ORGANISM EXPOSURE TO VOLATILE/SOLUBLE HYDROCARBONS FROM CRUDE OIL SPILLS—A FIELD AND LABORATORY COMPARISON

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Abstract
The acute toxicities of the water soluble fraction of crude oils or the aqueous solution of individual hydrocarbons were compared with the field exposure concentrations to dissolved hydrocarbons under crude oil slicks and emulsion plumes from chemically dispersed slicks. The exposures were related by expressing LC50 values for differing times and varying concentrations as a product (mean concentration × time = ppm-hours). Field exposures to soluble hydrocarbons under oil slicks on open water or in plumes of efficiently dispersed slicks are very low (from 150 to 1 million times lower) compared with exposures to cause half mortality for more than 50 marine species. This is so because oil slicks are thin, generally with average thickness between 0.1 and 0.01 mm. A high water-to-oil ratio limits the concentration of total oil to 10 to 100 ppm in the top meter of water, and 1 to 10 in 10 m. The soluble and volatile hydrocarbons quickly evaporate to the atmosphere from the slick or from near-surface waters. The field exposure of organisms in the water column is low initially and is transitory. Thus, oil spills and the chemical dispersion of slicks are unlikely to have measurable adverse effects on larval, juvenile, or adult marine organisms in the water column.

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