Risk potential of PAH concentrations in sediments near petroleum refinery wastewater discharges

A sediment characterization study was conducted to assess the potential for exposure of benthic organisms to phenanthrene, fluoranthene, and acenaphthene at four petroleum refineries discharging to an estuarine embayment. Replicate samples were collected at varying distances from each refinery's diffuser along a transact where typically the highest concentration of effluent was predicted to exist. Samples were analyzed for the three polycyclic aromatic hydrocarbons (PAH), total organic carbon (TOC), and sediment grain size. Concentrations of PAHs were normalized to organic carbon content and then compared to EPA's proposed Sediment Quality Criteria (SQC) to assess the potential risk. Ecological effects quotients (EEQ) were calculated as the quotient of the proposed sediment toxicological effects criteria (TEC) and the expected environmental concentration (EEC) (geometric mean of organic carbon normalized PAH data). At distances ranging from 3m to 150m, EEQs ranged from 1.0 x 10-3 to 1.0 x 10-4 when compared to freshwater SQC and from 7.8 x 10-4 to 1.1 x 10-5, when compare to saltwater SQC. Large percentages of silt and clay suggest that these sediments were indicative of deposition zones and thus reflect worst case exposure conditions. Consequently, the authors concluded that these and other petroleum refinery wastewaters receiving similar secondary treatment should pose little risk of impacting benthic organism as a result of these PAHs