Stock Photo - A tugboat pulls a barge loaded with petroleum coke (petcoke) along the Detroit River with the skyline of the city of Detroit, Michigan, USA in the background. Detroit residents, of what is already considered 'Michigan's most polluted zip code', began noticing that their cars, homes and lungs were being coated with a black dust. The coating caused some residents to suffer chemical burns and respiratory problems. After some investigation the source of this black dust was soon traced back to large mountains of petcoke being dumped along the shoreline of the Detroit River. Petcoke, also known as petroleum coke is a by-product of tar sand oil refining and has little value in the United States but the high-sulfur, high-carbon waste is sold, usually overseas, where it is burned as fuel. - DETROIT, MICHIGAN, USA, 28/10/2014