Xuanwei City and Fuyuan County of the Yunnan Province in south-west China are located in late Permian coal-accumulating areas. Both regions are rich in coal resources and have many coal mines. In the 1970s, epidemiologic studies demonstrated that lung cancer rates in Xuanwei were 4-5 times higher than the average in China [
1,
2]. The characteristics of these lung cancer incidences in the populations of Xuanwei and Fuyuan were described in previous studies. First, more women in Xuanwei and Fuyuan suffered from lung cancer, in comparison to other areas. The male-to-female ratio of lung cancer incidences in Xuanwei was 1.09∶1. However, almost all of these women did not smoke. In contrast, the male-to-female ratios of lung cancer incidences in China and the United States were 2.07∶1 and 1.8∶1, respectively [
3]. Second, the major type of lung cancer in women in Xuanwei and Fuyuan was adenocarcinoma [
4]. Third, the rural population suffered from lung cancer more than the urban population [
3]. Previous studies demonstrated that indoor air pollution caused by burning “smoky coal” in non-vented indoor fire pits was the main reason for lung cancer in Xuanwei [
5-
7]. Burning “smoky coal” releases cancer-causing substances such as polycyclic aromatic hydrocarbons [
8]. Animal experiments confirmed that the combustion products from burning “smoky coal” were more tumorigenic than those from wood and smokeless coal [
9]. In the 1970s, the local government and the Science and Technology Department of the Yunnan Province encouraged and supported the residents of Xuanwei and Fuyuan to modify their fire pits into stoves with chimneys. In the late 1980s, the stove improvement project was completed, and the levels of indoor air pollution as well as lung cancer incidences subsequently decreased [
10,
11].
However, the indoor air pollution was not able to fully explain the current characteristics of lung cancer in Xuanwei and Fuyuan. The total morbidity and mortality rates from lung cancer did not decrease even after the region-wide household stove improvement. Both rates increased in some towns and villages after the first decade. From 2002 to 2005, the total mortality from lung cancer in Xuanwei was still very high, and the lung cancer rate was 3.3 times higher than elsewhere [
12-
15]. Therefore, the reason for the unabated high incidence of lung cancer in Xuanwei and Fuyuan must be determined. We hypothesize that despite the elimination of indoor air pollution, industrial developments heightened the outdoor air pollution level. Consequently, the lung cancer rate increased. This hypothesis is supported by the following observations.
First, in Xuanwei, coal production and other coal-using industries (e.g., coal coking and thermal power generation) are very important. These industries very rapidly developed. Indeed, coal production, coal coking, and thermal power generation increased more than 5, 10, and 10 times, respectively, over the past 30 years. Within the same period, the mortality rate from lung cancer also increased 4 times (Fig. 1) [
12-
15]. This direct correlation has prompted us to examine some waste gas samples from facilities in Xuanwei. These findings reveal that the exhaust gases contain a high concentration of arsenic, hydrogen fluoride, hydrogen sulphide, phosphorus, and coal tar.
Second, the morbidity from lung cancer varies significantly in the different regions of Xuanwei and Fuyuan. Higher rates of lung cancer were associated with some industrial facilities, such as coking and metal smelting [
16]. In several towns and villages close to coal mines and coal industrial parks, higher rates of lung cancer were also observed. The pollution caused by these coal industries mainly involved smoke from coal burning, coal dust from coal mining and transportation, ash from weathered coal gangues, as well as ash from coal cinders. The following scenarios illustrate the relationship between coal-burning induced pollution and lung cancer.
