Trophic Transfer of a Sediment-Associated Organophosphate Pesticide from Meiobenthos to Bottom Feeding Fish

Experiments were conducted to examine the dynamics of a sediment-associated pesticide azinphosmethyl (APM) using a sublethal benthic based trophic transfer model (meiobenthic copepods to juvenile fish). Two predominant pathways for contaminant transfer during feeding, prey ingestion and sediment ingestion, were examined to determine their relative contributions to APM transfer and subsequent effects on fish brain AChE inhibition. Experiments were conducted in 1993 and in 1994. Field collected benthic copepods were exposed to 14-C labeled APM, a potent acetylcholinesterase (AChE) inhibitor, in sediments for 96 h. APM burdens were measured in the copepods, and these contaminated copepods were fed to the juvenile fish predator Leiostomus xanthurus in uncomtaminated sediments. After gut clearance, fish were examined for brain AChE activity and APM residues in the liver, heart, gut, muscle, gill, and remains. Similar experiments were conducted in which meals of uncontaminated copepods were fed to spot in APM contaminated sediments, to determine the relative contribution of contaminated sediments to APM transfer. Copepods exposed to APM at a mean sediment concentration of 1223 ng/g dry weight accumulated APM at the level of 2.5 &mgr;g/g dry tissue. Brain AChE activity was significantly depressed (23%) in the 1993 fish fed one meal of contaminated copepods, however there was no significant decline in AChE activity in the fish tested during 1994. APM accumulation in fish feeding in contaminated sediments was generally greater than in fish feeding on contaminated prey. Significant accumulation was found in bodily remains, gills, gut, and muscle in fish that fed in contaminated sediments. No significant APM accumulation was found in fish fed the contaminated copepods.