The combustion of coal releases precursor elements which form into ground-level ozone and acid rain, especially if the coal is not cleaned before combustion. An estimated 3 million people die each year as a consequence of outdoor air pollution from particulates, with major contributions from coal and biomass burning. Oil spills during transport at sea harms marine life; when oil ignites instead toxic gases are released to the atmosphere. Around 10% of global water use goes to energy production, mainly for cooling thermal energy plants. In already dry regions, this contributes to water scarcity. Bioenergy production, coal mining and processing and oil extraction also require large amounts of water.