The sources, pathway, and preventive measures for fluorosis in Zhijin County, Guizhou, China

The F content of several materials from households of Zhijin County, one of the most severe endemic fluorosis-stricken areas in western Guizhou, was determined using the pyrohydrolysis/fluoride ion-selective electrode method to determine the sources of F and the pathways causing the disease. The average F content of the coal burned is 237 μg/g, the clay used as a binder for fine coal is 2262 μg/g, with 828 μg/g in the mixed coal and clay, while the F content of corn is 1419 μg/g, with 110 μg/g in chilies. The binder clay is found to be the main F source for the endemic fluorosis. Fluorine in the clay not only occurs in apatite and hornblende, but also is associated with illite and mixed-layer clay minerals of smectite and illite. About 80% of the F is released during combustion of the mixture. The F content of corn and chilies is about 1000 and 110 times higher, respectively, than the permitted level of F in foodstuffs according to the Chinese Standard GB 4809-84. Most of the F in corn and chilies probably occurs either in smoke dusts attached to the surface or is adsorbed onto the outer peel, rather than being absorbed by the inner part. Thus, in addition to developing F-sequestration technologies, changing the living habits of the residents in the endemic area, for example, washing corn and chilies before cooking and peeling corn before being pulverized into corn flour, will remove a large proportion of the F, and thus it can play an important role in endemic fluorosis prevention.