Heavy metal accumulation in non-human primates: a global systematic review

Environmental pollution is a significant driver of biodiversity loss. Numerous synthetic chemicals, including heavy metals, are introduced into ecosystems with largely unknown impacts on wildlife. Heavy metals are a critical group of environmental pollutants due to their persistence and toxicity. Despite physiological similarities to humans, the health impacts of heavy metal exposure on non-human primates (NHPs) have largely been ignored. This systematic review aims to fill this gap by analyzing the global literature on heavy metal accumulation in NHP species, focusing on their current exposure status. We surveyed 765 articles from Web of Science, Scopus, and Google Scholar, and identified 45 studies that fit our predetermined inclusion criteria. Most studies focused on Macaca mulatta and Macaca fuscata, species commonly used in biomedical research due to their physiological similarities to humans. However, both species are classified as "Least Concern" by the International Union for Conservation of Nature, indicating research may disproportionately focus on less vulnerable species, potentially overlooking those at greater conservation risk. Additionally, while there is a notable emphasis on essential metals like zinc, copper, iron, and calcium, potentially toxic metals such as lead, cadmium, mercury, and arsenic - most hazardous per the Agency for Toxic Substances and Disease Registry - are less frequently studied. Currently, there are no established reference values for heavy metals in NHPs, whether essential or non-essential. Our findings highlight the urgent need to understand human impact on primate health and conservation, as NHPs serve as valuable bioindicators for assessing environmental and health risks to humans.