No abstract

The activity concentration of 222Rn, 226Ra and total uranium in groundwater samples collected from wells distributed throughout the state of Chihuahua has been measured. The values obtained of total uranium activity concentration in groundwater throughout the state run from <0.03 up to 1.34 Bq l-1. Generally, radium activity concentration was <0.16 Bq l-1, with some exceptions; in spring water of San Diego de Alcalá, in contrast, the value reached approximately 5.3 Bq l-1. Radon activity concentration obtained throughout the state was from 1.0 to 39.8 Bq l-1. A linear correlation between uranium and radon dissolved in groundwater of individual wells was observed near Chihuahua City. Committed effective dose estimates for reference individuals were performed, with results as high as 134 microSv for infants in Aldama city. In Aldama and Chihuahua cities the average and many individual wells showed activity concentration values of uranium exceeding the Mexican norm of drinking water quality.

In the preparation of electrodes Pt / C, one of the highlights is its characterization, particularly the possibility of determining the effective charge of platinum available to carry out a reaction by a nondestructive technique. Electrochemical impedance spectroscopy (EIS) is a technique that provides high precision measurements, producing a stable response without significantly altering the system under study. This paper proposes the use of a hydrogen evolution reaction (HER) mathematical model, validated by experimental data obtained from the implementation of the EIS technique to electrodes with different Platinum loads, in a wide range of frequencies and five different overpotentials. The model takes into account the kinetic, diffusive and adsorption aspects, and also allows to obtain the rate constants for each step of the HER reaction in each of the electrodes used. Although this methodology was used only for Pt/C electrodes suggests a much broader application that extends to any metal electrodes that are capable of evolving hydrogen, with minimal modifications for each particular case.

Treated wastewater is commonly used for park irrigation in arid zones of Mexico without considering groundwater contamination. The objective was to investigate the possibility of nitrogen compounds leaching into the groundwater and their subsequent reactions in the main types of soils. Lysimeters samples were taken to scrutinize the soil characteristics of the green areas irrigated with treated wastewater from the Northern Wastewater Treatment Plant in the city of Chihuahua. Testing samples were setup to recreate treated wastewater irrigation conditions. Nitrogen-based compounds were identified and measured before and after percolation through the soil columns. Based on the results, one meter of sand column was sufficient to remove 68 to 100% of nitrogen compounds present in the residual water. The removal of all nitrogen-based compounds as they percolate through one meter of clay soil column was not enough, due to the biochemical reactions that occur through the percolation process. Results indicate minimal risk of nitrate and nitrite leach into the aquifer, since the average static level depth is 20 m which provide broad filtration. This demonstrates an opportunity for in-situ investigations to reevaluate the standards for soil aquifer treatment recharge, based on the soil type and water quality of the area.

Concentrations of As, Cu, Fe, Hg, Pb and Zn and activity concentrations from 234,238U and 210Po in water, fillet, liver and gills were determined in three stocked fish species from the Luis L. Leon reservoir, located in Northern Mexico. The considered species were Lepomis cyanellus, Cyprinus carpio and Ictalurus furcatus. 238U and 234U activity concentration (AC) in fillet samples showed values of 0.007–0.014 and 0.01–0.02 Bq∙kg−1 wet weight (ww), respectively. Liver samples for L. cyanellus, C. carpio and I. furcatus present 210Po AC of 1.16–3.26, 0.70–1.13 and 0.93–1.37 Bq∙kg−1 ww. Arsenic, mercury and lead concentration intervals in fillet samples were 0.13–0.39, 0.005–0.126 and 0.009–0.08 mg∙kg−1 ww, respectively, while in gill samples they were 0.11–0.43, 0.002–0.039 and 0.02–0.26 mg∙kg−1 ww. The elemental Bioaccumulation Factor (BAF) for fish tissues with respect to their concentrations in water was determined. L. cyanellus showed the highest BAF values for As and total U, being BAFAs = 37 and 40 L∙kg−1 in fillet and gills, respectively, and BAFU total = 1.5 L∙kg−1 in fillet. I. furcatus showed the highest BAF values for Hg and Pb, being BAFHg = 40 and 13 L∙kg−1 in fillet and gills, and BAFPb = 6.5 and 22 L∙kg−1 in fillet and gills, respectively. Some metal(loid) concentrations are slightly higher than European regulations for fish fillets. The difference in concentrations of metal(loid)s in fillet among the studied species is probably due to their differences in diet and habitat.