San Francisco Bay Food-Web Bioaccumulation Model for PCBs
This model was developed by us for the San Francisco Regional Water Quality Control Board (Water Board) to assess the effects of PCBs in wildlife and fishermen in San Francisco Bay and to identify potential management actions. The model is documented in a report Gobas and Arnot (2005), that will be listed on the website of the San Francisco Bay Clean Estuary Partnership (CEP), a collaboration of the Bay Area Clean Water Agencies (BACWA), Bay Area Stormwater Management Agencies Association (BASMAA), and the Water Board. The model can be downloaded in the form of a Microsoft EXCEL® workbook: San Francisco Bay Food-Web Bioaccumulation Model for PCBs.
The purpose of this model is to estimate the concentrations of PCBs in a set of key species that reside in the Bay as a result of PCB concentrations in sediments and water in the Bay. The species that are the main focus of the study are the double-crested cormorant (Phalacrocorax auritus), the Forsters tern (Sterna Forsteri), and the harbor seal (Phoca vitulina richardsi), as well as three fish species that are frequently caught by fishermen in the Bay, i.e. shiner surfperch (Cymatogaster aggregata), jacksmelt (Atherinopsis californiensis) and white croaker (Genyonemus lineatus). The fish species are important end-points of the model because of their role in passing PCBs to fishermen. double-crested cormorants, Forsterss terns and harbor seals are included in the model because they have been identified as sensitive receptors of PCBs. The model can be used to determine what concentrations of PCBs in the water and sediments of the Bay need to be reached to achieve an adequate margin of safety in wildlife and humans exposed to PCBs in the Bay area. This information can be used as part of a Total Maximum Daily Loading (TMDL) characterization to formulate remedial actions to achieve desired water quality goals.
The PCB food web bioaccumulation model for San Francisco Bay is presented in an Excel® spreadsheet. It consists of two modules, i.e. a science module and a management module. The science module includes the actual model including the models external and internal variables, functional relationships, sensitivity analyses and model performance evaluations. It calculates the Biota Sediment Accumulation Factor (BSAF) for individual PCB congeners and total PCBs (PCBs). The BSAF is the main output of the model and represents the relationship between the PCB concentrations in biota (CB) and that in the sediment (CS), i.e. BSAF = CB/CS. The management module, includes a simple worksheet to conduct two types of calculations, i.e. forwards calculations to estimate the concentrations of PCBs in biota of the Bay from PCB concentrations in the sediments of the Bay and backwards calculations to calculate the PCB concentrations in the sediments of the Bay that are required to meet PCB concentration based criteria in fish and wildlife for the Bay. The backwards calculation is designed to determine target PCB concentrations in sediments that meet ecological and/or human health criteria.
San Francisco Bay Food-Web Bioaccumulation Model for PCBs