Bioaccumulation of current-use herbicides in fish from a global biodiversity hotspot: Lake St Lucia, South Africa.

Agricultural pesticides threaten aquatic systems and biodiversity at a global scale, but limited information is available on the accumulation of current-use herbicides in tissues of aquatic organisms. Here, we examine the potential exposure and accumulation of currently used herbicides in two species of fish from Lake St Lucia, a global biodiversity hotspot located in South Africa. Muscle tissue samples were analysed for 11 widely used multi-residue and phenoxy-acid herbicides. Herbicide residues were detected in all samples analysed, with total concentrations ranging from 44.3 to 238 ng g-1 (Clarias gariepinus) and 72.2-291 ng g-1 dw (Oreochromis mossambicus). The most prominent herbicides detected included the two phenoxy-acid herbicides, MCPA (17.6 ± 12 ng g-1) and 2,4-D (28.9 ± 16 ng g-1), along with acetochlor (15.4 ± 5.8 ng g-1), atrazine (12.7 ± 7.1 ng g-1) and terbuthylazine (12.4 ± 12 ng g-1). Results indicate that fish at Lake St Lucia accumulate a complex mixture of herbicides, some previously unreported in tissue, highlighting the potential threat that agricultural runoff may pose to conservation areas. However, assessing the impact of herbicide accumulation on wild fish populations is difficult at present and urgent toxicological data are needed to better understand chronic exposure effects on aquatic organisms. A preliminary human health risk assessment indicated minimal risk associated with the consumption of local fish, but potential additive and synergistic effects of contaminant mixtures remain unknown.

Herbicide residues in sediments from Lake St Lucia (iSimangaliso World Heritage Site, South Africa) and its catchment areas: Occurrence and ecological risk assessment.

The impact of agricultural pesticides on sensitive aquatic ecosystems is a matter of global concern. Although South Africa is the largest user of pesticides in sub-Saharan Africa, few studies have examined the toxicological threats posed by agricultural runoff, particularly to conservation areas of international importance. This study investigated the occurrence of 11 priority listed herbicides in sediments from Lake St Lucia, located on the east coast of South Africa. While characterised by exceptionally high levels of biodiversity, Lake St Lucia is affected by agricultural runoff primarily via inflow from two major rivers; the Mkhuze and Mfolozi. Sediment samples collected from Lake St Lucia and its two major fluvial inputs reveal widespread herbicide contamination of the aquatic environment. Residues were detected in the vast majority of samples analysed, with Mkhuze (27.3 ± 17 ng g-1) and Mfolozi (25.6 ± 20 ng g-1) sediments characterised by similar total herbicide levels, while lower concentrations were typically detected in Lake St Lucia (12.9 ± 12 ng g-1). Overall, the most prominent residues detected included acetochlor (3.77 ± 1.3 ng g-1), hexazinone (2.86 ± 1.4 ng g-1) and metolachlor (10.1 ± 8.7 ng g-1). Ecological assessment using Risk Quotients (RQs) showed that cumulative values for triazines and anilides/aniline herbicide classes presented low to medium risk for algae and aquatic invertebrate communities. Considering the biological importance of Lake St Lucia as a nursery for aquatic organisms, it is recommended that further research on the aquatic health of the system be undertaken. Additional monitoring and investigation into mitigation strategies is suggested, particularly as agricultural activities surrounding Lake St Lucia are likely to expand in the future.

Dietary exposure and risk assessment of organochlorine pesticide residues in rural communities living within catchment areas of iSimangaliso World Heritage Site, South Africa.

Dietary intake of contaminated food is a major route of human exposure to organochlorine pesticides (OCPs). Despite the prevalence of OCP usage in southern Africa for several decades, their impact on socioeconomically vulnerable communities remains largely overlooked. We investigated the accumulation of OCPs in crops commonly cultivated by rural communities surrounding iSimangaliso Wetland Park, South Africa. All samples analysed were found to be contaminated, with total OCP concentrations ranging between 190 and 240 ng g-1 ww. Elevated levels of OCP residues were detected in all products, with the majority of samples exceeding European Commission's maximum residue limits (MRLs). We combine these results with local OCP fish tissue estimates to assess potential dietary risks. Cumulative risk assessment indicated potential non-cancer risks associated with heptachlor epoxide, while a cancer risk as high as 1 in 10 was found to be associated with aldrin and dieldrin. This far exceeds USEPA guidelines and indicates that OCP residues in crops and fish from the study area pose a high risk to human health. The results of this study call for further attention to be given to the health implications of continued OCP use not only within the study area but also in Southern Africa in general.

Assessing the influence of human activities on river health: a case for two South African rivers with differing pollutant sources.

The impact of agricultural and anthropogenic activities can play a significant role in heavy metal precipitation and transport in water. Human activities along two rivers: the Palmiet and Sezela Rivers in KwaZulu-Natal, South Africa, have been classified and metal contamination (Cr, Cu, Pb and Zn) and mobility assessed using a range of factors including contamination and enrichment factors, pollution load indices and water quality parameters. The overall assessment of the Palmiet River, which is characterised by industrial zone (predominantly metal works), followed by residential areas and informal settlements shows significantly elevated metal concentrations with high mobility and bioavailability. In contrast, the Sezela River, characterised by agricultural activities and informal settlements, shows total metal concentrations that pose a limited-to-no threat to human health and very limited metal mobility. The overall environmental assessment indicates that both rivers show deterioration; the Palmiet River has been severely impacted by the type of industrial activity, whereas the Sezela River has been more impacted by agricultural activity. This study highlights the role of different anthropogenic activities on river health and the potential health implications with the associated metal mobility.

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.