Suspended Load and Solubility Affect Sedimentation of Petroleum Hydrocarbons in Controlled Estuarine Ecosystems

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Abstract
The concentrations of No. 2 fuel oil and a suite of hydrocarbons with varying chemical properties (perhydrofluorene, pristane, biphenyl, 1-methylnaphthalene, 9-methylanthracene, and pyrene) were measured over time in the water column, on suspended particles, and in the sediments of two controlled microcosms receiving different amounts of mixing energy. The initial aqueous concentrations of the No. 2 fuel oil and other hydrocarbons were 330–500 μg/L and 0.80–10.8 μg/L, respectively. The levels of suspended particles were 3–5 mg/L in the control microcosm and up to 160 mg/L in the highly mixed system. The simulated storm made no major difference in the overall fate of the hydrocarbons. The concentration on particles collected in sediment traps was considerably lower in the tank with high suspended loads, and roughly equal amounts of hydrocarbons were eventually measured in the sediments of each microcosm. The percentage sedimented and residence time in the sediment varied with the lipophilicity and degradability of each hydrocarbon. Fifty percent or more of the least soluble hydrocarbons (aromatics with three or more rings, and saturates) were transported to the sediments. Most of the saturates were more persistent in the sediment than the two-ring aromatics. Aromatics of this class with additional substituent aliphatic groups showed increases in their degrees of sorption and sedimentary residence times in a regular manner. Three- and four-ringed aromatics were similar to the saturates in their sedimentary behavior. After 23 wk, the sediments contained a reduced but still significant fraction (~1/7) of the added petroleum hydrocarbons, enriched in branched and cyclic saturates and high molecular weight aromatics.

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