Agustín Gómez-Álvarez

The impact of unconfined mine tailings in residential areas from a mining town in a semi-arid environment: Nacozari, Sonora, Mexico

Past mining activities in northern Mexico left a legacy of delerict landscapes devoid of vegetation and seasonal formation of salt efflorescence. Metal content was measured in mine tailings, efflorescent salts, soils, road dust, and residential soils to investigate contamination. Climatic effects such as heavy wind and rainfall events can have great impact on the dispersion of metals in semi-arid areas, since soils are typically sparsely vegetated. Geochemical analysis of this site revealed that even though total metal content in mine tailings was relatively low (e.g. Cu= 1000 mg kg(-1)), metals including Mn, Ba, Zn, and Cu were all found at significantly higher levels in efflorescence salts formed by evaporation on the tailings impoundment surface following the rainy season (e.g. Cu= 68,000 mg kg(-1)). Such efflorescent fine-grained salts are susceptible to wind erosion resulting in increased metal spread to nearby residential soils. Our results highlight the importance of seasonally dependent salt-formation and wind erosion in determining risk levels associated with potential inhalation or ingestion of airborne particulates originating from contaminated sites such as tailings impoundments. In low metal-content mine tailings located in arid and semi-arid environments, efflorescence salts could represent a human health risk and a challenge for plant establishment in mine tailings.

Metals in residential soils and cumulative risk assessment in Yaqui and Mayo agricultural valleys, northern Mexico

This investigation examines the extent of soil metal pollution associated with the Green Revolution, relative to agricultural activities and associated risks to health in the most important agricultural region of Mexico. Metal contents in bulk soil samples are commonly used to assess contamination, and metal accumulations in soils are usually assumed to increase with decreasing particle size. This study profiled the spatial distribution of metals (Ni, Cr, Pb, Cu, Fe, Cd, V, Hg, Co, P, Se, and Mn) in bulk soil and fine-grained fractions (soil-derived dust) from 22 towns and cities. The contamination of soil was assessed through the use of a geoaccumulation index (Igeo) and pollution index (PI). The results of this study indicated that a number of towns and cities are moderately to highly polluted by soil containing Be, Co, Hg, P, S, V, Zn, Se, Cr, and Pb in both size fractions (coarse and fine). Hazard index in fine fraction (HI(children)=2.1) shows that risk assessment based on Co, Mn, V, and Ni spatially related to power plants, have the potential to pose health risks to local residents, especially children. This study shows that risk assessment based on metal content in bulk soil could be overestimated when compared to fine-grained fraction. Our results provide important information that could be valuable in establishing risk assessment associated with residential soils within agricultural areas, where children can ingest and inhale dust.

Distribution of heavy metals in surface sediments of the Bacochibampo Bay, Sonora, Mexico.

Abstract The aim of this study was to determine the levels of heavy metals (Al, Cd, Cr, Cu, Fe, Mn and Pb) in the geochemical fractions of the coastal surface sediments from the Bacochibampo Bay in Sonora, Mexico. Two surveys were conducted (March and September) during 2004, at eight sampling stations inside the bay, and in three natural effluents discharged into this bay. The extraction of metals was carried out using a microwave oven method and the quantification was done by atomic absorption spectro-photometry. The highest detected concentration of total heavy metals in sediments was: Fe>Al>Mn>Pb>Cr>Cu>Cd, with the following concentration values: Fe (1.72%), Al (1.03%), Mn (416.31 mg kg−1), Pb (11.73 mg kg−1), Cr (11.41 mg kg–1), Cu (6.78 mg kg–1) and Cd (1.33 mg kg–1). The levels of total heavy metals (Al, Cr, Cu, Fe, Mn and Pb) were much less than the lowest observable effect level (LEL) which indicates that the sediments were not from polluted areas and that the origin of the metals was due to natural conditions. However, concentrations of Cd were much higher than the low effect level (LEL), over 40% of metal was detected in the exchangeable fraction and carbonates. The normalisation study showed a high degree of enrichment of Cd in all the sampling stations in the Bacochibampo Bay (samples EF 34–87) and in the natural flows that discharge into this bay (samples EF 22–35%), which exceeds by several orders of magnitude the value of sample EF 1, which indicates that Cd is anthropogenically induced. Based on these results, it is important that precautionary measures are established, since the deposited Cd in these fractions may be potentially toxic, due to the physicochemical changes that occur in the environment. Thus, future studies will focus on identifying problems involved with Cd bioaccumulation in different trophic levels.

