Environment and Health
Report for Medical Geology Newsletter
Report on the international workshop on the link between Upper Permian Coal and an exceptionally high incidence of lung cancer in Xuan Wei, Yunnan Province China.
Linwei Tian¹, David Large², Shona Kelly³, Longyi Shao´
Chinese health officials report that parts of Xuan Wei County (pop. 1.2 million), Yunnan Province, China have the highest known lung cancer mortality in non-smoking women (Figure 1). Peak lung cancer mortality in women in Xuan Wei reaches 400/105 up to 20 times mortality levels in the rest of China. This high mortality displays a clear spatial relationship to the mines producing coal from the uppermost Permian (C1) coal seam.
The exceptional lung cancer mortality rate has, for many years, been attributed to high concentrations of PAH’s produced during domestic coal combustion (Mumford et al, 1987). But the association between PAH levels in the smoke produced by the coal and cancer mortality is very weak and other etiologic factors have been sought. In particular, mineralogical analysis (Tian, 2005) has demonstrated that the concentration of fine grained (<1µm) silica in the coal correlates with the incidence of lung cancer.
In Xuan Wei coal is utilised for domestic cooking and heating which introduces both ash and volatiles into the home environment. Over the past two decades excellent measures have been taken to improve living standards in Xuan Wei and provide better ventilation in dwellings; however, the lung cancer mortality rate shows no sign of diminishing (Ning, 2001). In turn, this is hampering development in a region that, like most of China, is dependant on coal as the primary energy source.
Figure 1 Lung cancer mortality rate of women (age-adjusted to the 1964 population of China) in China showing the exceptionally high rates in Xuan Wei County. The map was produced by combining the 1990 administrative map (CASM and CIESIN, 1990) with 1973-1975 lung cancer map (National Cancer Prevention Office, 1980).
Many areas of China use coal in a similar way in unventilated domestic environments without the elevated incidence of lung cancer seen in Xuan Wei. So, many questions remain unanswered. Is it possible to demonstrate that some unique aspect of the coal chemistry is causing the lung cancer? What causes local variations in the lung cancer mortality rate? Are other local factors influencing the lung cancer epidemic? Why is the mortality rate in women so high? Are there tasks that women engage in that are rarely completed by men?
To determine the feasibility of collecting the information needed to investigate whether the increased risk for lung cancer in Xuan Wei was related to some constituent of the coal an international workshop was held from 23-28th Nov 2007 in Kunming and Xuan Wei with the assistance of the Yunnan Province Coal Geology Prospecting Institute. This workshop funded by the Royal Society, through the UK Office of Science and Innovation budget, involved cancer specialists, epidemiologists, fuel scientists, geochemists, geologists and medical geologists from China, the UK and the USA.
During two days of presentations the participants discussed medical, epidemiological and geological issues pertaining to the lung cancer epidemic. This highlighted a range of interesting and unresolved issues.
- Geological factors that may make this coal unique were debated. The C1 coal occurs at the very end of the Permian with the Permo-Triassic boundary occurring at the top of the coal seam. This creates the fascinating prospect that the environmental changes that resulted in the P-T boundary extinction event, the largest extinction event of the Phanerozoic, may have produced uniquely toxic coal chemistry. Many of the proposed causes of the end Permian extinction could have produced distinct coal chemistry. In particular atmospheric deposition related to massive volcanism and impact events.
- Pathology and toxicology research to establish a link between mineral matter in the coal ash and the lung cancer needs to be conducted.
- The spatial distribution of pneumoconioses (obstructive lung diseases) that may indicate mineral matter damage to the lungs has not been studied in detail.
- A wide range of epidemiological data that examines not only the coal combustion volatiles but also exposure to the ash still needs to be established.
- Patterns of fuel use need evaluating and a means of source apportionment is required to assess exposure. A possible option for doing this is isotopic source apportionment.
- Details of the silica mineralogy of coal remain unresolved and testing the link to lung cancer requires larger sample numbers and better spatial data.
- The possible influence of the trace elements in the coal was considered, particularly the potential for transition metals to cause DNA damage.
After the presentations two days were spent undertaking fieldwork in Xuan Wei. The purpose of this was to obtain sufficient preliminary data to form the basis for funding applications and to help us address some of the unanswered questions. Local women were interviewed, samples of ash and coal collected from high cancer districts and control (low cancer) districts, patterns of fuel utilisation observed and systematic coal samples collected from both exposures and mines
On the final day of the workshop a meeting was held to outline an integrated program of research. The consensus from the workshop was that the cause of the lung cancer epidemic could only be addressed via a partnership integrating both medical and geological expertise under the umbrella of medical geology.
References
- CASM and CIESIN (1990). County level boundaries of China, http://www.umich.edu/~iinet/chinadata/data2.htm accessed December 1999.
- Mumford, J. L.; He, X. Z.; Chapman, R. S.; Cao, S. R.; Harris, D. B.; Li, X. M.; Xian, Y. L.; Jiang, W. Z.; Xu, C. W.; Chuang, J. C.; Wilson, W. E.; Cooke, M. (1987) Lung Cancer and Indoor Air-Pollution in Xuan-Wei, China. Science, 235, 217-220.
- Ning, B. F. (2001) Lung cancer mortality rate in Xuan Wei, 1990-1992. Chinese Journal of Cancer Control and Treatment, 8 (Suppl.), 178-180.
- National Cancer Prevention Office (1980). Data Records of the Cancer mortality survey of China in 1973-1975. The People's Health Publishing House: Beijing.
- Tian, L. W. (2005) Coal Combustion Emissions and Lung Cancer in Xuan Wei, China (PhD dissertation); University of California: Berkeley, California.