Spatial, seasonal and ecological risk assessment of organohalogenated contaminants in sediments of Swartkops and Sundays Estuaries, Eastern Cape province, South Africa

Abstract

Run-off from industrial and agricultural activities has continued to be a major source of organohalogenated contaminants (OHCs) in the environment. Swartkops (SWE) and Sundays Estuaries (SDE) located in the city of Port Elizabeth, South Africa, were selected for this study because of their proximity to industrial and agricultural activities. In this study, we determined the levels, seasonal occurrence as well as the ecological risk monitoring of 18 organochlorine pesticides (OCPs), 17 polychlorinated biphenyls (PCBs) and six polybrominated diphenyl ethers (PBDEs) in the sediments of SWE and SDE using a gas chromatograph coupled with a micro electron capture detector. HCHs, BDE-17, tri- and tetra-CBs dominated the OHC profiles in sediments of both estuaries. The respective concentration ranges of OCPs, PCBs and PBDEs in SDE sediment were 0.06–0.93 μg g−1 dw, 0.08–1.71 μg g−1 dw and 0.08–32.41 ng g−1 dw while that of SWE in that order were 0.10–4.70 μg g−1 dw, 0.07–3.80 μg g−1 dw and 0.11–130.21 ng g−1 dw. The high concentrations of OHCs in SWE may be due to the high usage of its surrounding area for industrial activities. The concentrations of all OHCs with exception of PCBs were higher in spring for both estuaries probably due to the heavy rain experienced during spring season. Cluster analysis and spatial distribution of OHCs indicated that samples around the Motherwell Canal in the SWE were more polluted. Total organic carbon (TOC) was strongly correlated with most OHCs in SWE revealing that TOC controls the sorption of OHCs in this estuary. Risk analysis showed that most sampling points had PCBs and HCHs concentration greater than their respective sediment quality guideline (SQGL) indicating a high risk to benthic species in SDE and SWE. Samples collected from the SWE were more polluted than those collected from the SDE probably due to the extensive use of the catchment of SWE for industrial activities. In comparison with SQGL, most sampling points had PCBs and HCHs concentrations greater than their respective ERL and TEL values, indicating the potential risk to biota in SDE and SWE. Thus, an urgent need to manage and mitigate the OHCs concentrations in these estuaries is recommended.