Dissolved and particulate metals in water from Sonora Coast: a pristine zone of Gulf of California: metals in water from Sonora Coast.

The purpose of this study was to investigate the distribution of metals (Cd, Pb, Hg, Cu, Fe, Mn, and Zn) in dissolved and particulate fractions in seawater from Bacochibampo Bay, Northern part of Mexico. Water samples were collected from November 2004 to October 2005. Metal analysis was done by graphite furnace atomic absorption spectroscopy. Results indicated highest concentrations of dissolved Cd and Zn in the sites localized at the mouth and center of the bay. During summer and spring, the highest levels of Cd, Mn, and Fe were detected, Zn in fall, and Pb and Cu in winter and spring. Mercury was the only metal that was not found in this fraction. In particulate fraction, Fe, Hg, and Mn were the most abundant elements in all the sampling sites, followed by Zn, Cu, Pb, and Cd. The highest levels of the majority of the metals were observed in the coastline, suggesting a continental and/or urban source for these chemicals. The highest level of Cd was detected during the summer and the rest of the metals in the fall. Statistically significant correlations were observed between dissolved and particulate forms of Pb:Mn, Cu:Fe, and Cu:Mn. The mean partition coefficient values were as follows: Fe>Mn>Cu>Pb>Cd>Zn. All dissolved metal concentrations found, except Pb, were lower than EPA-recommended water quality values. The levels of dissolved metals in this study reveal low bioavailability and toxic potential. However, further toxicological and sediment chemistry studies in this area are needed for a full risk assessment.

Distribution of heavy metals and their chemical speciation in sediments from the Abelardo L. Rodríguez Dam, Sonora, México

Abstract The purpose of this study was to investigate the distribution of total and bioavailable metals (Cd, Cu, Cr, Fe, Mn, Pb and Zn) in sediments of the Abelardo L. Rodríguez (ALR) dam located in the eastern part of the city of Hermosillo, Sonora, Mexico. Seventy two sediment samples were collected in 2009 during four sampling campaigns in February (spring), May (summer), September (end of summer) and December (winter) in five different areas within the dam surface (Zones I, II, III, IV and V), including the Gate Station. Determination of heavy metals was carried out by flame atomic absorption spectrophotometry (FAAS). The results indicate high levels of total heavy metals in the following order: Fe>Mn>Zn>Pb>Cu>Cr>Cd. This is indicative of the impact of human activities located in areas surrounding the reservoir, specifically urban and industrial. The distribution and state of accumulation of trace metals in the sediment is largely dominated by the residual and Fe/Mn oxides geochemical phases. Fraction I (exchangeable) also presented high concentrations of metals (Cu, Fe, Mn and Zn). From enrichment factor analysis, the study area is prevalently enriched in Cd, Cu and Pb in Zones I, II, III, IV and Gate Station. This indicates that the sediments are impacted by anthropogenic activities such as downloads, domestic and industrial wastewater. Geoaccumulation index (Igeo) indicates that Zones I, II, III, IV and V (including Gate Station) do not show contamination by Cr, Fe, Mn and Zn. However, there is a moderate to heavy contamination by Cd, Cu and Pb (Igeo: 2–4) in all areas of study. The comparison between the results obtained with the sediment quality criteria (LEL and SEL), indicate that Zones I, II, III, IV, V and Gate Station, are contaminated with Cd, Cu and Pb, and severely contaminated by Fe. The elevated levels of heavy metals detected in the sediment of the ALR Dam require special attention, since in the exchangeable fraction, the metals are specifically adsorbed on the sediment and can be released when the ionic composition of water changes. However, additional studies are required in this reservoir on the chemistry and toxicology of metals for a full assessment of potential risks posed to biota and man.

