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PCB dose-response benthic injury models using equilibrium partitioning

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    The goal of this project was to develop a sediment PCB dose-response model based on benthic invertebrate effects to PCBs. We used an equilibrium partitioning (EqP) approach to generate predicted PCB sediment effect concentrations (largely Aroclor 1254) associated with a gradient of toxic effects in benthic organisms from effects observed in the aquatic toxicity studies. This report differs from all other EqP sediment investigations in that we examined a gradient of effects for multiple sites rather than a single, protective value. We reviewed the chronic aquatic toxicity literature to identify measured aqueous PCB concentrations and the associated benthic invertebrate effects. We control- normalized the aquatic toxic effect data and expressed results from various studies as a common metric, % injury. Then we calculated organic carbon (oc) -normalized sediment PCB concentrations (mg/kg-oc) from the aqueous PCB toxicity dataset using EqP theory based on EPA's (EPIWEB 4.1) derivation of Koc. Lastly, we constructed a non-linear dose-response numerical model for these synoptic sediment PCB concentrations and biological effects (Y = 100/1 + 10(logEC50-logX) " (Hill slope)). These models were used to generate easy to use 'look-up' tables reporting % injury in benthic biota for a range of Aroclor-specific sediment concentrations. For example, the model using the EPIWEB 4.1 Koc estimate predicts the mean benthic injury of 23.3%, 46.0%, 70.6%, 87.1% and 95% for hypothetical sediment concentrations of 1, 2, 4, 8, 16 mg/kg dry wt. of Aroclor 1254, respectively (assuming 1% organic carbon). Models for some Aroclors (1016, 1221, 1232, and 1268) could not be developed due to data gaps in the aquatic toxicity literature. Specific step-wise procedures are provided for predicting % benthic injury when sediment PCBs are reported as Aroclor, congeners, homolog groups or total PCBs. The report identifies and discusses the uncertainties associated with the numerical PCB dose-response models and the EqP approach and provides considerations for how other Koc values result in more or less conservative models. This paper provides recommendations for addressing outstanding issues, including the Koc calculation, the two-carbon model, and congener data. We recommend using the model presented for screening but suggest, when possible, to determine a site specific Koc; that along with the tables and equations herein allows users to create their own protective dose-response sediment concentration for a specific location. [doi:10.7289/V56971KR ( )]
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