Air pollution may up mouth cancer risk 

High levels of air pollutants especially fine particulate matter may increase the risk of developing mouth cancer. mouth cancer is increasing in many parts of the world according to the researchers including those from Asia University and Chung Shan Medical University in Taiwan. 
Known risk factors include smoking, drinking, human papillom virus, the chewing of betel quid or paan. 
Exposure to heavy metals and emissions from petrochemical plants and air pollution to be harmful to respiratory and cardiovascular health. Diagnoses of mouth cancer were then linked to local area readings for air pollutants taken in 2009. Some of the components of PM2.5 include heavy metals, as well as compounds such as polycyclic aromatic hydrocarbons known cancer causing agents.