Changes in juvenile coho salmon electro‐olfactogram during and after short‐term exposure to current‐use pesticides

Abstract For anadromous salmonids, olfaction is a critical sense, enabling return migration. In recent years, several pesticides have been identified that interfere with salmonid olfaction at concentrations in the μg/L range; thus, they may pose a risk to species longe]ity. In the present study, we investigated the acute effects of five agricultural pesticides on juvenile coho salmon (Oncorhynchus kisutch) olfaction using the electro‐olfactogram (EOG), a measure of odorant‐evoked field potentials. Electro‐olfactogram responses to the odorant L‐serine were measured during and following a 30‐min exposure of the left olfactory rosette to chlorothalonil, endosulfan, glyphosate acid, iodocarb (IPBC), trifluralin, and 2,4‐dichlorophenoxyacetic acid. With the relatively insoluble pesticides endosulfan and trifluralin, decreases in EOG amplitude were only apparent at relatively high concentrations (100 and 300 μg/L, respectively) following 20 min of exposure and were absent for chlorothalonil (1 mg/L). With the water‐soluble herbicide glyphosate, significant EOG reductions occurred within 10 min of exposure to 1 mg/L and more rapidly with higher concentrations. Recovery of EOG post‐glyphosate exposure was concentration‐dependent, and complete recovery was not observed with some concentrations at 60 min postexposure. Dichlorophenoxyacetic acid only affected EOG at high concentration (100 mg/L), where it eliminated EOG within 2 min of exposure. With IPBC, EOG was decreased at 25 min of exposure to 1 μg/L; higher concentrations caused decreases to occur more rapidly. Excluding IPBC and glyphosate, all EOG reductions occurred at concentrations greater than the current Canadian water‐quality guidelines and reported 96‐h lethality values. Our results show that olfactory neurons can be impaired rapidly by some current‐use pesticides, even at exposures in the low‐μg/L range.