For residents of several towns in Siberia, it is not uncommon to find their streets and rooftops covered in eerie black snow during the winter months.

The towns are located in the region of Kuzzbass, home to one of the world’s largest coal fields. According to The Guardian, the snow is coated with toxic black coal dust released into the air from open coal pits, owing to lack of proper maintenance of the nearby factories.

This year too, videos and pictures from the Kemerovo area showed jet-black flakes falling from the skies and tainting the landscape.

According to environmental activists, the dust coating the snow contains toxic metals, including arsenic and mercury. It has also had negative consequences on the region’s population, with life expectancy being three to four years lower than Russia’s national average. Tuberculosis, cancer and cerebral palsy rates are also above the national average in Kuzzbass.

Vladimir Slivyak, a member of the non-profit environmental action group Ecodefense said it is harder to find white snow than black snow during the winter. “There is a lot of coal dust in the air all the time,” he said. “When snow falls, it just becomes visible. You can’t see it the rest of the year, but it is still there.”