Heavy metals in drinking water sources in northern Mexico: a review of concentrations and human health risks assessment Open Access

Aquifers and rivers are essential drinking water sources for many communities in Mexico, especially in the northern and central areas of the country (Pacheco-Treviño & Manzano-Camarillo 2024; González-Horta et al. 2015). Unfortunately, population growth has induced hydrological changes and introduced contamination from minerals, heavy metals, and microorganisms, deteriorating the quality of these water sources and posing risks to human health (WHO 2017; Zhang et al. 2023).

Heavy metals are recognized as persistent pollutants that come from the Earth's crust and are distributed in the environment (Jomova et al. 2024; Singh & Kostova 2024). Unlike other metallic elements, heavy metals have a relatively high density (>4 g/cm³) (Jomova et al. 2024) and are toxic even in small concentrations (Zhang et al. 2023; Singh & Kostova 2024). Heavy metals can replace the functional group OH⁻ in enzymes, disrupting metabolic functions (Jomova et al. 2024) and often leading to enzyme inactivation, suppression of antioxidant defenses, and the generation of reactive oxygen species (ROS) in cells, which produce oxidative stress and lead to health conditions including congenital disorders, immune system problems, and tumor formation and progression (Balali-Mood et al. 2021; Zhang et al. 2023; Singh & Kostova 2024). Globally, the list of the most toxic heavy metals includes arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb) (Balali-Mood et al. 2021; Jomova et al. 2024). These metals contribute notably to ecological contamination (Singh & Kostova 2024) and are among the 13 metals included in the priority pollutant list of the United States (USEPA 2014); this classification is assigned to pollutants that have at least a 2.5% frequency of occurrence in water (USEPA 2024b). With the exception of Cr, these metals are also found in the global list of the ten chemicals of public health concern (WHO 2020).

Heavy metal concentrations in the environment have increased due to inputs from natural (e.g., soil mineral composition, hydrothermal activity, and volcanic activity) and anthropogenic (e.g., sewage and industrial waste) sources, although anthropogenic activities constitute the main source of these metals (Zhang et al. 2023). In northern Mexico, agriculture, aquaculture, mining, and other industrial activities are crucial sources of heavy metal environmental inputs and also influence their dispersion in the region (Jara-Marini et al. 2013). In addition to these sources, arsenic-rich minerals like arsenopyrite are responsible for natural As occurrence in groundwater in some parts of northern Mexico (Armienta & Segovia 2008); these minerals are widely distributed throughout Mexico and are susceptible to erosion by hot springs (Armienta & Segovia 2008; González-Horta et al. 2015).

In Mexico, chronic exposure to heavy metals in groundwater was first described in 1958 (McClintock et al. 2012). This exposure type has been associated with several adverse health effects, including nephropathy (Chávez-Gómez et al. 2017), a reduction of the intelligence quotient in infants (Thatcher et al. 1982), neurotoxicity, alterations in the cardiovascular and central nervous systems, cancer, and death (Londoño-Franco et al. 2016). Despite the health risks, people still use and consume water contaminated with heavy metals from household connections, public fountains, and wells (Sobsey et al. 2008). The quality of all water sources in northern Mexico cannot be evaluated due to the paucity of research. This has resulted in a lack of action or the implementation of ineffective measures, such as activated sludge systems (Guzmán-Colis et al. 2011) in certain sites where natural enrichment or heavy metal contamination has been detected. Therefore, the objective of this study was to compile reports of heavy metals in drinking water in northern Mexico from 1975 to 2021 and undertake a review of the associated carcinogenic and non-carcinogenic risks faced by the inhabitants of northern Mexico.

