Too many highly toxic chemicals and heavy metals are emitted by many large corporations. The health effects from these chemicals are very dangerous and are also associated with cancer. This category also includes automobiles, motorcycles, buses and truck smog which is very toxic and contains hundreds of toxic chemicals highly associated with poor health and cancer. Another HUGE contributor are oil refineries, wood processing plants, chemical plants and most industrial plants, coal-fired power generation, as well as coal mining in general.