Effects of Sublethal Chlorpyrifos Exposure on Postlarval American Lobster (Homarus americanus).

The organophosphate pesticide chlorpyrifos has been introduced to the marine environment via adsorption to agricultural soil runoff or as spray drift. Chlorpyrifos affects the survival of some larval decapod crustaceans, but no data exist on the impacts to the American lobster, Homarus americanus. The purpose of the present study was to assess the levels at which chlorpyrifos affects the survival of postlarval H. americanus. Using acute saltwater exposures, the 24- and 48-h median lethal concentrations were established for stage IV H. americanus (1.56 and 1.33 µg/L, respectively). Movement, acetylcholinesterase activity, intermoult period, specific growth rate, and moult increment were measured during exposure to sublethal concentrations. Movement patterns were assessed to establish a 48-h median inhibition concentration for cessation of normal movement (0.66 µg/L). Acetylcholinesterase activity was found to be inhibited immediately post-exposure to 0.50, 0.57, and 0.82 µg/L chlorpyrifos but could be recovered within a period (9-15 d) in clean seawater. Sublethal growth effects of increased intermoult period, decreased specific growth rate, and decreased moult increment were observed during exposure to an environmentally relevant concentration (0.82 µg/L). The present study suggests that H. americanus stage IV larvae were marginally less sensitive to chlorpyrifos compared with other decapods and that acute lethality of H. americanus postlarvae is not likely to occur with chlorpyrifos concentrations previously reported from aquatic environments. Environ Toxicol Chem 2019;38:1294-1301.