INTRODUCTION
Environmental geochemical study related to the relationship between earth materials and human health is becoming increasingly important. For example, determining the connection between releases of hazardous substances into the environment and effects on human health can be critical in the treatment of an affected population. Such investigations are often hindered by lack of knowledge regarding the nature and origin of the dangerous material and the pathways and timing of exposure. We are engaged in a collaborative program with Chinese and U.S. earth-science and medical researchers to address the specific occurrence of arsenic poisoning and dental and skeletal fluorosis related to domestic coal combustion in southwestern Guizhou Province, China (fig.1). Domestic combustion of coal for residential heating and food preparation is pervasive in the mountainous regions of this province. Approximately 10 million people in this area are deleteriously impacted by fluorosis. Arsenic and fluorine are the principal causes of the health problems attributed to domestic coal combustion, although there may be some evidence of mercury poisoning. This work discusses and illustrates arsenic poisoning.
Figure 1. Outline map
of China showing distribution of sedimentary rock-hosted "Carlin-type" gold
deposits
(red circles). The study area is in southwesernt Guizhou Province.
The areas where we have studied endemic arsenic poisoning from domestic coal combustion are in southwestern Guizhou Province, China. In figure 1, the red circles mark locations of sedimentary rock-hosted "Carlin-type" gold deposits. The formation of these gold deposits by As, Hg, Tl, U, and Au-forming fluids enriched adjacent coal beds with similar element assemblages. It is in these Upper Permian Longtan Formation coal beds that we find the arsenic enrichment.
ARSENIC
Arsenic poisoning is endemic in some isolated farming villages located in the mountainous terrain of southwestern Guizhou Province, China. The number of individuals displaying clinical symptoms of arsenic poisoning is approximately 10,000, of which 3,000 persons have been diagnosed with more severe manifestations. A considerable body load of arsenic is attained by eating arsenic-laden foods or inhaling arsenic-rich fumes and dust. The body tries to reject the arsenic by excretion and by moving it to the extremities (for example, skin, hair, and fingernails). The subtle but visible symptoms of the beginning of this process are a reddening of the skin and skin lesions. Cutaneous changes are characteristic yet nonspecific. An initial persistent erythematous flush (fig. 2) slowly, over time, leads to melanosis, keratosis, hyperkeratosis (fig. 3), Bowen's disease (fig. 4) and, finally, basal cell and squamous cell carcinoma. The hyperkeratosis occurs on the dorsal extremities.
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Figure 2. Young woman has developed freckles (melanosis), the beginnings of arsenic-caused skin lesions. |
Figure 3. Advanced hyperkeratosis. Shown
are extensive lesions on the extremities, hands (right) and feet (left).
Note dark, probable
cancerous lesions on feet.
 |
Figure 4. An example of extensive keratosis. Dark lesion above left breast was diagnosed as Bowen's disease. |
Initial investigation by Chinese earth-science researchers at the Institute of Geochemistry, Guiyang (fig. 1), has eliminated arsenic exposure as originating from contaminated water and has focused on food ingestion as the main pathway of exposure. The study region of Guizhou Province (fig. 5) is humid in the summer and cool in the winter and requires domestic coal combustion for heating and for drying vegetables and grains stored for future use. Coal has been used for these purposes since deforestation about 50 years ago eliminated the traditional reliance on wood for fuel. The coal is obtained locally at minimal expense and burned in stoves that do not have chimneys (fig. 6). The onset of arsenic poisoning in this population is directly related to the use of coal as fuel. In order to better understand the source of the arsenic poisoning, we have focused our research on the geology, mineralogy, and chemistry of the coal used in the affected villages. Results for selected coal samples (table 1) indicate arsenic contents are as high as 35,000 ppm. In these exceptionally As-enriched samples, the arsenic appears to be organically bound (figs. 7, 8). Coals used by the affected villages typically exceed 100 ppm arsenic, whereas the average arsenic content of U.S. coal is 17 ppm. The studied coals contain various arsenic-bearing phases, and metal enrichment appears to be related to local gold deposition. In some coals (fig. 9), there is abundant evidence for post-coalification arsenic-bearing fluid flow such as fracture fillings, replacement textures, and pseudomorphs. The coals also have abnormally high contents of mercury, antimony, gold, and fluorine. The primary path of human introduction appears to be through the transfer of arsenic from smoke produced by burning coal to the foodstuffs (fig. 10) being dried over open coal stoves in chimneyless dwellings. For example, the drying process increases the arsenic content of chili peppers from background levels (<1 ppm) to an average content of 500 ppm.
