Concentrations of Mercury and Other Inorganic Ions in Wet Precipitation Collected from a Mountain Mining Zone and an Urban Area in Central Mexico.

We measured and compared mercury (Hg) and other ions in rainwater collected in San Joaquin (mining zone) and Juriquilla (urban area), central Mexico, from 2009 to 2012. A total of 274 rainwater samples were collected and analyzed for pH, electrical conductivity, [Formula: see text] Cl-, [Formula: see text] Na+, K+, Ca2+, Mg2+ and Hg. Mercury concentrations in rainwater varied from 24.21 to 248.89 (x-bar = 86.97 ± 10.77) µg L- 1 in San Joaquin (mining zone) and 11.26 to 176.91 (x-bar = 81.51 ± 10.24) µg L- 1 in Juriquilla (urban area). Rainwater sample were collected over periods 1-3 days, depending upon precipitation frequency. Significant correlations (p < 0.05) were found between [Formula: see text] Cl-, [Formula: see text] Na+, K+, Ca2+, Mg2+ and Hg at the San Joaquin site. Significant correlations were obtained between [Formula: see text] Na+, K+, Ca2+, Mg2+ and Hg at the Juriquilla site. In order to determine if there were significant differences among each measured parameter in rainwater collected in San Joaquin and Juriquilla, Kruskal-Wallis test was applied to data. We emphasized that the distribution and concentrations of Hg and the studied ions in rainwater samples were affected by atmospheric dust and local meteorological conditions of wind-speed and direction.

Arsenic sorption by carbonate-rich aquifer material, a control on arsenic mobility at Zimapán, México.

Arsenic retention by carbonate-rich aquifer material at Zimapán, México, was studied to gain insight into the processes controlling arsenic mobility in natural systems. Batch experiments showed that retention of soluble As (V) on carbonate-rich aquifer material was 35.3-90% in the pH range of 7-9 found in Zimapán natural water. Chemical and mineralogical compositions, point of zero charge (PZC), and experimental arsenic retention at various pH of three composite samples of limestone (M1, M2, M3) showed that sorption (adsorption and coprecipitation) may be one of the main processes controlling arsenic mobility in the Zimapán As-polluted aquifer. The PZC values approximately corresponded to the PZC reported for the main minerals present in each sample: hydrous ferric oxides (M1), calcite (M2), and the range from hydrous ferric oxides and calcite (M3). The chemical and mineralogical compositions of each sample explain the obtained PZC values. Experimental and modeled arsenic retention at various pH values on sample M1 corresponded to reported arsenic adsorption onto hydrous ferric oxides. Coprecipitacion of complex Ca arsenates or arsenic adsorption onto calcite or clay minerals could be the main processes of arsenic retention on samples M2 and M3. Groundwater flow through the granular, carbonate-rich, shallow aquifer may decrease the water As content as a result of these interactions. A remediation method based on the promotion of polluted water flow into the shallow aquifer could be developed from these results.