As part of a collaborative project between ULg and several Brazilian research teams, the scientists wanted to check on the dolphins in Guanabara Bay and the surrounding area. They analysed concentrations of three pollutants in three cetacean species. “We looked for the presence of PCBs (Polychlorinated biphenyls), PCDDs (polychlorinated dibenzo-p-dioxins) and PCDFs (polychlorinated dibenzofurans) in Guiana dolphins, Rough-toothed dolphins, and False killer whales," says Krishna Das. The first species lives mainly on the coast, while the other two live in more open waters. "Guiana dolphins live inside the Bay and never leave it. Although Rough-toothed dolphins live outside the Bay, individuals of the species often come inside the Bay to feed," adds Krishna Das.

The multiple harmful effects of PCBs

The three kinds of pollutants have a very similar chemical composition and were selected because they originate in industrial processes. "Even though PCBs have been banned in Brazilian production since the 1980s, many items containing PCBs are still in circulation today," explains Krishna Das. "My Brazilian colleagues speculate that there is a black market for PCBs to repair these items when they break down." PCBs were used extensively from 1930 to 1970, since they are very good electrical insulators and have excellent dielectric and heat-conducting properties. But they cause a number of health problems, which led authorities in a number of countries to ban the substance and conduct tests for concentration levels in food for humans and animals. "In general these pollutants affect the immune system, the endocrine system, the nervous system, and to top it all off they are also carcinogenic," warns Krishna Das. "In marine mammals the suspected effects are mainly immune suppression. As a result, animals contract diseases more easily, and their endocrine systems are disrupted.” Scientists believe that the high pollutant concentrations in tissues of Guiana dolphins from Guanabara Bay may be hampering the reproductive success of these animal population.

These effects have also been noticed among humans, and more and more studies have shown the impact of PCBs on metabolic and functional disorders associated with obesity.