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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. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • We examine Pb concentrations in blood and fat tissues of free-ranging Nile crocodiles. • Highly elevated Pb levels attributed to incidental ingestion of Pb fishing weights. • Clinical signs of Pb toxicosis observed in individuals with blood Pb > 6000 ng ml−1 • Long-term Pb exposure associated with anaemia and severe tooth loss in individuals. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image • Investigated OCP bioaccumulation patterns in wild and captive Nile crocodiles • DDT metabolites found to be the principle contaminant in wild animals • Concentrations between males and females were similar and correlated with body size. • Significant difference in concentration burdens and profiles between sampling years • Temporal variations likely linked to environmental stress and dietary exposure [ABSTRACT FROM AUTHOR]