The groundwater characteristics in two areas, Tushan town (TS) in Laizhou County and Puzhuang town (PZ) in Changyi County, were compared to discuss the dynamics of fluorine enrichment. Groundwater has average fluorine levels of 2.33 mg/L in PZ town ranging from 0.65 to 9.87 mg/L and of 0.91 mg/L ranging from 0.27 to 1.25 mg/L in TS town. The geochemical indexes indicate seawater intrusion in the both areas, the more serious seawater intrusion in PZ town causes the higher pH, electrical conductivity (EC), total dissolved solids (TDS), HCO3− and Na+ than TS town, which can accelerate fluorine leach ability from rock/soil and result in higher fluorine than in TS town. So, the seawater intrusion is related to groundwater fluorine levels. Moreover, the groundwater shows the contrary process of cation exchange. That is, the exchange of Na+ to Ca2+ in TS town occurs and that of Ca2+ to Na+ occurs in PZ town during seawater intrusion. As a result, PZ town has relatively higher Na+ and lower Ca2+ than TS town, and the groundwater types transform from Ca-Cl type in TS town to Na-Cl type in PZ town with the ongoing seawater intrusion. Such a process decreases fluorine solubility in groundwater and contributes to lower fluorine levels in TS town. Therefore, the seawater intrusion and the special cation exchange explain well the different fluorine levels in the two areas, which should be considered when the fluorine enrichment is discussed in coastal regions.
Seawater intrusion and drinking-water fluorosis are frequently documented along coastal plains. Groundwater is characterized by high OH−, Na+, total dissolved solids, and low Ca2+ because of seawater intrusion, and such conditions favor sediment fluoride-leaching and fluorosis. But the geological process of seawater intrusion has not been noticed when high-fluoride groundwater along coastal areas is discussed. The groundwater and sediments in a typical seawater intrusion and fluorosis area are gained, and fluoride-leaching simulation experiments are performed. Sediment fluoride levels are equal to or lower than average sediment fluoride levels in China and Shandong province, but strong fluoride-leaching in aquifers is observed. Compared with the supplied water from the non-intruded neighboring area, the local groundwater has higher fluoride levels, together with higher pH, total dissolved solids, HCO3−, Cl−, Br−, SO42−, Na+, K+, and low Ca2+ because of seawater intrusion. Aquifer sediment fluoride-leaching ability increases with an increase in seawater (brine water) mixing ratios, and NaCl or NaHCO3 levels, but with a decrease in CaCl2 levels. This directly confirms that seawater (brine water) intrusion promotes sediment fluoride-leaching, and the high pH, Na+, HCO3−, and low Ca2+ levels caused by seawater intrusion are responsible for the high-fluoride groundwater along coastal plains.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.