John Wiley & Sons, Ltd.

Assessing the risk to green sturgeon from application of imidacloprid to control burrowing shrimp in Willapa Bay, Washington. I: Exposure characterization

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Willapa Bay and Grays Harbor, Washington comprise the largest region of commercial oyster cultivation on the Pacific Coast. The activities of two species of burrowing shrimp impair growth and survival of oysters reared on the intertidal mudflats. In order to maintain viable harvests, the oyster growers have proposed controlling the shrimp by applying the insecticide imidacloprid onto harvested beds. ESA‐listed green sturgeon forage on burrowing shrimp, and could be exposed to imidacloprid in the sediment porewater and through consumed prey. Studies were conducted to evaluate the likelihood that green sturgeon would be exposed to imidacloprid and to characterize the subsequent environmental exposure. Comparisons between treated and untreated control beds following test application of the insecticide suggested that green sturgeon fed opportunistically on imidacloprid‐impaired shrimp. The highest interpolated imidacloprid residue concentrations in field samples following chemical application were 27.8 and 31.4 μg kg‐1 in porewater and shrimp, respectively. Results from modeled branchial and dietary uptake, based on conservative assumptions, indicated that the porewater exposure route had the greatest contribution to systemic absorption of imidacloprid. The highest average daily uptake from porewater (177.9 μg per kg body weight) was 9.5‐fold greater than total dietary uptake (18.8 μg per kg body weight). Concentrations and durations of exposure would be lower than the levels expected to elicit direct acute or chronic toxic effects. This article is protected by copyright. All rights reserved

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