This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Mercury pollution from artisanal gold mining in tropical regions is finding its way into wildlife. A team from the University of Vienna and the Veterinary University of Vienna shows that mercury exposure impairs the glucocorticoid response that helps animals cope with acute stress.
This weakened stress response could reduce the caimans' chances of survival and reproduction. The findings, recently published in the journal Communications Biology, point to a previously overlooked endocrine threat to crocodylians. Working with wild smooth-fronted caimans (Paleosuchus trigonatus) in the rainforest of French Guiana, researchers found that individuals with higher mercury levels in their blood reached lower peak corticosterone levels during standardized stress tests.
This suggests that mercury acts as an endocrine-disrupting chemical that could compromise the crocodylians' capacity to cope with environmental change. Since preindustrial times, atmospheric mercury has increased by an estimated 300%–500%, largely due to fossil fuel combustion and gold mining. Mercury is a potent endocrine-disrupting chemical: in vertebrates, including humans, it can interfere with steroid receptors, among them the glucocorticoid receptor, which mediates the body's stress response.
The hypothalamic-pituitary-adrenal axis enables animals to maintain homeostasis during acute challenges, rapidly ramping up hormone levels such as corticosterone to mobilize energy and trigger appropriate behavioral responses. In healthy vertebrates, this peak is fast and pronounced. In caimans from mercury-contaminated environments, however, the research team observed a significantly dampened hormonal spike—evidence that the flexibility of this vital response system decreases as blood mercury concentrations increase.
A comparative analysis by the team further indicates that a cysteine residue within the ligand-binding domain of the glucocorticoid receptor, a site known to be targeted by methylmercury, is conserved across crocodylian species, offering a possible molecular explanation for the disruption observed. "Given the overlap of crocodylian habitats with gold mining activities, this is a conservation concern that deserves immediate attention," says Jérémy Lemaire from the University of Vienna, project lead and first author of this study. "A fast, robust stress response is essential for survival in the wild.
We show that even relatively low mercury burdens affect this response in caimans, potentially limiting their ability to cope with predators, extreme weather and human disturbance, and ultimately survive in the wild." In many tropical regions, mercury emissions from gold mining are prevalent and can travel worldwide through the atmosphere. As long-lived apex predators, caimans accumulate mercury through their diet over many years, making them sensitive indicators of contamination in their ecosystems. Crocodylian species are among the most threatened vertebrate groups worldwide.
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