Lethal and sublethal effects of chlorpyrifos exposure on adult and larval stages of the grass shrimp, Palaemonetes pugio

This study examined the effects of chlorpyrifos, an organophosphorus insecticide, on newly hatched to adult life stages of the grass shrimp, Palaemonetes pugio. In laboratory experiments, adult and 18‐day old larval grass shrimp were exposed in separate 96‐h acute toxicity tests to establish a range of LC50's for these two life stages. The adult 96‐h LC50 was 0.37 μg/L with the 18‐day old larval 96‐h LC50 being 0.44 μg/L. In order to simulate field conditions, 6‐h pulse exposures of chlorpyrifos at 10‰ salinity were performed every 5 days during the grass shrimp larval life cycle. The test was carried out to metamorphosis of the surviving larvae to postiarvae with four 6‐h pulse doses. The LC50's ranged from 0.94 μg/L after the first pulse exposure to 0.29 μg/L at the end of the study. Among the five chlorpyrifos concentrations and the control, there were no significant differences in larval molting and metamorphosis and growth (postlarval dry weight). An assay method for acetylcholinesterase (AChE) inhibition was adapted for use with grass shrimp larvae to gain further insight into sublethal effects of chlorpyrifos exposure. Larvae sampled for AChE activity showed increased activity in the 0.4 μg/L chlorpyrifos exposure group and depressed activity in the 1.6 μg/L chlorpyrifos exposure group.