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A comparative assessment of azinphosmethyl bioaccumulation and toxicity in two estuarine meiobenthic harpacticoid copepods

Aqueous, pore‐water, and whole‐sediment bioassays were conducted with meiobenthic copepods with different infaunal lifestyles to assess the acute and chronic toxicity of the organophosphorous pesticide azinphosmethyl (APM) and its bioaccumulation potential in sediments. Biota sediment accumulation factors were an order of magnitude higher for the deeper burrowing Amphiascus tenuiremis (26.6) than the epibenthic Microarthridion littorale (2.2). The female A. tenuiremis APM median lethal concentration (LC50; 3.6 μg/L) was twice the male LC50 (1.8 μg/L), in straight seawater exposures, and nearly 20% higher than males in whole‐sediment exposures (540 vs 456 ng/g dry weight). Amphiascus tenuiremis were 17 times more sensitive to sediment‐associated APM than M. littorale. In pore‐water‐only exposures, the adult mixed‐sex A. tenuiremis LC50 (5.0 μg/L) was nearly twice the seawater mixed‐sex LC50 (2.7 μg/L). Dissolved organic carbon in pore water was five times higher (20 mg/L) than in seawater‐only exposures (4 mg/L). Differences in acute toxicity within exposure media were driven by species‐ and sex‐specific differences in lipid content. Amphiascus tenuiremis likely experienced greater exposure to sediment‐associated toxicants via longer periods of direct contact with pore water than M. littorale and, therefore, exhibited correspondingly higher bioaccumulation and acute toxicity. Copepod reproduction was significantly reduced (>60%) in 14‐d sediment culture exposures at sublethal APM levels, suggesting that chronic field exposure to sediment‐associated APM would result in sharp declines in copepod population growth.