USING OIL SPILL DISPERSANTS ON THE SEA

Abstract

ABSTRACT Primary consideration in this critical review was given to treating oil spills at sea with the intent of reducing the environmental impact of that oil if it should reach the shore. The general conclusions reached were:In carefully planned and monitored laboratory and sea tests, oil has been effectively dispersed; but at many field tests and at accidental spills, reported effectiveness has been low—perhaps because of poor targeting and distribution of aerial sprays, because the oils were too viscous to be dispersable, or the observations of effectiveness were inconclusive.The acute lethal toxicities of dispersant formulations currently in use are usually lower than those of the more volatile and soluble fractions of crude oils and their refined products; hence the toxicity of dispersed oil is due primarily to the oil and not to the dispersant.Sublethal effects of dispersed oil observed in the laboratory occur in most cases at concentrations comparable to or higher than those expected in the water column during treatment of an oil slick at sea (1 to 10 ppm) but seldom at concentrations less than are found several hours after treatment (less than 1 ppm). Since the times of exposure in the laboratory are much longer than predicted exposures during slick dispersal at sea (one to three hours), the effects would be correspondingly less.In open waters, organisms on the surface will be less affected by dispersed oil than by an oil slick, but organisms in the upper water column will experience greater exposure to oil components if the oil is dispersed. In shallow habitats with poor water circulation, benthic organisms will be more immediately affected by dispersed than untreated oil. Long-term effects of dispersed oil on some habitats, such as mangroves, are less, and the habitat recovers faster if the oil is dispersed before it reaches that area.Because the principal benefit of dispersant use is to prevent oil stranding on sensitive shorelines, and because dispersability of oil decreases rapidly with weathering, prompt response is essential.