Examining the Correlational Interaction of Environmental Fluoride and Selenium and Its Impact on Dental Fluorosis in Coal-Burning Regions of Southwest China

Epidemiological and geochemical evidence suggests that coal-burning fluorosis in Southwest China is mechanistically linked to the presence of fluoride-rich geochemical anomalies. However, the severity of dental fluorosis does not consistently align with the distribution pattern of fluoride geochemistry, suggesting that other factors may interfere with the dose-effect relationship of fluorosis. To investigate the potential biotoxicity impacts of fluoride, this study conducted an analysis of soil fluoride-selenium spatial correlation in the central areas of coal-burning fluorosis in China. The results revealed that 59.1% of soil fluoride contents were more than the average soil fluoride content of China (800 mg·kg^-1) and 77.9% of soil selenium contents were above 0.45 mg·kg^-1. Soil fluoride (1.11 × 10³ mg·kg^-1) and selenium contents (0.78 mg·kg^-1) were significantly high states, but agricultural products and drinking water sources showed relatively low levels, not significantly influenced by soil conditions. The severity of fluorosis was evaluated using Dean's dental fluorosis index (DFI). The spatial association of soil selenium or fluoride with DFI suggested that there was a reverse relationship between soil selenium or selenium/fluoride and the DFI. The generalized additive model (GAM) showed the onset of DFI correlated with soil fluoride content, showcasing a distinctive "W" pattern, while DFI decreased steeply or gradually as soil selenium content or selenium/fluoride ratio increased. In conclusion, our findings suggest that the geochemical anomaly of soil fluoride likely contributes to the occurrence of fluorosis. However, the significantly elevated levels of soil selenium might alleviate the severity of dental fluorosis to some extent.