Abstract-A method is presented for developing water quality criteria (WQC) for type I narcotic chemicals in general and PAHs in particular. The criteria can be applied to any individual or mixture of narcotic chemicals using only the chemical's octanol-water partition coefficient K OW . It is derived from a database of LC50s comprising 156 chemicals and 33 species, including fish, amphibians, arthropods, mollusks, polychaetes, coelenterates, and protozoans. A target lipid model is proposed that accounts for variations in toxicity due to differing species sensitivities and chemical differences. The model is based on the idea that a target lipid is the site of action in the organism. Further, it is assumed that target lipid has the same lipid-octanol linear free energy relationship for all species. This implies that the slope of the log(LC50)-log(K OW ) relationship is the same for all species. However, individual species may have varying target lipid body burdens that cause toxicity. The target lipid LC50 body burdens derived from concentration data in the water only are compared to measured total lipid LC50 body burdens for five species. They are essentially equal, indicating that the target lipid concentration is equal to the total extracted lipid concentration. The precise relationship between partitioning in target lipid and octanol is established. The species-specific body burdens are used to determine the WQC final acute value, i.e., the 95-percentile level of protection. An acute-to-chronic ratio is used to compute the body burden corresponding to the WQC final chronic value, which is the procedure used to derive the U.S. Environmental Protection Agency water quality criteria. The criteria are expressed either as dissolved concentrations in the water column or as tissue concentrations.

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An extension of the simultaneously extracted metals/acid-volatile sulfide (SEM/AVS) procedure is presented that predicts the acute and chronic sediment metals effects concentrations. A biotic ligand model (BLM) and a pore water-sediment partitioning model are used to predict the sediment concentration that is in equilibrium with the biotic ligand effects concentration. This initial application considers only partitioning to sediment particulate organic carbon. This procedure bypasses the need to compute the details of the pore-water chemistry. Remarkably, the median lethal concentration on a sediment organic carbon (OC)-normalized basis, SEM*(x,OC), is essentially unchanged over a wide range of concentrations of pore-water hardness, salinity, dissolved organic carbon, and any other complexing or competing ligands. Only the pore-water pH is important. Both acute and chronic exposures in fresh- and saltwater sediments are compared to predictions for cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) based on the Daphnia magna BLM. The SEM*(x,OC) concentrations are similar for all the metals except cadmium. For pH = 8, the approximate values (micromol/gOC) are Cd-SEM*(xOC) approximately equal to 100, Cu-SEM*(x,OC) approximately equal to 900, Ni-SEMoc approximately equal to 1,100, Zn-SEM*(x,OC) approximately equal to 1,400, and Pb-SEM*(x,OC) approximately equal to 2,700. This similarity is the explanation for an empirically observed dose-response relationship between SEM and acute and chronic effects concentrations that had been observed previously. This initial application clearly demonstrates that BLMs can be used to predict toxic sediment concentrations without modeling the pore-water chemistry.

A method is presented for developing sediment quality guidelines (SQG) for narcotic chemicals in general and polycyclic aromatic hydrocarbons (PAHs) in particular. The guidelines can be applied to any individual or mixture of narcotic chemicals including PAHs using only the chemical's octanol/water partition coefficient. They are derived using the final chronic values for type I narcotics developed from a database consisting of LC50s for 145 chemicals and 33 species, including fish, amphibians, arthropods, mollusks, polychaetes, coelenterates, and protozoans. The target lipid model is used that accounts for the variations in toxicity due to differing species sensitivities as well as chemical differences. The SQGs are derived using the equilibrium partitioning model (EqP), and the results are compared to other sediment quality guidelines. The criterion for a mixture of PAHs is based on the known additivity of narcotic chemicals. The toxic unit concentration corrected for solubility is calculated for each chemical in the mixture and then summed. A total toxic unit greater than one indicates a toxic mixture. The prediction is compared to the results from an experiment using sediment spiked singly and with a mixture of PAHs. The toxicity and amphipod abundance of field-collected sediments are also examined.

A method is presented for developing scientifically defensible, numeric guidelines for residual petroleum-related constituents, specifically monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs), in the water column. The guidelines are equivalent to a HC5 (i.e., hazard concentration to 5% of the tested species, or the concentration that protects 95% of the tested species). The model of toxicity used in this evaluation is the target lipid model (TLM) that was developed for assessing the toxicity of type I narcotic chemicals. An acute to chronic ratio is used for chronic expression and sublethal effects. The TLM is evaluated by comparing predicted and observed toxicity of these petroleum components. The methodology is capable of predicting both the acute and chronic toxicity of MAHs and PAHs in single exposures and in mixtures. For acute exposures, the TLM was able to predict the toxicity to within a factor of three to five. The use of toxic units was an effective metric for expressing the toxicity of mixtures. Within the uncertainty bounds, the TLM correctly predicted where sublethal effects of edemas, hemorrhaging, and other abnormalities were observed to occur in early life-stage exposure to PAHs. The computed HC5s were lower than no-observed-effect concentrations based on growth, reproduction, and mortality endpoints and sublethal effects. The methodology presented can be used by the oil spill community to compare residual concentrations of PAHs against defensible, numeric guidelines to assess potential ecological impacts.