How to cite: Romo-Morales, D., Moreno-Rodríguez, V., Rader, S., Loredo-Portales, R., Espinoza-Maldonado, I. G., Valencia-Moreno, M., López-Teros, V., Salas-Beyliss, F. E., & Del Rio-Salas, R. (2026). Potentially toxic elements and Pb isotope data of regional food from the Sonoran River basin: Tracing the nature of the sources. Revista Mexicana de Ciencias Geológicas, 43(2), 174–187. DOI: https://dx.doi.org/10.22201/igc.20072902e.2026.2.1919

Revista Mexicana de Ciencias Geológicas, v. 43, num. 2, August 2026, p. 174–187

DOI: https://dx.doi.org/10.22201/igc.20072902e.2026.2.1919

Potentially toxic elements and Pb isotope data of regional food from the Sonoran River basin: Tracing the nature of the sources

Diana Romo-Morales1, a, Verónica Moreno-Rodríguez1, b, Shelby Rader2, René Loredo-Portales3, 4, Inocente Guadalupe Espinoza-Maldonado1, d, Martín Valencia-Moreno3, e, Verónica López-Teros5, Francisco Eduardo Salas-Beyliss6, f, and Rafael Del Rio-Salas3, 4, g, *

1 Departamento de Geología, Facultad Interdisciplinaria de Ciencias Exactas y Naturales, Universidad de Sonora, Blvd. Luis Encinas y Rosales s/n, Hermosillo, Sonora, Mexico, C.P. 83000.

2 Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, IN, USA. 47408.

3 Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, Colosio y Madrid s/n, Hermosillo, Sonora, Mexico, C.P. 83000.

4 Laboratorio Nacional de Geoquímica y Mineralogía-LANGEM, Mexico City, Mexico, C.P. 04510.

5 Departamento de Ciencias Químico-Biológicas, Facultad Interdisciplinaria de Ciencias Biológicas y de Salud, Universidad de Sonora, Blvd. Luis Encinas y Rosales s/n, Hermosillo, Sonora, Mexico. C.P. 83000.

6 Departamento de Ciencias del Deporte y de la Actividad Física, Facultad Interdisciplinaria de Ciencias Biológicas y de Salud,Universidad de Sonora, Blvd. Luis Encinas y Rosales s/n, Hermosillo, Sonora, Mexico, C.P. 83000.

 

*Corrresponding author (R. Del Río Salas): rdelriosalas@gmail.com

a 0000-0003-2434-8258; b 0000-0001-9033-6824, c 0000-0002-9146-1253, d 0000-0002-6574-3599, e 0000-0003-1212-6682, f 0009-0006-9252-3889, g 0000-0002-4474-172X

 

ABSTRACT

The upper Sonora River basin in northwestern Mexico is a region with active and historical mining, as well as vigorous agricultural and livestock activity. The Buenavista del Cobre mine spill that occurred in 2014 raised major concerns among residents, including food safety. In this study, potentially toxic elements, PTE, (Al, As, Ba, Cd, Cr, Cu, Fe, Ni, Pb, Zn, and Tl) and Pb isotope ratios were measured in samples of regional foods and food products [beef chorizo, shredded beef jerky, beef liver, beef top round, farmer’s cheese, and red chili (powdered dried mild pepper)] collected from representative sites along the basin. Compared to international guidelines, only two out of 20 beef samples exceeded the Pb limit of 0.1 mg/kg set by FAO/WHO and the EU, mainly in prepared products (chorizo, shredded beef jerky). One liver sample exceeded the FAO/WHO Pb limit of 0.2 mg/kg. For red chili, one sample exceeded the Pb guideline of 0.6 mg/kg (FAO/WHO). Overall, Pb levels did not surpass FAO/WHO recommendations. Pb isotope compositions in most food samples align with the range of North American rocks, indicating limited influence from mining. Variability in Pb isotope composition may be related to preparation methods and geogenic anomalies. Although the mine spill represented a major environmental disturbance, PTE concentrations measured in foods and food products are consistent with the geochemical background of the basin. This interpretation is supported by Pb isotope compositions, indicating that Pb in food and food products primarily originates from natural sources, with no clear evidence of significant contributions from mining activities.

