Detection and assignment of inorganic aqueous polymers relevant to environmental nanogeoscience by direct infusion electrospray ionization mass spectrometry

Inorganic polymers in aqueous solutions are being proposed as essential components in new theories concerning nonclassical nucleation and growth of nanominerals relevant to environmental nanogeosciences. The study of those complex natural processes requires multi-technique analytical approaches able to characterize the solutions and their constituents (solutes, oligomers, polymers, clusters and nanominerals) from atomic to micrometric scales. A novel analytical approach involving an electrospray ionization source (ESI) coupled to time-of-flight mass spectrometry (TOF/MS) was developed to identify inorganic polymers in aqueous solution. To this end, the presence of initial Al oligomers and their polymerization processes was studied during a nanomineral aqueous synthesis (hydrobasaluminte, Al₄ SO₄ (OH)₁₀ ·12-36H₂ O). Ensuring the feasibility and robustness of the methodology as well as the stability of the polymers under study (avoiding undesirable fragmentation), a meticulous study of the ESI-TOF MS working conditions was performed. Precision of the methodology was evaluated obtaining relative standard deviations below 3.3%. For the first time in the study of inorganic polymers in the earth sciences, the mass accuracy error (ppm) has been reported and the use of significant decimal figures of the m/z signal has been taken into account. Complementary to this, a four-step polymer assignment methodology and a database with the Al^- and Al-SO₄ ^2- polymers assigned were created. Several polymers have been assigned for the first time, including Al (SO₄ )⁺ ·H₂ O, Al₂ O(SO₄ )²⁺ ·H₂ O, Al₅ O₄ (OH)₅ ²⁺ ·2H₂ O, and Al₃ O₅ (OH)^2- ·4H₂ O, among others. The results obtained in the present study help create a foundation to include mass spectrometry as a routine analytical technique to study mineral formation in aqueous solution.

Biomarker responses of the freshwater clam Corbicula fluminea in acid mine drainage polluted systems

The environmental quality of an acid mine drainage polluted river (Odiel River) in the Iberian Pyrite Belt (SW Spain) was assessed by combining analyses of biomarkers (DNA strand breaks, LPO, EROD, GST, GR, GPx) in freshwater clams (Corbicula fluminea) exposed during 14 days and correlated with metal(loid) environmental concentrations. Results pointed that enzymatic systems are activated to combat oxidative stress in just 24 h. Along exposure, there were homeostatic regulations with the glutathione activity that influenced in lipid peroxidation oscillations, provoking significant DNA strand damage after 14 exposure days. EROD activity showed no changes throughout the exposure period. The Asian clam displayed balance biomarkers of exposure-antioxidant activity under non-stressfully environments; meanwhile, when was introduced into acid polymetallic environments, such as the acid mine drainage, its enzymatic activity was displaced towards biomarkers of effect and the corresponding antioxidant activity.

Sulfate reduction processes in salt marshes affected by phosphogypsum: Geochemical influences on contaminant mobility

Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosphogypsum stack was examined by pore-water and solid analysis, selective extractions, microscopy and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The negative impact of this stack on estuarine environments is a concerning problem. In the weathering profile, total concentrations of most pollutants increase with depth; instead, dissolved contents in pore-waters increase to middle of the saturated zone but then decrease drastically down to reach the marsh due to sulfide precipitation. Excess of acid-volatile sulfide plus pyritic sulfur over metals bound to the oxidizable fraction indicates that sulfide precipitation is the main mechanism responsible for metal removal in the marsh. Thus, abundant pyrite occurred as framboidal grains, in addition to other minor sulfides of As, Zn and Cu as isolated particles. Moreover, high contents of elemental sulfur were found, which suggest partial sulfide oxidation, but marsh may have capacity to buffer potential release of contaminants. The importance of sulfur species was quantitatively confirmed by XANES, which also supports the accuracy of selective extraction schemes. Accordingly, managing pore-water quality through organic carbon-rich amendments over phosphogypsum stacks could lead to a decrease in contaminant loading of leakages resulting from weathering.

