UC Riverside

Hydrophobic organic contaminants (HOCs) are anthropogenic compounds that have been used for many decades in a wide range of applications. Due to human activities and improper disposal, many HOCs have been deposited into aquatic environments where they strongly sorb to hydrophobic matrixes like bed sediments and can pose risk to aquatic organisms. Therefore, understanding the processes and factors that influence the bioavailability of HOCs is important for predicting and refining risk assessments, particularly for coastal marine sediments where contamination from adjacent urban centers is expected while relatively much less is known. Here we evaluated the bioavailability of aged DDTs and PCBs in historically contaminated sediment from the Palos Verdes Shelf Superfund Site. Total HOC concentrations remain as high as 41,000 mg/kg. However, these aged HOC residues had dramatically reduced bioaccessibility; the bioaccessible fraction was generally <20%, and biota-sediment accumulation factor (BSAF) values ranged from 0.11-29. Therefore, it is important to consider the history and bioavailability of HOCs when conducting risk assessments. A subsequent study evaluated the use of different types of black carbon as an amendment to enhance sequestration and immobilization of HOCs. All amendment materials decreased Cfree and bioaccumulation, with Cfree ranging from nd-1.34 ng/L, and BSAFs from nd-0.024. Although the PAC resulted in significantly higher sequestration, the relative reductions were small, and the limited changes were likely due to the sediment’s high organic matter content (5.4 %) and that the HOCs already had reduced bioavailability due to extensive aging. Therefore, the use of black carbon amendments may not be ideal for remediation of sediments with aged contaminants. The last study evaluated the distribution and source of urban-use insecticides in marine sediments off the coast of Los Angeles. Pyrethroids and a fipronil degradate, fipronil sulfide, were frequently detected across the PV Shelf in concentrations that may pose toxicity (nd-170 µg/kg). Some of these insecticides were attributed to WWTP effluent emission, while the rest were associated with nonpoint sources. These findings highlight the need for more systematic studies on toxicity of legacy and current-use HOCs for marine organisms and development of strategies to minimize their emission into the coastal environment.