Interactive dynamics of essential and potentially toxic elements in three native tilapia species during a drought period: associations suggestive of ionic mimicry and competitive uptake in a tropical lake

This study examined associations between essential and potentially toxic elements in muscle tissue of three native tilapia species from Lake Itezhi-Tezhi, Zambia, sampled during the 2023–2024 El Niño-associated drought. Calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) were quantified in Coptodon rendalli, Oreochromis andersonii and Oreochromis macrochir from five sites. Nachisenga recorded the highest Cd concentrations across species (0.84–0.85 mg kg −1 dry weight) and comparatively high Pb concentrations (1.64–2.05 mg kg −1 dry weight). O. macrochir generally had the highest Pb concentrations, whereas C. rendalli had the highest Ca concentrations. Principal Coordinates Analysis explained 76.3% of the total variation, separating a dimension dominated by Ca, Mg, Cu and Zn from one associated with Cd and Pb. Positive Ca–Pb associations in O. andersonii and C. rendalli, and negative Zn–Cd and Zn–Pb associations in O. macrochir, were consistent with hypotheses of ionic mimicry and competitive uptake, although spatial exposure may also have contributed. Factor analysis explained 64.6% of the variation. Target hazard quotient and hazard index values for Cu, Zn and Cd remained below 1, with Cd contributing most to the estimated non-carcinogenic hazard. Overall, elemental accumulation varied by species and location and generated testable hypotheses concerning physiological regulation and ionic interactions.