The continental territory of Mexico covers 1,959,248 km² and borders the United States of America, Guatemala, and Belize (CONAGUA 2018). Mexico also has 11,122 km of coastline, with 15,000 km² of coastal lagoons and 29,000 km² of inland water bodies (SEMARNAT 2020). Mexico is ranked 94th in renewable water (renewed via the hydrological cycle) per capita among 152 countries, with 3,656 m³ of available water/inhabitant/year (CONAGUA 2018). However, according to the National Water Commission (Comisión Nacional del Agua [CONAGUA]), five hydrological-administrative regions located in northern Mexico exhibit high hydrological stress (40–100%), which is the amount of offstream water that is used out of the total amount available (CONAGUA 2018). In addition, the northwestern and central areas of Mexico cover two-thirds of the country and receive less than 500 mm of annual rainfall due to their arid and semi-arid climates; the northern, central, and northwestern regions host four-fifths of the population but only have access to one-third of the renewable water in the country (CONAGUA 2018).

At present, 115 of the 653 aquifers in the country are overexploited (SEMARNAT 2020). In addition, 168 of the 757 hydrological basins exhibit water deficits (negative water availability), with most of these basins located in northern Mexico (Salinas-Rodríguez & Martínez Pacheco 2024). This has notable implications for water management. To date, Mexico has established 147 decrees that ban groundwater use in certain areas, 3 aquifer regulations, 3 zone regulations, and 3 declarations of reserve zones for urban public use, which collectively protect approximately 55% of the national territory (CONAGUA 2018). Despite these measures, water management has not been effective, partly due to a lack of monitoring.

The National Water Quality Monitoring Network (Red Nacional de Medición de Calidad del Agua [RENAMECA]) has 5,028 monitoring stations; however, none of the RENAMECA stations monitor concentrations of hazardous elements such as heavy metals (CONAGUA 2018). The surface waters in the country are contaminated due to untreated municipal and industrial wastewater discharges, as well as agrochemical inputs (SEMARNAT 2020). Water contamination has led to a loss of ecosystem services, which have particularly affected rural communities and indigenous people (SEMARNAT 2020), given that rural populations, especially in arid northern areas, depend on groundwater (CONAGUA 2018).

After applying the inclusion and exclusion criteria, 55 studies that contained 316 concentrations of heavy metals were selected from 1975 to 2021. If a report presented multiple concentrations at the same metal for the same site, then the maximum and minimum values across these concentrations were considered. Similarly, if a report presented concentrations for multiple sites, the maximum and minimum values reported for each site were considered. If reports did not present multiple concentrations, then the value reported (usually a mean) was used. Some reports only presented a range of values. When results were represented solely by maps or graphs, concentration values ​​were extracted manually. Only a few reports included Supplementary data.

The following information related to the sampling area was also extracted from the studies: region (city or town), sample origin (e.g., well or river), sample collection year, and additional comments related to the selection of the report (Supplementary Table S1).

We estimated the quartiles of metal concentrations and represented their distributions with interquartile ranges (box plots). Different methods have been used to establish maximum concentrations of metals in water, soil, and air while minimizing the impact of extreme values (Frank et al. 2019; da Silva et al. 2020; USEPA 2021); among them, the 90th and 95th percentiles have been widely used (Spektor 1998; Frank et al. 2019; da Silva et al. 2020; USEPA 2021). Given that the 95th percentile has been used to establish the maximum concentration of metals in water (UKTAG 2020; Ravalli et al. 2022; Proshad et al. 2025), it was considered as the probable maximum concentration present in the water of northern Mexico (excluding extreme values). The 95th percentiles were calculated according to the National Institutes of Health guidelines (National Institutes of Health 2017). For this calculation, the difference between the 3rd quantile and the 1st quantile of heavy metal concentrations was determined (Supplementary Table S2). Then, the outliers to be eliminated were determined (Supplementary Table S3), and the 95th percentiles were calculated from the remaining data using the ‘PERCENTILE.INC’ function in Excel.

