Fluoride in groundwater in the north-central region of Mexico and its possible origin

The highest concentrations of fluoride (F-) in groundwater in Mexico occurs in mainly two areas: arid zones in the north-central part of the country and in regions containing hot springs. The former is the drinking water source for a large number of people, and it is the focus of this study. A database containing 1117 data (2017-2019) was used to investigate the origin of this contaminant and its association to arsenic (As) content as well as several physical and chemical parameters reported as potential enrichment factors. The higher abundance of felsic volcanic rocks in the alluvial fill, their distribution and high F content, point to these rocks as the main source of this contaminant. The concentration of F- varied between 0.03 and 27.9 mg/L, with 52, 45 and 36 % of samples above the 1.5 mg/L guideline established by the NOM-127, for the states of Zacatecas, Chihuahua and Durango, respectively. Significant correlation was found between F- and As in all three states; the highest correlation was obtained in Zacatecas (r = 0.801, p < 0.01). No correlation was found between F- and temperature, F- and total dissolved solids, and F- and Ca/Na. The high content of F- and its co-occurrence with As makes imperative the application of a strategic plan to protect public health in this region through the implementation of water treatment on wells with high content of this element.