There are many ways you can classify pollution. It can be chemical, radioactive, or simply the presence of improperly disposed waste products. While some places, like Mexico City, have a very obvious problem with their heavy smog, do not be misled. The much more serene looking Lake Karachay in Russia would have you dead within an hour of sitting on its banks due to heavy radioactive contamination. So, whether the pollution is visible or not, take note because these are the 25 most polluted places on Earth....

http://list25.com/the-25-most-polluted-places-on-earth/