In risk characterizations, contaminant exposure levels are compared against chemical-specific toxicity criteria (established through research reports) to determine if the contamination levels constitute a health concern (USEPA 2001). The health risk associated with heavy metal exposure varies according to the metabolic state of individuals, the contamination source, environmental concentration, exposure time, chemical characteristics, and metal toxicity (Echeverry et al. 2015). In general, health risks can be classified as carcinogenic or non-carcinogenic and are calculated according to institutional guidelines such as those established by the United States Environmental Protection Agency (USEPA) (USEPA 2001, 2005). This agency recommends that reasonable exposure frequency estimates should be considered when there are no statistical data (USEPA 2001). Given that drinking water is a vital liquid associated with long-term exposure, we assumed a daily exposure frequency to calculate health risks. Some authors prefer to state that hazard assessments are ‘theoretical’ because mathematical formulas are used to calculate approximate measures (Hirano 1990) that do not represent the exact level of risks. However, for reasons of clarity in the text, the word ‘theoretical’ will not be included when mentioning risks.

Due to the lack of references that established a classification of HQ values, the HQ classification (Table 3) was arbitrarily chosen according to the HQ values calculated in this study.

The review identified 55 studies with 316 heavy metal concentrations. Twelve states were considered for the review. Heavy metal contaminations in the water resources of northern Mexico varied by state. Pollution in Aguascalientes has been mainly due to aquifer overexploitation (González et al. 2012; CONAGUA 2019). In addition, the main water resource in the state, the San Pedro River, has been seriously polluted by wastewater discharges and the municipal slaughterhouse (Guzmán-Colis et al. 2011). The presence of heavy metals in Baja California Sur has been strongly influenced by mining activity, regional geothermalism, and the presence of chloro-fluoro green rocks and arsenopyrite (Cassassuce et al. 2005). In an exhaustive water quality study of 500 wells in Baja California Sur (2004–2005), it was reported that the wells used for human consumption contained 10–500 μg As/L, which was likely due to mineral residues and mine tailings; some residents, such as those in the community of San Antonio, drank water purified from municipal treatment plants, but in other ranches and communities, such as El Rosario, Valle Perdido, and Texcalama, people drank water directly from contaminated sources (Cassassuce et al. 2005).

Chihuahua has been recognized for having high As concentrations in its water bodies (Westerhoff et al. 2004), which are mainly due to volcanic processes, arsenopyrite deposits in hot spring areas, and anthropogenic contributions related to mining and metal smelting (Camacho et al. 2011). This type of contamination has been reported since 1995, when the central water well of La Casita contained As concentrations between 7,000 and 11,000 μg/L, which caused chronic arsenicosis in 8% of the inhabitants of the town (Ochoa-Reyes et al. 2009). Years later, in 2009, the water from the well in La Casita contained 2 μg As/L; however, prolonged exposure to high As concentrations has caused the inhabitants of the town to develop diseases (Ochoa-Reyes et al. 2009).

Numerous wells in the Guadiana Valley (Durango) were also studied, with As concentrations ranging from 5 to 167 μg/L and suspected contamination of geological origin (Alarcón-Herrera et al. 2001). Recently, Alcázar-Medina et al. (2020) reported that the community wells of San José de Avino (Panuco de Coronado municipality) contained 5,250 μg Cd/L, 2139.2 μg Pb/L, and 60.5 μg Cr/L; in general, contamination was considered to be of geological origin (Gamboa-Loira et al. 2020). A similar situation was observed in Nuevo León, where the most important water resource of this state, the Río San Juan basin, has exhibited variable heavy metal concentrations over the last two decades (Flores-Laureano 1997). Indeed, it is possible that ∼37% of the inhabitants of Nuevo León are drinking water with As concentrations greater than 10 μg/L (maximum of 34.54 μg As/L) (Gamboa-Loira et al. 2020). Similarly, children from communities in San Luis Potosí may have suffered adverse effects due to high As levels in drinking water (Díaz-Barriga et al. 1993). López-Álvarez et al. (2013) suggested the presence of cemeteries, mine tailings, wastewater discharges, solid waste disposal, and gas stations as possible pollution sources.

