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.

Trace Metal Accumulation in Eggs of Wild Nile Crocodiles (Crocodylus niloticus) from Lake St Lucia, South Africa: Implications for Biomonitoring in a Global Biodiversity Hotspot.

Nile crocodiles (Crocodylus niloticus) at Lake St Lucia, South Africa, have some of the highest blood lead (Pb) concentrations ever recorded in wildlife globally. Although exposure to Pb is known to pose major risks to wildlife reproductive success, potential impacts on crocodile reproduction at Lake St Lucia have yet to be examined. In this study, we investigated the accumulation of Pb and other trace metals (Al, V, Cr, Co, Cu, Ni, Zn and Cd) in eggs (n = 20) collected from five wild crocodile nests at Lake St Lucia. All metals analysed in this study were detected in egg contents, although concentrations varied considerably among nests and within clutches. Lead was detected in the contents of all eggs, but only at relatively low concentrations (43 ± 26 ng g-1 dry weight). Although sampling limitations commonly associated with wild population surveys prevent a complete assessment of exposure variability, our findings suggest maternal transfer may not be a significant depuration pathway for Pb and females possibly clear Pb through other mechanisms (e.g. sequestration into claws, bone and osteoderms). Metal concentrations in eggshells and shell membranes were poorly correlated with concentrations measured in egg content and thus do not provide viable non-lethal indicators for monitoring metal exposure in Nile crocodiles. Intra-clutch variability accounted for a considerable proportion of the total variance in egg content metal concentrations, suggesting the "one egg" sampling strategy often applied in reptile studies may not be an effective biomonitoring tool for wild crocodilian populations. Although maternally derived Pb does not appear to present widespread toxicological concern at Lake St Lucia, adverse effects of Pb exposure on other reproductive functions (e.g. spermatogenesis) cannot be discounted and warrant further investigation.

High lead exposure and clinical signs of toxicosis in wild Nile crocodiles (Crocodylus niloticus) from a World Heritage site: Lake St Lucia estuarine system, South Africa.

Lead (Pb) exposure is a widespread wildlife conservation threat, but impacts on reptile populations remain poorly documented. In this study, we examined Pb exposure and accumulation in a wild population of Nile crocodiles (Crocodylus niloticus) at Lake St Lucia, South Africa. Recreational angling has occurred in the area since the 1930s and incidental ingestion of Pb fishing weights has previously been identified as a major source of Pb poisoning in the local crocodile population. In 2019, we sampled blood and tail fat tissues from wild (n = 22) and captive (n = 3) crocodiles at Lake St Lucia to investigate potential impacts of chronic Pb exposure on crocodilian health. Lead was detected in blood samples of all wild crocodiles, although concentrations varied widely between individuals (86-13,100 ng ml-1). The incidence of Pb poisoning was higher in male crocodiles, with mean blood lead (BPb) concentrations in males (3780 ± 4690 ng ml-1) significantly (p < 0.001) higher compared to females (266 ± 230 ng ml-1). Blood Pb concentrations were correlated with concentrations measured in tail fat tissue (n.d - 4175 ng g-1 wet wt.). Although most of the crocodiles sampled appeared to be in good physical condition, highly elevated BPb concentrations (>6000 ng ml-1) were associated with markedly suppressed packed cell volumes (4.6-10.8%) and severe deterioration in tooth condition. These findings suggest that anaemia and tooth loss may be clinical signs of long-term environmental exposure to Pb. Although previously undocumented in crocodilians, these symptoms are consistent with Pb poisoning observed in birds and mammals, and suggest that crocodilians may be more susceptible to the long-term toxic effects of Pb than previously thought. In light of these findings, we suggest that the impact of accumulated Pb on crocodilian fitness, reproduction and mortality requires urgent attention.

Accumulation of commonly used agricultural herbicides in coral reef organisms from iSimangaliso Wetland Park, South Africa.