Keywords: Potentially Toxic Elements; regional food; Pb isotopes; traceability; Sonora River basin; Mexico

 

RESUMEN

La cuenca superior del río Sonora, en el noroeste de México, es una región con minería activa e histórica, así como con una intensa actividad agrícola y ganadera. El derrame en la mina Buenavista del Cobre, ocurrido en 2014, generó gran preocupación entre las comunidades, incluida la seguridad alimentaria. En este estudio, se midieron elementos potencialmente tóxicos, EPT, (Al, As, Ba, Cd, Cr, Cu, Fe, Ni, Pb, Zn, y Tl) y las razones isotópicas de Pb en muestras de alimentos y productos alimenticios regionales (chorizo de res, machaca (carne seca) de res, hígado de res, pulpa de res, queso fresco y chile colorado) recolectadas en sitios representativos a lo largo de la cuenca. En comparación con las directrices internacionales, solo dos de 20 muestras de carne de res superaron el límite de Pb de 0.1 mg/kg establecido por la FAO/OMS y la UE, principalmente en productos preparados (chorizo, machaca). Una muestra de hígado superó el límite de Pb de la FAO/OMS (0.2 mg/kg). Para el chile colorado, una muestra excedió la directriz de Pb de 0.6 mg/kg (FAO/OMS). En general, los niveles de Pb no sobrepasaron las recomendaciones de la FAO/OMS. Las composiciones isotópicas de Pb en la mayoría de las muestras de alimentos coinciden con el rango de rocas de Norteamérica, lo que indica una influencia limitada de la minería. La variabilidad en la composición isotópica de Pb puede estar relacionada con los métodos de preparación y anomalías geogénicas. Aunque el derrame en la mina representó un importante desastre ambiental, los EPT en alimentos y productos alimenticios son consistentes con el fondo geoquímico de la región. Esta interpretación es apoyada por las composiciones isotópicas de Pb, lo que indica que el plomo en los productos alimenticios es de fuente natural (geogénico), y no hay evidencia clara de aporte de Pb asociado a actividad minera.

Palabras clave: elementos potencialmente tóxicos; comida regional; isótopos de plomo; trazabilidad; cuenca del río Sonora; México

 

 

INTRODUCTION

Rapid industrial development has significantly increased the pollution by potentially toxic elements (PTE) in the environment (Jiang et al., 2017). PTE are considered hazardous due to their capacity for bioaccumulation, biomagnification, toxicity, and environmental persistence. When present in high concentrations, they can impact the quality of water bodies, the atmosphere, soil, and living organisms (Li et al., 2014; Boente et al., 2020; Rehman et al., 2020). Some elements (e.g., Cu, Fe, Zn) are essential for organisms due to their fundamental biological roles and participation in various enzymatic reactions (Rodríguez-Marín et al., 2019). However, relatively high concentrations can be harmful for organisms (Kamunda et al., 2016; Bonanno et al., 2017; Zhou et al., 2020). In contrast, elements such as As, Cd, Cr, Hg, Pb, and Tl lack confirmed biological functions in organisms and can be toxic, even at low concentrations.

PTE can originate from both geogenic (e.g., rock erosion, pedogenesis, volcanism) or anthropogenic sources (e.g., mining, agriculture, industrial emissions, urban effluents) (Loredo et al., 2003; Ihedioha et al., 2017; Marrugo-Negrete et al., 2017; Duan et al., 2020). Mining, while economically important from the local to the global level, generates large amounts of waste, for instance, mine tailings containing As, Cd, Cu, Hg, Pb, Sb, Sn, and Zn (Anawar, 2015). Moreover, PTE can persist in the environment for centuries after ceasing mining operations (Coelho et al., 2012; Peña-Ortega et al., 2019). Other significant PTE sources include the growing industrial and urban activities, contributing pollutants to air, soil, and water (Pan et al., 2018; Ali et al., 2019; Müller et al., 2020).

Once in the environment, PTE can interact with humans through inhalation, dermal absorption, and ingestion. The latter is the main route of PTE exposure due to consuming food contaminated with PTE (Bi et al., 2018; Khan et al., 2020). Therefore, monitoring PTE concentrations in edible products is crucial, particularly in regions with mining activities (e.g., Liu et al., 2010; Alturiqui et al., 2012; Zhao et al., 2016; Wang et al., 2019).

Identifying contaminating sources is challenging (Cheng & Hu, 2010). Isotope geochemistry, particularly Pb isotope systematics, provides an effective tool for tracking Pb sources in the environment. Pb has four naturally occurring stable isotopes (204Pb, 206Pb, 207Pb, and 208Pb); 204Pb is non-radiogenic, while 206Pb, 207Pb, and 208Pb are the decay products of 238U, 235U, and 232Th, respectively (Dickin, 2018). A particularity of the Pb isotopic ratios is the lack of fractionation during emission, transport, and deposition processes, enabling source identification (geogenic vs. anthropogenic) and tracing of PTE in environmental media (Yoo et al., 2014; Brewer et al., 2016; Lee et al., 2019; Mihaljevič et al., 2019; Yu et al., 2024).