Contamination has also affected the indigenous communities of Sonora. Several towns in the Yaqui Valley (southern Sonora) were exposed to 4.71–49.26 μg As/L from 2001 to 2002 (Meza et al. 2004, 2005). The most recent study in the Yaqui and Mayo Valleys reported 57 wells with As concentrations ranging from 2.7 to 98.7 μg As/L (García-Rico et al. 2019). Similar contamination levels have been observed in Coahuila; wells in the southwest had Pb and CD concentrations of 8–51 and 1–18 μg/L, respectively (Saldarriaga et al. 2014).

Zacatecas is abundant in metallic minerals. Mining activity in the state is high, which has resulted in the pollution of many aquatic resources in the San Ramón system (González-Dávila 2013). The municipal water of Ojocaliente City contained 40 μg As/L (Sandoval-Alvarado et al. 2020), exceeding the Official Mexican Standard (DGN 1994). Fortunately, the Cr concentrations in the water sources of the Mazapil municipality did not exceed the Official Mexican Standard (<10 μg/L) (Escamilla-Rodríguez et al. 2021).

Overall, 316 concentrations of heavy metals were reported in 55 studies from 1975 to 2021. Of these, 174 concentrations were of As, with values ranging from 0 to 11,100 μg/L; 55 concentrations were of Cd, with values ranging from 0 to 5,250 μg/L; 24 concentrations were of Cr, with values ranging from 0 to 350 μg/L; 8 concentrations were of Hg, with values ranging from 0 to 25 μg/L; and 55 concentrations were of Pb, with values ranging from 0 to 9,470 μg/L. The averages and standard deviations of the metal concentrations are shown in Table 4.

All reported concentrations were highly variable over time and study area. On average, 43.04% of heavy metal concentrations exceeded the concentration limits established by the Official Mexican Standard NOM-127-SSA1-1994, and 50.63% exceeded the concentration limits established by the WHO (Table 5). Many of the As concentrations reported in the studies exceeded the Official Mexican Standard, with some exceeding the concentration limit by 200 times.

The distribution of heavy metal concentrations in the drinking water of northern Mexico (Supplementary Figure S1) indicates that Coahuila and Nuevo León exhibited the highest As contamination over the years; this metalloid comes from natural compounds, such as arsenite and arsenate, and its concentration in water has increased mainly due to hydrothermalism, arsenical pesticides, and arsenical chemical waste (Jaishankar et al. 2014). Durango and Tamaulipas contained the highest Pb concentrations; this contamination may have come from fertilizers and pesticides, ore smelting, factory chimneys, soil wastes, and wastes from the battery industry (Jaishankar et al. 2014).

The maximum heavy metal concentrations were used to calculate the highest non-carcinogenic HQ that was most likely to occur in northern Mexico (Table 6). From the 54 HQ values, 28 ​​exceeded the value of 1 (Supplementary Figure S3). The highest HQ values were found in children younger than 6 years. The population that may be at greatest risk was comprised of children between 1 and 2 years in age; these values exceeded those of children under 1 year, given that children aged 1–2 years tended to drink more water.

If the Cr ion that is consumed is Cr⁺³, then the consumption of this heavy metal would not represent a health risk; however, studies specifying Cr valence are scarce. Based on the HQ categories, the HQ values for Cd and Hg in drinking water indicate that there is either no risk or a slightly high health risk. The HQ values for Pb indicated no risk to a slightly high health risk. The HQ values for Cr⁺⁶ indicated a slightly high to medium-high health risk. Arsenic was responsible for the highest health risks, with extremely high hazard values (>40).

The maximum heavy metal concentrations were also used to calculate the most likely CR values in people in northern Mexico by age. According to the CR classification (Supplementary Table S6), the carcinogenic risks related to As for all ages were extremely high (>1 × 10⁻³) (Table 7). The CR values for Cr⁺⁶ varied from medium-high to extremely high risk. It should be noted that most international standards do not establish a limit for the concentration of Cr⁺⁶ in water, although they do establish limits for total Cr; Cr⁺⁶ is the only form of Cr reported to have carcinogenic effects (USEPA 2000). The CR values for Pb reflected low-medium risk and medium risk.

