90 Ma and Yu: Global Burden of Cancer Figure 4. Male age-specific incidence and mortality in more or less developed coun- tries, 2002. (All sites but skin: male, 2002) 2002, which was 40 mg/m3 (area breathing zone concentration) [7]. In 2002, the occu- pational standard for benzene in China was modified and significantly lowered, but the current standards (10 mg/m3 for short-term exposure limit and 6 mg/m3 for time- weighted average) are still higher than the U.S. standard [7]. Given that hematological toxicity is observed in workers with benzene exposures below the level of 1 ppm [8], the current occupational standards for benzene may still need to be reviewed and evaluated. Environmental contamination Exposure to environmental contamina- tion, such as indoor air pollution and pesti- cides, is known to increase the risk of cancer. More than half of the world’s popu- lations rely on dung, wood, crop waste, or coal to meet their most basic energy needs [9]. Cooking and heating with such solid fuels on open fires or stoves without chim- neys lead to indoor air pollution. This indoor smoke contains a range of health-damaging pollutants, including small soot or dust par- ticles, that are able to penetrate the lungs, in- creasing the risk of lung cancer and other diseases of the respiratory tract. In poorly ventilated dwellings, indoor smoke can ex- ceed acceptable levels for small particles in outdoor air 100-fold. Exposure is particu- larly high among women and children, who spend the most time near the domestic hearth. The use of polluting fuels thus poses a major burden on the health of poor fami- lies in developing countries [9]. As for pes- ticides, the global market value is estimated at $32 billion in 2000, with the share of de- veloping countries around $3 billion [10]. Around 30 percent of pesticides marketed in developing countries do not meet interna- tionally accepted quality standards, and the problem is particularly widespread in sub- Saharan Africa. These poor-quality pesti- cides frequently contain hazardous substances and impurities that already have been banned or severely restricted elsewhere and, therefore, pose a serious threat to human health and the environment [10]. Infectious agents In 2002, an estimated total of 1.9 mil- lion cancer cases, or 17.8 percent of the global cancer burden, were attributed to var- ious infections [11]. Several infectious agents are considered to be causes of cancer