In Laibin Town in Xuanwei, the morbidity and mortality rates of lung cancer were the highest in Xuanwei. Laibin is one of the most important coal-production and coal industry areas. The outdoor air pollution caused by the coal-burning smoke, coal dust, as well as weathered coal gangue and cinder ashes was also immense (unpublished data). In Huashan Town in Xuanwei, where there are several large chemical plants and coking plants, the morbidity from lung cancer was also high (unpublished data). In Fuyuan, the morbidity from lung cancer was 3.3 times above the average in China in 2002-2004. Within this period, the morbidity was also higher than that in the 1970s. Additionally, the morbidity in the north villages was higher than that in the south villages [
17], possibly because of the numerous small coke-ovens used in the north villages in the 1980s (Fig. 2). Coal-burning smoke, containing coal tar with cancer-causing substances (e.g., polycyclic aromatic hydrocarbons) was largely released from the coke ovens into the atmosphere. In fact, the outdoor air pollution in the northern villages near coke plants was very serious. Lastly, in the Gaojiacun and Xingcun coal mines in the Dongshan Town of Qujing City, the incidences of lung cancer were 3.8‰ and 4.5‰, respectively, in 2008. These rates were several times higher than those in other non-mining regions. Dongshan is close to Fuyuan, and the situations are similar for both locations. The outdoor air pollution caused by the coal-burning smoke, coal dust, as well as weathered coal gangue and cinder ashes was serious (unpublished data).
Third, the morbidity of lung cancer in the north-east part of Xuanwei was higher than that in the south-west part. Some industrial facilities such as the thermal power plant are distributed in south-west Xuanwei. Xuanwei is located in a mountain valley (Fig. 3), wherein wind moves from south-west to north-east in most cases. Therefore, the downwind areas (north-east part of Xuanwei) have more intense air pollution and higher morbidity rates of lung cancer than the upwind areas (south-west part of Xuanwei) (unpublished data).
Fourth and last, a very recent study demonstrated that lung cancer rates proportionally increased with the amount of smoky coal burning, but were not associated with smokeless coal combustion [
16]. As aforementioned, burning smoky coal produces more carcinogens and leads to more serious air pollution. In Xuanwei and Fuyuan, the concentrations of benzo(a)pyrene (the best index for PAH carcinogenicity) in both indoor and outdoor air were higher than the national criterion for China [
18]. Hence, the indoor and outdoor pollution resulting from “smoky coal” burning is the evident cause of the high incidences of lung cancer in Xuanwei and Fuyuan.
Taken together, the increased rates of lung cancer in Xuanwei and Fuyuan are closely associated with environmental pollution. Interestingly, “lung cancer families” (more than three lung cancer patients in one family) frequently occurred in both areas. In a village in Fuyuan, one extreme example was a family comprising 13 people with lung cancer, wherein 11 died of the disease. We believe that several factors, such as the same living environment, the same lifestyle, and genetic factors may be associated with this special phenomenon. A current study demonstrated that the use of late Permian C1 coal and the cumulative exposure to nanoquartz were associated with an elevated risk of lung cancer in these regions [
19]. The effect of smoking on lung cancer risk becomes considerably stronger after chimney installation in Xuanwei [
20]. Several studies suggested that tuberculosis and food contamination by environmental polycyclic aromatic hydrocarbons may be risk factors for lung cancer in Xuanwei [
21,
22]. Indeed, the causes of lung cancer in Xuanwei and Fuyuan are complex. Multiple parameters (e.g., indoor and outdoor air pollution levels, genetic defects, etc.) and their interactions among one another should be systematically studied.
Regarding the outdoor air pollution in Xuanwei and Fuyuan, many improvements were realized in recent years. The local government adopted measures to improve coke manufacture, and a number of small coke ovens in Fuyuan were closed. In some large plants in Xuanwei, exhaust gases were purified, thereby decreasing the contents of arsenic and coal tar in the waste gas. In some coal mines, the amounts of coal dust as well as weathered coal gangue and cinder ashes decreased. After these measures were enacted, the outdoor air pollution was controlled to some extent. However, there is still much to do in order to completely repress the high incidences of lung cancer in Xuanwei and Fuyuan.
In summary, environmental pollution (outdoor, indoor, and workplace) is the most important factor in the development of lung cancer in the residents of Xuanwei and Fuyuan. Nowadays outdoor air pollution caused by industrial activities may be becoming the primary contributor to lung cancer in these regions. Certainly, the current study is a pilot survey and the present data are limited. Further investigation should be performed to permit final conclusions. However, the effect of outdoor air pollution on lung cancer risk should be closely examined. In addition, the cases of lung cancer in the populations of Xuanwei and Fuyuan are very good models for research, especially for studying the relationship between environmental factors and this fatal disease.
Higher Education Press and Springer-Verlag Berlin Heidelberg
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