Water resources affected by potentially toxic elements in an area under current and historical mining in northwestern Mexico.

Rio Sonora watershed and its aquifer-located in northwest Mexico-have been influenced by mining operations for 140 years, possibly causing emissions of potentially toxic elements (PTE) and affecting health of exposed populations. On the basis of available data from governmental surveys (2014-2017) and recent sampling (2018), this study constructed reliable PTE total concentration database that allowed us to report temporal/spatial variations in surface and groundwater and their associated health risks to the population living in the central part of the Rio Sonora basin. The data clearly showed that a mining spill that took place in 2014 has had an adverse impact on total PTE concentrations in surface water. They also indicated the presence of different PTE point source locations that have continued to cause contamination of surface water at levels of health concern. Data also suggested slight impacts of the spill event on groundwater possibly related to soil neutralizing potential. Two metal groups were detected for surface waters (Pb-Cd-As-Ni-Cr and of Zn-Al-Cr) and groundwaters (Cr-As-Cu-Cd and Zn-Al), which suggest that they have different sources or are being released by different processes. The potential health impacts of PTE concentrations were associated with specific age groups, dates, and areas. The results indicate that in this complex semi-arid rural system, current and historical mining activities, as well as contrasting hydrological conditions, have impacted surface and groundwater quality with important ecological and human health risks.

Mobility and accessibility of Zn, Pb, and As in abandoned mine tailings of northwestern Mexico.

Generation, storage, and management of waste coming from industrial processes are a growing worldwide problem. One of the main contributors is the mining industry, in particular tailings generated by historical mining, which are barely maintained, especially in developing countries. Assessing the impact of a mining site to surrounding soils and ecosystems can be complex, especially when determining mobility and accessibility of the contaminants is required to perform ecological and human health risk assessment. As an effort to obtain information regarding mobility and accessibility of some potentially toxic elements (Zn, Pb, and As) from an historical mining site of northwestern Mexico, the abandoned mine tailings of San Felipe de Jesús in central Sonora and adjacent agricultural soils were investigated. Mobility and accessibility were assessed by means of sequential extraction procedures and using simulated physiological media. Additionally, an assessment of accidental oral intake was calculated considering the bioaccessible fractions. Results show that higher concentrations of contaminants were found in sulfide-rich tailings (Zn = 92,540; Pb = 21,288; As = 19,740 mg kg-1) compared with oxide-rich tailings (Zn = 43,240; Pb = 14,763; As = 13,401 mg kg-1). Concentrations in agricultural soils were on average Zn = 4755, Pb = 2840, and As = 103 mg kg-1. Zinc was mainly recovered from labile fractions in oxide-rich tailings (~ 60%) and in a lower amount from sulfide-rich tailings (~ 30%). Pb and As were mainly associated with residual fractions (80-95%) in both types of tailings. The percentage of mobile fractions (sum of water-soluble, exchangeable, and bound to carbonate fractions) in agricultural soils was as follows: Zn ~ 60%, Pb ~ 15%, and As ~ 70%. Regarding the phytoaccessible fraction, the studied elements in mine tailings and agricultural soil samples exceeded the threshold limits, except for As in agricultural soils. According to data obtained, toxic effects were also calculated. As for daily oral intake for non-carcinogenic effects in adults and children, only Pb and As exceeded reference dose values, especially in children exposed to sulfide-rich tailings and agricultural soils. Regarding carcinogenic effects of Pb and As, most of the samples were above acceptable risk values.

N2O emission factors from a wastewater irrigated land in a semiarid environment in Mexico.

Irrigation with wastewater is an increasing practice around the world triggered by the large needs of water for agriculture. Many times this source of water is added by flooding to the fields, creating short temporal oxygen-depleted environments, where nitrous oxide (N2O) emissions are promoted. Agriculture is responsible for up to 60% of the global annual emissions of this gas, and its emission factors (EF) must be reported. During 21 months, we installed closed chambers to measure the N2O emissions from a wastewater irrigated plot in the Mezquital Valley. Here, alfalfa, rye grass, and maize were grown in succession, receiving mainly organic N contained in the untreated wastewater and the residues of the previous crop; only maize received extra mineral fertilization of 100 kg of N ha-1. We obtained a time series where the gaps were filled by linear interpolation. EF and N2O direct emissions were estimated by the Tier 1 approach of the IPCC. We found that the alfalfa and rye grass, which only receive organic nitrogen, produced minor N2O emissions, that reflected in lower EF (0.004 and 0.001, respectively), compared with the default value of the IPCC (0.01). In contrast, maize, which receives organic and inorganic N, lost 1% of this N input as N2O, the same as the default value (0.01). It seems that the form of N, the crop age and type influence greatly the N dynamics in this wastewater irrigated land-use system. Therefore, the Tier I approach of the IPCC seems to underestimate the N efficiency of this agroecosystem and overestimates the N2O direct emissions from alfalfa and rye grass.

Seropositividad de la infección por HCV y HBV, en estudiantes universitarios del Estado de Nuevo León, México / Positive serology for HCV and HBV infection in univertity students of the state on Nuevo Leon, Mexico

Antecedentes: La hepatitis viral es una enfermedad infectocontagiosa. Los pacientes infectados con virus de la hepatitis B (HBV) o con virus de la hepatitis C (HCV) pueden evolucionar a un estado crónico sintomático o asintomático que ocasiona cirrosis y un riesgo muy alto de carcinoma hepático. Objetivo: Los sujetos asintomáticos portadores del antígeno de superficie del HBV (Hbs-Ag) o de anticuerpos dirigidos contra HCV son potencialmente infectantes, por lo que desde el punto de vista de salud pública, es muy importante detectarlos. Métodos: En este trabajo se buscó la frecuencia de seropositividad de HBs-Ag y de anticuerpos anti-HCV en una población de 774 jóvenes de nuevo ingreso a la Facultad de Medicina de la Universidad Autónoma de Nuevo León, con una edad promedio de 188 años. Para detectar HBs-Ag se usó una prueba de ELISA de segunda generación y una prueba confirmatoria de neutralización. Los anticuerpos anti-HCV se midieron por un ELISA de segunda generación y por una prueba confirmatoria de un inmunoensayo en línea o RIBA. Tesultados: Se detectaron tres sueros positivos en HBs-Ag por ELISA, y sólo un suero (0.13 por ciento de las muestras analizadas) se confirmó por neutralización. En cambio se obtuvieron 12 sueros con anticuerpos dirigidos contra HCV por ELISA, de los cuales 8 fueron confirmados por RIBA ( 1.03 por ciento de la población total analizada). Dos sueros positivos mostraron bandas de reactividad intensa y 6 dieron bandas de reactividad débil. Los 4 sueros negativos representan el 0.5 por ciento de falsos positivos de la prueba de ELISA para determinar anti-HCV. Conclusiones: En este estudio se encontró que la frecuencia de anticuerpos anti-HCV fue 7.95 veces más alta que la de HBs-Ag. Todos los sujetos seropositivos estaban asintomáticos, pero son considerados potencialmente infectantes. Este trabajo pone de manifiesto la necesidad de implantar en forma rutinaria las técnicas de detección de HBs-Ag y de los anticuerpos anti HCV, para poder establecer la prevalencia de estas enfermedades virales en nuestra región.