Coral reefs are amongst the most biodiverse ecosystems on earth, but are significantly impacted by agricultural runoff. Despite herbicides being commonly detected in coastal waters, the possibility of herbicide accumulation in coral reef species has largely been overlooked. We investigate the accumulation of several herbicides in five species of coral reef invertebrates collected from ten sites along the Maputaland coast, South Africa. Multiple herbicide residues were detected in 95% of the samples, with total average concentrations across sites ranging between 25.2 ng g-1 to 51.3 ng g-1 dw. Acetochlor, alachlor and hexazinone were the predominant herbicides detected at all sites, with atrazine and simazine detected less frequently. Significant interactive effects were detected between sites nested in reef complex crossed with species, based on multiple and total herbicide concentrations. In general, multivariate herbicide concentrations varied significantly between species within and across most sites. Contrastingly, the concentrations of the different herbicides and that of total herbicide did not differ between conspecifics at most sites nested in their respective reef complexes. On average, highest total herbicide concentrations were measured in soft coral (Sarcophyton glaucum; 90.4 ± 60 ng g-1 and Sinularia gravis; 42.7 ± 25 ng g-1) and sponge (Theonela swinhoei; 39.0 ± 40 ng g-1) species, while significantly lower concentrations were detected in hard corals (Echinopora hirsutissima; 10.5 ± 5.9 ng g-1 and Acropora austera; 5.20 ± 4.5 ng g-1) at most sites. Agricultural runoff entering the ocean via the uMfolozi-St Lucia Estuary and Maputo Bay are likely sources of herbicide contamination to coral reefs in the region. There is an urgent need to assess the long-term effects of herbicide exposure on coral reef 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.

Organochlorine pesticide accumulation in fish and catchment sediments of Lake St Lucia: Risks for Africa's largest estuary.

Although use of organochlorine pesticides (OCPs) has been banned or severely limited on a global basis, concerning concentrations continue to be reported in many tropical and subtropical regions of the world. These habitats often support high levels of unique biodiversity and vulnerable communities that depend on the environment for their survival. We investigated threats associated with OCP contamination at Lake St Lucia, a global hotspot for biodiversity and a UNESCO World Heritage Site in South Africa. Lake St Lucia is sustained largely by surface runoff from catchment areas where significant quantities of OCPs have historically been used in agriculture and where DDT continues to be used for disease control. Sediments (n = 40) collected from the two largest fluvial inputs to Lake St Lucia showed that these rivers represent important sources of contaminants, with ∑OCP concentrations ranging between 74 and 510 ng g-1. Measured HCH, dieldrin, ∑DDT and ∑chlor concentrations exceeded NOAA sediment toxicity guidelines in the majority of samples analysed. Bioaccumulation was assessed by examining residue concentrations in muscle tissues from two abundant fish species from Lake St Lucia. OCPs were detected in all samples analysed, with total concentrations ranging 860-5000 ng g-1 lw and 390-3200 ng g-1 lw for Oreochromis mossambicus (n = 17) and Clarias gariepinus (n = 41), respectively. A health risk assessment indicated potential dietary risk associated with exposure to aldrin, dieldrin and heptachlor, although the cumulative effect of OCPs on human health, ecosystem biodiversity and long-term ecotourism sustainability remains unknown.

Organochlorine pesticide bioaccumulation in wild Nile crocodile (Crocodylus niloticus) fat tissues: Environmental influences on changing residue levels and contaminant profiles.

Biologically significant concentrations of organochlorine pesticides (OCPs) continue to be reported in wildlife populations and are of particular concern in species that occupy the highest trophic levels. Nile crocodiles (Crocodylus niloticus) are important apex predators occurring throughout much of tropical and subtropical sub-Saharan Africa, where they inhabit estuarine and freshwater habitats often impacted by contamination. In this study we examined pesticide residue accumulation in fat tissue from Nile crocodiles at Lake St Lucia, South Africa, where historically large quantities of OCPs have been used for agriculture and disease control. During 2019, we collected tail fat samples from wild (n = 21) and captive (n = 3) individuals to examine the influence of habitat, body size and sex on variations in bioaccumulation. The principal contaminant found was p,p'-DDE, a major persistent metabolite of DDT, which continues to be used in the region for combating malaria. Tissue p,p'-DDE concentrations in wild crocodiles (95-1200 ng g-1 ww) were significantly (p < 0.05) higher compared to captive individuals (23-68 ng g-1 ww) and strongly correlated (R2 > 0.70) to body length. Male (n = 14) and female (n = 7) wild crocodiles exhibited similar contaminant body burdens, however, total concentrations were substantially lower than those measured in the same population during 2016/2017. Marked differences in residue levels and profiles appear to reflect changes in food availability and dietary exposure associated with a shift in environmental conditions. These findings suggest that periods of environmental stress may be associated with enhanced toxicological risk in crocodiles. Additional work is needed to better understand contaminant accumulation and elimination mechanisms in crocodiles, and their potential effects on reproductive health.

