Receptor-mediated potencies of polycyclic aromatic hydrocarbons in urban sediments: comparisons of toxic equivalency risk assessment

The Klip River, flowing through South Africa’s most populated urban area—Soweto and Lenasia—is subject to various pollution and anthropogenic influences, including great concentrations of polycyclic aromatic hydrocarbons. The aims were to determine the aryl-hydrocarbon receptor-mediated potencies of the 16 priority polycyclic aromatic hydrocarbons in sediments of the Klip River, using chemical- and bio-analytical assessments of hazard, and to compare these results with international sediment quality guidelines. Sediment samples were collected from nine sites during the dry seasons of 2013 and 2014. Two sets of toxic equivalents were calculated from analytically obtained polycyclic aromatic hydrocarbon concentrations using: (1) 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalency factors and (2) relative potency factors for fish. The fraction of the sediment extracts containing polycyclic aromatic hydrocarbons was assayed with the H4IIE-luc reporter gene bio-assay, and the aryl-hydrocarbon receptor potency expressed as bio-assay equivalents. The bio-assay equivalents and tetrachlorodibenzo-p-dioxin equivalency factors were compared to Canadian sediment quality guidelines and of the three approaches, the bio-assay equivalents and the relative potency factors for fish proved the most protective. Results of this study are proof of the utility of combining biological analysis with instrumental analysis when predicting hazard. Even though there were instances where the bio-assay equivalents were orders of magnitude greater than the tetrachlorodibenzo-p-dioxin equivalency factors, the results still showed similar trends. It was concluded that hazard from aryl-hydrocarbon receptor-mediated potency to adversely affect aquatic organisms in the Klip River was relatively great, which indicated the need for further investigation into possible mitigation