In Guanabara Bay in Southeastern Brazil, Guiana dolphins are highly contaminated by PCBs. Tissue samples taken from the cetaceans showed PCB concentrations that are among the highest in the world, according to a study conducted by researchers from Brazil and Liège who were concerned about the health of Guanabara Bay’s 12 millions residents.

Known for its beaches, sun, music, carnival, and tropical forests, Brazil is a major tourist attraction. But while Europeans still see Brazil as a land of unspoilt nature, this emerging nation has actually undergone extensive industrial development. And industrialisation unfortunately brings its share of pollution. The South-eastern part of Brazil has been particularly affected. This is where the city of Rio de Janeiro is located, on the shores of the great Guanabara Bay. The Bay stretches inland 30 kilometres from the coast and is almost as wide, with 150 km of beaches and a 1 km-wide mouth. Within the Bay there are no less than 130 islands, which contribute to its image as paradise on earth.

But appearances can be deceiving, for Guanabara Bay is far from idyllic given its high pollution levels. The small population of Guiana dolphins (Sotalia guianensis) that live in the Bay are suffering the consequences. These were the findings of researchers Krishna Das (The University of Liège’s Oceanography Laboratory), Gauthier Eppe (CART – the University of Liège’s Centre for Analytical Research and Technology), and Paulo Dorneles (Université Fédérale de Rio de Janeiro and a Visiting Professor at ULg in January 2014) in an article that will soon be published - and is already available online  - in the journal Science of The Total Environment (1).

Marine mammals, victims of bioMAGNIFICATION

"All of the land-based contaminants resulting from industrialisation in the region can be found in the marine environment," explains Krishna Das, a FRS-FNRS Research Associate at the University of Liège’s Oceanography Laboratory – MARE Research Centre. "Cetaceans are at the top of the food chain and thus accumulate all these contaminants," the scientist explains. In fact, the higher up you go in the food chain, the more toxic substances are consumed and stored. This is called biomagnification. For example, if an planktonic organism ingests one unit of a toxic substance, a small fish that eats 10 of these organisms absorbs 10 units of this toxic substance. And when the biggest fish eats 10 of these little fish, it accumulates 100 units of toxic substances, and so on. Since cetaceans are at the top of the marine food web, they are particularly affected by this problem.

(1)  Dorneles PR, Sanz P, Eppe G, Azevedo AF, Bertozzi CP, Martínez MA, Secchi ER, Barbosa LA, Cremer M, Alonso MB, Torres JP, Lailson-Brito J, Malm O, Eljarrat E, Barceló D, Das K. High accumulation of PCDD, PCDF, and PCB congeners in marine mammals from Brazil: A serious PCB problem. Science of The Total Environment. Volumes 463–464, 1 October 2013, Pages 309–318