PAHs (polycyclic aromatic hydrocarbons) comprise a group of toxic chemicals that are generated during industrial processes involving combustion. In St. Lawrence Estuary region, it has been found that the major cause of deaths for Beluga whales is gastrointestinal cancers, which result from ingestion of benthic invertebrates that have been contaminated with PAHs.
The movement of PAHs starts from the aluminum smelters located near the seas and the rivers within Saguenary-Lac-Saint-Jean region of Canada. The smelters dig up aluminum, which is found near seabeds and riverbeds. The process of converting raw aluminum mineral into usable form involves melting the mineral under high temperatures. During the melting process, some aluminum, in vapor form, finds its way into the atmosphere. The aluminum vapor is then blown away by the wind and settles onto land and water surfaces eventually. Aluminum vapor that settles onto water surfaces sinks into the bottom of water bodies, forming thick sediments of aluminum in the rivers and seas down-stream. Similarly, aluminum vapor, which settles onto land surfaces, is carried by run-off water, and ends up in rivers and seas located downstream. The aluminum then settles in the bottom of these rivers and seas, forming thick residuals of aluminum.
Once the aluminum settles into the bottom sediments of water bodies, benthic invertebrates take it in, either through consumption of aquatic plants and animals, or through absorption into their bodies by the process of osmosis. Belugas feed on benthic invertebrates. In SLE region, invertebrates living in the sediments of water-bodies have high concentrations of PAHs in their bodies. St. Lawrence Estuary beluga whales dig into the sediments and feed on these invertebrates. Once these contaminated invertebrates are ingested, the PAHs inside them find their way into the digestive tracts of beluga whales. These PAHs are activated into carcinogenic compounds, which cause various types of gastrointestinal cancers, which cause death in SLE beluga whales.