INFLUENCE OF CADMIUM ON PHYSIOLOGY AND REPRODUCTION IN FRESHWATER CHELONIANS: A SYSTEMATIC REVIEW

Cadmium (Cd) exposure in freshwater turtles has significant physiological and reproductive impacts. Cd is a non-essential and toxic heavy metal that enters freshwater ecosystems primarily through mining, industrial discharges, and fossil fuel combustion. Ecotoxicological studies in freshwater turtles are mainly based on field reports of contaminant accumulation in tissues, but the mechanisms of absorption, clearance, accumulation, and the toxicological effects of inorganic pollutants remain poorly understood. Turtles occupy multiple levels of the food chain, leading to bioaccumulation that varies with the species' diet. This systematic review investigated the effects of cadmium (Cd) on the physiology and reproduction of freshwater turtles. We searched PubMed, Scopus, and Web of Science, identifying 32 studies on metallic contaminants in freshwater turtles. Of these, Cd was reported in eight, copper (Cu) in nine, and mercury (Hg) in 24. Dietary exposure studies in the red-eared slider turtle (Trachemys scripta elegans (Wied 1838)) showed that Cd accumulates predominantly in the kidneys and liver, with accumulation correlating with exposure duration and concentration. Others reported bioaccumulation in the pond slider turtle (Trachemys scripta (Thunberg, 1972)) and the painted turtle (Chrysemys picta (Schneider, 1783)) only in the carapaces and liver, suggesting filtering and metabolic strategies for these substances. Exposure to Cd has been associated with reduced germ cell numbers in embryos and increased oocyte apoptosis in neonates, suggesting potential long-term reproductive impairment. However, a bioaccumulation study in Podocnemis shows higher Cd levels in eggshells, suggesting that maternal transfer of toxic elements to eggs may benefit females, as they can regularly reduce metal concentrations in their bodies during nesting events. Therefore, more research is needed to fully understand the ecological impacts of Cd contamination and to develop mitigation strategies to reduce its effects on freshwater turtle reproduction.