Fluorine pollution in a sheep fluorosis area of the northern Helan Mountains, Ningxia, China

The relationship between endemic sheep fluorosis and coal mining and combustion in Helan Mountain, Ningxia, China, is lacking clear research and understanding. A total of 137 samples of topsoil and grass were collected in this area and fluorine, sulfate, and pH levels were determined. The mean fluorine content in topsoil is 707 ± 126 μg g−1 (n = 77), which is significantly higher than that of standard Chinese topsoil. The mean fluorine content of pasture is 218 ± 42 μg g−1 (n = 28), which suggests that sheep fluorosis may be associated with high fluorine levels in topsoil and pasture. Sulfate content in topsoil is 1771 ± 130 μg g−1 (n = 77) and pH is 5.92 ± 0.82. The pH and sulfate content of acidic topsoil are positively correlated (r = 0.72), which implies that the acidity may be due to the presence of acidic sulfates, such as NaHSO4 or KHSO4. High fluorine, sulfate, and acidity may be connected with the long history of coal mining, coal use, and coal combustion, where deposition of fluoride results in coexistence with acidic sulfate.