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 i nsecticide, on newly hatched to adult life stages of the grass shrimp, Palaemonetes pugio. In laboratory experiments, adult and 18-day old l arval 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 mug/L with the 1 8-day old larval 96-h LC50 being 0.4 4 mug/L. In order to simulate field conditions, 6-h pulse exposures of chlorpyrifos at 10 parts per thousand. 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 postlarvae with four 6-h pulse doses. The LC50's ranged from 0.94 mug/L after the first pul se exposure to 0.29 mug/L at the end of the study. Among the five chlo rpyrifos concentrations and the control, there were no significant dif ferences in larval molting and metamorphosis and growth (postlarval dr y weight). An assay method for acetylcholinesterase (AChE) inhibition was adapted for use with grass shrimp larvae to gain further insight i nto sublethal effects of chlorpyrifos exposure. Larvae sampled for ACh E activity showed increased activity in the 0.4 mug/L chlorpyrifos exp osure group and depressed activity in the 1.6 mug/L chlorpyrifos expos ure group.