An Analysis of Historical Risk Issues Involving Herbicides, Pesticides, Salmonids, and Their Food Organisms: Yakima River Basin. R. D. Cardwell, Parametrix, Inc.
In the late 1980s, more than 120 substances were applied to a variety of crops in the Yakima Valley Basin, and the concentrations of many of these were studied by the US Geological Survey. In a retrospective assessment, the potential risks posed to juvenile salmonids and their food organisms by more than two dozen herbicides and pesticides were examined. The substances included several organophosphate insecticides, chlorophenoxy herbicides, triazine herbicides, DDT and other compounds. Risk issues examined in this paper included those associated with effects, namely acute-chronic ratios (ACR), differential toxicity to different groups of fish, invertebrates and plants, and the speed of toxic action. Exposure issues included the frequency and duration of occurrence of chemical concentrations in surface waters. In some instances, the toxicological data support abandoning the fixed ACR and replacing it with a regression equation based on the relative magnitudes of acute versus chronic toxicity. Pesticides and herbicides frequently affect taxonomic groups at much different magnitudes, especially fish, arthropods, and aquatic plants. Risks based on species sensitivity curves for these three groups are contrasted. Risks also often fail to consider the duration of exposure and the duration needed for bioaccumulation to elicit toxic effect. The potential risk outcomes from consideration of these factors is contrasted.
The Yakima Basin Joint Board and Parametrix supported some of the analyses included in this presentation.
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