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What is causing the high rate of cancer in St. Lawrence beluga whales?
 
In-depth: Belugas

Beluga Whales Under Threat
by Xenia Shih

Beluga whales are native to arctic and sub-arctic waters and even frequent the shallow bays and estuaries of larger rivers, like the St. Lawrence River where it runs through eastern Canada. But these days, human-caused pollution in the St. Lawrence puts the belugas that live there at an alarming risk.

beluga
The St. Lawrence beluga whale population is protected under Canada's Species at Risk act. (Photo credit: Carrie Vonderhaar)
Click to enlarge

Between 1983 and 1999, University of Montreal veterinary pathologist Daniel Martineau and his team conducted a study of 129 dead St. Lawrence belugas and found that 27 percent of the adults they studied had cancer, including cancer of the small intestines, stomach and liver, making it the leading cause of death in that particular population. Cancer in the St. Lawrence belugas accounts for 40 percent of all cancers reported in cetaceans; sadly, the St. Lawrence belugas suffer from the highest rate of cancer of any wild mammal species -- comparable to the rate among human adults, in which cancer causes about 25 percent of deaths in the United States.

Meanwhile, research indicates that belugas of the Canadian Arctic -- same species, different habitat -- don't suffer from cancer at all.

So what causes cancer in St. Lawrence belugas?

The likely culprit is industrial pollution. Water from the Great Lakes watershed drains into the St. Lawrence River, bringing with it pollutants from the many industries that line the Great Lakes. The St. Lawrence River is highly contaminated by toxic chemicals, including polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT) and polycyclic aromatic hydrocarbon (PAH). The chemicals PCB and DDT are now known to be toxic to humans and animals, and PAH is a carcinogen, a substance that causes cancer. The PAH found in the water is likely from the aluminum smelting plants that line the Saguenay River, which also drains into the St. Lawrence.

You might wonder just how these toxins wind up in the belugas' tissues. The answer lies in their feeding habits: Toxins from the industrial plants settle in the river's sediment, which the belugas dig in to feed on invertebrates. The belugas are exposed both during the digging and when they eat the contaminated animals. Some of these toxins are difficult to break down and end up accumulating in the belugas' blubber over the course of their lives.

beluga
Toxins from the industrial plants lining the St. Lawrence River settle in the river's sediment, which the belugas dig in to feed on invertebrates.
Click to enlarge

In other words, St. Lawrence belugas are quite literally poisoned to death, slowly but surely. Under Canadian law, a PCB level of 500 parts per million (ppm) is considered toxic waste, and PCB levels in St. Lawrence belugas range from 240 ppm to 800 ppm. Technically, some belugas from this region can themselves be classified as toxic waste.

But for the St. Lawrence belugas, cancer isn't the only unfortunate outcome of their exposure to toxins: Their immune systems are weakened, making them very susceptible to disease and infections, and even their reproductive abilities are compromised. Pierre Béland, a toxicologist at the St. Lawrence National Institute of Ecotoxicology in Montreal, found that only 20 percent of female St. Lawrence belugas were pregnant or had recently given birth, as opposed to 66 percent of their female counterparts in the Canadian Arctic. And the reproductively successful St. Lawrence belugas pass toxins along to their offspring via the placenta and the mother's milk.

Beluga whales in the St. Lawrence region are not the only mammals showing signs of damage from exposure to toxins. Compared with people living in other parts of Canada, people living in the St. Lawrence region have higher rates of cancer, particularly lung, urinary and digestive cancers.

What is being done to address the problem?

Today, the St. Lawrence beluga population is protected under numerous Canadian federal acts, such as the Species at Risk Act and the Fisheries Act. In addition, in 1996, the Beluga Committee was established to oversee the St. Lawrence Beluga Recovery Plan, which includes such strategies as reducing toxic contaminants, reducing disturbances by humans, preventing ecological catastrophes (like oil spills) and monitoring the state of the population.

beluga
The University of Montreal offers a whale autopsy program where students study beluga diseases.

Although it is impossible to be certain that industrial runoff from aluminum smelting plants is the direct cause of cancer in St. Lawrence belugas, the evidence is compelling enough that government agencies, wildlife advocates and the public have exerted pressure on the smelting plants in the region to reduce the amount of toxins they produce and release into the river.

There is reason to believe that the welfare of the St. Lawrence belugas has improved because the population appears to have stabilized. Back in 1983, the Committee on the Status of Endangered Wildlife in Canada listed the St. Lawrence belugas as Endangered (both because the pollutants in their habitat were likely killing them and because they'd been legally hunted until 1979), but in 2004, their status was reexamined and upgraded to Threatened, meaning that the species is no longer in danger of immediate extinction, but could still disappear in the future.

This is good news not only for belugas, but also for humans, since we all share the same environment. And while surely public awareness and a change of habits among humans in the St. Lawrence region has made a difference, don't forget that what you do in your community, from disposing of chemicals properly to sharing what you've learned about belugas with your family and friends, can make a difference, too -- for all of us.

Sources:

Alaska Ocean Observing System: Beluga Whale

CA online: Cancer Statistics, 2005

"Deadlier than the harpoon?" NewScientist

Environmental Health Perspectives: "Cancer in Wildlife, a Case Study: Beluga from the St. Lawrence Estuary, Quebec, Canada," by Daniel Martineau et al.

Environmental Health Perspectives: "St. Lawrence beluga whales, the river sweepers? A Correspondence," by Daniel Martineau et al.

Fisheries and Oceans Canada: Beluga Whale

"Pollution blamed for cancer ravaging Quebec's whales," NewScientist

"Pollution is Blamed for Killing Whales in St. Lawrence," The New York Times

Species at Risk Public Registry, Government of Canada

Whales on-line: The St. Lawrence Beluga

Wikipedia.org: Beluga