Are St-Lawrence belugas contaminated (2015)
The St. Lawrence beluga lives in the heart of a densely populated and highly industrialized region. In the 1970s, scientists revealed that the species was heavily contaminated with heavy metals, PAHs and PCBs, which led to regulatory changes. We’re beginning to see the beneficial effects of these measures. Some of these contaminants, which were present in record concentrations in belugas in the 1980s, have since declined. Cancers, which were the main cause of mortality in adults in the 1980s and 90s, have also become less frequent, and no beluga born after 1971 has succumbed to cancer. However, other toxic substances are increasing such as PBDEs, which have increased exponentially through the 1990s and which can affect the survival of the young or the ability of females to care for them.
Belugas accumulate in their fats a number of toxic compounds of human origin. Since the beluga carcass recovery program was spearheaded in 1982, samples (fatty tissue, liver, etc.) have been taken from carcasses to determine the composition and concentration of the toxic substances present. A biopsy, program undertaken in 1994 has revealed that living belugas are just as contaminated as those found dead.
What have we learned?
In the 1980-90s, the high concentrations of toxins in the tissues of St. Lawrence belugas were substantially greater than those measured in Arctic belugas. Concentrations of heavy metals such as lead and mercury were 2 to 15 times higher; those of PCBs (polychlorinated biphenyls) and the insecticide DDT (dichlorodiphenyltrichloroethane), up to 25 times higher; and those of the pesticide Mirex, 100 times higher. These differences suggest that St. Lawrence belugas have long been exposed to multiple sources of contamination by way of their prey.
Like PCBs, organochlorines are contaminants called immunosuppressants, meaning that that can weaken the belugas’ immune systems, making them more vulnerable to infections and cancers. It was the St. Lawrence belugas that exhibited the highest rates of cancer, compared to Arctic belugas or any other wild mammal species. Cancer types that have been identified include those of the intestines, mammary glands, ovaries, uterus, skin, stomach, salivary glands, thymus and bladder. Several studies have attempted to establish a correlation between cancers in belugas and their exposure to PAHs (byproducts of combustion of fossil and wood material), which are powerful carcinogens emitted into the atmosphere by aluminum smelters. However, scientific proof of such a relationship between PAHs and cancers in belugas (and Man) is far from conclusive and several groups of researchers have had criticisms in this regard.
Since the aforementioned time period, with the adoption of new regulations for these toxic products, new practices in the aluminum sector, as well as a possible change in the belugas’ diet, the levels of some contaminants have decreased in the marine sediment as well as in the fat of belugas, as is the case for PCBs and DDT, while no change has been noted for Mirex. Lastly, no cancer has been diagnosed in any animal born after 1971.
The toxicity of PBDE (polybrominated diphenyl ethers) was discovered well after their widespread deployment in the environment. These products, used to improve fire resistance in plastic materials, have increased drastically since the 1990s despite legislation introduced in Canada and the United States in the 2000s. Like PCBs, these contaminants are resistant to degradation and accumulate in organisms. In total, 181 dead belugas (males, females and newborns) were sampled between 1987 and 2012. The similar concentrations observed between females and newborns clearly illustrate the efficient transfer of contaminants through the mothers’ milk, and adult females of the St. Lawrence are believed to be more heavily contaminated than those of other populations. The concentration levels of these chemicals in animals found stranded – females and newborns alike – do not differ from those measured previously; concentrations of these contaminants plateaued between 1995 and 2012.
LThe role of PBDEs in recent newborn mortalities and complications during calving (see article St. Lawrence belugas declining) could not be determined, but an increasing number of studies shows that persistent organic pollutants (POP) such as PBDEs are endocrine disruptors that cause hormonal and neurological disorders, which can affect the reproduction and development of offspring in mammals.
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