By studying polar bear feces, researchers aim to understand how chemicals get trapped in the body

A new University of Toronto study is using analysis of polar bears to reveal how certain chemical pollutants can get trapped – and build up – inside the body.

Polar bears tend to store some contaminants in their bodies because they are at the top of the food chain, have very fatty diets, and have evolved to absorb high amounts of fat.

A polar bear feeds at the Toronto Zoo. Image credit: Toronto Zoo

“They are like a trap for these chemicals,” says Frank Waniaa professor in the department of physics and environmental sciences at U of T Scarborough, one of the study’s authors.

“Their pollutant levels are very high, but their discharge capacity is very low.”

For research, published in a magazine Environmental Science & Technology, Wania and Ph.D. student Yuhao Chen developed a new method to study how certain chemicals, called polychlorinated biphenyls (PCBs), accumulate inside polar bears from contaminated food. They analyzed the diet and faecal samples of polar bears from the Toronto Zoo to see how much trapped PCBs compared to what was excreted.

Polar bears experience so-called biomagnification, where more toxins build up in the food chain. Since polar bears came out on top, they consumed the highest amount of contaminants in their diets. (A polar bear has higher levels of contaminants than the seals it eats, seals have more cod, cod more than small fish, etc.)

Additionally, the researchers found that PCBs tended to be biologically exaggerated at a higher rate in polar bears due to their high-fat diets and the ability of their digestive systems to absorb those fats.

While animals and humans are generally good at getting rid of most chemicals that shouldn’t be in the body, some contaminants are more difficult to remove due to their properties. Persistent and lipid-soluble substances, including the pesticides DDT and some types of PCBs, can accumulate in body tissues because they cannot be broken down or excreted easily through the digestive system.

Sarra Gourlie, the supervisor of nutritional science at the Toronto Zoo, who provided fecal and dietary samples for the study, said polar bears have evolved to absorb nearly all the fat they eat. – mainly from seal fur.

“They were able to extract about 97 percent of the fat from their diet, so very little of the fat was actually passed out,” she says.

Polar bears at the Toronto Zoo are not fed wild seals, which can contain high levels of PCBs. Chen says polar bears living in the wild have much higher levels of pollution than those in zoos, which have a cleaner diet.

He says it’s important to monitor these levels of pollution because of the harm they can cause. Studies have linked high levels of PCBs in wild polar bears to lower levels of testosterone, which can affect reproduction. It has also been linked to disruptions of the immune and endocrine systems, which can reduce survival rates.

“The PCB levels have exceeded worrying levels to the point where they are thought to have a negative impact on polar bears living in the wild,” said Wania.

PCBs are a group of highly toxic chemicals that have been banned globally but can last a long time in the environment. While the researchers only looked at PCBs in this study, they say the method could also help track other chemicals trapped through biological magnification.

A non-invasive method for top predators and humans

The traditional method for studying biomagnification relies on tissue analysis, which can only be performed on dead animals or humans. As a result, there are almost no studies on biomagnification in humans or endangered predators. The researchers hope the method they have developed can be used on other apex predators in the wild, such as lions or tigers.

It can also be used on humans. Chen said he is currently looking at analyzing food and stool samples from different people to see how biologically magnified the contaminant is inside the body and whether there are individual differences. are not.

“We know these pollutants are present in humans, and we know how the body absorbs these pollutants,” he said.

“What we don’t know is how much of these contaminants is stored or expelled by our bodies when we eat a contaminated amount of food.”

Source: University of Toronto