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Wastewater-based epidemiology offers a time- and cost-effective way to monitor SARS-CoV-2 spread in communities and therefore represents a complement to clinical testing. WBE applicability has been demonstrated in a number of cases over short-term periods as a method for tracking the prevalence of SARS-CoV-2 and an early-warning tool for predicting outbreaks in the population. This study reports SARS-CoV-2 viral loads from wastewater treatment plants (WWTPs) and hospitals over a 6-month period (June to December 2020). Results show that the overall range of viral load in positive tested samples was between 1.2 × 103 and 3.5 × 106 gene copies/l, unveiling that secondary-treated wastewaters mirrored the viral load of influents. The interpretation suggests that the viral titers found in three out of four WWTPs were associated to clinical COVID-19 surveillance indicators preceding 2-7 days the rise of reported clinical cases. The median wastewater detection rate of SARS-CoV-2 was one out of 14,300 reported new cases. Preliminary model estimates of prevalence ranged from 0.02 to 4.6% for the studied period. This comprehensive statistical and epidemiological analysis demonstrates that the applied wastewater-based approach to COVID-19 surveillance is in general consistent and feasible, although there is room for improvements.

Microplastic (MP) environmental contamination has been widely studied in Mexico. However, the evaluation of the associated risk to MPs in environmental compartments is scarce. Therefore, this study addresses this issue using diverse indicators such as the Pollution Load Index (PLI), the Polymer Risk Index (PRI), and the Potential Ecological Risk Index (PERI). The results of a meta-analysis revealed high MP contamination levels in most of the studied compartments, which included marine and estuarine waters, beach sand, freshwater, sediments, and biota. Regarding the risk assessment indicators, PLIs indicated low (56%), dangerous (22%), moderate (12%), and high (10%) levels across compartments. Meanwhile, PRIs displayed concerning values, with 36%, 35%, 20%, and 9% exhibiting dangerous, high, moderate, and low levels, respectively. Thus, high PRI values emphasized the significant rise in MP pollution, largely attributed to high-hazard polymer compositions. Otherwise, PERIs showed low (56%), very dangerous (29%), moderate (6%), high (5%), and dangerous (4%) levels. Thus, the ecological risk in Mexico is widespread and mainly linked to MP abundance, polymer type, environmental matrix, and characteristics of organisms. This study represents the first attempt at MP ecological risk assessment in Mexico, providing crucial insights for developing mitigation strategies to address concerns about MP contamination. [Display omitted] • First study on MPs' ecological risk in Mexico's environmental compartments. • Spatial distribution of MPs in environmental matrices is widespread. • MP contamination levels were predominantly high in most environmental compartments. • MP risk in Mexico assessed with PLI, PRI, and PERI shows widespread results. • Ecological risk is tied to MP abundance, polymer type, matrix, and organism traits. [ABSTRACT FROM AUTHOR]

Abstract The evolution of several trace elements was evaluated in shallow groundwater of an agricultural area located in a semi-arid region of northeastern Mexico. A Principal Component Analysis (PCA) was performed to assess the geochemical processes controlling the distribution and mobility of these elements. Five principal components (PC) were significant. PC1 indicates that Ti and Si come from soil/silicate weathering. Sulfate, Mo and U were grouped in PC2, indicating the same redox behavior. PC3 shows similar sources for Rb and Cs (halite weathering), whereas the PC4 grouped the immobile elements Cd and Pb. The correlation found between Zn and Cu in PC5 indicates a similar behavior of both elements during the weathering and transport. Although the measured trace elements were detected in groundwater, their concentrations were lower than the guidelines values for safe drinking water proposed by international organizations, suggesting that these elements do not pose any significant threat to consumers. [ABSTRACT FROM AUTHOR]

The article presents a study on the groundwater geochemistry of the Chihuahua City region in the Rio Conchos Basin in northern Mexico, and its implications for water resources management. Results showed that the background groundwater chemistry upstream of Chihuahua City results from feldspar weathering but beyond Chihuahua City, the chemical conditions are strongly modified owing to the disposal of sewage from public and industrial water supplie into the Rio Chuviscar. As a consequence, anions like chloride and and sulphate are mainly linked to surface sources, while nitrate is controlled in part by sewage from public supply and industry and in part by agricultural practices.

