Contamination of the St. Lawrence beluga by persistent organic pollutants – a review
The population of beluga from the St. Lawrence Estuary (SLE) is a wildlife species threatened with extinction. One of the possible causes explaining the current status of the population is its exposure to toxic chemicals. This review paper gathers the published data on the contamination of the SLE belugas by persistent organic pollutants (POP). Parameters and processes influencing the concentrations and the temporal trends of POPs in SLE belugas are discussed. The paper also presents the strengths and limits of monitoring contaminants in the SLE belugas for the population itself and as a sentinel species of its habitat. Between 1980 and 2007, more than 20 scientific papers have reported the presence of a variety of POP in the SLE belugas. Polychlorinated biphenyls (PCB) and dichlorodiphenyltrichloroethane (DDT) and its metabolites have been the most frequently reported POP in SLE belugas. Most chemical analyses have been done on beluga tissues collected from stranded carcasses. Concentrations of POP that have been regulated in Canada, including PCB and DDT, are decreasing or stable in SLE belugas. However, concentrations of polybrominated diphenyls ethers, an emerging chemical used as flame retardant, are doubling every 2-3 years in beluga blubber. Concentrations and temporal trends of POP in SLE beluga are influenced by several factors such as the age and sex of animals as well as the time period of their exposure. The quality and the representativeness of samples analyzed or changes in analytical methods can also affect concentrations of POP measured in beluga. In addition, regulations on the use of POP but also changes in beluga diet have affected the exposure of beluga to POP in time. The SLE carcass program has been essential in collecting samples and complementary information on beluga in order to characterize POP contamination and temporal trends in this population. Belugas should not be considered as a good bioindicator species of the decrease of POP in its habitat, but they should be considered as a sentinel species of the presence of bioaccumulative emerging POP entering its habitat.