Question of the month

During an interview with Michel Lebeuf, Researcher at the Maurice Lamontagne Institute, Whales on-line asked him the following question:

Are there any new chemical compounds polluting the St. Lawrence and is this cause for concern for the beluga whale population?

M. L. :

It is well known that the maritime portion of the St. Lawrence, more specifically the St. Lawrence Estuary, is an area that is favourable to the accumulation of numerous contaminants in both its sediment and organisms. Contrary to what was once assumed, this portion of the St. Lawrence does not represent a vast basin for the dilution of pollutants. Prevalent oceanographic conditions—the pulsation of the tide, the salinity gradient and abrupt changes in depth—tend to facilitate retention and settling of fluvial waters and the contaminants they carry. The St. Lawrence beluga whale bears witness to this fact: it tops the list of species most contaminated by persistent organic compounds such as PCBs and DDT.

Despite measures taken in the 1970s and 1980s to stem rising levels of these compounds in beluga whales, there has been but a slight decline in the contamination of this population by persistent organic compounds. A beluga whale already accumulates large quantities of contaminants through the placenta during gestation, as well as after birth by way of its mother’s milk. It will then continue to consume contaminated marine organisms over the course of its adult life. All in all, the presence of persistent organic contaminants in beluga whale habitat results in a major accumulation of these compounds in the whales, and this will go on for some time to come.

The use of new persistent chemical products in Canada is increasingly limited and often prohibited. Yet, there are a certain number of long-ago-sanctioned persistent chemical products that are still in use. As a rule, when the production of these compounds is low, environmental problems are limited. Nevertheless, there are the exceptions of increasingly popular compounds, the production of which has risen dramatically over the years. Such is the case of organobromines, including PBDEs.

However, it should be noted that persistent compounds are not the only products that can potentially affect St. Lawrence beluga whales; other compounds that do not permanently accumulate may also affect their health. Pesticides used in both the small and large-scale spraying of crops are generally not very persistent in the environment or in living organisms. They are, however, very toxic. Pharmaceutical products currently in use in modern society also eventually find their way into the aquatic environment. These products can adversely affect aquatic organisms. Moreover, certain compounds like benzo-a-pyrene are metabolized and rapidly transformed by beluga whales. The activation of a beluga’s defence mechanisms to eliminate these compounds seriously drains the animal’s energy resources, reducing the ability of its immune system to combat certain pathogens. Presently, the only programme in place to track contamination in the St. Lawrence beluga whale environment—as sampled in beluga whale fat—targets certain metals and persistent organic compounds for which Canadian environmental norms are already in place.

Portrait of Michel Lebeuf