Estimating the Toxicity of Polynuclear Aromatic Hydrocarbons

As discussed in previous sections, there are numerous factors that can modify the toxicity of materials. The prediction of the toxicity of mixtures is also difficult. One of the best attempts at toxicity prediction has been formulated by Swartz et al. (1995) and predicts the sediment toxicity of polynuclear aromatic hydrocarbons. The model is based on the concentration of 13 PAHs in collected sediments, the predicted concentration in the sediment pore water, and the toxicity of these concentrations as determined by a large toxicity data set. 

The IPAH model incorporated a number of factors that can modify the toxicity of the sediment-borne PAHs. Equilibrium partitioning was used to estimate the concentration of each PAH in the pore water of the sediment. The assumption was that the pore water material is the fraction that is bioavail-able. QSAR was also used to estimate the interstitial water concentration based on the octanol-water partition coefficient of several PAHs. Amphipods were used as the test organism to represent environmental toxicity. A toxic unit (TU) approach was used and the toxicity is assumed to be additive. The assumption of additivity is justified since each of the PAHs has a similar mode of action. Finally, a concentration-response model was formulated using existing toxicity data to estimate the probability of toxicity. 

The estimates of toxicity are expressed as not toxic, uncertain, and toxic. These classifications are based on the estimated percent mortality as generated by the concentration-response model. A percentage of mortality less 

The estimates of toxicity were confirmed using a variety of sediment samples with measurements of PAH concentrations and amphipod toxicity tests. At sites where the PAHs were the principal cause of contamination, the frequency of correct predictions was 86.6%. When the samples were collected from sites where PAHs were not the principal contaminant, the frequency of correct prediction was 56.8%. 

Acute Toxicity to Amphipods Predicted from Sediment Concentrations of 10 PAHs 

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