The use of the fungicide Hexachlorobenzene has been prohibited since 2004. However, the substance is persistent and it accumulates in Polar Regions where, among other things, humpback whales restore their annual fat reserves. Recent studies on humpback whale cells conducted by the Swiss Federal Institute of Aquatic Science and Technology EAWAG, show that Hexachlorobenzene might not be acutely toxic; it can however directly harm the genetic make-up. Hexachlorobenzene (HCB) was mostly used as fungicide and belongs to the first twelve substances, whose usage was banned worldwide by the Stockholm Convention on Persistent Organic Pollutants (POPs) in 2004. Due to the fact that the chemical compound is highly persistent it only decomposes very slowly in the environment.

HCB is not only persistent, but under certain circumstances it can be volatile as well. It can enter the air and be transported to other places. This is especially the case in tropical or moderate zones, whereas in regions with rain or snow, HCB falls back to earth. Because of this so-called “Grasshopper effect” HCB reaches the Polar Regions as well. As the poles are cold, the pollutant HCB remains there and enriches itself in the environment. And it is exactly there, in the waters of the Arctic and Antarctic, where the summer quarters of the humpback whales are located.