Organochlorine pesticide contamination in sediments from Richards Bay, South Africa: spatial trends and ecotoxicological risks.

The occurrence and distribution of organochlorine pesticides (OCPs) in aquatic systems is a matter of global concern and poses significant toxicological threats to both organisms and human health. Despite the extensive use of OCPs for pest and disease control in southern Africa, relatively few studies have examined the occurrence and toxicological risks of OCP residues in the region. This study investigates the composition, distribution, and potential sources of OCP contamination in sediments from Richards Bay, a rapidly developing industrial port on the northeast coast of South Africa. Surface sediments collected from Richards Bay Harbour and surrounding areas indicate that OCP contamination in the region is widespread. Total concentrations (∑OCP) in surface samples ranged from 135 to 1020 ng g-1, with hexachlorocyclohexanes (∑HCH; 35-230 ng g-1) and dichlorodiphenyltrichloroethanes (∑DDT; 12-350 ng g-1) the dominant contaminant groups detected. Metabolite isomeric compositions indicate that the presence of aldrin and endosulfan likely result from historical agricultural usage, while recent input of γ-HCH, heptachlor, and endrin may be linked to the illegal use of old pesticide stockpiles. Total DDT concentrations were dominated by p,p'-DDT (80 ± 64 ng g-1), which was attributed to its ongoing use in malaria vector control in the region. A 210Pb-dated sediment core revealed that OCP input to the local environment increased dramatically from relatively low concentrations in the mid-1940s (∑OCP, 355 ng g-1) to peak levels (∑OCP, 781 ng g-1) in the 1980s/1990s. An overall decrease in ∑OCP concentration from the mid-2000s is likely related to restrictions on use following the Stockholm Convention in 2004. Despite current restrictions on use, OCP concentrations exceeded sediment quality guidelines in the vast majority of cases, raising concerns for protected estuarine and mangrove habitats in the area, as well as for local fishing and farming communities.

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.