The variation in heavy metal concentrations in drinking water in northern Mexico was mainly due to geological origin, with metals originating naturally from soil minerals (e.g., silicate, carbonate, oxide, hydroxide, and sulfide structures) and being present in dissolved, particulate, or complex (bonded to other metals) forms in aquatic ecosystems due to natural processes (e.g., weathering, volcanic eruptions, erosion, and runoff) or anthropogenic waste (Zhang et al. 2023). The distributions may also be influenced by the presence of arsenopyrite in northern Mexico and the extensive generation sites of arsenic trioxide (arsenolite), a by-product of gold and silver extraction, especially in the mining regions of Baja California Sur (Carrillo-Chávez et al. 2000). The anthropogenic sectors that may have contributed the most to heavy metal concentrations in drinking water are likely those that have received the greatest amounts of water from the Mexican government: agriculture (76.04%), electric (non-hydroelectric) power (4.72%), industry (4.86%), and public supply (14.38%) (CONAGUA 2018). The variability of heavy metal concentrations was also due to the mobility and bioavailability of metals being affected by chemical processes, such as sorption, desorption, and precipitation–dissolution reactions (Caporale & Violante 2016).

In northern Mexico, 35.6% of the concentrations of As in drinking water exceeded 50 μg/L. This is similar to what was reported in Bangladesh, where 50% of the tube wells contained As concentrations greater than 50 μg/L (Khan et al. 2003). While the outlook is better for northern Mexico than for Bangladesh, the situation in northern Mexico is still worrying. If members of a community drink 1 L of water with 50 μg/L of a heavy metal each day, then 13 out of every 1,000 people could develop a malignant neoplasm (Aryan et al. 2024), such as skin, liver, or other types of cancer, due to oxidative stress, chromosomal anomalies, and altered growth factor expression (Balali-Mood et al. 2021).

It is important to highlight that the range of As concentrations found in drinking water sources was greater than the concentration range found in the groundwater of South Asia: India (0–3,700 μg As/L, 2008–2022), Pakistan (0–4,730 μg As/L, 2009–2022), Bangladesh (0.5–4,730 μg As/L, 2010–2022), Nepal (0–2,620 μg As/L, 2006–2021), and Sri Lanka (0–400 μg As/L, 2013–2019) (Aryan et al. 2024). This situation is extremely worrying, as more than 100,000 deaths have been attributed to groundwater contamination in India, and in Bangladesh, ∼43,000 people die every year for the same reason (Aryan et al. 2024). Thus, a relatively high number of northern Mexicans may be dying due to high concentrations of As in drinking water. Furthermore, in Antofagasta, Chile, from 1958 to 1965, people were exposed to drinking water with 860 μg As/L, which was responsible for 18–24% of all infant deaths during that period (Ferreccio & Sancha 2006). Considering that children in northern Mexico have been exposed to similar and even higher concentrations in drinking water, As-contaminated drinking water may be responsible for a comparable infant mortality rate in Mexico.

Lead and Cd concentrations in water sources in northern Mexico were higher than those in the streams, wells, and stormwater in Anambra, Nigeria (Pb: 0–370 μg/L; Cd: 100–350 μg/L) (Emmanuel et al. 2022). However, Hg concentrations were lower than those reported in Anambra (50–380 μg/L) (Emmanuel et al. 2022). The mean concentrations of As, Cd, and Pb in drinking water from northern Mexico (264.84, 159.64, and 282.19 μg/L) were also higher than the average concentrations found in 71 dug-well water samples from houses from Polonnaruwa, Sri Lanka (As: 0.37 μg/L; Cd: 0.03 μg/L; Pb: 0.09 μg/L), in which people with chronic kidney disease (CKD) of unknown etiology (CKDu) were living. A disease similar to CKDu, CKD, is currently a public health problem in Mexico; it is one of the top 10 causes of mortality among patients of the Mexican Social Security Institute (∼377 cases per million inhabitants) (Chávez-Gómez et al. 2017). Although the presence of Pb, Cd, As, and Hg in water could not be associated with CKDu incidence (Kulathunga et al. 2022), CKD has been shown to be related to exposure to heavy metals (Chávez-Gómez et al. 2017).