The upper basin of the Sonora River (Figure 1) is a region historically linked to mining, agriculture, and livestock farming. The region includes significant mining operations such as the Buenavista del Cobre (Cu-Mo) mine in Cananea, the Las Chispas mine, the Santa Elena (Au) mine in Banámichi, and the San Felipe de Jesús area (Cu, Pb, Zn, and Au). Previous studies have assessed the environmental impact of mining in this region, particularly after the Buenavista del Cobre mine spill in 2014 (e.g., Aguilar-Hinojosa et al., 2016; Díaz-Caravantes et al., 2016; Calmus et al., 2018; Rivera-Uria et al., 2018; Escobar-Quiroz et al., 2019; Romero-Lázaro et al., 2019; Romo-Morales et al., 2020). Dispersion, bioaccessibility, and toxicity of historic mine tailings have also been examined (Del Rio-Salas et al., 2019; Loredo-Portales et al., 2020).

 

 

While mining and agriculture are vital to economic development, they can contribute to the release of PTE into the environment, posing risks to ecosystems and human health. The presence of PTE in food is a growing concern in the region due to its potential public health implications. Dietary exposure to PTE requires careful assessment, especially considering the dietary habits of the Mexican population (e.g., Galeana-Pizaña et al., 2023). Elevated concentrations of PTE may exacerbate the country’s burden of non-communicable diseases, such as type 2 diabetes and cardiovascular disease (Reyes-Pablo et al., 2020; Villerías Alarcón, I., & Juárez Gutiérrez, 2021), by increasing vulnerability, inducing oxidative stress, or causing direct damage to key organs such as the kidneys or liver (Niede & Benbi, 2022).

This research evaluates the PTE concentrations in regional food products most commonly consumed in settlements located in the Sonoran River basin. Here, Pb isotope measurements are incorporated to estimate the contributions of anthropogenic and geogenic sources in food products. Studied products include beef (i.e., chorizo, liver, top round, and shredded beef jerky), farmer’s cheese, and red chili. These products are not only consumed on a daily basis but also have deep cultural roots in these communities (Sandoval-Godoy & Camarena-Gómez, 2012). Beyond the scientific importance, this study has significant social implications, since Pb isotope systematics allow differentiation between natural and anthropogenic sources of contamination, offering insight for future assessments of risk associated with the consumption of locally produced foods. Moreover, this research can help to strengthen trust in local foods and food products and empower affected communities by keeping them informed and engaged in environmental and public health decision-making processes.

 

ENVIRONMENTAL FRAMEWORK

Site description

The Sonora River is born east of Cananea at an altitude of 2400 m a.s.l. and flows south along 294 km. The Sonora River basin region comprises an area of ~27000 km2 and is characterized by a subhumid climate in the northern part, becoming more arid in the lower part (Pérez-Quezadas et al., 2021). It has bimodal precipitation, with a winter period consisting of frontal systems and a summer period with convective storms (Robles-Morua et al., 2015). Much of the precipitation in the Sonora River basin is associated with the North American monsoon, which occurs from early July to mid-September (Pérez-Quezadas et al., 2021). Topographic differences in the area result in a wide range of mean annual precipitation, from 350 mm/ year in the southern part of the basin to 700 mm/year in the northern part (Robles-Morua et al., 2015). During most of the year, the Sonora River may represent the only source of surface water for living beings in the region, as well as for the development of productive activities.

 

Geology of the region

The Sonora River basin is located on the southwestern margin of the North American craton, where the Proterozoic basement is composed of crystalline rocks from the Mazatzal and Yavapai provinces, which were accreted 1.63 Ga (Iriondo & Premo, 2011). The Mazatzal province is characterized by the Pinal Schist, which has an age of 1.69 to 1.64 Ga (Anderson & Silver, 2005; Page et al., 2010) and was intruded by Mesoproterozoic plutons, such as the 1.44 Ga Cananea granite (Anderson & Silver, 1977; Noguez-Alcántara, 2008). The Yavapay province is characterized by metamorphic rocks that were intruded by the 1.73 Ga Crestón granite (Valenzuela-Navarro et al., 2005). Neoproterozoic and Paleozoic rocks are poorly represented in the upper Sonora River basin; only a few outcrops are found in the Bacoachi area and west of Cananea, as well as roof pendants in the El Jaralito batholith (Roldán-Quintana, 1991) west of Baviácora. In the Hermosillo area, Paleozoic rocks are represented by intercalations of limestones and sandstones (Peña-Leal et al., 1999) (Figure 2).

