Molecular and geochemical basis of microbially induced carbonate precipitation for treating acid mine drainage: The case of a novel Sporosarcina genomospecies from mine tailings.

Microbially induced carbonate precipitation (MICP) immobilizes toxic metals and reduces their bioavailability in aqueous systems. However, its application in the treatment of acid mine drainage (AMD) is poorly understood. In this study, the genomes of Sporosarcina sp. UB5 and UB10 were sequenced. Urease, carbonic anhydrases, and metal resistance genes were identified and enzymatic assays were performed for their validation. The geochemical mechanism of precipitation in AMD was elucidated through geo-mineralogical analysis. Sporosarcina sp. UB5 was shown to be a new genomospecies, with an average nucleotide identity < 95 % (ANI) and DNA-DNA hybridization < 70 % (DDH) whereas UB10 is close to S. pasteurii. UB5 contained two urease operons, whereas only one was identified in UB10. The ureolytic activities of UB5 and UB10 were 122.67 ± 15.74 and 131.70 ± 14.35 mM NH4+ min-1, respectively. Both strains feature several carbonic anhydrases of the α, ß, or γ families, which catalyzed the precipitation of CaCO3. Only Sporosarcina sp. UB5 was able to immobilize metals and neutralize AMD. Geo-mineralogical analyses revealed that UB5 directly immobilized Fe (1-23 %), Mn (0.65-1.33 %) and Zn (0.8-3 %) in AMD via MICP and indirectly through adsorption to calcite and binding to bacterial cell walls. The MICP-treated AMD exhibited high removal rates (>67 %) for Ag, Al, As, Ca, Cd, Co, Cu, Fe, Mn, Pb, and Zn, and a removal rate of 15 % for Mg. This study provides new insights into the MICP process and its applications to AMD treatment using autochthonous strains.

Environmental, Economic, and Social Aspects of Human Urine Valorization through Microbial Fuel Cells from the Circular Economy Perspective.

Population growth increases the challenge of meeting basic human needs, such as water, a limited resource. Consumption habits and water pollution have compromised natural resources to unsustainable levels. Sustainable effluent treatment practices, such as decentralized systems focused on energy, nutrients, and water recovery, have attracted the attention of the scientific community. Human urine (HU) is a physiological liquid waste whose main component is water (~95%). HU has a significant amount of nutrients, such as N, P, K, and organic matter, which are usually lacking in fecal coliforms. Therefore, the possibility exists of recovering nutrients and energy from HU using sustainable and non-sustainable technologies. Treating HU in bioelectrochemical systems (BES) is a novel alternative to obtaining byproducts from this effluent more sustainably than in electrochemical systems. Microbial fuel cells (MFCs) are an interesting example, contributing to HU revalorization from unwanted waste into a valuable resource of nutrients, energy, and water. Even when urine-operated MFCs have not generated attractive potential outputs or produced considerable amounts of bioelectricity, this review emphasizes HU advantages as nutrients or water sources. The aim of this review was to analyze the current development of BES for HU treatment based on the water circular economy, discussing challenges and perspectives researchers might encounter.

Genotoxic Biomonitoring in Children Living near the El Fraile Mine Tailings in Northern Guerrero State, Mexico.

A genotoxic study was conducted with 101 elementary school children (56 girls and 45 boys) in the 6-7, 8-9, and 10-12 age ranges from El Fraile rural community, which is located beside the El Fraile mine tailings in Taxco of Alarcon City, in northern Guerrero State, Mexico. For this, we used the alkaline comet assay in exfoliated buccal mucosa cells, scoring three genotoxic parameters: tail intensity, tail moment, and tail length. Additionally, we detected oxidative DNA damage through urinary 8-OHdG levels by enzyme-linked immunosorbent assay. We also evaluated a control group consisting of 101 children in the same age ranges from Chilpancingo City, Guerrero, who had never lived near mining zones. Genotoxic results showed that there was a significant increase in three genotoxic parameters and urinary 8-OHdG levels in the exposed children group compared with the control group. Analysis of MANOVA revealed that boys aged 8 and 9 years had higher DNA damage than girls from the same exposure group, and Spearman's analysis identified a positive correlation between DNA damage and sex and age. This study provides the first valuable genotoxic data in children living in areas with environmental pollution.