The HQ results are highly concerning, as they were many orders of magnitude greater than 1. When heavy metals enter the human body, they bind to blood proteins and are distributed to various organs, especially the small intestine, liver, kidneys, brain, and bones; a portion of the ingested concentration is stored in organs, and the rest is excreted through urine and feces (Chávez-Gómez et al. 2017). In addition, pathological symptoms due to heavy metal exposure can be up to 5-fold more severe in children than in adults and may be exacerbated by iron deficiencies (Chávez-Gómez et al. 2017). Thus, many people in northern Mexico are at risk of organ malfunction and other diseases related to heavy metal exposure.

The maximum HQ values calculated for adults and children from the probable maximum concentrations of As, due to the As concentrations in this study, were found to carry a higher risk than that posed by the groundwater samples from India, Pakistan, Bangladesh, Nepal, and Sri Lanka (Badeenezhad et al. 2023); groundwater from Shiraz, Iran (0.426–0.183) (Badeenezhad et al. 2023); and groundwater and surface water from Maharashtra, India (5.5108) (Mawari et al. 2022) (Supplementary Table S7). Most of the estimated non-carcinogenic risks for children and adults exposed to Cd, Pb, and Hg in drinking water in this study were lower than those reported for the same elements in streams, wells, and stormwater in Anambra, Nigeria (1.57–107.56) (Emmanuel et al. 2022). In addition, the Cd, Pb, and Hg risks were higher than those established for these elements in the groundwater of Shiraz, Iran (0.004–0.066) (Badeenezhad et al. 2023) and for groundwater and surface water in Maharashtra, India (0.0033–0.4724) (Mawari et al. 2022). In addition, the HQ values for As, Cd, and Pb in this study were also higher than those for the same elements in the water collected from wells that had been dug outside the houses of CKDu patients from Sri Lanka (0.00169–0.04) (Kulathunga et al. 2022).

The CR values related to As ​​were similar to those reported in groundwater from India, Pakistan, Bangladesh, Nepal, and Sri Lanka (4.95 × 10⁻⁴ to 2.10 × 10⁻¹) (Aryan et al. 2024) (Supplementary Table S8). This is especially worrying considering that As has been reported in various parts of northern Mexico. The CR values for Pb were similar to the incremental lifetime cancer risks established for streams, wells, and stormwater in Anambra, Nigeria (5.34 × 10⁻⁶ to 5.88 × 10⁻⁵) (Emmanuel et al. 2022).

It is crucial to highlight that in northern Mexico, all CR values ​​for As fell within category VII of extremely high risk. In 2022, 89,574 deaths from malignant tumors were reported in Mexico, accounting for 10.6% of all deaths that year (INEGI 2024). In addition, Sonora, Chihuahua, and Nuevo León are the states in northern Mexico with the highest death rates due to malignant tumors (74.71–95.96 deaths per 100,000 inhabitants) (INEGI 2024). In addition, indigenous children in northern Mexico who were exposed to high As through drinking water exhibited significant increases in DNA damage (Maldonado-Escalante et al. 2018); thus, it is possible that the high concentrations of As in drinking water in northern Mexico are related to the high incidence of cancer in the region. It is imperative that adequate monitoring and management measures are implemented for aquatic resources; in addition, water treatment processes must be established, and the quality of public water pipes must be improved.

