In the Camargue, populations of European pond terrapin contaminated by trace metals

Trace metals (TMEs) are a major source of pollution and a significant threat to aquatic ecosystems and organisms. Contamination by these pollutants can vary considerably on a local scale, depending on the characteristics of the environment (hydrosystem, trophic resources) and the individual characteristics of the organisms affected (age, sex). Because of their high position in the trophic chain and their long life expectancy, freshwater turtles are particularly vulnerable to bioaccumulation and biomagnification, making them potentially highly exposed to these contaminants.

This study examines the concentrations of TMEs in the blood of two populations of European pond terrapin (Emys orbicularis) living in the Tour du Valat Regional Nature Reserve. The two populations, monitored by Capture Marking Recapture (CMR) since 1997, differ in terms of their habitats and water regimes (irrigation or drainage channels). A total of seven TMEs[1], including mercury and lead, were detected in the turtles’ blood samples. The results show that contamination levels vary depending on the site and individual characteristics.

Concentrations of mercury, lead, selenium and zinc are higher in individuals living at l’Esquineau than at Les Faïsses (contrary to what was shown for pesticides in a previous article). Irrigation of the l’Esquineau site with water directly from the Rhône, a river particularly contaminated by TMEs, is one of the main hypotheses to explain this result.
The study also revealed positive correlations between the age and body size of individuals and mercury concentrations, suggesting greater exposure in older turtles.
A similar correlation was observed for lead levels, but with a differential effect according to sex. For the first time, it has been shown that females have blood lead levels that increase with age, unlike males whose levels decrease. This result contradicts the hypothesis that females detoxify by laying eggs.
CMR monitoring also showed that mercury, lead and selenium levels varied little within individuals from one year to the next in multi-captured individuals. These results suggest chronic exposure to TMEs in these populations. Although concentrations remain moderate, this exposure could have deleterious effects on this long-lived species.
Finally, ETM levels did not appear to be related to the trophic position of the individuals.

Further studies are needed to examine the potential ecophysiological effects of this exposure to ETMs, in particular the differences between the sexes. This priority is all the more important as these Cistude populations have recently been identified as being highly exposed to organic contaminants, which could give rise to worrying synergistic effects.

[1] Cu, Fe, Hg, Mn, Pb, Se and Zn

Bibliography :

L-A. Merleau, A. Goutte, A. Olivier, M. Vittecoq, P. Bustamante, C. Leray, O. Lourdais, (2024). Blood levels of metallic trace elements are influenced by sex, age and habitat in the European pond turtle (Emys orbicularis), Science of The Total Environment, Volume 957, 177487. ISSN 0048-9697. https://doi.org/10.1016/j.scitotenv.2024.177487

This second article from Leslie-Anne MERLEAU’s thesis is the result of a project carried out between 2018 and 2020 by Marion Vittecoq and Anthony Olivier (Tour du Valat), with Aurélie Goutte (UMR METIS), Olivier Lourdais (CEBC) and Paco Bustamante (La Rochelle University). It was made possible thanks to the work of several trainees and civic services and Carole Leray (Tour du Valat), who played an active part in the captures and blood sampling.

Contact

Leslie-Anne MERLEAU – Doctoral student co-supervised by Tour du Valat, the UMR METIS (Milieux Environnementaux, Transferts et Interactions dans les Hydrosystèmes et les Sols) and the Centre d’Etudes Biologiques de Chizé.