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Assessing the Toxicity of Mixtures of Surface Washing Agents and Oil to Marine and Freshwater Species.

DescriptionToxicity testing required for registration in the National Contingency Plan Product Schedule includes testing of 1:10 mixtures of spill response chemical agent to Number 2 Fuel oil. Toxicity data of these mixtures is only required for two estuarine species, mysid shrimp (Americamysis bahia) and inland silversides (Menidia beryllina). The sensitivity of A. bahia and M. beryllina is not consistently predicative of the sensitivity of other estuarine or marine species. Additionally, the sensitivity of freshwater species to oil and spill response chemical agent mixtures is uncertain. To address these data gaps for a selection of surface washing agents, a study was conducted assessing the toxicity of Alaskan North Slope crude oil (ANSCO) and surface washing agent mixtures to the standard estuarine species A. bahia and M. beryllina as well as two freshwater species, a crustacean (Ceriodaphina dubia), and fathead minnow (Pimephales promelas). The aims of the study were to assess if toxicity of mixtures was significantly different than oil alone, and if testing of mixtures on A. bahia and M. beryllina was consistently predicative of freshwater counterpart species sensitivities. One of the factors to consider in contingency planning is both the inherent toxicity of a chemical response agent, and its toxicity when combined with oil as a result of use. This work demonstrates that there is an unknown uncertainty around the representativeness of toxicity data from the two standard species required (A. bahia and M. beryllina), and that mixture toxicity may present additional uncertainties in risk estimations.

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