PARENT SESSION
PM25 - Agrochemicals
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P436) Do Organophosphate and Pyrethroid Insecticides Affect the Neuromuscular Development of Topsmelt?

Wilson, Barry¹, Fry, William^*,1, ¹ UC Davis, Davis, CA, USA

ABSTRACT- The agricultural application of organophosphate and pyrethroid insecticides results in their inadvertent introduction, through leaching and runoff, into downstream aquatic systems including coastal rivers, estuaries, and bays. The organophosphates (O.P.) and particularly the pyrethroids, are known to be highly toxic to aquatic organisms and their principal target is the nervous system. Here we propose to study the effects of sub-lethal concentrations of these insecticides on the neuromuscular development of an endemic species Topsmelt (Atherinops affinis) in a laboratory setting. Topsmelt embryos, newly hatched larvae, and 7 day old larvae will each be exposed to the following sub-lethal concentrations of the O.P. diazinon and the pyrethroids permethrin and esfenvalerate for 7 days: diazinon (100ppb and 10ppb), permethrin (6.25ppb and 0.625ppb), and esfenvalerate (0.025ppb and 0.0025ppb). Following exposure larvae will be subjected to physiological testing (determination of critical swimming velocity) and then sacrificed and examined histologically. Through histological examination of the tissues we expect to see increased programmed cell death of motor neurons (determined by counting motor axons from Epon-embedded transverse sections of the spinal cord at the level of the ventral root) and transformation of the lateral slow-twitch muscle fibers towards fast-twitch fibers (assayed by staining serial sections of the lateral musculature for myosin ATPase activity). Additionally critical swimming velocity of exposed fish will be compared to controls to correlate any pesticide-induced changes in the neuromuscular system (observed by histology) with changes in swimming performance. This work will be done in collaboration with Gary Cherr and others at the UC Davis Bodega Marine Lab and is supported in part by the UC TSRTP fellowship program and the PEEIR grant.

Key words: sub-lethal, aquatic toxicology, neuromuscular, pesticides