Stable Isotopes (strontium-87, deuterium and oxygen-18, carbon-13) have been used to reveal different sources of groundwater and mixing processes in the aquifer of the Silao-Romita Valley in the state of Guanajuato, Mexico. Calcite dissolution appeared to be the main process of strontium release leading to relatively equal 87Sr/86Sr ratios of 0.7042-0.7062 throughout the study area which could be confirmed by samples of carbonate rocks having similar Sr ratios (0.7041-0.7073). δ13C values (-11.91- -6.87‰ VPDB) of groundwaters confirmed the solution of carbonates but indicated furthermore influences of soil-CO2. Deuterium and 18O contents showed a relatively narrow range of-80.1- -70.0 ‰ VSMOW and-10.2- -8.8 ‰, VSMOW, respectively but are affected by evaporation and mixing processes. The use of δ13C together with 87Sr/86Sr revealed three possible sources: (i) carbonate-controlled waters showing generally higher Sr-concentrations, (ii) fissure waters with low-strontium contents and (iii) infiltrating water which is characterized by low δ13C and 87Sr/86Sr ratios. The third component is affected by evaporation processes taking place before and during infiltration which might be increased by extraction and reinfiltration (irrigation return flow). [ABSTRACT FROM AUTHOR]

The identification of nitrate (NO 3 −) sources and biogeochemical transformations is critical for understanding the different nitrogen (N) pathways, and thus, for controlling diffuse pollution in groundwater affected by livestock and agricultural activities. This study combines chemical data, including environmental isotopes (δ2H H2O , δ18O H2O , δ15N NO3, and δ18O NO3), with land use/land cover data and a Bayesian isotope mixing model, with the aim of reducing the uncertainty when estimating the contributions of different pollution sources. Sampling was taken from 53 groundwater sites in Comarca Lagunera, northern Mexico, during 2018. The results revealed that the NO 3 − (as N) concentration ranged from 0.01 to 109 mg/L, with more than 32% of the sites exceeding the safe limit for drinking water quality established by the World Health Organization (10 mg/L). Moreover, according to the groundwater flow path, different biogeochemical transformations were observed throughout the study area: microbial nitrification was dominant in the groundwater recharge areas with elevated NO 3 − concentrations; in the transition zones a mixing of different transformations, such as nitrification, denitrification, and/or volatilization, were identified, associated to moderate NO 3 − concentrations; whereas in the discharge area the main process affecting NO 3 − concentrations was denitrification, resulting in low NO 3 − concentrations. The results of the MixSIAR isotope mixing model revealed that the application of manure from concentrated animal-feeding operations (∼48%) and urban sewage (∼43%) were the primary contributors of NO 3 − pollution, whereas synthetic fertilizers (∼5%), soil organic nitrogen (∼4%), and atmospheric deposition played a less important role. Finally, an estimation of an uncertainty index (UI90) of the isotope mixing results indicated that the uncertainties associated with atmospheric deposition and NO 3 −−fertilizers were the lowest (0.05 and 0.07, respectively), while those associated with manure and sewage were the highest (0.24 and 0.20, respectively). Image 1 • Sources, transformations and contributions of nitrate pollution in groundwater investigated. • Thirty-two percent the samples exceeded the WHO limit for safe drinking water. • Mainly the application of manure and sewage leaks drove the increase of nitrate concentration. • Mixing process among evaporated soil water and recirculated water from irrigation identified. • Different nitrate transformation processes in recharge, transition and discharge areas. The combined approach estimated a number of nitrate pollution sources and transformation processes in groundwater, whereby manure and sewage leakages were the main drivers. [ABSTRACT FROM AUTHOR]

