But "it's difficult to simply respond if this is good or bad news," a researcher says.
Beluga whales of the St. Lawrence Estuary are less exposed to chemical contaminants, according to a study published recently by researchers from three Quebec universities, but they stop short of saying the problem has been fixed.
Some products remain in the waters of the estuary and can still potentially interfere with the immune system or hormones of belugas, say experts with the Université de Montréal, Université du Québec à Rimouski and Université du Québec à Montréal.
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The best news concerns polycyclic aromatic hydrocarbons (PAH), dumped into the Saguenay River by industrial activities and considered a major cause of cancer in belugas. The study showed the level of PAH returned to pre-industrial levels.
News was also encouraging for polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). Levels of PCBs, banned since 1977, have declined, but because the compound bioaccumulates, and belugas are at the top of the food chain, the substances could continue to affect their health, making them more vulnerable to infections or affecting their immune systems.
PBDEs are organic pollutants that are very persistent and toxic and interfere with thyroid hormones among humans and belugas. The study showed a reduction of contamination over the last few years, but they can still affect the thyroid gland, which may explain mortality issues among females.
“It’s difficult to simply respond if this is good or bad news,” said professor Zhe Lu of the UQAR. “We know the frequency of detection (of contaminants) is low. But at the same time, there are very elevated levels of certain contaminants among belugas, so we see that they can still accumulate in some cases.”
The study was conducted on carcasses that beached on the shores. It is therefore possible that the animals were dead for a certain time before being analyzed, and the levels of contaminants in their tissues do not reflect the levels in living animals. The data could also be tainted by the fact that the animals analyzed, by definition, were not healthy, Lu noted.
“We don’t have real data on how the contaminants affect healthy belugas,” he said, “but other studies show that these compounds can cause liver tumours in mice or affect hormonal systems in fish, or even influence gene expression in some animals.”
The researchers note that the chemical pollutants are only one of many threats to beluga whales, as the animal is also very vulnerable to climate change.
Veterinarian Stéphane Lair, of Université de Montréal, said it is important to regulate industries, ban toxic contaminants and monitor new products that replace them, but also reduce our dependence on fossil fuels and limit consumption of goods and services.
The conclusions of the study were published by the journal Science of the Total Environment.