 

 

The tectonic evolution from the upper Permian to the Upper Miocene was mainly controlled by the subduction of the Pacific oceanic plates beneath the North American plate. In the study area, the Mesozoic rocks range from the Middle Triassic to the Upper Cretaceous. The Triassic is mainly represented by sandstones and limestones that outcrop east of Hermosillo (Peña-Leal et al., 1999). In the study area, Jurassic rocks record magmatic arc activity as well as the development of back-arc basins along the continental margin (Dickinson & Lawton, 2001; Mauel et al., 2011). During the Early Cretaceous, shallow marine sedimentary rocks of the Bisbee Group were deposited during marine transgression from the Gulf of Mexico. During the Late Cretaceous and Paleocene, intense igneous activity occurred along the North American Cordillera between 80 and 40 Ma, known in Sonora as the Cretaceous-Eocene Mexican Magmatic Arc (Valencia-Moreno et al., 2021); this event is well represented in the study area, mainly by the Aconchi batholith and the volcanic rocks of the Tarahumara and Mesa formations. The igneous activity continued during the Cenozoic, corresponding to the westernmost manifestations of the Sierra Madre Occidental volcanic province (González-León et al., 2011). During the late Oligocene-Miocene (Gans, 1997; González-León et al., 2010), the Basin and Range extensional event thinned the crust, resulting in N-S to NNW-SSW elongated ranges and valleys bounded by normal faults. The extension was characterized by exhumation controlled by low-angle normal fault activity, marked by a high erosion rate and the supply of the large volumes of clastic sediments of the Báucarit Formation and the Sonora Group (Grijalva-Noriega & Roldán-Quintana, 1998; González-León et al., 2010).

 

METHODOLOGY

Elemental concentrations

A total of 40 samples of foods and food products were collected from the upper Sonora River basin from the most representative settlements along the basin: Aconchi, Arizpe, Bacoachi, Banámichi, Baviácora, Chinipa, Huépac, La Capilla, Mazocahui, Ranchito de Huépac, San Felipe de Jesús, and Ures (Figure 1b). The samples included beef chorizo (n=9), beef liver (n=3), shredded beef jerky (n=3), beef top round (n=8), farmer’s cheese (n=5), and red chili (n=11). Each sample was placed in polyethylene bags and transported in coolers to a refrigerator for storage until analysis. Beef samples were washed with distilled water to remove external contamination and cut into small pieces with a stainless-steel knife.

The food samples were subjeted to acid digestion using a wet method in a closed system in 100 mL PFA digestion Savillex vessels. Around 10 g (beef and cheese) and 5 g (red chili) were weighed into Savillex containers; 10 mL of concentrated nitric acid was added, and the samples were left at room temperature for 12 hours. Subsequently, a gentle heating was applied for 3 hours until the solid particles disappeared. Then, 3 mL of 30% H2O2 was added at 15-minute intervals until the solutions turned from amber to clear. Next, the samples were evaporated at low temperature until reaching a volume of 5 mL. The elemental determination was carried out in triplicate using a Perkin Elmer Avio 500 ICP-OES at the Facultad de Química, Universidad Nacional Autónoma de México. For quality control, blanks, spiked blanks, certified reference material (BOVM-1), and an internal standard for continuous calibration and verification were used. The detection limits during measurements are shown in Tables 1 and 2. Element recoveries were ± 20% for all elements, except for Pb, which recoveries were within 5%.

 

 

 

Pb isotope ratios

In addition to the food samples, one sample of mine waste was collected from the El Lavadero, located 5 km east of San Felipe de Jesús town. Also, two river sediment samples from the Sonora River were collected, along with a pyrite sample and a porphyry rock from the Buenavista del Cobre mine. The digestion of the pyrite, tailings, and river sediment samples was done with aqua regia (double-distilled acids) for one night. The whole rock sample was digested with HF (29 M) and HNO3 (16 M) in ultraclean Savillex screw-cap vessels at 100 °C overnight. The solution was evaporated to dryness, then HNO3 (16 M) was added, and the mixture was heated at 100 °C overnight. The solution was evaporated, and HCl (10M) was added and kept at 100 °C overnight to ensure total digestion.