This study analyzed the dynamics of major ions and trace elements along the groundwater flow path of the coastal sedimentary Todos Santos aquifer in Baja California Sur, Mexico, moderately impacted by anthropogenic activities. The results indicate that the elements Ca2+, Mg2+, Ba2+, Sr2+ and Li+ are mobilized from the aquifer matrix during seawater intrusion, whereas the alkali-elements Na+, K+ and Rb+ are removed from solution, possibly due to cationic exchange process. The anions HCO3– and SO 4 2− and the elements I and B are mobilized due to carbonate mineral weathering, whereas dissolved silica and the halides Br− and F− behave conservatively during salinization. Groundwater NO 3 − is provided by sewage infiltration. Regarding trace elements behavior, we identify three groups: i) elements that are mobilized during saline intrusion (Fe, Co, V, Se, Re), ii) elements revealing low or no mobilization (Mo, Ni, Cr, Ta, W) and iii) elements that show an undefined tendency (U, As, Ge, Sb, Cu, Mn). The U and NO 3 − levels in groundwater should be considered carefully because several wells have concentrations close to the permissible levels. This study may be useful as reference for knowing the possible effect of salinization in coastal aquifers under sea level rise scenarios driven by climate change. Unlabelled Image • Ca, Mg, Sr and Ba are exchanged from the sediment by Na, K, Rb during salinization. • Unexpectedly, Li is released into solution during saline intrusion by cation exchange. • B, I, HCO 3 – and SO 4 2− are mobilized into solution by chemical weathering. • Fe, Co, V, Se and Re are mobilized whereas Mi, Ni, Cr, Ta and W are not mobilized. • U, As, Ge, Sb, Cu and Mn show undefined tendency during seawater intrusion. [ABSTRACT FROM AUTHOR]

The Mezquital Valley system is the world's oldest and largest example with regard to use of untreated wastewater for agricultural irrigation. Because of the artificial high recharge associated with the Mezquital Valley aquifers, groundwater is extracted for human consumption, and there are plans to use this groundwater as a water resource for Mexico City. Thus, this study analyzed 218 organic micro-contaminants in wastewater, springs, and groundwater from Mezquital Valley. Five volatile organic compounds (VOCs) and nine semi-volatile organic compounds (SVOCs) were detected in the wastewater used for irrigation. Only two SVOCs [bis-2-(ethylhexyl) phthalate and dibutyl phthalate] were detected in all the wastewater canals and groundwater sources, whereas no VOCs were detected in groundwater and springs. Of the 118 pharmaceutically active compounds (PhACs) and 7 reproductive hormones measured, 65 PhACs and 3 hormones were detected in the wastewater. Of these, metformin, caffeine, and acetaminophen account for almost sixty percent of the total PhACs in wastewater. Nevertheless, 23 PhACs were detected in groundwater sources, where the majority of these compounds have low detection frequencies. The PhACs sulfamethoxazole, N,N-diethyl-meta-toluamide, carbamazepine, and benzoylecgonine (primary cocaine metabolite) were frequently detected in groundwater, suggesting that although the soils act as a filter adsorbing and degrading the majority of the organic pollutant content in wastewater, these PhACs still reach the aquifer. Therefore, the presence of these PhACs, together with the high levels of the endocrine disruptor bis-2-(ethylhexyl) phthalate, indicate that water sources derived from the recharge of the studied aquifers may pose a risk to consumer health. [ABSTRACT FROM AUTHOR]

