ECOTOXICOLOGICAL ENVIRONMENTAL RISK LIMITS FOR TOTAL PETROLEUM HYDROCARBONS ON THE BASIS OF INTERNAL LIPID CONCENTRATIONS

A method is described for deriving ecotoxicological environmental risk limits (ERLs) for total petroleum hydrocarbons (TPH). Toxicity data for two oil types ( light and heavy) to benthic organisms and corresponding estimated internal lipid concentrations, calculated by equilibrium partitioning, are used as a measure of toxicity by narcosis. It is assumed that uptake by organisms takes place from the aqueous phase, and for partitioning, both oil droplets or coating and organic carbon of sediment are taken into account. To distinguish between the different fractions of TPH, the method used is based on a fraction analysis approach in which aliphatic and aromatic compounds are regarded separately and both are further divided into different fractions. A toxic unit approach is applied to these fractions to take additivity into account. Lethality of the lighter oil type ( internal concentration 28-204 mmol/L-lipid) was in good agreement with data on internal concentrations retrieved from the literature. For the heavier oil type the observed toxicity was slightly higher and can probably be attributed to physical soiling of the organisms by oil or oxygen depletion due to biodegradation of the oil. For deriving ERLs, chronic endpoints are considered. The most sensitive chronic endpoints appear to be similar for both types of oil. The distribution of estimated total internal concentrations for chronic endpoints (1.38-149 mmol/L-lipid) is used as a basis for the ERLs. The resulting ERLs for the mixture of TPH are comparable with ERLs for single compounds.