Legacy (Organochlorine) and Current Use (Neonicotinoid) Pesticides in Fish from Two Subtropical River Basins

The rapid population growth across Africa has increased the demand for food production, resulting in increased pesticide use. South Africa is among the top four pesticide importers in Sub-Saharan Africa, raising significant concerns regarding the contamination of freshwater ecosystems. Organochlorine pesticides (OCPs), historically used for agriculture and vector control, persist in the environment due to their high lipophilicity and long half-lives. Despite bans on many OCPs, residues remain in aquatic systems, potentially affecting non-target organisms such as fish. Similarly, neonicotinoids, introduced as safer alternatives, are now linked to adverse effects on aquatic biota, yet little is known about their bioaccumulation in wild fish species in southern Africa. This study investigated 13 neonicotinoids and 19 OCPs in fish muscle tissue from the Inkomati and Letaba catchments. Only two OCPs, p,p'-DDE and p,p'-DDD, were detected, likely due to ongoing DDT use in malaria control. Concentrations were generally low and varied between sites, with higher values found in the Letaba catchment. Neonicotinoids were detected at low concentrations, with acetamiprid and imidacloprid being the most prevalent, although the concentrations were lower than those reported globally. Muscle tissue, representing long-term exposure, may underestimate total pesticide burdens due to lower lipid content than other tissue types. Findings suggest that the detected residues reflect the persistent legacy of historical DDT use, potential ongoing localised DDT use for malaria vector control, as well as ongoing neonicotinoid use in agricultural systems. Although concentrations were below levels of concern for vertebrates, this study highlights the need for continued monitoring and expanded tissue analysis to better understand bioaccumulation and ecological risks in southern African freshwater systems.