# Caimans in French Guiana with higher blood mercury show a weaker corticosterone response to stress

- Published: 2026-11-05 09:53 UTC
- Section: Planet › Ecology & recycling
- Tags: mercury pollution, smooth-fronted caiman, Paleosuchus trigonatus, corticosterone, stress response, hypothalamic-pituitary-adrenal axis, glucocorticoid receptor, endocrine-disrupting chemical, crocodylians, University of Vienna
- URL: https://realtech.media/news/rt-8c8d587872f388e914fd4fc5_caimans_in_french/

**Wild smooth-fronted caimans with more mercury in their blood reached lower peak corticosterone in standardized stress tests, University of Vienna researchers report.**

![Caimans in French Guiana with higher blood mercury show a weaker corticosterone response to stress](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/a9795c23dfa2a96a.jpg)
*Dariusz Jakubczyk, Wikimedia Commons, CC BY 3.0*

Researchers from the University of Vienna and the Veterinary University of Vienna studied wild smooth-fronted caimans (Paleosuchus trigonatus) in the rainforest of French Guiana. According to a paper in Communications Biology, published on 28 October 2026, animals with higher mercury (Hg) concentrations in their blood reached lower peak corticosterone levels during standardized stress tests. [1] The university describes the tests as capture-and-handling procedures.

Blood mercury correlated negatively with corticosterone responsiveness. The authors interpret this as impairment of the hypothalamic-pituitary-adrenal axis and as a dampened maximal stress response. [1] They conclude that mercury contamination is associated with reduced stress responsiveness and physiological flexibility.

## Stress axis and mercury

The ability to regulate corticosterone release after a stressful event is part of the physiological flexibility needed to maintain homeostasis. [1] The hypothalamic-pituitary-adrenal axis raises hormone levels such as corticosterone to mobilize energy and trigger behavioral responses. In healthy vertebrates this peak is fast and pronounced, according to the university.

The release states that atmospheric mercury has increased by an estimated 300-500% since pre-industrial times, largely because of fossil fuel combustion and gold mining. In vertebrates, including humans, mercury can interfere with steroid receptors, among them the glucocorticoid receptor, which mediates the stress response.

## Possible mechanism and scope

The team found that a cysteine in the glucocorticoid receptor that is sensitive to methylmercury is highly conserved across vertebrates. [1] The authors suggest this points to a shared molecular mechanism of mercury effects on glucocorticoid signaling. The study itself shows an association between mercury levels and hormone response, not a direct test of this mechanism.

Caimans are long-lived apex predators and accumulate mercury through their diet over many years. The university reports that the effects appeared at mercury concentrations within the range already reported for crocodylian species elsewhere in the world.

Jérémy Lemaire, project lead and first author, said that crocodylian habitats overlap with gold mining areas and that a fast stress response is essential for survival in the wild. Given the widespread mercury pollution in tropical ecosystems, the authors describe mercury as an endocrine-disrupting chemical in crocodylians. [1]

## Sources

1. [Communications Biology](https://doi.org/10.1038/s42003-026-11022-0)
2. [EurekAlert](https://www.eurekalert.org/news-releases/1150407)

---

Source: RealTech, realtech.media — https://realtech.media/news/rt-8c8d587872f388e914fd4fc5_caimans_in_french/