Crude oil contains thousands of compounds with a wide range of physical-chemical properties and biological activities. Therefore, it is a challenge to predict the toxi-city of such complex mixtures among the many varieties of marine organisms. Over the years, toxicologists have utilized both single- and multiple-compound oil exposures to examine toxic effects in numerous marine species. However, we need to recognize that species variation makes it very difficult to accurately predict toxicity. It is also very difficult to estimate the toxicity of a mixture by combining single-component information, due to chemical interactions within the mixtures.
Several oil spill impact models have been developed to estimate the fate of oil and its impacts on marine organisms and the ocean. The Spill Impact Model Application Package (SIMAP) developed by the US Natural Resource Damage Assessment for oil spills is one oil impact model attempting to incorporate as many factors as possible. Weather conditions, wind, wave and current actions, and the geological environment work in combination to determine the disposition of oil on the surface, in the water column, on the seashore, and in sediments. The model also attempts to evaluate biological exposure, considering both the movement of biota and oils, acute toxic effects (lethal and sublethal), indirect effects of acute exposure via food chain and habitats, non-density-dependent population level impacts from mortality and sublethal effects, and the biological effects of treatment (blooming and dispersant). Oil distribution is relatively easy to predict if accurate measurements of physical and geological factors are made. However, characterization of toxicity traditionally focusing on acute LC50 (mortality) is problematic. In addition, impacts ofdevelopment, reproduction, and animal behavior are difficult to estimate at sublethal levels of exposure. Ecological data, such as the distribution of wildlife in contaminated areas during an oil spill episode, are also very limited. Thus, when considering oil impacts on ecosystems, basic toxicological and ecological information is crucial for agencies to both make the best professional estimate of ecosystem impacts and further develop ecosystem-based oil spill management techniques.
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