Marc S. Humphries

Bioaccumulation and risk assessment of organochlorine pesticides in fish from a global biodiversity hotspot: iSimangaliso Wetland Park, South Africa

Organochlorine pesticides (OCPs) have been used extensively in the eastern regions of South Africa for agricultural and malaria control purposes, yet few data exist on the local environmental and social impacts of these compounds. Such issues have become of increasing concern in the iSimangaliso World Heritage Site, where the continued use of OCPs may pose risks to several sensitive and protected species. This study was designed to examine the bioaccumulation of OCPs in two common fish species, Oreochromis mossambicus (Mozambique tilapia) and Clarias gariepinus (African sharptooth catfish) from iSimangaliso Wetland Park. These species are targeted by local subsistence fishermen and sustain substantial bird and crocodile populations. Our findings indicate widespread contamination of the aquatic environment, with ΣOCP fish tissue concentrations in the range of 6907-8740ngg-1 lw and 2953-5874ngg-1 lw for C. gariepinus and O. mossambicus, respectively. HCHs (471-1570ngg-1 lw), DDTs (645-2399ngg-1 lw), drin-related residues (589-1960ngg-1 lw), chlor-related residues (455-2162ngg-1 lw) and endosulfans (457-1495ngg-1 lw) were detected in all tissue samples. Concentrations detected in the majority of samples exceeded European Commission maximum residue limits and a health risk assessment indicated potential dietary risk associated with exposure to heptachlor, heptachlor epoxide and dieldrin. This study represents the first investigation into OCP bioaccumulation in fish species from iSimangaliso Wetland Park. Our findings highlight the need for more detailed investigations into the bioaccumulation and ecotoxicological effects of these contaminants in the food web and the associated risks to local ecosystems and human health. CAPSULE High levels of OCPs detected in two common fish species at iSimangaliso Wetland Park highlight potential human health and ecotoxicological threats to a globally important biodiversity conservation hotspot.

Recent trends in sediment and nutrient accumulation rates in coastal, freshwater Lake Sibaya, South Africa

Eutrophication of aquatic systems has emerged as one of the most pressing issues confronted by scientists and environmental managers. In this study, we used two sediment cores from Lake Sibaya, a coastal freshwater lake in South Africa, to infer historical variations in bulk sediment accumulation and nutrient (C, N and P) biogeochemistry. Cores were dated using 210Pb, 137Cs and 14C, and dates were used to calculate bulk sediment accumulation rates and nutrient concentrations over the last 250 years. In the western section of the lake, stratigraphic variations in total carbon, nitrogen and phosphorus increased abruptly to near-constant levels around the beginning of the 20th century, a trend that appears to be consistent with the onset of human settlement and land clearance in the catchment. In contrast, sedimentation rates have remained relatively constant over this period, despite recent land use change in the catchment. Results of this study suggest that recent increases in development pressure have yet to further influence sedimentation in Lake Sibaya, thus providing values against which future monitoring efforts can be compared. This study represents the first report on recent trends in sedimentation and nutrient biogeochemistry in Lake Sibaya. The results have broad implications for other ecologically sensitive areas within the Maputaland ecoregion of coastal southern Africa.

Accumulation of organochlorine pesticides in reef organisms from marginal coral reefs in South Africa and links with coastal groundwater

Coral reefs support rich levels of biodiversity, but are globally threatened by a multitude of factors, including land-sourced pollutants. Concentrations of organochlorine pesticides (OCPs) in three species of coral reef invertebrate at five sites along the Maputaland coast, South Africa were quantified. We aimed to assess spatial and interspecies variations in pesticide accumulation. Markedly high levels of a range of OCP residues were detected within tissues, with total concentrations (ng g-1 ww) ranging from 460 to 1200 (Sarcophyton glaucum), 1100-3000 (Sinularia gravis) and 450-1500 (Theonella swinhoei), respectively. A decreasing gradient in total pesticide concentrations was detected southward from Regal Reef, opposite Lake Sibaya, the hypothesised source of the pollutants. Observed gradients in pesticide concentrations and nitrogen isotope signatures indicated coastal groundwater to be the likely source of the pollutants. Further studies are required to assess the potential ecotoxicological impacts of these contaminants at the organismal and ecosystem level.

Accumulation of organochlorine pesticides in fat tissue of wild Nile crocodiles (Crocodylus niloticus) from iSimangaliso Wetland Park, South Africa

Nile crocodiles (Crocodylus niloticus) are important apex predators in many tropical and subtropical aquatic habitats throughout much of sub-Saharan Africa. In South Africa, large crocodile populations inhabit lakes and wetlands that are impacted by organochlorine pesticides (OCPs). Despite the continued use of these compounds and their potential adverse effects on key wildlife populations in southern Africa, limited ecotoxicoloigcal data exist. In this study, we examined the accumulation of OCPs in fat tissues of live, wild Nile crocodiles from iSimangaliso Wetland Park, a region of significant biological importance. All samples (n = 15) contained multiple contaminants in highly elevated concentrations, with total residue burdens varying between 3600 and 8000 ng g-1 ww. DDT and its metabolites were the dominant compounds detected in most samples, with ∑DDT concentrations ranging between 520 and 3100 ng g-1 ww. Elevated levels of other OCPs were also detected, including lindane (67-410 ng g-1 ww), aldrin (150-620 ng g-1 ww) and heptachlor (170-860 ng g-1 ww). Our findings show that crocodiles are exposed to OCPs throughout their range within iSimangaliso Wetland Park and contain some of the highest concentrations ever recorded in crocodilian tissue. Results indicate the need for a greater understanding of the impacts of OCP exposure and toxicological responses in crocodiles from iSimangaliso, and in Nile crocodile populations in general. The novel surgical technique described in this study provides an effective method for assessing relationships between contaminant body burdens and their potential reproductive and developmental consequences in crocodilians.