Record levels of contamination

The blubber and liver samples that Krishna Das, Gauthier Eppe, and Paulo Dorneles tested were collected from animals that were stranded or incidentally captured in fishing nets, according to international protocols. "For our analyses, we extracted the lipids from these samples, since the pollutants we were looking for are lipophilic,” says Krishna Das. "In order to do this, we ground the tissue and extracted the lipid phase using organic solvents. After purifying this fat fraction, we used gas chromatography and mass spectrometry techniques to separate and quantify the target molecules.” These analyses were mainly conducted at ULg and in Spain. “I remember when Paulo arrived at the Centre for Analytical Research and Technology with the samples. They were so contaminated that Gauthier Eppe and his colleagues were worried that the dolphin samples would contaminate their entire system!" And for good reason: the results showed that the samples from Guiana dolphins living in Guanabara Bay contained concentrations of PCBs that were among the highest in the world! “The Bay is connected to the Atlantic Ocean, but water renewal is very slow since the mouth is so narrow,” explains Krishna Das. “Since the water is stagnant, pollutants are not washed out to sea.” In the 1990s, there were more than 100 Guiana dolphins in Guanabara Bay. Only 40 remain today.

If these findings about marine mammals are sad and worrisome, what about the health of the 12 million men, women, and children who live on the Bay and eat its fish every day?

The need for awareness

“Guiana dolphins are the sentinels of pollution in Guanabara Bay. This type of study could bring awareness to the issue, and thus attract the attention of policymakers, and may help to bring about changes in regards to environmental protection,” says Krishna Das. In the near future, the researchers are planning to continue their study by examining contamination levels in the Bay’s fish, and study the way pollutants are exported beyond the Bay via fish movements. “We would like to quantify this flow of pollutants. We also want to better understand the Bay's food web, using stable isotopes of carbon and nitrogen. This is the subject of a parallel study whose results were just published in the journal Ecological Indicators," adds the scientist. The researchers would also like to examine the human health impact of the high levels of pollution in Guanabara Bay, in collaboration with the medical community. “People need to become aware of the problem,” insists Krishna Das. 

And finally, this Belgian-Brazilian collaboration could even give rise to a new method for examining contamination levels in marine mammals. “Brazil is a tropical country and the carcasses of stranded animals decay very quickly. It can therefore be hard to obtain good quality samples, particularly for histopathology studies, or for biomarker research,” explains Krishna Das. “But bones remain well-preserved for much longer, and pollutants tend to reduce bone density. Paulo Dorneles and his colleagues therefore decided to develop a method to quantify bone density, and to compare this density to pollutants that have already been analysed,” says the researcher.