Presence and Bioavailability of PAHs in the Saguenay and St. Lawrence Ecosystem

By Émilien Pelletier, Institut des sciences de la mer de Rimouski (ISMER), Université du Québec à Rimouski

Are belugas victims of polycyclic aromatic hydrocarbons (PAHs)? This question has come to the fore since the recent publication of a study by researchers from the Université de Montréal that implicates PAHs produced by the aluminum smelters of the Saguenay region in the development of intestinal cancers in some belugas found dead along the shores of the St. Lawrence over the course of the past 20 years. Scientific proof of this link has yet to be established. However it is impossible to reject this hypothesis out of hand as the presence of PAHs in sediment and organisms of the Saguenay and the St. Lawrence is in fact poorly documented and the only published data are 15 years old. The trophic transfer of carcinogenic PAHs is a known process in laboratory animals and in a few highly contaminated ports and industrial zones, yet it is virtually unknown in a vast estuarine ecosystem like that of the St. Lawrence.

This project began in 2000 with the detailed analysis of PAHs (26 different molecules) in 5 sediment cores taken at different stations in the Saguenay Fjord. Each core sample was cut into 18 different sub-samples in order to determine the contamination history of the Ford over the past 50 years. These first results has been made public at an international conference on contaminated sediment held in Québec City in May 2003. Our project continued in 2001 and 2002 with the sampling of benthic and pelagic organisms all along the Saguenay Fjord, as well as at two sampling stations in the St. Lawrence, near the mouth of the Fjord. During these cruises, organisms were taken from all trophic levels, including annelids, gastropods, echinoderms, bivalves, crustaceans (crab, shrimp and krill) and several species of fish. The analysis of these animals commenced in May 2003 and will continue for more than a year. The purpose of these analyses is to determine not only PAH concentrations, but also levels of metabolites produced by several species as a defence mechanism against contamination. Another sampling cruise was done in the spring of 2003 and has encompassed the entire length of the St. Lawrence between Orleans Island and Anticosti Island. The goal of this cruise is to evaluate the contribution of PAHs from the St. Lawrence River to habitats used by beluga whales and other marine mammals living in the Estuary.

At the same time, we began a more basic study on the sequestration chemistrysequestration chemistry of PAHs in marine and lake sediment in 1999. It has already been established that PAHs and certain other organic contaminants have a tendency to become imprisoned by sedimentary particles over time as sediment ages. We have studied the physical and chemical factors that influence this sequestration process and eventually reduce the bioavailability of toxic molecules. This study has demonstrated that between 10 and 20 percent of all PAHs are available to burrowing organisms at the bottom of the Saguenay, depending on their depth. We have also demonstrated that PAHs that are newly released into the aquatic environment take between 20 and 60 days before being completely imprisoned by suspended particles.

All of these data will be used to determine whether or not PAHs are present in beluga whale food. If they are present, we will follow their movement through the St. Lawrence food web and determine what threat they could pose to the environmental health of the St. Lawrence.

This project will require the efforts of six MSc and PhD students, along with several trainees and two research professionals over five years.

These projects are supported by the Saguenay—St. Lawrence Marine Park, Natural Sciences and Engineering Research Council of Canada (NSERC), Fonds québécois de recherche sur la nature et les technologies (FQRNT) and Alcan Ltd.