T4 AM Endangered Species and Environmental Contaminants: Status of the Science (Part 1)
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in Ballroom 4

(SCH-1117-825933) Neurochemical and behavioral indicators of sublethal toxicity in Pacific salmon exposed to organophosphate and carbamate insecticides.

Scholz, N¹, Laetz, C¹, Labenia, J¹, Baldwin, D¹, Stark, J², ¹ NOAA Fisheries, Northwest Fisheries Science Center, Seattle, WA, USA² Washington State University, Department of Entomology, Puyallup, WA, USA

ABSTRACT- Organophosphate and carbamate insecticides are widely detected in surface waters that provide habitat for several threatened or endangered species of Pacific salmon (Oncorhynchus spp.) in the western United States. These chemicals interfere with acetylcholine-mediated synaptic transmission in the nervous systems of fish via the inhibition of acetylcholinesterase (AChE) enzyme activity. We have recently shown that the organophosphate chlorpyrifos inhibits brain AChE activity in juvenile salmon at low, environmentally realistic exposure concentrations (< 0.5 g/L) and that this inhibition correlates closely with impairments of spontaneous swimming and feeding behaviors [Sandahl et al., 2005, Environ Toxicol Chem, 24:136-145]. However, anticholinesterase insecticides commonly co-occur in the environment. This raises the possibility of antagonistic, additive, or synergistic neurobehavioral toxicity in salmon exposed to mixtures. To investigate the joint toxicity of anticholinesterase mixtures in vitro, we extracted AChE from salmon nervous system and investigated the inhibitory effects of organophosphates (the oxon derivatives of diazinon, chlorpyrifos, and malathion) and carbamates (carbaryl and carbofuran), alone and in two-way combinations. The joint toxicity of anticholinesterase mixtures can be accurately predicted from the inhibitory potencies of individual chemicals within a mixture. This indicates that organophosphate and carbamate insecticides are non-interactive in terms of AChE inhibition, and that it may be possible to estimate the cumulative neurotoxicity of mixtures using simple dose-addition. Since organophosphates and carbamates are likely to have additive impacts on the neurobehavior of salmon under natural exposure conditions, ecological risk assessments that focus on individual anticholinesterases may underestimate the actual risk to salmon in watersheds where mixtures of these chemicals occur.

Key words: salmon, pesticide, mixture, behavior