Persistent organic pollutants in biotic and abiotic components of the Orange-Senqu River basin

Abstract

The Orange-Senqu River Basin (OSRB) stretches over four southern Africa countries that are all Parties to the Stockholm Convention on Persistent Organic Pollutants (SCPOPs). The main tributary, the Vaal River on the eastern side of the basin drains a large industrial region before it confluences with the Orange-Senqu River. The Orange-Senqu River with its origin in Lesotho flows west providing irrigation water for agricultural activities. It confluences with the Vaal River near Douglas before continuing westwards, flowing past mining, rural, and agricultural activities, discharging into the Atlantic Ocean. Persistent organic pollutants (POPs) are omnipresent in the environment and concerns about the pollution in the OSRB prompted several surveys. Two matrices, an abiotic and a biotic matrix were selected to investigate the pollution in the basin. Due to their physical and chemical properties, POPs bioaccumulate in higher trophic level species. Bird eggs were selected as a biotic matrix since birds inhabit many niches and trophic levels. In Chapter 2, I review the Cattle Egret (Bubulcus ibis) as a suitable near-global indicator of terrestrial pollution. It is the most wide-spread Ardeid with an extensive natural expansion, occurring in high numbers and breed in colonies with other Ardeids. In Chapter 3 I evaluate the effectiveness of eggs as indicators of POPs pollution of nine Ardeids species collected from four locations and analysed for 21 pesticides, five polybrominated diphenyl ethers (PBDEs), 18 polychlorinated biphenyls (PCBs) including 6 non dioxin-like PCBs (NDL-PCBs) and 12 dioxin-like PCBs (DL-PCBs), 17 polychlorinated dibenzo-p-dioxins and dibenzo-p-furans (PCDD/Fs), and perfluorooctane sulfonate (PFOS). The evaluation showed that aquatic predators had higher PFOS and PCB concentrations than terrestrial predators and scavengers, while PCDD/F dominated in eggs of terrestrial species. The highest organochlorine pesticide (OCP) concentrations were in eggs from the industrial regions of Gauteng. PFOS concentrations (2300 ng/g wm) in eggs collected at Bloemhof Dam pose a severe risk and I identified this location as a PFOS hotspot. The evaluation of the data showed the importance of multi-species studies sampling from multiple locations to assess the risk that POPs pose to avian populations as hotspots and species at risk may be missed by species- and site-restricted studies. In Chapter 4, sediment as the abiotic matrix were collected in 2002 from 22 sites across South Africa and analysed for DL-PCBs and PCDD/Fs. The concentrations quantified in sediment ranged considerably between sites (41–25 000 ng/kg dm) with the highest toxic equivalency quotient (ΣTEQ) of 22 ngTEQ/kg dm quantified from the highly industrialised Gauteng province. The ΣTEQ concentrations from seven sites, all close to industrial activities, exceeded international sediment quality guidelines (ISQG). In Chapter 5, sediment collected in 2009, from 61 sites across the OSRB were analysed for all POPs listed in the SCPOPs in 2010. Nine sites near industrial regions had quantifiable ΣOCP concentrations, while four of the sites exceeded ISQG for dichlorodiphenyltrichloroethanes (DDTs; max 9 ng/g dm). No quantifiable concentrations of PFOS were detected in sediment from hotspots identified from the bird egg study. Lindane was quantified at three sites in the upper Orange-Senqu River that all exceeded SQGs (1 ng/g dm). PBDE concentrations (15 ng/g dm) were highest near the confluence of the Orange-Senqu River and Vaal River than in the industrial region. However, PCB concentrations (Sum DL-PCB and NDL-PCB) were highest in industrial regions (340 ng/kg dm) and even higher near mining activities (1053 ng/kg dm). Most of the sediment samples had quantifiable concentrations of PCDD/F most notably on the eastern side of the basin near industry. Industry is therefore likely the main contributor to POPs pollution in the basin. The temporal trend suggests that PCB and PCDD/F concentrations in Gauteng are decreasing. Future studies should therefore concentrate on POP concentrations in sediment on the eastern side of the basin near industry. However, bird eggs are more sensitive matrixes and should therefore be selected over sediment. Furthermore, POPs added to the SCPOPs since 2010 would need a wider survey. Studies along freshwater systems should prioritise biota rather than sediments to enable better assessments of current pollution trends.