Contaminant levels and their effects on the American continent chelonian: A systematic review

Abstract

Excessive metal pollution from anthropogenic activities like mining and industrial waste discharge has increasingly impacted freshwater ecosystems. Freshwater chelonians (Testudines) are bioindicators of environmental pollution because of their longevity, ecological diversity, and trophic positioning. This systematic review assessed toxic metal bioaccumulation in freshwater turtles across the American continent, focusing on mercury (Hg), a global public health and ecological concern. A comprehensive search on PubMed, Scopus and Web of Science identified 620 papers, of which 32 met the inclusion criteria. The United States and Brazil (93.6%) contributed the most data, with Chelydra serpentina and Podocnemis expansa frequently studied, followed by Canada (4.26%) and Colombia (2.13%). Hg was the predominant contaminant (75% of studies), with the highest concentrations observed in hatchlings and keratinized tissues, such as carapace and claws. Bioaccumulation patterns varied by region, species and life stage, emphasizing physiological and reproductive impacts. This review highlights the need for noninvasive sampling methods and long-term monitoring to guide conservation strategies and assess ecosystem and turtle health. It also highlights the significant lack of data in South America and the lack of studies on juveniles and eggs. Freshwater chelonians remain essential for understanding contamination dynamics and mitigating environmental degradation in aquatic habitats.