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.

Validation of a modified QuEChERS method for the analysis of organochlorine pesticides in fatty biological tissues using two-dimensional gas chromatography.

The monitoring of organic contaminants in the environment has gained tremendous traction in recent times, however, little attention has focused on the development of appropriate methods for the analysis of biological tissues from key sentinel species. In this study, a rapid, low-cost method is presented for the analysis of organochlorine pesticides (OCPs) in fatty biological tissues using a modified QuEChERS (Quick, Easy, Cheap, Efficient, Rugged and Safe) approach. The adapted extraction procedure is tested on biological samples of varying fat content, including fish muscle tissue and two previously untested matrices; coral and adipose tissue. Residue analyses were conducted by two-dimensional gas chromatography-time-of-flight mass spectrometry (GCxGC-TOF-MS). The method was fully validated through the evaluation of recoveries, limits of detection, linearity and precision. Mean recoveries (n = 3) for all 18 target compounds ranged between 69 and 102% across all matrices, with relative standard deviations (RSD) <10% in most cases. Limits of detection (LOD) ranged from 0.1 to 2.0 ng g-1. The method was successfully applied to the analysis of real samples collected from iSimangaliso Wetland Park World Heritage Site, South 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.

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.

The distribution of organochlorine pesticides in sediments from iSimangaliso Wetland Park: Ecological risks and implications for conservation in a biodiversity hotspot.

The iSimangaliso Wetland Park World Heritage site, located on the east coast of South Africa, spans ∼3300 km2 and constitutes the largest protected estuarine environment for hippopotami, crocodiles and aquatic birds in Africa. Given the ecological importance of this site and continued use of organochlorine pesticides (OCPs) in the region, this study focused on the nature, distribution and potential sources of organochlorine contamination within iSimangaliso Wetland Park. OCPs were widely distributed in surface sediment samples obtained from the four main Ramsar wetland systems within the park (Lake St Lucia, Mkhuze, Lake Sibaya and Kosi Bay). ∑HCH and ∑DDT were the dominant contaminants detected with concentrations in the range of 26.29-282.5 ng/g and 34.49-262.4 ng/g, respectively. ∑DDT concentrations revealed a distinctive gradient, with significantly higher concentrations at Kosi Bay and Lake Sibaya attributed to the application of DDT for malaria control. p,p'-DDE and p,p'-DDD were the dominant isomers detected, but the detection of p,p'-DDT in a number of samples reflects recent inputs of technical DDT. Highest concentrations of HCH, endosulfan and heptachlor were detected in sediments from Mkhuze and reflect the substantial residue load these wetlands receive from agricultural activities within the catchment area. Isomeric compositions indicate that endosulfan and heptachlor residues are derived mainly from historical application, while inputs of HCH, aldrin and endrin could be attributed to more recent usage at several sites. OCP sediment concentrations from iSimangaliso represent the highest yet recorded in South Africa and some of the highest reported globally this century. Sediments found within the lakes and wetlands of iSimangaliso represent large reservoirs of contaminants that pose ecotoxicological threats to this globally important biodiversity hotspot. Detailed investigation into the bioaccumulation and toxicological risks of OCPs within the wetland park is urgently required.

DDT residue contamination in sediments from Lake Sibaya in northern KwaZulu-Natal, South Africa: implications for conservation in a World Heritage Site.

Maputaland in northern KwaZulu-Natal is a biodiversity hotspot and host to a number of ecologically important systems, including Lake Sibaya, southern Africa's largest natural freshwater lake. The region is malaria endemic and this study reports the presence of DDT and its metabolites in the sediments of Lake Sibaya that have resulted from the widespread and continued use of DDT in the region. DDT residues (p,p'-DDT, p,p'-DDD, and p,p'-DDE) were detected at all 11 sites sampled, with total concentrations ranging from 0.8 to 123 ng g(-1). Total DDT concentrations at Lake Sibaya represent some of the highest levels reported in South Africa, with most samples exceeding sediment quality guideline values. The findings from this study raise concerns and indicate that urgent further work is needed to investigate the potential for bioaccumulation, which could adversely affect breeding fish, bird, and crocodile populations in the region. While this study represents the first report on DDT contamination in Lake Sibaya, results have important implications for a number of other aquatic ecosystems within the Maputaland ecoregion, as well as the many local people who depend on them.