In 2012, pollution – in the form of contaminated soil, water, and both indoor and outdoor air – was responsible for 8.4 million deaths in developing countries, finds Pollution: The Silent Killer of Millions in Poor Countries. That’s almost three times more deaths than those caused by malaria, HIV/AIDS and tuberculosis combined: Malaria claimed 600,000 lives in 2012, HIV/AIDS caused 1.5 million deaths and tuberculosis killed 900,000 individuals.