The Implications of Membranes Used as Separators in Microbial Fuel Cells.

Microbial fuel cells (MFCs) are electrochemical devices focused on bioenergy generation and organic matter removal carried out by microorganisms under anoxic environments. In these types of systems, the anodic oxidation reaction is catalyzed by anaerobic microorganisms, while the cathodic reduction reaction can be carried out biotically or abiotically. Membranes as separators in MFCs are the primary requirements for optimal electrochemical and microbiological performance. MFC configuration and operation are similar to those of proton-exchange membrane fuel cells (PEMFCs)-both having at least one anode and one cathode split by a membrane or separator. The Nafion® 117 (NF-117) membrane, made from perfluorosulfonic acid, is a membrane used as a separator in PEMFCs. By analogy of the operation between electrochemical systems and MFCs, NF-117 membranes have been widely used as separators in MFCs. The main disadvantage of this type of membrane is its high cost; membranes in MFCs can represent up to 60% of the MFC's total cost. This is one of the challenges in scaling up MFCs: finding alternative membranes or separators with low cost and good electrochemical characteristics. The aim of this work is to critically review state-of-the-art membranes and separators used in MFCs. The scope of this review includes: (i) membrane functions in MFCs, (ii) most-used membranes, (iii) membrane cost and efficiency, and (iv) membrane-less MFCs. Currently, there are at least 20 different membranes or separators proposed and evaluated for MFCs, from basic salt bridges to advanced synthetic polymer-based membranes, including ceramic and unconventional separator materials. Studies focusing on either low cost or the use of natural polymers for proton-exchange membranes (PEM) are still scarce. Alternatively, in some works, MFCs have been operated without membranes; however, significant decrements in Coulombic efficiency were found. As the type of membrane affects the performance and total cost of MFCs, it is recommended that research efforts are increased in order to develop new, more economic membranes that exhibit favorable properties and allow for satisfactory cell performance at the same time. The current state of the art of membranes for MFCs addressed in this review will undoubtedly serve as a key insight for future research related to this topic.

Cytogenotoxicity in uroepithelial cells of women exposed to mercury in a mining area.

OBJECTIVE: To investigate biomarkers of cytogenotoxicity in women exposed to mercury in a mining area. Mercury has been associated with cytogenotoxicity in human and animal models but has not been considered carcinogenic in humans, even though genotoxic effects following exposure to inorganic mercury compounds have been observed. METHODS: A cross-sectional study and micronucleus assay in uroepithelial cells were performed in 104 women (12-84 years of age). First urine void samples were taken to determine creatinine-adjusted mercury levels in urine (HgUCr), to isolate cells and to quantify cytogenetic damage. RESULTS: The geometric average level for HgUCr was 4.9 microg/g (range, 0.4-85). In the generalised linear model, after controlling for other co-variables, we observed that for each 10 microg/g increase in HgUCr, the OR of developing a genotoxic effect was 2.37 (95% CI 1.79 to 2.84), while for cytotoxic damage in uroepithelial cells the OR was 1.34 (95% CI 1.10 to 1.79). These results suggest a possible association between cytogenotoxicity and HgUCr. CONCLUSION: Living in a mining area with exposure to inorganic mercury and having higher mercury levels in urine increased the risk of developing uroepithelial cytogenotoxicity.

Bioimmobilization of toxic metals by precipitation of carbonates using Sporosarcina luteola: An in vitro study and application to sulfide-bearing tailings.

