Pesticides in the Arctic are Causing the Feminization of Polar Bears
The Arctic is one of the last places on Earth untouched by humans. However, a new study shows that pesticides, even ones that are no longer in use, are found in Arctic Waters. These toxic chemicals reach the Arctic waters because of their inability to degrade over a long period of time. Even more worrisome, these persistent pesticides are having a major effect on the Arctic’s top predator, the polar bear.
The polar bear is called an apex predator because it sits on top of the food chain, regulating all of the lower levels so that the ecosystem is in balance. Polar bears are especially at risk from pollutants at the Arctic due to an effect called biomagnification. This means that each step up the food chain, the amount of pollutants in the species increases. By the time the pollutant reaches the polar bear, it is in dangerous concentrations.
Another reason why the polar bear is at a higher risk than other species is due to their fat-rich diet. Polar bears mainly eat seals which are high in fat content. Pollutants such as pesticides are easily stored in fats. Thus, the polar bears’ high fat diet allows for the fast accumulation of these toxins. This fragile balance in the Arctic food chain is now at risk from pollutants reaching these previously thought to be untouchable regions of the Earth.
A recent study that took place in Svalbard, a remote collection of islands outside Norway, looked specifically at the relationship between pesticides levels and sex hormone levels in polar bear blood. More specifically, the researchers looked at a category of hormones called androgens. This refers to testosterone, estrogen, and progesterone. These hormones are regulated by an enzyme, aromatase, in order to develop sex-defining characteristics such as body size and sexual organ development. Aromatase breaks down testosterone into estrogen, regulating the amount of different sex hormones that are in the body. Hence, the levels of estrogen versus testosterone determines the sexual characteristics of the bears. During development, the activity of aromatase can vary. This occurs because secondary sexual characteristics are developed during puberty.
However, the presence of pesticides in the Arctic ecosystem is shifting this balance between androgens during development. The scientists in Svalbard found that as the concentration of pesticides in the polar bear blood increased, there was a decrease in androgens such as testosterone. This means that the male polar bears are becoming more feminine in terms of their hormone make up.
In addition, another study done in Greenland in 2006 found that testes size in male polar bears decreased after pesticide exposure. However, this study did not look at hormone levels in the polar bears. Future research needs to be done in order to determine whether the decrease in testosterone is responsible for the change in testes size seen in male polar bears in Greenland.
Clearly, there is a significant effect of these toxic pesticides on the development on sexual characteristics. Due to this alteration in sexual development of polar bears, we can predict that there will be a detrimental effect on the polar bear population due to their diminished ability to reproduce. It is critical that polar bear populations continue to be monitored in order to determine the long-term effects of toxic pesticide exposure.
Unfortunately, the World Wildlife Fund already classifies the polar bear population as vulnerable. This is mostly due to their loss of habitat. The sea ice extent in the Arctic is already 40% less than it was in 1980.
Polar bears rely on the sea ice in order to hunt seals. When the sea ice melts, the bears enter a period of fasting while the wait for the sea to freeze again. Since it the period of time where there is sea ice cover decreases each year, the amount of time that the polar bears fast is increasing. The combination of the changing habitat and increase of pollutants in the Arctic is referred to as a “flank attack” on the polar bears. This term is in reference to the multifaceted threats that exist to polar bear populations.
In order to better protect polar bears, steps need to be taken to limit the amount of pesticides that reach the Arctic. However, even though The Stockholm Convention banned DDT in 2001, DDT was still found in the polar bear blood samples almost two decades later. Thus, it is critical that everyone stops all toxic pesticide use immediately in order to best mitigate the long-term effects of toxic chemical exposure. If no action is taken, the polar bears’ reproductive ability will decrease, and populations will decline. In order to best mitigate the effects of the “flank attack” on bears, toxic chemical use needs to be reduced or eliminated and carbon emissions need to be regulated in order to preserve the polar bear habitat in the Arctic.
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