The present study relied on summary data of varying quality, including minimum, mean, and maximum values, which precluded any distributional development or trend analyses of metal concentrations over the analyzed time period. Comparisons between HQ and CR values were conducted in the context of the major differences in data sources; we recognize that they might not truly reflect the real differences. Possible relationships were conjectured between the results and disease incidence; these relationships were based on results and background, without considering other environmental variables. This article does not provide a probabilistic model that specifies the exact relationships between metal concentrations and disease incidence.

In all, 316 heavy metal concentrations were reported in 55 studies from 1975 to 2021: 174 As concentrations (0 to 11,100 μg/L), 55 Cd concentrations (0 to 5,250 μg/L), 24 Cr concentrations (0 to 350 μg/L), 8 Hg concentrations (0–25 μg/L), and 55 Pb concentrations (0 to 9,470 μg/L). The states of Coahuila and Nuevo León had the highest levels of As contamination over the years included in the study; in addition, Durango and Tamaulipas had the highest recorded Pb concentrations. All reported concentrations exhibited high variability with respect to time and the study area.

Almost half of the reported concentrations (43.04%) exceeded the limits established by the Official Mexican Standard NOM-127-SSA1-1994, and 50.63% exceeded the concentration limits established by the WHO. Moreover, 65.5% of the As concentrations exceeded the concentration limit established by the WHO. The analyses indicated that the probable maximum concentrations were 244.55 μg As/L, 10.00 μg Cd/L, 56.00 μg Cr/L, 1.68 μg Hg/L, and 90.35 μg Pb/L.

The non-carcinogenic risk calculated for As, Cd, Cr, Hg, and Pb resulted in HQ values that ranged from 0.0011 to 404.62. Arsenic exhibited the highest health risks, with extremely high HQ values (>40). The CR values for Cr⁺⁶ varied from medium-high (>1 × 10⁻⁴ to 5 × 10⁻⁴) to extremely high (>1 × 10⁻³) risk, and CR values for Pb varied from low-medium (>1 × 10⁻⁵ to 5 × 10⁻⁵) to medium-high (>5 × 10⁻⁵ to 1 × 10⁻⁴) risk. Furthermore, all CR values for As represented an extremely high risk, with CR values from 2.29 × 10⁻¹ to 7.77 × 10⁻¹. Based on the HQ and CR values, the highest risks were found in children under 6 years of age.

Although not all concentrations exceeded those established by the Official Mexican Standard, most of the associated non-carcinogenic HQ and CR were high, indicating that some standards do not consider the established RfD or CSF values. Therefore, it is necessary to revise the current guidelines and lower the maximum permissible concentrations. In addition, financial support must be increased for research on the distribution, concentrations, and dispersal of heavy metals and their consequences in Mexico. Management actions should also be improved. It is necessary to conduct massive sampling campaigns of various aquatic resources in northern Mexico to determine heavy metal concentrations and evaluate the real risks faced by the population. In particular, heavy metal monitoring programs for water bodies must be expanded, especially those led by RENAMECA. Awareness campaigns must also be created and implemented that educate the public on the risks associated with heavy metal exposure. Lastly, adsorption instruments should be installed in factory effluent outlets, and public purification and distribution systems for drinking water must be improved to remove heavy metals. Collectively, these actions will serve to safeguard the drinking water sources in northern Mexico, lowering the potential health risks associated with the consumption of heavy metals and improving the quality of life of people in the region.

The authors are thankful to Dr Andrea Lievana MacTavish for professionally editing this article.

This study was partially supported by the Universidad Autónoma de Sinaloa through PROFAPI [PRO_A2_025].

M.R.-C.: conceptualization, design, data curation, formal analysis, visualization, and writing – original draft. O.E.-S.: conceptualization, funding acquisition, supervision, validation, and writing – review & editing. M.B.-L.: conceptualization, supervision, validation, and writing – review & editing. M.G.F.-E.: validation and writing – review & editing. N.Y.Z.-A.: validation and writing – review & editing. C.C.O.-M.: validation and writing – review & editing. All authors approved the final version.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.