An anomalous metal-rich phosphogypsum: Characterization and classification according to international regulations

Phosphogypsum is the main waste generated by the phosphate fertilizer industry. Despite the high level of pollutants found in phosphogypsum and the proximity of stacks to cities, there are no specific regulations for the management of this waste. This study addresses this issue by applying to phosphogypsum, from a fertilizer plant in Huelva (SW Spain), the leaching tests proposed by the current European and US environmental regulations for wastes management and classification. Two main conclusions were obtained: 1) the anomalous metal and metalloid concentrations (e.g. As, Fe, Pb, Sb, Mn, V and Cu) and higher mobility observed in the Huelva phosphogypsum compared to other stacks worldwide, and 2) the discrepancies observed between EU and US regulations dealing with hazardousness classification of these materials. This latter finding suggests the need to use complementary assessment protocols to obtain a better characterization and classification of these wastes. An evaluation of the potential risk to the aquatic life according to the US EPA regulation is proposed in this study. The results warn about the acute and chronic effects on the aquatic life of this waste and suggest the adoption of more strict measures for a safe disposal of phosphogypsum stacks.

Initial geochemical characteristics of fluid fine tailings in an oil sands end pit lake

Geochemical characteristics of fluid fine tailings (FFT) were examined in Base Mine Lake (BML), which is the first full-scale demonstration oil sands end pit lake (EPL) in northern Alberta, Canada. Approximately 186Mm(3) of FFT was deposited between 1994 and 2012, before BML was established on December 31, 2012. Bulk FFT samples (n=588) were collected in July and August 2013 at various depths at 15 sampling sites. Temperature, solid content, electrical conductivity (EC), pH, Eh and alkalinity were measured for all samples. Detailed geochemical analyses were performed on a subset of samples (n=284). Pore-water pH decreased with depth by approximately 0.5 within the upper 10m of the FFT. Major pore-water constituents included Na (880±96mgL(-1)) and Cl (560±95mgL(-1)); Ca (19±4.1mgL(-1)), Mg (11±2.0mgL(-1)), K (16±2.3mgL(-1)) and NH3 (9.9±4.7mgL(-1)) were consistently observed. Iron and Mn concentrations were low within FFT pore water, whereas SO4 concentrations decreased sharply across the FFT-water interface. Geochemical modeling indicated that FeS(s) precipitation was favoured under SO4-reducing conditions. Pore water was also under-saturated with respect to gypsum [CaSO4·2H2O], and near saturation with respect to calcite [CaCO3], dolomite [CaMg(CO3)2] and siderite [FeCO3]. X-ray diffraction (XRD) suggested that carbonate-mineral dissolution largely depleted calcite and dolomite. X-ray absorption near edge structure (XANES) spectroscopy revealed the presence of FeS(s), pyrite [FeS2], and siderite. Carbonate-mineral dissolution and secondary mineral precipitation have likely contributed to FFT dewatering and settlement. However, the long-term importance of these processes within EPLs remains unknown. These results provide a reference for assessing the long-term geochemical evolution of oil sands EPLs, and offer insight into the chemistry of pore water released from FFT to the overlying water cover.

Sources of mercury in groundwater and soils of west Gijón (Asturias, NW Spain)

This work aimed to determine the cause of the presence of high concentrations of mercury in several springs that exhibit a low concentration of metals in the bedrocks of their recharge areas in Gijón, NW Spain and the extent of this contamination. On the basis of geological mapping, different lithological substrata were analysed at the regional scale with the objective of establishing the base level of mercury in natural soils. The mercury content was simultaneously analysed in several water samples, and the following parameters were also determined: major anions and cations, As, Pb, δ(34)S, and δ(18)OSO4. The soils of the recharge area of the springs exhibited Hg concentrations that were higher than the base level established for sandstone at the regional level, and four of the total number of springs analysed exhibited Hg concentrations higher than 1 μg/l. In addition, the sulphate concentration exceeded the values that this type of aquifer shows in other parts of the region. A comparison between the regionally geochemical background of soils and mercury concentration in springs and soils of the study area did not exhibit a direct relationship, suggesting an anthropogenic and timely origin (most likely from industrial emissions) for this metal. The δ(34)S and δ(18)OSO4 values of dissolved sulphate from the springs with a higher Hg concentration also indicate an anthropogenic origin.