Hydrogeochemical controls on fluorosis in the abandoned Yellow River flooding delta, East China

Fluorosis is the most widespread and serious endemic disease in the abandoned Yellow River flooding delta of East China. Regional geochemical investigation indicates that host rocks containing F rich minerals of Archaean and Proterozoic stages are the geochemical source for the high fluoride groundwater. Over 1500 times flooding of the Abandoned Yellow River forms the flooding delta and refigures the local landform, which particularly provides favorable conditions for the fluoride accumulation in groundwater. 310 groundwater samples were collected in the central part of the flooding delta to address the chemistry of high fluoride groundwater. Test results indicate that fluoride concentration of the groundwater ranges from 0.2-6.7mg/L. 72.8% groundwater samples have fluoride above the China maximum permissible limit of 1.0mg/L for drinking water. In Heze, Feng, Pei and Tongshan Counties, groundwater with more than 6 mg/L fluoride was even observed. Local people are high exposure to naturally occurring fluoride in shallow groundwater of the abandoned Yellow River flooding delta. The groundwater in high fluoride is plotted on HCO₃-K+Na, SO₄-K+Na, HCO₃-Mg type of the Piper classification. F" in the groundwater are positively correlated with HCO₃^- and Na⁺+K⁺ and negatively correlated with Ca2+.Groundwater with F^- concentration of over 3.5 mg/L generally occurs in the alkaline environment. Activity of different fluorine complex spices was quantified using PHREEQC package. According to the calculation, MgF⁺ and CaF⁺ in the groundwater are the poisoning parameters controlling the endemic fluorosis of the abandoned Yellow River flooding delta.