South Africa's coal-mining heartland has the worst air quality in the world, according to a recent study by environmental organization Greenpeace. The 12 large coal mines in this area make it the world’s hotspot for toxic nitrogen dioxide emissions. Residents and health experts say the effects of this are ruining their health and their lives. VOA’s Anita Powell went to the coal heartland of Middelburg, South Africa, and filed this report. VOA Khmer's Sou Pichchinda narrates.