Mobility and Bioavailability of Metals in Stream Sediments Impacted by Mining Activities: the Jaralito and the Mexicana in Sonora, Mexico

This study aims at investigating heavy metal mobility and bioavailability in sediments from the Mexicana and Jaralito streams, Northern Mexico. A chemical partition analysis (sequential extraction) was performed to determine geochemical phases in which metals are found. Geoaccumulation index (Igeo) and enrichment factor values were obtained from analytical results and geochemical baseline data. Sediments showed high concentrations (mg/kg) of Cd (below detection limit, BDL-3.50), Cr (3–41), Cu (238–1090), Fe (41267–61033), Mn (678–1143), Ni (18–35), Pb (51–124), and Zn (116–356). Metal concentrations in geochemical phases exhibited the following order: residual > interchangeable > Fe/Mn oxide > carbonate >organic matter/sulfide. Both streams presented high degree of enrichment for Cu, Fe, Mn, Ni, Pb, and Zn, indicating anthropic origin of these metals. Metal mobilities in Jaralito and the Mexicana were Fe > Cu > Mn > Pb > Zn > Ni > Cr and Fe > Cu > Mn > Zn > Ni > Pb > Cr > Cd, respectively. Jaralito and the Mexicana sediments exhibit a mostly gravel-sandy texture with higher metal contents than in fine fractions. Sediment Geoaccumulation index values suggest that Jaralito features moderate to strong contamination by Ni, Pb, and Cu, whereas the Mexicana features strong contamination by Cd, Cu, Pb, and moderate contamination by Ni, Pb, and Zn. The quality criteria comparisons (LEL and SEL) indicate these areas are contaminated by metals and represent a substantial environmental risk because of high metal mobility and availability. Future studies on water chemistry and biota are needed to fully assess pollution impact in the Jaralito and Mexicana streams. The probability of adverse biological effects from high metal levels in those streams confirms the urgency of implementing effective environmental management practices.

Hidden sources of mercury in clinical laboratories.

The healthcare sector is an important contributor to mercury (Hg) pollution because of the potential presence of mercury in thermometers, blood pressure cuffs, amalgams, etc. There are also other potential sources of mercury in this sector which are used frequently and in high volumes where the presence of the metal is not obvious and which might be collectively contributing to pollution. For instance, some chemicals used for the clinical diagnosis of illness may contain mercury. The goal of this study was to investigate potential sources of mercury pollution, which originate from clinical laboratory discharges, using an exploratory approach. The focus was on the residue generated during automatic analysis of patients’ bodily fluids at a medical center in Hermosillo, Sonora, Mexico. This study shows an overview of what might be happening in the region or the country related to non-obvious sources of mercury in the healthcare sector. The results showed measurable levels of mercury in the residues coming from urine sediment analysis. These amounts do not exceed the maximum allowed by Mexican environmental regulations; nevertheless, the frequency and cumulative volume of residues generated, combined with the potential for persistence and the bioaccumulation of mercury in the environment, warrant attention. The work carried out in this study is being taken as a model for future studies for pollution prevention in the healthcare sector with the goal of measuring mercury emissions to the environment from clinical laboratory wastewater, including identifying sources which—while not obvious— could be important given the frequency and volume of their use in the clinical diagnosis.

Adsorption of arsenic on pre-treated zeolite at different ph levels

Abstract Natural zeolites are widely used to minimise the impact of some pollutants in the environment, such as the removal of metals in various water sources as well as effluents used in the mining and metallurgical industry and in the treatment of mining acid solutions. The most common varieties of zeolites are analcime, chabazite, clinoptilolite, heroinite, ferrierite, mordenite. Researchers have studied for decades their synthesis, structure and proprieties, and as a result a large number of patents have been obtained on the preparation of different types of zeolite in conjunction with metals or metal compounds as selective adsorbents for anions and cations of water solutions. For example, iron, zirconium and magnesium hydroxide show selectivity in the adsorption of arsenic among other industrial applications of great interest. This study shows the importance of using natural pre-treated zeolites in the adsorption of arsenic in water due to the adsorption percentages that are higher than 90%, controlling the pH in the pre-treatment. Samples were treated at different pH levels, getting a better adjustment of isotherms of adsorption at pH = 9 with ZP-9.