Question of the month

During an interview with Émilien Pelletier, who holds the title of Research Chair of Canada in Marine Ecotoxicology at ISMER (Institut des sciences de la mer de Rimouski), Whales online asked him the following question:

Is the St. Lawrence in better shape than it was 20 years ago?

É.P.: Improvements to the state of the fluvial portion of the St. Lawrence have been remarkable over the past twenty years. The condition of the Estuary, on the other hand, is more alarming.

The St. Lawrence Estuary and the Saguenay Fjord are extremely rich and diversified habitats. Oceanographic phenomena, such as the deep water upwelling that takes place here, are favourable to the entire food web. Numerous species of phytoplankton and zooplankton, invertebrates, fish, birds and marine mammals depend on this environment. The Saguenay–St. Lawrence Marine Park was recently created in order to preserve this exceptional area. Yet, could the Estuary and Fjord be more subject to pollution than previously thought? Apparently they are.

Contrary to a long-standing notion, the St. Lawrence Estuary and the Saguenay Fjord are not basins for the dilution of pollutants. Rather, due to prevalent oceanographic conditions, like the diurnal pulsation effect of the tides and the abrupt change in depth, they are more retention and decanting basins for fluvial waters.

What about the various toxic substances in the St. Lawrence Estuary and the Saguenay Fjord? In general, levels of heavy metals (mercury, cadmium, lead, zinc and copper) have diminished quite substantially, mostly in the Fjord, but also in the Estuary. Regulatory efforts, and the fact that these metals have been withdrawn from certain manufacturing processes, have made a difference. As for mercury contamination, which was particularly high in the Fjord, there has been a clear decrease in mercury levels in shrimp, the biological indicator for this metal. Mercury concentrations have only recently dropped to a level where shrimp from the Fjord are now deemed fit for human consumption. The main sources of mercury were point source and have been eliminated since the mid-1970s. Existing mercury pollution is now atmospheric in nature and its principal source is the burning of coal in the Great Lakes area and the American Midwest. Quantities of PAHs have decreased measurably in Fjord sediments. However, there is no recent data concerning living organisms. In fact, PAHs are metabolized by numerous species, including mammals, and are hard to detect. As for PCBs and DDT, the main biological indicator is the beluga whale. Concentrations of PCBs and DDT in St. Lawrence belugas do not appear to have diminished significantly in the past 20 years. Even though we have detected a decrease in concentrations in sediment, that has not had the effect of reducing quantities present in the animals. The elimination of these persistent products will take longer than we thought initially. As for PCBs, sources exist that continue to contaminate the waters of the St. Lawrence. These sources are sufficient in themselves to explain PCB levels in belugas, even without the inclusion of the contribution from quantities accumulated in sediment.

Recently, researchers have begun to concentrate on other products that are cause for concern. For example, I am interested in tributyltin (TBT), a powerful biocide that is added to paint used on merchant vessels and warships to reduce fouling by algae and adhering organisms. This product is highly immunotoxic (even more so than PCBs) for all aquatic species tested to date, including mammals. It acts also as an endocrine disrupter. Another case: polybrominated diphenylethers (PBDE), with chemical structures similar to PCBs, are used for fireproofing a wide variety of materials. They are present in organisms living in the St. Lawrence Estuary, but so far their environmental toxicity remains practically unknown. The environmental toxicity of toxaphen (an organochlorine insecticide) has been clearly demonstrated for several marine species; work is in progress on samples from the St. Lawrence.

As well as chemical pollution, there is concern about the reduction of oxygen in the deeper waters of the Estuary. Oxygen content in these waters appears to have diminished by 50 percent in less than 20 years. Is the eutrophization of the Estuary under way? The phenomenon of eutrophization is better known in lakes and rivers, yet it exists in numerous bays and small estuaries that are over exposed to organic contamination and, more importantly, to nutrients (nitrogen, phosphorous…) from agriculture, industrial animal farms and municipal sewage. The resulting proliferation of plants, algae and organic waste stimulates bacteria and, in the end, provokes the asphyxiation of the environment. In the case of the Lower Estuary, the excessive and rapid development of micro-algae could lead to a lack of oxygen in the deep waters where renewal is very slow. A drastic reduction of oxygen in the lower part of the water column of the Estuary could lead directly to major changes of the benthic ecosystem. These could include the reduction of biodiversity and implementation of species that are more tolerant to low oxygen levels. Also, because they are more active than worms or echinoderms and they have a constant need for well-oxygenated water, we could see the migration of fish and crustacean species towards sites that are more aerated.

We must ask the questions that urgently require answers. What impacts do agriculture and the rearing of farm animals have on the Estuary? How can we further reduce present levels of contaminants that find their way into the St. Lawrence and the Saguenay? How do we end the use of marine paints that contain pesticides without perturbing maritime traffic, which is essentially less polluting than transportation by land? How do we raise public awareness and convince those in power of the importance of crucial decisions that must be made for the future of our Estuary? How do we go about coordinatingco-ordinating the efforts of Ministries and concerned agencies?

This overview of the health for the Estuary indicates that nothing can be taken for granted and that we must increase our decontamination efforts. Dilution is definitely not the solution.