The Occurrence of Endemic Dental and Skeletal Fluorosis from Domestic Combustion of Coal in Guizhou Province, China
Poster

INTRODUCTION

Environmental geochemical study related to the positive and negative relationships 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 American earth-science and medical researchers to address the specific occurrence of dental and skeletal fluorosis and arsenic poisoning related to domestic coal combustion in southwestern Guizhou Province, China. 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 attributed to domestic coal combustion.

FLUOROSIS

Endemic fluorosis is very prevalent in China, occurring in 29 provinces, municipalities, and various autonomous regions. The affected areas can be classified into three types according to the source of fluorine: pollution from domestic coal combustion, high fluoride groundwater, and fluorine-rich tea (brick tea). The occurrence of dental and skeletal fluorosis is much more widespread throughout China than other diseases related to earth materials such as coal-related arsenic-poisoning or selenium deficiency. Figure 1 shows the location of the prevalence of dental fluorosis caused by three factors, domestic coal combustion, fluorine-rich groundwater, and fluorine-rich tea. The location of cases of skeletal fluorosis is similar to but more restricted than the areas of dental fluorosis.

Figure 1. Map of China showing the distribution of dental fluorosis by prevalence rate by county.
[To see a higher quality PDF image, click on the figure.]

Our collaborative study in Guizhou Province concerns only fluorosis associated with domestic coal combustion. Both dental and skeletal fluorosis have been identified. Clinical symptoms range from slight to severe mottling of teeth and slight to severe osteosclerosis in skeletal fluorosis patients.

As part of a broader geochemical investigation of arsenic and trace element enrichment in Guizhou Province coals, we have analyzed coals, associated rocks, and clays for fluorine by means of the proton-induced gamma emission (PIGE) technique. Our preliminary results (fig. 2), consistent with previous studies, show that mineralized coals have fluorine contents between 150 and 2300 ppm, whereas non-mineralized coals in the region typically contain about 100 ppm F or less. It is important to point out that, throughout China, coal burned domestically is usually mixed with clay. The typical rural household mixes clay with crushed coal to form a briquette in order in control the burning intensity and duration. The local clay that we have analyzed contains about 800 ppm F, although values as high as 10,000 ppm have been reported. Figure 3 shows the relationship between potassium and fluorine in the coal and strongly suggests that fluorine substitutes for the OH group in the crystal structure of the clays.

Figure 2. Histogram showing the fluorine concentration in coals, clay, shale and briquette.

Figure 3. Scatter plot showing the good correlation between fluorine and potassium in coals from the Jiaole and Haizi areas, southwesern t Guizhou Province, China. INAA = instrumental neutron activation analysis.

ETIOLOGY

The etiology of fluorine intake by the population is related to the combustion of fluorine-rich coal (fig. 4), which converts relatively insoluble fluoride to soluble fluoride. Although the air and dust in houses that burn a fluorine-rich coal/clay mixture is contaminated, the predominant vector for human intake is ingestion of contaminated food. More work is needed to determine the relative contribution of coal and clay to the fluorine problem in various areas of China, and to map out and identify acceptable alternative fuel sources.

Figure 4. Map showing the two highest prevalence rates for dental fluorosis related to all causes and overlain onto the distribution of coal-bearing regions. One can see the excellent correspondence in the study region of Guizhou Province (red arrow). [To see a higher quality PDF image, click on the figure.]

Much of Guizhou Province is underlain by a thick sequence of carbonates producing a classic karst-weathering topography (fig. 5). The elevations between 600 and 1000 meters have a cool, damp climate during crop harvest and throughout winter. Rural populations in Guizhou Province and in similar rural provinces traditionally dry various foodstuffs in their houses over open coal fires. Coal is used primarily in open, unvented stoves for cooking, heating, and drying various vegetables (fig. 6). Corn is a minor but widespread crop in southwest China. Corn (fig. 7) is also dried over open stoves and Zheng and Huang (1989) have studied the absorption of fluorine by various foods (chili peppers, wheat, corn, and vegetables). They determined that corn preferentially absorbs fluorine from the coal smoke significantly more than the other food stuffs.

Figure 5. Typical karst terrain in the study region, southwest Guizhou Province, China.

Figure 6. Village woman sitting by a typical open coal-fired stove. Chili peppers are drying above.	Figure 7. Corn drying from the rafters of a village house.

Symptoms of the ingestion of excess fluorine in humans typically begin with dental fluorosis. This can be mild to severe mottling of the teeth (fig.8) sometimes leading to their embrittlement. Continued excess fluorine (abetted by poor nutrition) can lead to skeletal fluorosis (fig. 9). Skeletal fluorosis deformities such as hunchback and severe limb curvature and immobility have been recorded.

Figure 8. Severe mottling of teeth from excess fluorine ingestion.	Figure 9. Severe skeletal fluorosis from excess fluorine ingestion and poor nutrition.

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 (the cases of arsenic-poisoning) to more regional, widespread areas affected by dental and skeletal fluorosis. The incidence of arsenosis is effectively being reduced by detailed geological and geochemical analysis of local coal deposits and the closing of the more arsenic-rich mines. Fluorosis may prove to be more difficult to abate as fluorine enrichment in coals and admixed clays may be more widespread and complex. Such efforts will depend on the close cooperation between geoscientists and the local public health officials.

REFERENCE

Zheng, B., and Huang R., 1989, Human fluorosis and environmental geochemistry in southwest China, in Development in geoscience, Contribution to 28th International Geological Congress: Beijing, Science Press, p. 171-176.