median effective concentration (EC50) and median lethal concentration (LC50) values for the pyrethroid bifenthrin were determined for taxa not traditionally used for toxicity testing but of interest as salmonid prey, including a chironomid, caddisflies, mayflies, and stoneflies. A laboratory was constructed on the banks of the American River to expose macroinvertebrates, Chinook salmon, and steelhead trout to flow-through river water containing urban runoff during storm events. Bifenthrin from urban runoff was found in river water following 5 rain events, reaching 14.6 ng/L. Mortality to the exposed salmonids was not observed, and sublethal effects were not seen in vitellogenin or sex steroid levels. Indirect effects via toxicity to salmonid prey are possible. Mortality to Hyalella azteca, a potential prey, was observed in every event tested, and peak bifenthrin concentrations were comparable to the 96-h EC50 of the caddisfly, Hydropsyche sp., the most important prey species on a biomass basis for American River Chinook salmon. The other invertebrates tested had EC50s exceeding bifenthrin concentrations seen in the American River, though could potentially be at risk at concentrations previously reported in smaller urban tributaries. Environ Toxicol Chem 2015;34:649-657. © 2014 SETAC.

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

“…The converse is true for C. dilutus with effect levels for bifenthrin at least 25 times greater than concentrations seen in the creeks (the maximum concentration observed of 9.9 ng/l compared to 96-h EC50 N 253 ng/l; Weston et al, 2015). However, C. dilutus toxicity would be expected at the observed concentrations of fipronil, fipronil sulfone and fipronil sulfide (96-h C. dilutus EC50 = 32.5, 7.7, and 9.9 ng/l, respectively; .…”

“…Weston et al (2015) determined bifenthrin 96-h EC50s for 12 benthic macroinvertebrates, most from northern California. Bifenthrin concentrations seen in the urban creeks flowing to Suisun Marsh were one-third to one-half the 48 to 96-h EC50 of two mayflies, a stonefly, and a caddisfly.…”

Adaptation, not acclimation, is the likely mechanism for reduced sensitivity of some wild Hyalella populations to pyrethroid insecticides

“…We do not question the authors' assertion that H. azteca in the American River are exposed to winter pulses of pyrethroids related to storm water runoff. We documented such pulses ourselves (see Weston et al [13] and 2 of our prior studies cited therein). But even so, we would be extremely uncomfortable proposing that such pulses have led to "acclimation," when the data of Clark et al on seasonal patterns of pyrethroid resistance consist only of 2 points in time.…”

Contaminant Effects on California Bay–Delta Species and Human Health

“…Pyrethroids have been found in sediments of agricultural and urban waters upstream of the Delta at concentrations that are acutely toxic to numerous benthic and epibenthic macroinvertebrates (Amweg et al 2005;Holmes et al 2008;Weston et al 2008;Weston et al 2015b).…”