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Figure 5. Typical karst terrain in southwestern Guizhou Province, China. |
Figure 6. Typical stove using coal without a chimney. Note chili peppers drying above. |
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Figure 7. Scanning electron microscope (SEM) back-scattered electron image of a polished block of arsenic-rich coal. The dark areas are coal, bright areas are minerals (mostly low-As pyrite), and milky colored areas are organically bound arsenic (arsenate). |
| Figure 8. Electron microprobe (JEOL JXA-8900) wave-length dispersive spectroscopy, x-ray map of the same view in figure 7 showing the distribution of arsenic in coal. Red areas are high concentrations, and blue areas are low concentrations. Compare the distribution of arsenic to the outline of the milky area in the SEM photomicrograph of figure 7. This coal has an arsenic content of between 3 and 3.5 wt percent on a whole-coal basis. |  |
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Figure 9. These three scanning electron microscope (SEM) back-scattered images show alteration of original arsenic-poor iron sulfide framboids (left image) to arsenic-bearing iron oxide structures. |
| Figure 10. Typical cooking area in the homes of villages in our study area. Chili peppers, a staple crop in southwestern China, characterize the regional "Sichuan-style" cuisine. |  |
| Table 1. Geochemistry of selected
Chinese coal samples from three sampling areas (Jiaole, Haizi,
and Xingyi) located in southwestern Guizhou Province,
China [All analyses on a whole coal, dry basis. As, Sb, and Au determined by instrumental neutron activation analysis. Hg determined by cold vapor atomic absorption spectroscopy. nd, not determined.] |
|||||
| As (ppm) |
Sb (ppm) |
Hg (ppm) |
Au (ppm) |
||
|---|---|---|---|---|---|
| JiaoleTownship | |||||
| RBF96-As-102 | 1695 | 73 | 15 | nd | |
| RBF96-As-103 | 2223 | 55 | 14 | nd | |
| As-d | 1591 | 132 | 45 | 569 | |
| As-e | 7931 | 165 | 8.5 | 347 | |
| J5 | 607 | 40 | 29 | 193 | |
| J10 | 405 | 29 | 2.0 | 28 | |
| JL-AS5-97A | 239 | 38 | nd | 324 | |
| Haizi Township | |||||
| RBF96-H2-105 | 35037 | 209 | 4.1 | nd | |
| RBF96-H2-106 | 33885 | 205 | 3.2 | nd | |
| H2 | 32316 | 140 | 5.8 | <130 | |
| H4 | 48 | 8 | 0.32 | 3.5 | |
| H7 | 318 | 13 | 0.48 | 6.1 | |
| H9 | 203 | 24 | 2.2 | 5.8 | |
| H10 | 124 | 9 | 0.64 | 7.1 | |
| HZ-AU7-97A | 7816 | 364 | nd | nd | |
| Xingyi City | |||||
| As-a | 5.2 | 0.4 | 0.1 | 183 | |
| As-b | 274 | 0.7 | 0.48 | 2.0 | |
| As-c | 386 | 0.5 | 0.41 | 258 | |
| G4 | 1100 | 1.6 | 0.26 | 6.4 | |
| DD-2-97A | 925 | 0.4 | nd | nd | |
SUMMARY
Diseases related to domestic coal combustion can be very difficult to separate from other factors. In China, special cultural, environmental, and geological circumstances have led to local but severely affected populations with cases of arsenosis. The incidence of arsenosis is effectively being reduced by detailed geological and geochemical analysis of local coal deposits, which has resulted in the closing of the more arsenic-rich mines. Such abatement efforts will depend on close cooperation between geoscientists and local public health officials.