Azinphosmethyl exposure to grass shrimp (Palaemonetes pugio) life stages with emphasis on larval acetylcholinesterase activity

For the organophosphorus pesticide, azinphosmethyl, 96-h acute toxicity bioassays were conducted in adult and two larval stages of grass shrimp, Palaemonetes pugio, and acetylcholinesterase (AChE) activity was determined in larvae following pulse-dose exposures. The 96-h LC sub(50) values for the different life stages ranged from 0.38 to 164 mu g/l for 18-d-old larvae and adults, respectively. The 18-d-old larvae were significantly more sensitive to azinphosmethyl than newly hatched larvae. At all azinphosmethyl concentrations used in the pulse-exposure test, whole-body AChE activity was reduced significantly from controls after 6 h of exposure. The AChE levels at day 15 suggested that recovery of AChE levels occurred between the four pulse doses.