Arsenic and fluorine in groundwater in northern Mexico: spatial distribution and enrichment factors

Abstract

North-central Mexico has groundwater contaminated with arsenic (As) and uoride (F). Based on the dispersion patterns of these solutes, their sources are linked to felsic volcanic rock fragments and secondary minerals (clays, iron oxyhydroxides) within the alluvium ll of the aquifers. However, little is known about the effect of the enrichment factors for F and As in this area. Natural enrichment factors include evaporation, Ca/Na, and competitive adsorption and desorption from solid phases. This study used 1,237 groundwater quality data measurements from 305 sampling sites collected between 2012 and 2019 in the state of Durango in north-central Mexico. To determine the contribution of enrichment factors to As and F content, the study area was divided into four sections, two being in the mountainous part of the state and two in the high plateaus. The data were compared among sections and analyzed using Spearman correlation and Piper and Block diagrams. The results indicate that the main solute enrichment mechanism are evaporation and weathering of silicates and evaporites. Among the four sections, As, pH, and HCO 3 seemed not to vary, F varied slightly, and nitrate and total dissolved solids varied the most. The lack of variation in As among sections is associated to its strong adsorption to clay minerals and iron oxyhydroxides, whereas the diminished F content in the eastern sections is likely linked to the adsorption of F to precipitating calcite (, since groundwater is saturated with respect to calcite ( SI calcite = 0.43) and undersaturated for uorite (SI uorite = -1.16). These processes shed light on the distribution of F and As in this area, and are likely operating in other states in northern Mexico and in semi-arid areas elsewhere.

Hydrogeochemical Characterization of an Intermontane Aquifer Contaminated with Arsenic and Fluoride via Clustering Analysis

“…Taking into account the semiarid and volcanic nature of the Valle del Guadiana aquifer, several mineral sources of fluoride can be considered since it is present in the amorphous material of rhyolites in the Sierra Madre Occidental [18]. In the Valle del Guadiana Summarizing, hydrogeochemical processes involving As and F − were grouped into four clusters (K1 to K4) based on variations in Na + , Ca 2+ , As, and F − .…”

“…In Mexico, states located in the north-central part have been identified as the most affected [11]. Several studies have been conducted at the local or regional level on fluoride distribution and health risk assessment [12][13][14][15] and the co-occurrence of both As and F − has been reported in many of these studies, concluding that this pollution has geological origins, mainly associated with the dissolution of felsic rocks and desorption from secondary minerals [16][17][18].…”

Enrichment and Temporal Trends of Groundwater Salinity in Central Mexico

“…Central Mexico is an area where water quality has been given much attention in recent years because of the high As and F concentrations in groundwater [30][31][32]. Due to the predominant semiarid climate and abundance of endorheic basins in Central Mexico, salinization of groundwater is a major concern [24,[33][34][35].…”

“…Groundwater quality studies have multiplied in the recent past due to the high concentrations of geogenic arsenic (As) and fluoride (F) present [31,32,37,40,41]. The presence of anthropogenic contaminants associated with urban centers (sewage), agriculture (excess fertilizers), and cattle grazing (manure) are expected, due to the concentration-by-evaporation effect in endorheic basins under an arid/semiarid climate.…”

“…Normal faults during Cenozoic extensional episodes formed horsts and graben structures [38]. Through time, erosion filled the grabens (basins) with rock fragments, secondary minerals, among which iron oxyhydroxides were a common component, and clays [32,33]. About half of the basins are endorheic and the rest discharge to the Pacific Ocean.…”