Environmental contaminants and reproductive and stress hormone levels in brown bears

The development of civilization, in addition to improving the quality of human life, has also resulted in increasing environmental pollution. Some of these pollutants have a high potential for endocrine toxicity. These are substances known as endocrine disrupting chemicals (EDCs), that is, substances that can cause changes in the functioning of the endocrine system, thus affecting also other functions of an organism. Exposure to them can cause many negative health effects. Such compounds include heavy metals, but data on their effects on the endocrine system of wildlife, especially large terrestrial carnivorous mammals, are scarce. We investigated the exposure to environmental contaminants, such as arsenic (As), cadmium (Cd), mercury (Hg) or lead (Pb), in brown bears from two populations: Carpathian (in its Polish part) and Dinaric (in its Croatian part). We also determined the concentrations of cortisol (a stress hormone), progesterone and testosterone (reproductive hormones), and performed an analysis, taking into account the aforementioned contaminants, biological, environmental and sampling factors to study the potential effects of this exposure. We analyzed hair samples from 46 individuals from Croatia and 27 individuals from Poland. We detected an association of elevated testosterone levels with higher mercury levels in both males and females. Individuals with a lower body condition index had higher cortisol levels, but lower progesterone levels. Year of sampling and sampling conditions were significant for the variation in cortisol levels, and age for the progesterone levels (lower progesterone concentrations in cubs and yearlings compared to subadult and adult bears). These results suggest that environmental pollution that deposit in the animal tissues may affect the hypothalamic-pituitary-gonadal axis (HPG) responsible for the normal function of the reproductive system, and therefore have a negative impact at the individual and population level.

Lazarus, M., Sergiel, A., Ferenčaković, M., Orct, T., Kapronczai, L., Pađen, L., Janz, D. M., Reljić, S., Zwijacz-Kozica, T., Zięba, F., Selva, N., Huber, D. 2023.  Stress and reproductive hormones in hair associated with contaminant metal(loid)s of European brown bear (Ursus arctos). Chemosphere 325: 138354  https://doi.org/10.1016/j.chemosphere.2023.138354

by Agnieszka Sergiel