Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Morris H. Roberts


Several aspects of effects of the organophosphate pesticide diazinon on the American oyster Crassostrea virginica Gmelin were investigated. Uptake of diazinon directly from water was compared with uptake of diazinon sorbed to either fine sediment or algae; the primary route of assimilation seems to be from the water. Concentrations of diazinon between 0.91 and 2.03 mg/L inhibit shell growth during 96 hours of exposure; there is a sharp threshold of effect for this response which is probably an indirect one caused by lack of food during shell closure. Acetylcholinesterase inhibition is significant in oyster heart tissue at concentrations of approximately 1 mg/L and greater. Even when inhibition is as great as 72%, however, it is not fatal. During a six-week exposure at high temperatures (22-24&\sp\circ&C), diazinon accelerated depletion of glycogen stores but had no long-term effect on total lipid reserves. Because of the disruption of the energy balance caused by the high temperature, glycogen stores in all oysters were depleted by the end of the period and little reproductive conditioning occurred. There is a suggestion of some early gametogenic activity because there was an increase in total lipid content during the first 21 days in the controls and low dose but not in the two highest doses. This increase may have resulted from conversion of some glycogen to lipid for vitellogenesis. Diazinon is rapidly accumulated and metabolized by oysters. The pesticide and its biotransformation products are quickly eliminated from the animal when exposure ends; more than 90% is removed within two days. A small fraction of the nonpolar byproducts, however, appears to be stored in the lipids. The bioconcentration factor calculated from results of an accelerated uptake test is 56; although this is low compared with that of many compounds, it is higher than that reported for diazinon in other invertebrates.



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