Combustion of organic matter such as firewood, charcoal, grass or dung produces biomass smoke. Biomass smoke contains variable organic and inorganic constituents some of which are known to be carcinogenic. The World Health Organisation recognised indoor household pollution as one of the top ten risks for worldwide burden of disease. Over 70% of the African population relies on biomass fuels with proportions as high as 97% in some rural settings. By contrast, the use of biomass fuel in developed countries is less than 5%. Health consequences of long-term or in many cases lifetime exposure to biomass smoke are poorly investigated. Biomass smoke exposure has been linked to several cancers sites including the mouth, nose, throat, lungs and distant locations such as the cervix. Recently, there has been growing evidence of an association between upper gastrointestinal cancers (oesophagus and stomach) and biomass smoke. Cigarette smoking has long been established as a risk factor for many of these cancers. Some of the known carcinogenic constituents of cigarette smoke such as polycyclic aromatic hydrocarbons are also present in biomass smoke. Therefore, biomass smoke could influence carcinogenesis in ways similar to cigarette smoke. Other probable mechanisms include the induction of genetic mutations and increased states of oxidative stress. There is also evidence of genetic polymorphisms that may confer increased disease susceptibility of some individuals exposed to biomass smoke. Interventions that have been suggested to try and limit exposure to biomass smoke, include use of modernised high efficiency biomass stoves and building of chimneys in houses reliant on these fuels. There is therefore, an urgent need to comprehensively understand the extent of health, economic and environmental consequences arising from use of biomass fuels. This will in turn encourage policy markers and African leaders to prioritise programmes aimed at reducing the reliance on traditional biomass fuels.

Primary prevention is key to reducing the global cancer burden, a disease responsible for ~ 9.6 million deaths per year and predicted to rise beyond 13 million by 2030. The role of environmental geochemistry - i.e. the chemical composition of Earth's surface - in the aetiology of many cancers (and other non-communicable diseases) should not be understated. This is particularly pertinent in low- and middle-income countries, where 70% of global cancer deaths occur and reliance on local geochemistry for drinking water and subsistence crops is widespread. This talk will outline the value of effective collaborations between Environmental Geochemists and Cancer Epidemiologists and how multidisciplinary approaches might yield significant breakthroughs in unravelling the aetiology of cancers in many settings. A case study of the extraordinarily high incidence rates of oesophageal cancer in the East African Rift Valley, which may have a geochemical contribution, will be discussed.