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Dolphins, whales and human pollution

The dolphins of the Everglades National Park are less impacted by organic pollutants than their fellow creatures on the south coast of Florida. However, they are far more contaminated by mercury!

The Everglades National Park , inscribed on the UNESCO World Heritage List in 1979, was also designated a wetland of international importance in 1987. It is home to a large number of species including the common bottlenose dolphin, Tursiops truncatus (Flipper!). As a top predator, this mammal is high up in the food webs. Consequently, it has the misfortune to accumulate high concentrations of toxic pollutants in its tissues (e.g. mercury and persistent organic pollutants - POPs- such as PCBs). So what about the dolphins in Florida?

Dauphins baleines POP 

This question was the subject of international research involving the collaboration of several researchers from the University of Liège, including Krishna Das, F.R.S-FNRS senior research associate (Laboratory of Oceanology, University of Liège). These results have just been published in the journal Environmental Pollution (1) in collaboration with Florida International University (Prof. J. Kiszka) and the University of Groningen (Prof. M. Fontaine), among others. The first author of the article is France Damseaux, FNRS research fellow at the Laboratory of Oceanology, who did her master's thesis in biology on the subject. This research aimed to determine concentrations in total mercury (T-Hg) and in certain organic pollutants in the common bottlenose dolphin in South Florida. Skin and fat biopsies were performed on dolphins from the Everglades National Park and Key West (in the Keys - small islands in South Florida) in order to understand the influence of their habitat on their levels and profiles of contamination. 

As expected, the dolphins tested in the Keys have PCB concentrations that are three times greater than the dolphins tested in the Everglades National Park. The impact of pollution on the environment of the Keys is far from negligible: there is a great deal of industrial activity, atmospheric pollution, tourism, etc. The good news is, though, that these concentrations are nevertheless lower than those observed in other populations of common bottlenose dolphins in the south-east of the United States, closer to large industrial hubs. It is worth noting that various clean-up measures were also implemented in 2000 in order to protect the ecosystems of the Everglades and the Keys.

However, contrary to organic pollutants, the concentrations in total mercury in the skin were three times higher in the dolphins from the Everglades compared with the dolphins from the Keys. As far as we know, these concentrations are among the highest ever recorded in common bottlenose dolphins, and can be explained by the biogeochemistry of the Everglades' mangroves and the historical contamination of this now protected site (the mangrove contains a lot of organic matter whose bacteria absorbs and retains the mercury discharged from coal plants in particular).

(1) Spatial variation in the accumulation of POPs and mercury in bottlenose dolphins of the Lower Florida Keys and the coastal Everglades (South Florida), Damseaux F. et al. Environmental Pollution, Jan. 2017.

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