The acids used during digestion and treatment for measuring Pb isotope ratios were distilled twice in a Savillex distiller, and the solutions were prepared using ultrapure (18.2 MΩ) Milli-Q water. To determine the Pb isotope ratios, the digested samples were evaporated and dissolved in HNO3 (8M) to perform chromatographic procedures. The digested samples were reconstituted with HNO3 (8 M) for chromatography using Sr-Spec™ resin, following the procedures of Stegink and Rader (2024) and Del Rio-Salas et al. (2025). The resin was cleaned and preconditioned with HCl (8M) and HNO3 (8M). The removal of matrix elements was performed by elution with HCl and HNO3. Later, Pb was collected by eluting it with HCl (8M), according to the procedure reported by Deniel and Pin (2001). The Pb solution was then evaporated and reconstituted with 2% HNO3 to perform the Pb isotope ratios measurements on a Nu Plasma II Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) in the Department of Earth and Atmospheric Sciences Metal Isotopes Laboratory at Indiana University-Bloomington. The isotope ratios 208Pb/206Pb, 207Pb/206Pb, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb are reported after being normalized to Galer and Abouchami (1998). All Pb isotope results were Hg-corrected, albeit the Hg correction was nominally to zero, and corrected online for mass discrimination using the known Tl ratio of the NIST-997 spike. Precision and accuracy were constrained using the NBS-981 standard (n=33), with errors during the measurements at the Indiana University-Bloomington laboratory being 208Pb/206Pb = 2.1677 (0.0001-0.0006 2σ), 207Pb/206Pb = 0.9148 (0.00003-0.0002 2σ), 206Pb/204Pb = 16.9405 (0.0014-0.0042 2σ), 207Pb/204Pb = 15.4963 (0.0012-0.0049 2σ), and 208Pb/204Pb = 36.7219 (0.0033-0.0160 2σ).

 

RESULTS AND DISCUSSION

Elemental concentrations

Tables 1 and 2 display the concentrations of Al, As, Ba, Cd, Cr, Cu, Fe, Ni, Pb, Zn, and Tl (mg/kg) in foods from the upper Sonora River basin. Comparing these values to the Upper Continental Crust (UCC) (Rudnick and Gao, 2003), and the local geochemical background (Calmus et al., 2018) (Tables 1 and 2), the liver samples nearly tripled the Cu values. Liver samples from Aconchi and one from Ures, shredded beef jerky from Aconchi and San Felipe de Jesús, and top round samples from Baviácora, Huépac, and Banámichi, exceeded the Zn value for the UCC and the local geochemical background. One liver sample from Aconchi and red chili samples from Aconchi, Mazocahui, Banámichi, and San Felipe de Jesús exceeded the Cd value of the UCC.

The Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) through the Codex Alimentarius (FAO/WHO, 2023), the European Union (EU, 2023), and the National Food Safety Standard for Maximum Levels of Contaminants in Food GB-2762-2022 established by China (Foreign Agriculture Service [FAS], 2022) have set recommendations for the maximum permissible concentration of Pb and Cd. Specifically, the FAO/WHO sets limits of 0.1 mg/kg for Pb in beef and 0.2 mg/kg in beef liver. Likewise, the European Union recommends a maximum allowable concentration of Pb at 0.1 mg/kg in beef and 0.2 mg/kg in liver, as well as a maximum limit for Cd at 0.05 mg/kg in beef and 0.5 mg/kg in beef liver (EU, 2023). Conversely, GB-2762-2022 recommends a Pb limit for beef (0.2 mg/kg), beef offal (0.5 mg/kg), beef derivatives (0.3 mg/kg), dairy derivatives (0.2 mg/kg), and spices (1.5 mg/kg), while also establishing Cd limits in beef (0.1 mg/kg), beef liver (0.5 mg/kg), and beef derivatives (0.1 mg/kg).

Based on these reference values, the Pb concentrations in chorizo samples from Bacoachi, Arizpe, Huépac, Banámichi, Aconchi, and Ures are below the maximum permissible levels set by the European Union and FAO/WHO. In contrast, the C53 chorizo sample from Baviácora exceeds this limit but remains within the limits of GB-2762-2022 (Figure 3). The Pb concentrations in shredded beef jerky samples collected from San Felipe de Jesús and Arizpe exceeded the maximum permissible values established by FAO/WHO and the European Union (Figure 3) but are below the recommended limit for beef derivates (0.3 mg/kg) according to GB-2762-2022.

