RP8 Ecotoxicology of Agrochemicals and Pharmaceuticals
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(GRU-1117-927301) Brain cholinesterase inhibition in juvenile Chinook exposed to carbaryl in seawater-Implications for Willapa Bay, Washington.

Cabarrus, Jennifer¹, grue, christian¹, Grassley, James¹, Major, Walter¹, ¹ University of Washington, seattle, WA, USA

ABSTRACT- Efforts to restrict the use of carbaryl to control burrowing shrimp in Willapa Bay, Washington have been in part driven by concerns over potential effects on salmonids. In 2003, we studied the use of treated areas in the Bay by salmonids in an effort to quantify their actual exposure to carbaryl. The only salmonid captured before and after treatment were juvenile Chinook (Oncorhynchus tshawytsha). Brain AChE inhibition (ca. 10%) occurred during the first tide post treatment in one of the two spray events with recovery to pre-spray levels of AChE by the second tide post-treatment. Both spray events showed significant increases (ca. 5-10%) in AChE levels by the third tide post treatment. This increase in enzyme activity, particularly in the more soluble fraction, was also documented in juvenile rainbow trout exposed to 6.3 ppb carbaryl as the formulated product (Sevin®80 WSP) used in the Bay. To determine if we could also document this apparent hormetic effect in Chinook smolts in seawater under laboratory conditions, we exposed smolts to concentrations of carbaryl (ai, in the formulated product) from 0 to 3,800 ppb for 6 h or 0 to 1,000 ppb for 96 h under static conditions. We then compared levels of brain AChE inhibition in the soluble fraction of the enzyme (no Triton X-100) with those when the detergent was added yielding total AChE activity (soluble + membrane bound fractions). A marked increase in the soluble fraction (> controls) was observed in smolts exposed to 6.3 ppb carbaryl for 96-h. Otherwise, inhibition was similar between the two assays to 39 ppb, but then diverged with inhibition in the total greater than that in the soluble fraction. Results suggest that, based on concentrations of carbaryl reported in the Bay, Chinook smolts would not be expected to suffer enzyme inhibition of greater than ca. 10%.

Key words: carbaryl, seawater, juvenile salmon, AChE activity