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WP4 Pesticides in Pacific Northwest (USA) Watersheds
() A hierarchical ecotoxicological approach used to evaluate organophosphate pesticide effects on Pacific Northwest aquatic organisms.
Foster, E.1, St. Aubin, C.1, Grange, G.1, Sievers, J.1, Lowrance, M.2, Abrams, M.1, 1 Oregon Department of Environmental Quality, Portland, Oregon, USA2 Portland State University, Portland, Oregon, USA
ABSTRACT- Steelhead (Oncorhynchus mykiss) were listed as threatened under the Endangered Species Act in the Hood River Basin, an area of mixed land use. The causes of the population declines are unknown but orchard pesticide use was identified as one potential stressor because pesticide application overlaps with sensitive life stages of steelhead in small streams adjacent to orchards and the organophosphate insecticides used are toxic to aquatic life at low concentrations. The goal of this study was to determine the indirect effects to steelhead from changes in food web resources and the direct biochemical effects to steelhead from exposure to organophosphate insecticides that occur in Hood River Basin streams. Macroinvertebrates were collected before and after orchard insecticide spraying upstream and downstream of orchard areas. In-stream bioassays with hatchery juvenile steelhead and water sampling for pesticides and general chemistry were conducted during the spray season. Macroinvertebrates were identified to lowest taxonomic order. Brain acetylcholine esterase (AChE) activity was measured by spectrophotometer. Water column organophosphate insecticides were measured by GC/NPD. Macroinvertebrate species diversity was lower downstream of the orchard areas with a shift to species that are not preferred prey items of juvenile steelhead. This coincided with depressed juvenile steelhead brain AChE activity in these same sample reaches. The organophosphate insecticides chlorpyrifos and azinphos methyl were detected downstream of orchard areas but not upstream. The weight of evidence indicates that orchard use of organophosphate insecticides may have been adversely affecting steelhead indirectly through changes in food web structure and directly by inhibition of AChE in some of the steelhead producing streams in the Hood River Basin.
Key words: acetylcholine esterase, pesticides, fish, macroinvertebrates
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