 

 

Regarding Cd contents, none of the studied samples exceeded the GB-2762-2022 recommended values of 0.1 mg/kg for beef and beef derivatives or the European Union values of 0.05 mg/kg. In the case of Cd in the liver samples, none of them exceed the established maximum limit of 0.5 mg/kg (EU, 2023; FAS, 2022) (Figure 4). Cu and Zn are considered essential micronutrients. So far, no limits have been established by food safety regulations worldwide for these elements in meat and meat derivatives. However, chronic exposure to Cu may cause adverse health effects (More et al., 2023; National Institutes of Health, 2024). Values for Cd, Cu, and Pb in beef products from the Sonora River region are similar to those reported for the Zhejiang Province, southeast China, where a relatively low health risk was observed (Han et al., 2022).

 

 

In the case of the red chili samples, only the C36 sample from Mazocahui slightly exceeded the maximum permissible value recommended for Pb (0.6 mg/kg) established by the European Union (Figure 5). However, the value does not surpass the GB-2762-2022 recommended value (1.5 mg/kg). No permissible limits have been set for Cd, Cu and Zn in red chili. Nonetheless, these elements may cause toxic or carcinogenic effects at high doses (National Toxicology Program, 2021; More et al., 2023). Cadmium content in red chili from the upper Sonoran River basin is similar to that reported from a mining region in the Guizhou Province, southern China, with an average of ~0.06 mg/kg (Zhou & Liu, 2024).

 

 

Regarding farmer’s cheese, GB-2762-2022 sets a limit of 0.2 mg/ kg of Pb in dairy products and derivatives, whereas FAO/WHO establishes a limit of 0.02 mg/kg. Pb contents in the cheese samples from the upper Sonoran River basin do not exceed such limits; therefore, there is no concern associated with the consumption of these goods. No limits have been established for Cd, Cu and Zn in farmer’scheese.

The relatively high values found in some foods and food products can be attributed to the natural geochemical anomalies in the region (Calmus et al., 2018). However, according to the data reported in the region, the concentrations of Cu, Pb, and Zn in surface sediments along the Bacanuchi and Sonora rivers (León-García et al., 2021; Figure 1) are similar to or even lower than those of the UCC. Even so, considering the element mobility reported by Aguilar-Hinojosa et al. (2016) in river sediments very close to the Buenavista del Cobre mine, where the 2014 spill occurred, Zn mobility is relatively high (up to

248 mg/kg), while that of Cd and Pb is practically negligible. Further south in the basin, at an abandoned mining site in San Felipe de Jesús, nearby agricultural soils showed mobile Zn concentrations of 4400–4100 mg/kg and Pb concentrations of 552–689 mg/kg; phytoaccessible fractions in these soils ranged from 380 ppm for Zn to as high as 136 mg/kg for Pb (Loredo-Portales et al., 2020). In this area, the high mobility of these elements is associated with the oxidation of sulfides of the San Felipe de Jesús tailings, which are characterized by high metal concentrations (Del Rio-Salas et al., 2019).

For the other elements listed in Tables 1 and 2, no international regulatory limits have been set for Cr, Ba, Al, Fe, and Ni in meat products or red chili. However, these elemental concentrations should serve as a reference for future assessments in the region in the event of any other anthropogenic incident. In the case of As, the Codex Alimentarius (FAO/WHO, 2023) recommends limits for specific products (edible fats, oils, fat and blended spreads, mineral water, rice, and salt), and such limits do not apply to the food products in this study. However, further investigations are warranted for red chili due to its relatively high As content (Table 2).

 

Pb isotope composition

The Pb isotope ratios of edible product samples collected in the upper Sonora River basin are listed in Table 3. Table 4 shows the Pb isotope composition of sediments from the Sonora River and mine tailings in the San Felipe de Jesús region (Del Rio-Salas et al., 2024). Samples of pyrite and a porphyritic rock from the Buenavista del Cobre mine in Cananea and a galena from the inactive El Gachi mine (Del Rio-Salas et al., 2024) were also considered in the study. Table 4 also includes the Pb isotope composition of the fluid spilled from the Buenavista del Cobre mine in 2014, and a sample of sediment from the Tinajas 1 dam, where the spill originated (Romo-Morales et al., 2020). Finally, the Pb isotope composition of the lithology from the southern part of the basin (Puerta del Sol area; González-Becuar et al., 2017), and the lithology located further north in the basin (González-León et al., 2011), as well as the lithology from the southern state of Arizona (Bouse et al., 1999), are included.

