Effects of petroleum hydrocarbons on the physiology of the American oyster, Crassostrea virginica, Gmelin.
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Oysters rapidly accumulated saturated and aromatic hydrocarbons from oil- water dispersions. Aromatic hydrocarbons were accumulated to a greater extent than n-paraffins relative to their respective concentrations in the exposure water. Saturated hydrocarbons were accumulated in higher amounts from crude than from refined oils. When uptake of oil by oysters was measured over a period of several days, the levels of accumulation of oil-derived petroleum hydrocarbons did not consistently increase. Following return to oil-free seawater, oysters depurated the saturated chains and most aromatic fractions rapidly. Depuration was nearly completed within 30 days. Two partially refined oils, Venezualan bunker C and No. 2 fuel, were found to be more toxic than two crude oils tested, South Louisiana and Kuwait. Oysters demonstrated greater resistance to test oils than to the reference toxin, dodecyl sodium sulfate. Valve closure by oysters made it difficult to determine percent mortality data in 96-hour static bioassays with petroleum hydrocarbons. In salinity studies, measurements of osmotic and chloride ion concentration of the pericardial fluid from control oysters showed that the fluid conformed to the ambient medium throughout the non-lethal range. The pericardial fluid remained very slightly hyperosmotic to the environment. Those animals transferred to salinities between 4 and 8 ppt reached a new steady state of fluid concentration at a slower rate than those moved to higher salinities. Analyses of chloride ion concentrations after transfer demonstrated a similar pattern of delayed conformity, but the resulting concentrations were slightly lower than the medium. Changes in percent body water and percent ask as a result of salinity alterations occurred at slower rates than osmotic and chloride changes in pericardial fluid, but final values were proportional to the extent of seawater dilution. Oysters exposed to near-lethal levels of petroleum fractions were slower to reach osmotic equilibrium after transfer to media of different salinities. The osmotic concentrations of pericardial fluid from control and from oil-exposed animals did not differ significantly after 10 days. Exposure to petroleum hydrocarbons resulted in respiratory rates slightly greater than those of controls. Oxygen consumption of whole animals exposed to oil returned to control levels within approximately two weeks. Gill tissue from oysters exposed to near-lethal concentrations of petroleum showed higher oxygen consumption than gill tissue from controls. Control oysters had a greater resistance to heated seawater than either oil-exposed or diseased oysters. Oysters exposed to oil and temperatures greater than 40 degrees C showed mortalities similar to controls, but below this temperature the greater resistance of controls became increasingly apparent. No differences in growth were noted between control and oil-exposed oysters.