17. 02. 2017

The population of one of the largest land predators may drop rapidly in the future according to some predictions of scientists. The reason can become not only a lack of Arctic ice retreating due to the influence of global warming, but also some of the toxic substances produced by man. For example, polychlorinated biphenyls, chemicals that persist in the environment for decades, damage the hormonal balance of organisms and can thus decrease fertility. The study is dedicated to the impact of these toxic contaminants on reproduction of polar bears in Greenland and Spitzbergen, the main author which is Viola Pavlová from the Institute of Hydrobiology of the Biology Centre of the CAS and which was published in the journal Proceedings of the Royal Society B.   

Polychlorinated biphenyls (PCB) were used as additives to paints, lacquers, or fillers for transformers and capacitors from the 1930s. In the 1960s, it was demonstrated that they get into the environment and from there into the food chain. Since they dissolve in fats, they accumulate in the tissues of animals, particularly the predators at the top of the food chain, including people. The toxicological tests showed that PCBs have many negative effects on health, inter alia they cause cancer, liver damage and infertility. Their production was halted in Czechoslovakia in 1984.

During the 1980s and 1990s, a large number of PCBs accumulated in the organs of polar bears, which the bears received in their food in the consumption of contaminated seals. Polychlorinated biphenyls thus could disrupt the hormonal balance of the bears and cause lower female fertility or worse quality of the sperm of the males.

Eco-toxicological studies most often assess the negative effects of toxic substances in the environment on the reproductive ability of females, but the work of Viola Pavlová focused on the reproductive health of males. “Our study provides a new perspective on the impact of contaminants on the dynamics of the population of polar bears by putting possible male infertility into a context with the Allee effect, which happens in bears,” says the author of the study Viola Pavlová. Because if an infertile male competes for a healthy female with a fertile male and the infertile individual wins, young will not be born that year. For the bear females, it is thus a large risk that they will not find a partner in time and miss one of the few opportunities to multiply that they have in their lives. The result can be a decrease in the actual population.

The research was based on analyses of the data from previous studies and computer models. “This is a vulnerable animal species, which is protected. It would be difficult, therefore, to test the impact of toxic substances experimentally in animals in captivity. In wild animals, it would have been completely impossible, not only for ethical but also for logistical reasons,” explains Viola Pavlová


Mgr. Viola Pavlová, Ph.D., scientific employee, Institute of Hydrobiology of the Biology Centre of the CAS, tel. 774 988 342, e-mail:

Mgr. Daniela Procházková, publicity officer, Biology Centre of the CAS, tel. 387 775 064, 778 468 552, e-mail:

Pavlová V., Nabe-Nielsen J., Dietz R., Sonne C., Grimm V. (2016) Allee effect in polar bears: A potential consequence of polychlorinated biphenyl contamination. Proceedings of the Royal Society B283: 20161883/1–9. .DOI: 10.1098/rspb.2016.1883