 

 

 

The isotope ratios 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in the samples of edible products of animal origin averaged 19.012, 15.712, and 38.836, respectively. In contrast, the red chili samples showed averages of 18.904 (206Pb/204Pb), 15.674 (207Pb/204Pb), and 38.886 (208Pb/204Pb). Figure 6 shows the scatter diagram of 207Pb/206Pb vs. 208Pb/206Pb, revealing a trend in the isotope values of the edible product samples with a positive slope, characterized by a correlation factor of r=0.97. This trend indicates more radiogenic lead (relatively lower values of 207Pb/206Pb and 208Pb/206Pb) and less radiogenic lead (relatively higher values of 207Pb/206Pb and 208Pb/206Pb). Figure 6 displays the fields of Pb isotope compositions of lithologies associated with the Caborca and North America blocks according to data reported in the region by Bouse et al. (1999), González-León et al. (2011), and González-Becuar et al. (2017).

 

 

Even though most of the food samples were obtained from settlements that lay in the Caborca block (i.e., downstream of the study area), the majority of the Pb isotope composition data is located within the composition field of rocks from the North America block, except one chorizo sample from Arizpe, one farmer’s cheese sample from Chinapa, and one shredded beef jerky sample from Aconchi. This suggests that the lithology of the North American block influences the isotope composition of downstream sediments because of sediment contributions from the upstream basin. Additionally, the configuration of basement rocks may explain the composition of edible products; the magmatic activity beneath the Caborca block also interacted with rocks from the North America block, imprinting the isotope composition in rocks and derivatives (e.g., soils, sediments).

Figure 7 presents the Pb isotope data normalized to 204Pb. The fields defining the isotope composition of rocks from the Caborca (more radiogenic) and North America (less radiogenic) blocks are also clearly defined. In contrast, the Pb composition of edible products is quite dispersed, and no logical trend or pattern is observed, which is typical of geological samples (e.g., rocks, soils, sediments). This dispersion in the isotope composition data may be linked to food preparation, as the composition of Pb can be influenced by interactions with artifacts used during preparation and transportation (Nerín et al., 2016; Pakdel et al., 2023).

 

 

Mining activity is considered a potential source of anthropogenic PTE inputs in the study area. The dispersion of PTE is associated with mine tailings impoundments from both active and inactive facilities (Romero et al., 2007; Peña-Ortega et al., 2019; Rubinos et al., 2021; Reddy et al., 2022). The Pb isotope compositions from the Buenavista del Cobre mine mineralization, the 2014 spilled solution, and the associated sediments are shown in Figure 7 (Romo-Morales et al., 2020; Del Rio-Salas et al., 2024). The Pb isotope composition of the pyrite sample related to the mineralization at the Buenavista del Cobre mine closely resembles that of the sediments containing the spilled solution. In contrast, the spilled solution exhibits a more radiogenic signature regarding the 207Pb/204Pb and 208Pb/204Pb ratios, suggesting a mixture with additional components, including chemical reactants used to extract the metals of interest. This suggests that the 2014 spilled solution from Buenavista del Cobre mine has not influenced the composition of food products in the region, as indicated by the Pb composition of watercress from the study area (Romo-Morales et al., 2020). Figure 7 illustrates the sulfide-rich and oxide-rich tailings from San Felipe de Jesús (Del Rio-Salas et al., 2024) and the El Lavadero facility. The latter resembles the composition of the sulfide-rich tailings from San Felipe de Jesús, indicating a link with the sulfide mineralization exploited in the region (e.g., the inactive El Gachi mine; Del Rio-Salas et al., 2024).

Studies of cattle exposed to mining areas yielded higher concentrations of Pb and Cd in the liver and kidneys (Yabe et al., 2011), whereas in beef tissue, the concentrations were within acceptable ranges (e.g., Cai et al., 2009). Similar findings were observed in goats exposed to historical mining areas in southern Mexico (Salgado-Souto et al., 2025), pointing to the effectiveness of Pb isotope signatures in tracing exposure to PTE. However, there is no clear influence of the environment impacted by mining activities (both active and inactive) in the Sonoran River basin. Rather, the Pb isotope composition of most edible food products falls within the area defined by rocks of the North American block, while some are positioned close to its margin. However, human involvement in the preparation process can affect the elemental content of edible products, particularly in shredded beef jerky, chorizo, ground beef, red chili, and farmer’s cheese. During preparation, tools, condiments, and other items can alter the Pb isotope composition.

