There is no correct answer for which cities have the worst pollution. The lists can be different based on what is considered a pollutant or which pollutants are considered to be worse. Water, ground, and air pollution are all bad, but depending on which ranking one looks at, some may be considered worse than others. Still, some cities in the world tend to make many of the lists. At least in these cases, there is some consensus.
One of those cities is Kabwe, Zambia. This African city known for its lead and copper mines is also known for its pollution. As the mines ran without government environmental regulation for nearly a century, the toll on the local population began to show. Even with the mines no longer in operation, children in and around the city show lead levels five to ten times the amount considered acceptable by the United States Environmental Protection Agency.
Another town that is known for contamination is that of Sumgayit, Azerbaijan. It was one of the centers for the production of pesticides and other chemicals during the height of the Soviet Union, but that came with a toll. Hundreds of thousands of tons of chemicals were released into the atmosphere as a result of the production process. Now, cancer rates in the town are one of the highest in the world.
While much of the world has heard about the pollution problem in Beijing, China, it is the Chinese city of Linfen that is on nearly every list of most polluted cities, often occupying the number one spot. Clouds of coal dust often settle over the city, making breathing difficult. That may be the least of the worries in Linfen, however, as arsenic in the drinking water may be the worst of the concerns.
In addition to being one of the coldest major population centers in the world, Norilsk, Russia, located in Siberia, is also one of the dirtiest. The city has been polluted with heavy metal smelting and mining. In fact, the city is so polluted, it is said there is not a single living tree within 30 miles (48 km). The life expectancy in the town is 10 years below the Russian average.
In North America, two of the most polluted cities are Mexico City, Mexico, and Pittsburgh, Pennsylvania. One of Mexico City's biggest problems is simply the amount of people living there. Pittsburgh's air, with the soot and heavy metals, can make for a fair amount of smog.