Xuanwei and Fuyuan (E 103[degrees]35'30"-104[degrees]49'48", N 25[degrees]02'38"-26[degrees]44'50") cover around 9,300 [km.sup.2] in Yunnan province in southwest China. Xuanwei, with a population of more than 1.4 million people, was found to have unusually high female lung cancer incidence, i.e., eight times the national average for women. It has a lung cancer incidence four times higher than the national average for men as well (Mumford, He, & Chapman, 1987). Lung cancer incidence in Fuyuan, which is adjacent to Xuanwei with a population of more than 700,000 people, is also among the highest in the world (Lu, Ding, & Li, 2003) (Figure 1). Indoor polycyclic aromatic hydrocarbon emission generated by burning smoky coals in unvented households (Figure 2) has been considered the most important cause of the unusual incidence, while other possible carcinogens, e.g., specific trace metals and radon in Xuanwei and Fuyuan, have not been emphasized enough. Their pollution levels, distribution in different communities, and relation to lung cancer have not been studied before.
Many trace metals and metallic compounds are harmful to humans. The International Agency for Research on Cancer (IARC) has classified arsenic and arsenic compounds, cadmium and cadmium compounds, hexavalent chromium, and nickel compounds into Group 1 (carcinogenic to humans); inorganic lead compounds into Group 2A (probably carcinogenic to humans); and many other metals into Group 2B (possibly carcinogenic to humans) (IARC, 2006). Trace metals in water and soil can be accumulated in the human body via the food chain and then distributed to many organs, e.g., liver, kidneys, and lungs by the circulation system, and impact these organs negatively. Trace metals in soil are a significant source of those in air particles, which can be easily transported deep into the respiratory system and become an important cause of lung cancer.
Radon was classified as a Group 1 carcinogen (carcinogenic to humans) in 1987 (IARC, 2006). The isotope (222) radon in the atmosphere decays into (218) polonium and (214) polonium that can emit radioactive [alpha]-rays, damage people's respiratory epithelia, and finally lead to lung cancer (Henderson, 1989). Li and co-authors also reported the incidences in Fuyuan were remarkably correlated with the types of local coal used (Li, Tang, & Yin, 2004). The difference in composition of coal in the two communities might be an important cause of different lung cancer incidence. Considering the high lung cancer incidence in Xuanwei and Fuyuan, a survey on radon levels in air and hazardous metal concentrations in soil, water, and coal was performed in our study. Our study will be helpful for a future detailed environmental survey and in exploring the relationship of these substances to lung cancer. To the best of our knowledge, no previous studies have determined the concentrations and distributions of these substances except radon in air in Xuanwei by Deng and co-authors (2001).
Water and soil samples at 25 sites were collected. Most sites were chosen in communities with high lung cancer incidence to evaluate the current situation of hazardous elements pollution as shown in Figure 1 and the previous study in our lab (Lu et al., 2009). Wude and Diandong, which have the lowest lung cancer incidence and where wood is used as fuel and no industrial pollution sources are nearby, were chosen as reference sites in Xuanwei and Fuyuan, respectively. Sites of radon and mercury in indoor and outdoor air are listed in Table 1. Sites of coal samples were located according to He and co-authors (2012). A total of 18 and 14 coal samples were collected in Xuanwei and Fuyuan, respectively, which represented all four and six coal types, eight and seven main mining regions, and were supplied as main fuel for 14 and 9 communes in the two counties, respectively. Well water is the main drinking water source for the local residents, so all the water samples were collected from wells except Kuaize River. About 1-L water samples were collected using polyethylene (PE) bottles at the surface (0-20 cm) and stored in darkness before transporting and frozen in laboratory. Soil samples (0-10 cm soil layer) were collected from different locations. Each soil sample (about 2 kg) collected with a stainless steel scoop was composed of 20-30 soil samples at different locations in an area of about 10 m x 10 m. Samples were packed in PE bags and transported to the laboratory where they were air dried at room temperature, ground, sieved through a 2 mm sieve, and stored at -20[degrees]C before analysis. Coal samples were all collected directly from mines according to the local lifestyle except for Ayicun, a site with very high lung cancer incidence, where coal samples were collected from local farmers' homes. About 5 kg of coal composed of samples the size of 1-30 [cm.sup.3] were collected in PE bags, transported to the laboratory, ground until all passed through a 75-[micro]m sieve, and prepared for use.
Radon in air was monitored by RCM-2 online radon analyzer. Mercury in air was monitored by Lumex RA-915+. Both elements were monitored for two or three hours, and we acquired the hourly average concentration. RCM-2 online radon analyzer could monitor radon in air ranging from 1 to 9,999 Bequerels per cubic meter (Bq/[m.sup.3]) with a detection limit of 0.7 cph/Bq/[m.sup.3]. The error should be less than 2% in a working period of 200 hours. The detection limit of mercury in air by Lumex RA-915+ was 0.3 ng/[m.sup.3]. The acquired data were averaged every hour.
Element analysis in water was carried out by direct...