A more detailed comparison between the Pb isotope composition of edible products and the main potential sources of Pb in the region indicates that most samples do not overlap with the compositions defined by mine tailings, mineralization, or the 2014 mine spill and associated sediments. This suggests that these anthropogenic sources have not contributed to the Pb composition of regional food. Most of the edible products are plotted by the field defined by the regional lithologies, particularly those from the North American block, highlighting the geogenic nature of Pb.

 

Implications

The PTE concentrations in most measured food and food product samples are below the recommended limits set by the FAO/WHO and European Union guidelines, suggesting no contamination in regional products of the study area. A limited number of samples exceeded the recommended Pb values, suggesting local variability rather than a regional pattern. A previous study by Calmus et al. (2018) determined the natural geochemical background of the region, considering all the lithological units outcropping in the area; the findings were that some elements of environmental interest (i.e., Pb, Cu, Zn, As, Ag, among others) were slightly enriched with respect to the UCC. These geochemical anomalies may influence the composition of soils and sediments and, ultimately, contribute to the composition of food and food products. The Pb isotope compositions of regional food products support this, as they are similar to the Pb isotope compositions of the lithological units, indicating their geogenic nature and excluding anthropogenic sources, with no clear evidence of mining-related impacts. Although this investigation does not provide a quantitative health risk assessment, the results highlight the importance of monitoring PTE contents in food and food products, particularly in regions where historical mining has been a major economic activity.

 

Limitations of the study

A limitation of this study is the relatively small number of samples analyzed, which may not fully represent the variability of PTE concentrations throughout the Sonora River basin. Future research should include a larger sample size and adopt a more systematic sampling approach to improve statistical data and spatial representativity. Moreover, this study lacks detailed data on food consumption patterns (frequency and amount) and dietary surveys. Future studies should include this information to provide a more complete context for the presence of PTE in food products, and ultimately, perform a risk assessment.

 

CONCLUSIONS

The concentrations of Al, As, Ba, Cd, Cr, Cu, Fe, Ni, Pb, and Zn found in regional foods, including chorizo, liver, top round, shredded beef jerky, farmer’s cheese, and red chili, commonly consumed in the upper Sonoran River basin, showed variations among the different settlements. When using the Upper Continental Crust as a reference, some of these products exceeded the Cu, Zn, and Cd levels, which may be due to the region's natural geochemical anomaly. However, limited processed foods, such as chorizo and beef jerky, exceeded the Pb limits set by the FAO/WHO and the European Union, indicating isolated variability rather than a consistent regional contamination pattern. Most of the Pb isotope compositions of these regional edible products fall within the compositional field of North American block rocks, indicating that Pb is mainly derived from geogenic sources, with no clear evidence of significant influence from mining activities (both active and inactive). Variability in isotope composition may be related to the preparation process, where human involvement can influence elemental content, especially in shredded beef jerky, chorizo, ground beef, red chili, and farmer’s cheese. These findings highlight the value of Pb isotope systematics as a tool for tracing contamination sources in food systems, even at low concentrations.

 

Acknowledgments. We are grateful to D. Ramos Pérez for determining the elemental contents, and to J.F. Martínez Rodríguez and E. González Becuar for providing laboratory and logistic support. We also thank Departamento de Geología, Universidad de Sonora and the Laboratorio de Ciencias Ambientales at Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, for their support to the project.

Author contributions. DRM (Writing - Original Draft; Conceptualization; Formal analysis, Visualization), VMR (Writing - Original Draft; Writing - Review & Editing, Conceptualization), SR (Writing - Review & Editing, Formal analysis, Resources, Data curation), RLP (Writing - Review & Editing, Formal analysis, Resources), IGEM (Writing - Review & Editing, Funding acquisition, Interpretation), MVM (Writing - Review & Editing, Interpretation), VLT (Writing - Review & Editing, Interpretation), FESB (Writing - Review & Editing, Interpretation), RDS (Writing - Original Draft, Writing - Review & Editing, Conceptualization).

Declaration of competing interests. The authors declare that they have no financial, academic, or personal relationships that could be perceived as influencing the research presented in this manuscript. The study was conducted independently of any organizations or individuals that could benefit from the results.

Data availability statement. All data utilized in this study are fully available and are provided in the accompanying tables.

Funding. This investigation was partially supported by project IA205524 (PAPIIT-DGAPA-UNAM) granted to Loredo-Portales.

 

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Editors:

Luigi A. Solari

Alexis Del Pilar Martínez

Rafael Del Rio-Salas

 

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