Comparison of Aquifer Sediment Fluoride Levels and FTIR Characteristics in Seawater Intrusion Area and Soil Salinization Areas along Coastal Plains in Shandong Province, China

Seawater intrusion and soil salinization, the most common environmental problems along coastal plains, both result in high levels of pH, Na + and low level of Ca 2+ , which favors sediment fluoride-leaching. But interestingly, groundwater in soil salinization area has lower fluorine levels than that in seawater intrusion area although it is more intruded. A seawater intrusion area (Buzhuang Town) and a soil salinization area (Kenli District) were selected along Laizhou Bay, Shandong Province. The sediment fluoride levels and FTIR characteristics were determined to reveal the differences of fluoride evolution in the two areas. The sediment fluoride levels in the two areas are within the safe limit. However, fluoride levels in aquifer sediments in Buzhuang Town (130–272 mg/kg) are extraordinarily lower than those in Kenli District (554–609.8 mg/kg), although Buzhuang Town is characterized by drinking-water fluorosis and Kenli District is not. This indicates Buzhang Town has stronger fluoride leaching-ability in the aquifer sediments than Kenli District, which is the important cause for the high-fluorine groundwater in Buzhuang Town. The sediments in Kenli District have higher intensities of OM (organic matter), OH – and CaCO 3 bands than those in Buzhuang Town. The stronger adsorption of OM to F – lowers sediment fluoride-leaching in Kenli District. The more mixture of seawater in Kenli District causes the higher sediment OH – , and the F-O exchange contributes more to fluoride-leaching than OH–F exchange. Moreover, the higher Ca 2+ in Kenli District restricts fluoride-leaching and causes higher sediment CaCO 3 bands, which is the important factor influencing sediment fluoride-leaching. While the extraordinarily increasing Na + levels in Kenli District contribute less to fluoride-leaching when the fluoride-leaching is restricted by Ca 2+ levels. A model of FTIR evolution in aquifer sediments with the effect of seawater intrusion is forwarded, which is significant for fluorosis along coastal plains.