Plasma cholinesterase activity as a biomarker for quantifying exposure of green sturgeon to carbaryl following applications to control burrowing shrimp in Washington State

Willapa Bay (Washington State, USA) has been 1 of the rare intertidal locations where large‐scale pesticide applications occur. Until recently, carbaryl was applied to control burrowing shrimp that decrease commercial oyster productivity. The bay is a critical habitat for green sturgeon (Acipenser medirostris), an anadromous species listed as threatened under the US Endangered Species Act. However, the hazard that carbaryl poses is unknown. Surrogate seawater‐acclimated white sturgeon (A. transmontanus) were exposed to 0 μg L−1, 30 μg L−1, 100 μg L−1, 300 μg L−1, 1000 μg L−1, and 3000 μg L−1 carbaryl for 6 h, and brain acetylcholinesterase (AChE) and plasma butyrylcholinesterase (BChE) activities were measured. Enzyme recovery was measured in an additional cohort exposed to 1000 μg L−1 carbaryl for 6 h. Activity of AChE was reduced (p ≤ 0.001) at concentrations ≥ 100 μg L−1 with recovery in the 1000 μg L−1 cohort by 72 h. Surprisingly, BChE activity was greater than controls at concentrations ≥ 300 μg L−1 (p > 0.05), a finding confirmed in additional fish exposed to 3000 μg L−1 for 6 h (+30%, p < 0.001) with apparent recovery by 48 h. Plasma samples were collected from free‐living green sturgeon before and 4 d to 5 d after application of carbaryl in Willapa Bay. Activity of BChE after application was reduced 28% (p