John Wiley & Sons, Ltd.

Assessing the risk to green sturgeon from application of imidacloprid to control burrowing shrimp in Willapa Bay, Washington. II: Controlled exposure studies

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The activities of two species of burrowing shrimp have a negative impact on the growth and survivalofoysters reared on intertidal mudflats in Willapa Bay and Grays Harbor, Washington. In order to maintain viable harvests, oyster growers proposed the application of the neonicotinoid insecticide imidacloprid onto harvested beds for the control of burrowing shrimp. In test applications, water column concentrations of imidacloprid were relatively low and dissipated rapidly. The foraging activities of the ESA‐listed green sturgeon could result in exposure to higher, more sustained imidacloprid concentrations within sediment porewater and from the consumption of contaminated shrimp. Controlled experiments were conducted using surrogate white sturgeon to determine acute and chronic effects concentrations, examine overt effects at more environmentally realistic concentrations and durations of exposure, and assess chemical depuration. The 96 h LC50 was 124 mg L‐1, and the predicted 35 d NOAEC was 0.7 mg L‐1. No overt effects were observed following environmentally relevant exposures. Imidacloprid half‐life in plasma was greater than 32 h. Measured concentrations of imidacloprid in porewater were significantly lower than the derived acute and chronic effects concentrations for white sturgeon. Exposure risk quotients were calculated using the effects concentrations and estimated environmental exposure. The resulting values were considerably below the level of concern for direct effects from either acute or chronic exposure to an endangered species. This article is protected by copyright. All rights reserved

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