Impacts of carbamate pesticides on olfactory neurophysiology and cholinesterase activity in coho salmon ( Oncorhynchus kisutch)

Abstract

Many freshwater aquatic environments in the Pacific Northwest of North America contain neurotoxic pesticides, an issue of concern given the use of many of these habitats by Pacific salmon ( Oncorhynchus sp.). Pesticides such as carbamates are known to affect fundamental physiological systems (such as the enzyme acetylcholinesterase (AChE)), and have been shown to affect salmonid olfactory-mediated behaviors. A neurophysiological measure of olfactory function, the electro-olfactogram (EOG), was used in this study to examine the impacts of acute localized exposure to three carbamates (the insecticide carbofuran, the antisapstain IPBC, and the fungicide mancozeb) on olfactory function in the coho salmon ( Oncorhynchus kisutch). We also examine the potential for these pesticides to alter AChE levels in the primary olfactory system and brain with brief exposures (30 min to only the olfactory rosette (OR)). In results, we find that the EOG in coho salmon is highly sensitive to brief localized exposures of two of these three carbamate pesticides. The effective nominal concentration required to cause a 50% reduction in EOG amplitude (EC 50) for carbofuran was 10.4 μg/l and for IPBC was 1.28 μg/l. For mancozeb, the EC 50 was higher at 2.05 mg/l. All three carbamates also affected AChE activity levels in the OR and brain (BR): carbofuran exposure at 200 μg/l significantly inhibited AChE activity in the OR, and both IPBC and mancozeb significantly increased AChE activity in BR at multiple concentrations with acute localized exposure. These carbamate effects highlight the sensitivity of salmon olfactory neurophysiology to pesticides acting not only potentially via AChE-inhibition, but also by other currently unknown modes of action.