This review compiles the studies (2007–2021) regarding the occurrence of emerging organic contaminants (EOCs) and endocrine disruptors (EDs) in wastewater, surface water and groundwater in Mexico. A total of 174 compounds were detected, including pharmaceuticals, hormones, plasticizers, personal care products, sweeteners, drugs, and pesticides considered as EDs. The levels of EOCs and EDs varied from ng/L to 140 mg/L, depending on the compound, location, and compartment. Raw wastewater was the most studied matrix, showing a greater abundance and number of detected compounds. Nevertheless, surface waters showed high concentrations of bisphenol-A, butylbenzil-phthalate, triclosan, pentachlorophenol, and the hormones estrone, 17 α-ethinylestradiol, and 17 β-estradiol, which exceeded the thresholds set by international guidelines. Concentrations of 17 α-ethinylestradiol and triclosan exceeding the above-mentioned limits were reported in groundwater. Cropland irrigation with raw wastewater was the principal activity introducing EOCs and EDs into groundwater. The groundwater abundance of EOCs was considerably lesser than that of wastewater, highlighting the attenuation capacity of soils/aquifers during wastewater infiltration. However, carbamazepine and N,N-diethyl-meta-toluamide showed higher concentrations in groundwater than those in wastewater, suggesting their accumulation/concentration in soils/pore-waters. Although the contamination of water resources represents one of the most environmental concerns in Mexico, this review brings to light the lack of studies on the occurrence of EOCs in Mexican waters, which is important for public health policies and for developing legislations that incorporates EOCs as priority contaminants in national water quality guidelines. Consequently, the development of legislations will support regulatory compliance for wastewater and drinking water, reducing the human exposure. [Display omitted] • Occurrence of EOCs and EDs in WW, SW and GW of Mexico was reviewed. • Naproxen, BPA and ibuprofen were the most studied/detected compounds. • Carbamazepine and DEET showed higher concentrations in GW than those in WW. • Triclosan and 17 α-ethinylestradiol exceeded the Australian thresholds in GW. • There are critical needs for the assessment of EOCs and EDs in water matrices. [ABSTRACT FROM AUTHOR]

Abstract: Mexico ranks 9th in the world in crude oil reserves, 4th in natural gas reserves in America and it is also highly rich in renewable energy sources (solar, wind, biomasss, hydropower and geothermal). However, the potential of this type of energy has not been fully exploited. Hydropower is the renewable energy source with the highest installed capacity within the country (11,603MW), while geothermal power capacity (958MW) makes Mexico to be ranked 4th in the use of this energy worldwide. Wind energy potential is concentrated in five different zones, mainly in the state of Oaxaca, and solar energy has a high potential due to Mexico's ideal location in the so called Solar Belt. Biomass energy has the highest potential (2635 to 3771PJ/year) and has been the subject of the highest number of research publications in the country during the last 30 years (1982–2012). Universidad Nacional Autonoma de Mexico has led research publications in hydropower, wind, solar and biomass energy and Instituto de Investigaciones Electricas in geothermal energy during this period. According to the General Law for Climate Change the country has set the goal of generating 35% of its energy needs from renewable sources by 2024. This paper presents an overview of the renewable energy options available in Mexico, current status, main positive results to date and future potential. It also analyses barriers hindering improvements and proposes pertinent solutions. [Copyright &y& Elsevier]

Abstract: Nitrate isotopic values are often used as a tool to understand sources of contamination in order to effectively manage groundwater quality. However, recent literature describes that biogeochemical reactions may modify these values. Therefore, data interpretation is difficult and often vague. We provide a discussion on this topic and complement the study using halides as comparative tracers assessing an aquifer underneath a sub-humid to humid region in NE Mexico. Hydrogeological information and stable water isotopes indicate that active groundwater recharge occurs in the 8000km2 study area under present-day climatic and hydrologic conditions. Nitrate isotopes and halide ratios indicate a diverse mix of nitrate sources and transformations. Nitrate sources include organic waste and wastewater, synthetic fertilizers and soil processes. Animal manure and sewage from septic tanks were the causes of groundwater nitrate pollution within orchards and vegetable agriculture. Dairy activities within a radius of 1000m from a sampling point significantly contributed to nitrate pollution. Leachates from septic tanks caused nitrate pollution in residential areas. Soil nitrogen and animal waste were the sources of nitrate in groundwater under shrubland and grassland. Partial denitrification processes helped to attenuate nitrate concentration underneath agricultural lands and grassland, especially during summer months. [Copyright &y& Elsevier]