title: Impacts of hypersaline acclimation on the acute toxicity of the organophosphate chlorpyrifos to salmonids.
abstract: Acclimation to hypersaline conditions enhances the acute toxicity of certain thioether organophosphate and carbamate pesticides in some species of euryhaline fish. As the organophosphate chlorpyrifos is commonly detected in salmonid waterways, the impacts of hypersaline conditions on its toxicity were examined. In contrast to other previously examined pesticides, time to death by chlorpyrifos was more rapid in freshwater than in hypersaline water (16ppth). The median lethal time (LT50) after 100μg/L chlorpyrifos exposure was 49h (95% CI: 31-78) and 120h (95% CI: 89-162) for rainbow trout (Oncorhynchus mykiss) in freshwater and those acclimated to hypersaline conditions, respectively. Previous studies with hypersaline acclimated fish indicated induction of xenobiotic metabolizing enzymes that may detoxify chlorpyrifos. In the current study, chlorpyrifos metabolism was unaltered in liver and gill microsomes of freshwater and hypersaline acclimated fish. Acetylcholinesterase inhibition in brain and bioavailability of chlorpyrifos from the aqueous exposure media were also unchanged. In contrast, mRNA expression of neurological targets: calcium calmodulin dependent protein kinase II delta, chloride intracellular channel 4, and G protein alpha i1 were upregulated in saltwater acclimated fish, consistent with diminished neuronal signaling which may protect animals from cholinergic overload associated with acetylcholinesterase inhibition. These results indicate targets other than acetylcholinesterase may contribute to the altered toxicity of chlorpyrifos in salmonids under hypersaline conditions.
authors.affiliation: Department of Environmental Sciences, University of California, Riverside, CA 92521, United States. Electronic address: lmary001@ucr.edu.
authors.forename: Lindley A
authors.initials: LA
authors.lastname: Maryoung
authors.affiliation: Department of Environmental Sciences, University of California, Riverside, CA 92521, United States.
authors.forename: Ramon
authors.initials: R
authors.lastname: Lavado
authors.affiliation: Department of Environmental Sciences, University of California, Riverside, CA 92521, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Schlenk
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D004390:Chlorpyrifos / Q000633:toxicity*; D005618:Fresh Water; D005786:Gene Expression Regulation; D005880:Gills / Q000187:drug effects; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008861:Microsomes / Q000187:drug effects; D054712:Salinity; D012487:Salmonidae / Q000502:physiology*; D012623:Seawater; D015398:Signal Transduction; D016019:Survival Analysis; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D014874:Water Pollutants, Chemical; D004390:Chlorpyrifos
keywords: Acute toxicity; Chlorpyrifos; Hypersalinity; Salmonids; Signal transduction