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Groundwater is the main source of drinking water supply in most urban environments around the world. The content of potentially toxic elements is increasing in many groundwater systems owing to inadequate groundwater recharge, aquifer overexploitation, natural source release, or various anthropogenic activities that lead to groundwater quality degradation. The ingestion of groundwater contaminated with potentially toxic elements has been reported to have harmful health effects. This study aimed to assess the presence of several potentially toxic elements (Al, As, B, Cr, Cu, Fe, Mn, and Zn) in groundwater of the Monterrey metropolitan area in Northern Mexico and the carcinogenic and noncarcinogenic human health risks associated with exposure. Multivariate statistics and geospatial analysis were applied to identify the causative determinants that modify the groundwater quality along the metropolitan area. Mean concentrations of trace metals remained below drinking water standards and World Health Organization guidelines. The risk of harmful effects on human health due to ingestion of all eight metal(loid)s in groundwater was assessed as 2.52 × 10−2 for adults and 2.16 × 10−2 for children, which can be considered as negligible chronic risk and a very low cancer risk. However, the risks of oral consumption of Cr being carcinogenic to children and adults were 7.9 × 10−3 and 9.2 × 10−4, respectively. As these values exceeded the target risk of 1 × 10−4, it can thus be considered "unacceptable". [ABSTRACT FROM AUTHOR]

Contamination from wastewater infiltration, typically from leaky sewers, poses a threat to urban groundwater resources. Artificial sweeteners (Asws), used as sucrose substitutes in many products of daily consumption, are released into groundwater systems and may be used as tracers of wastewater in urban groundwater environments, because most of these compounds are discharged directly into sewer systems. Here, for the first time, we investigated the occurrence of Asws in an urban groundwater system in Mexico. Artificial sweetener concentrations of acesulfame (ACE), aspartame (ASP), cyclamate (CYC), saccharin (SAC), and sucralose (SUC) were tested in 42 production wells in the Monterrey Metropolitan Area (MMA). The detection frequencies of quantified Asws observations were in the order ACE (57%) > SUC (54%) > SAC (7%), with SUC being the most abundant Asws, with concentrations below the quantification limit (BQL) of 2.9 µg/L, followed by ACE (BQL 0.73 µg/L) and SAC (BQL 1.4 µg/L). ASP and CYC were not detected at any sampling site. Considerable Asws ingestion amongst the MMA population is the main input source of Asws into the city's wastewater network, percolating into the urban groundwater system due to leaky sewers. Our work shows that the application of Asws as wastewater tracers (SUC and ACE) effectively determines wastewater sources affecting urban groundwater. [ABSTRACT FROM AUTHOR]

Over the past decades, groundwater quality has deteriorated worldwide by nitrate pollution due to the intensive use of fertilizers in agriculture, release of untreated urban sewage and industrial wastewater, and atmospheric deposition. Likewise, groundwater is increasingly polluted by sulfate due to the release of domestic, municipal and industrial wastewaters, as well as through geothermal processes, seawater intrusion, atmospheric deposition, mineral dissolution, and acid rain. The urbanized and industrialized Monterrey valley has a long record of elevated nitrate and sulfate concentrations in groundwater with multiple potential pollution sources. This study aimed to track different sources and transformation processes of nitrate and sulfate pollution in Monterrey using a suite of chemical and isotopic tracers (δ2H–H 2 O, δ18O–H 2 O, δ15N–NO 3 , δ18O–NO 3 δ34S–SO 4 , δ18O–SO 4) combined with a probability isotope mixing model. Soil nitrogen and sewage were found to be the most important nitrate sources, while atmospheric deposition, marine evaporites and sewage were the most prominent sulfate sources. However, the concentrations of nitrate and sulfate were controlled by denitrification and sulfate reduction processes in the transition and discharge zones. The approach followed in this study is useful for establishing effective pollution management strategies in contaminated aquifers. Image 1 • Groundwater nitrate and sulfate sources and transformation were investigated. • Water chemistry, stable isotopes, and a Bayesian mixing model were combined. • Soil nitrogen and sewage were the most important nitrate sources. • Atmospheric deposition, marine evaporites and sewage were the main sulfate sources. • Contamination was controlled by denitrification and sulfate reduction processes. [ABSTRACT FROM AUTHOR]