Metal release from mining wastes is a major environmental problem affecting ecosystems that requires effective, low-cost strategies for prevention and reclamation. The capacity of two strains (UB3 and UB5) of Sporosarcina luteola was investigated to induce the sequestration of metals by precipitation of carbonates in vitro and under microcosm conditions. These strains carry the ureC gene and have high urease activity. Also, they are highly resistant to metals and have the capacity for producing metallophores and arsenophores. SEM, EDX and XRD reveal that the two strains induced precipitation of calcite, vaterite and magnesian calcite as well as several (M2+)CO3 such as hydromagnesite (Mg2+), rhodochrosite (Mn2+), cerussite (Pb2+), otavite (Cd2+), strontianite (Sr2+), witherite (Ba2+) and hydrozincite (Zn2+) in vitro. Inoculation of the mixed culture of UB3+UB5 in tailings increased the pH and induced the precipitation of vaterite, calcite and smithsonite enhancing biocementation and reducing pore size and permeability slowing down the oxidation of residual sulfides. Results further demonstrated that the strains of S. luteola immobilize bioavailable toxic elements through the precipitation and coprecipitation of thermodynamically stable (M2+)CO3, Fe-Mn oxyhydroxides and organic chelates.

Source apportionment of lead in the blood of women of reproductive age living near tailings in Taxco, Guerrero, Mexico: An isotopic study.

The concentration and isotopic composition of lead in the blood of forty seven women of reproductive age (15-45y) exposed to multiple sources in two rural communities of the mining region of Taxco, Guerrero in southern Mexico were determined in order to identify specific contributing sources and their apportionment and to trace probable ingestion pathways. Our data indicate that >36% of the studied women have blood lead concentrations above 10µgdL-1 and up to 87% above 5µgdL-1. Tailings contain between 2128 and 5988mgkg-1 of lead and represent the most conspicuous source in the area. Lead contents in indoor dust are largely variable (21.7-987mgkg-1) but only 15% of samples are above the Mexican Regulatory Guideline for urban soils (400mgkg-1). By contrast, 85% of glazed containers (range: 0.026-68.6mgkg-1) used for cooking and food storage are above the maximum 2mgL-1 of soluble lead established in the Mexican Guideline. The isotopic composition indicates that lead in the blood of 95% of the studied women can be modeled in terms of a mixing system between local ores (and derivatives), glazed pottery and Morelos bedrock, end-members, with the two former being largely the most important contributors. Only one sample shows influence of indoor paints. Indoor dust is dominated by ores and derivatives but some samples show evidence of contribution from a less radiogenic source very likely represented by interior paints. This study supports the application of lead isotopic ratios to identify potential sources and their apportionment in humans exposed to multiple sources of lead from both, natural and anthropogenic origin.

Geochemistry of leachates from the El Fraile sulfide tailings piles in Taxco, Guerrero, southern Mexico.

Leachates from the El Fraile tailings impoundment (Taxco, Mexico) were monitored every 2 months from October 2001 to August 2002 to assess the geochemical characteristics. These leachates are of interest because they are sometimes used as alternative sources of domestic water. Alternatively, they drain into the Cacalotenango creek and may represent a major source of metal contamination of surface water and sediments. Most El Fraile leachates show characteristics of Ca-SO(4), (Ca+Mg)-SO(4), Mg-SO(4 )and Ca-(SO(4)+HCO(3)) water types and are near-neutral (pH=6.3-7.7). Some acid leachates are generated by the interaction of meteoric water with tailings during rainfall events (pH=2.4-2.5). These contain variable levels of SO(4) (2-) (280-29,500 mg l(-1)) and As (<0.01-12.0 mg l(-1)) as well as Fe (0.025-2,352 mg l(-1)), Mn (0.1-732 mg l(-1)), Zn (<0.025-1465 mg l(-1)) and Pb (<0.01-0.351 mg l(-1)). Most samples show the highest metal enrichment during the dry seasons. Leachates used as domestic water typically exceed the Mexican Drinking Water Guidelines for sulfate, hardness, Fe, Mn, Pb and As, while acidic leachates exceed the Mexican Guidelines for Industrial Discharge Waters for pH, Cu, Cd and As. Speciation shows that in near-neutral solutions, metals exist mainly as free ions, sulfates and bicarbonates, while in acidic leachates they are present as sulfates and free ions. Arsenic appears as As((V)) in all samples. Thermodynamic and mineralogical evidence indicates that precipitation of Fe oxides and oxyhydroxides, clay minerals and jarosite as well as sorption by these minerals are the main processes controlling leachate chemistry. These processes occur mainly after neutralization by interaction with bedrock and equilibration with atmospheric oxygen.