Amalgamation was heavily used in mining since 1557 in Spanish Colonies. In Mexico and other parts of Latin-America,this process generated tailings which were left aside in the mine backyards. In the valley of Zacatecas, tailings were carried out of the mines due to the run-off from the mountains and contaminated most of the Zacatecan Valley which most important economic activity is agricultural (crop and livestock raising). The main concern in this area is the high level of total mercury found in previous studies. So far, various research studies have been conducted in Mexico toidentify the contamination by total mercury in contaminated soils. However, research has not been developed to determine the available fraction by an analysis of the chemical species present in contaminated sites, which represent a risk to human health and the environment. The aim of this study is to develop a mercury sequential chemical extraction methodology with appropriate conditions for identifying: 1) water-soluble fraction, 2) elemental fraction, 3) interchangeable fraction, 4) strongly bound fraction, 5) organic fraction, 6) fraction as sulphides and 7) residual fraction. With this, it might be determined if the mercury species present in mining soils in the state of Zacatecas, Mexico represent a potential risk because of its mobility in the different environmental compartments. Results show that chemical species in the towns of Osiris and La Zacatecana (HgS and amalgamated mercury) have high stability and low mobility.
, Soil contamination, Mining wastes,Chemical selective extraction
The growth of Bacillus pumilus and Halomonas halodurans under different concentrations of NaCl, MgCl 2 , Na 2 SO 4 and MgSO 4 was investigated. The objective was to demonstrate whether these cultures have the ability to grow, not only in media enriched with sodium chloride, but also with other salts of astrobiological interest. The importance of this monitoring was to evaluate the fitness of these strains to the hypothetical salt content and composition of extraterrestrial sites, such as the ocean of Europa, one of the satellites of Jupiter.The mechanism of fitness used by these bacteria was investigated by characterizing the compatible solutes accumulated by each strain. Bacillus pumilus was cultivated at 0.23 M and 0.33 M NaCl (a w of 0.995 and 0.990, respectively) while Halomonas halodurans was cultivated at 0.44 M and 0.89 M NaCl (a w of 0.985 and 0.965, respectively). B. pumilus seems to accumulate principally betaine while H. halodurans accumulates betaine and glutamate, depending on the salt content of its environment. These results are discussed in the context of the salinity and salt composition of Europa's ocean and under their implications for the habitability of this Jovian satellite.Keywords: Water activity, Europa's habitability, icy satellites, halophiles, compatible solutes.
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