Low Chronic Additions of No. 2 Fuel Oil: Chemical Behavior, Biological Impact and Recovery in a Simulated Estuarine Environment

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Abstract
Three long-term experiments were conducted in estuarine microcosms with a water-accommodated fraction of No. 2 fuel oil. The water column and benthic compartments (structure and processes) were assessed for impact of chronic oil concentrations (190 and 90 ppb in the water column), and recovery from exposure to 90 ppb oil concentration. Oil impacts were a function of concentration, oil residence time and temperature. The 190 ppb concentration reduced zooplankton; both 190 and 90 ppb reduced benthic fauna. Within 1 yr after additions ceased, the benthic fauna did not recover from 90 ppb. Effects on and oil residence time in the water column were transitory; effects on and oil residence time in the benthos were long lasting. Effects on benthic fauna were most severe during the warm summer months. Hydrocarbon constitution, age, form and toxicity in the estuary may or may not be equivalent to the No. 2 fuel oil used. Chronic water column concentrations of 100 ppb and sediment concentrations of 500 ppm, which are commonly found at the heads of estuaries, indicate a potential for benthic degradation due to hydrocarbons.