Natural Weathering of Oil in Marine Sediments: Tissue Contamination and Growth of the Littleneck Clam. Protothaca staminea

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Abstract
Three groups (90 per group) of small (<30 mm) littleneck clams, Protothaca staminea, were placed in the intertidal environment of Sequim Bay, Washington for 1 yr to measure the effects of oiled sediment on growth and tissue contamination. Detailed glass capillary gas chromatographic analyses of initial and final sediment samples and tissues were used to describe the fate of specific oil components in the sediment, with depth, and the uptake by the clams. Concentrations of oil in sediments receiving a top layer (3 cm) of highly contaminated sediment reached background levels after 1 yr, while sediment mixed to depth (10 cm) with oil still contained measurable contamination at the 5–10 cm depth. The pattern of specific hydrocarbon loss is in agreement with results of spill studies, molecular weight relationships, and biodegradation data. The ratios of tissue concentrations to final sediment concentrations for phenanthrenes, alkylnaphthalenes, and dibenzothiophenes were all between 0.16 and 0.18. This suggests that the sulfur-containing compounds were not preferentially retained in tissues. Statistical analyses of 31–48 individually measured and marked clams (per group) showed that growth in oil-treated sediment was significantly (P < 0.001) slower than in clean sediment. In addition, oil mixed into sediment (10 cm) produced greater tissue contamination and more reduction in growth (P < 0.01) than a layer (3 cm) of oiled sediment.

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