Carcinogenicity of household solid fuel combustion and of high-temperature frying

Abstract

In October, 2006, 19 scientists from eight countries met at the International Agency for Research on Cancer (IARC) in Lyon, France, to assess the carcinogenicity of household solid fuel combustion (coal and biomass) and of high-temperature frying. These assessments will be published as volume 95 of the IARC Monographs. About half of the world’s population, mostly in low-resource and mediumresource coun tries, use solid fuels for cooking or heating, often in poorly ventilated spaces. WHO identifi ed in door smoke from combustion of solid fuels as one of the top ten risks for worldwide burden of disease. Products of incomplete combustion contain respirable (coarse, fi ne, and ultrafi ne) particles and many volatile and nonvolatile organic compounds, including carcinogens such as benzo[a]pyrene, formaldehyde, and benzene. Average indoor concen trations of particulate matter (<10 μm) can be as high as several milligrams per cubic metre, with peak concentrations an order of magnitude higher. Women and young children who are at home for most of the day are most highly exposed. Although occupational exposure to the combustion products of coal by inhalation is known to cause lung cancer, many studies, mostly from China, now show similar eff ects from household use of coal. The problem was fi rst noted in the county of Xuan Wei, China, where the type of coal used produces especially smoky emissions. Two case–control studies from Xuan Wei reported a positive exposure– response relationship between the amount of coal used and the risk of lung cancer. Subsequently, a cohort intervention study showed transition to the use of a stove with a chimney from one without reduced this risk. A large study in Shenyang, China, noted positive exposure–response associations for diff erent measures of exposure to coal smoke—including a cumulative index of indoor exposure— after adjust ing for smoking and education. Furthermore, a study of non-smoking women in Harbin, China, reported a strong exposure–response relationship between years of use of a coal stove and lung cancer. Case– control studies from Taiwan and the USA have also reported a twofoldincreased risk for lung cancer as a result of coal-smoke inhalation after adjusting for potential confounders. In experiments with animals, inhalation of emissions from coal, burned under conditions similar to those in Xuan Wei, increased the incidence of various types of malignant lung tumours in male and female Kunming mice and of squamous-cell carcinomas in male and female Wistar rats. In another study, the incidence of adenocarcinoma of the lung was increased in male and female Kunming mice exposed to combustion emissions of coal obtained from Harbin. On the basis of suffi cient evidence in both humans and experimental animals, the Working Group concluded that indoor emissions from household combustion of coal are “carcinogenic to humans (Group 1)”. Mechanistic data from studies of humans and animals are consistent with this conclusion. Biomass fuel is much more widely used than coal but the adverse health eff ects have been studied less. In Taiwan, women who burned wood for cooking had a threefold increase in the risk of lung cancer after adjusting for potential confounders. Additionally, a large multicentre European case– control study recorded an adjusted 20–30% increased risk of lung cancer in people who burned wood but not coal, compared with people who never used coal or wood for cooking or heating. Studies in Japan and Mexico also found an increased risk of lung cancer in non-smoking women, which was related to their exposure to smoke from wood or straw. These studies suggest that exposure to smoke from wood combustion is associated with an increased risk of lung cancer; however, the results on exposure duration and intensity are diffi cult to interpret. In animal experiments, exposure to emissions from wood, burned under conditions similar to those in Xuan Wei, increased the incidence of lung adenocarcinomas in male and female Kunming mice, but not in Wistar rats. Extracts from wood smoke, applied to the skin or given subcutaneously, produced cancer in mice and rats. Combustion emissions from wood are mutagenic because of the presence of compounds from various chemical classes, including polycyclic aromatic hydrocarbons and acidic or polar substances. Molecular data, which include changes in expression and phosphorylation of P53 in patients with lung cancer who were exposed to wood smoke, and systemic genotoxicity in charcoal workers and in women who burn cow dung or wood, supports evidence of carcinogenicity of emissions from burning wood. On the basis of limited evidence of carcinogenicity of biomass combustion emissions (mainly from wood) in humans and experimental animals; suffi cient evidence of carcino genicity of wood-smoke extracts in experimental animals; and strong evidence of mutagenicity, Upcoming meetings