J.R. Gallego

Investigation of trace element sources from an industrialized area (Avilés, northern Spain) using multivariate statistical methods

In the industrialized urban area of Avilés (Spain), pooled soil samples from grassland sites were taken after careful sampling design and then investigated for their content of trace elements. A combination of statistic and geostatistic techniques proved to be a reliable tool in the interpretation of the analytical results. Geochemical groups and areas influenced mainly by anthropogenic activities were distinguished by means of classic multivariate methods (factor analysis and cluster analysis) and innovative geostatistical tools (Fourier spectral analysis). The constitution of the groups is supported by the linked results of methods sequentially distributed in order to extract as much information as possible from the original data.

Geochemical characterisation of mercury mining spoil heaps in the area of Mieres (Asturias, northern Spain)

Abstract Asturias has important and abundant mercury deposits, and the legacy of the historical mining activities remains in the form of old and abandoned industrial installations. In areas where years of mercury mining has occurred, large amounts of wastes with high contents of Hg and As were disposed on the surface, without any preventive measures to avoid ore leaching and the dispersion of toxic elements into the environment. In proximity to Mieres village, three spoil heaps (El Terronal, El Rucio, and Los Rueldos) were selected to undertake a multielemental geochemical study of soils, water and plants. In soils, systematic sampling was carried out at the site of the old mining and metallurgical works in El Terronal. Spoil heaps were also systematically sampled at the sites of El Terronal, El Rucio and Los Rueldos. In the area of El Terronal, different types of plants have been sampled, including grass, fruit trees, edible crops and thickets. The soluble fraction resulting from a strong acid attack of the sample was analysed by FAA and ICP. Superficial water was sampled monthly, upstream and downstream of mining works; data obtained from filtered samples include pH, Eh, and arsenic and mercury concentrations. Soil samples from the mined areas show mercury concentrations between 1.7 and 472.1 mg/kg, and arsenic concentrations between 6 and 7287 mg/kg. Arsenic content in samples of spoil heaps is in the range 4746–62,196 mg/kg (Los Rueldos), and 192–2057 mg/kg (El Rucio); mercury content is in the range 14–2224 mg/kg (Los Rueldos), and 21–1984 mg/kg (El Rucio). Arsenic content of superficial water upstream and downstream of the mining works is lower than 0.005 mg/l (analytical detection limit), and 0.9–5.6 mg/l, respectively; mercury concentrations upstream and downstream of mining works are always lower than 0.001 mg/l (analytical detection limit). Leachates collected at the bottom of the Los Rueldos spoil heap show acidic pH (between 2.43 and 2.50), Eh around 550 mV, arsenic concentrations between 5.3 and 8.3 mg/l, and mercury concentrations always lower than 0.001 mg/l (analytical detection limit). Maximum values of As and Hg content in grass in the mined area are 53 mg/kg and 4.84 mg/kg, respectively.

Metaproteogenomic insights beyond bacterial response to naphthalene exposure and bio-stimulation.

Microbial metabolism in aromatic-contaminated environments has important ecological implications, and obtaining a complete understanding of this process remains a relevant goal. To understand the roles of biodiversity and aromatic-mediated genetic and metabolic rearrangements, we conducted ‘OMIC’ investigations in an anthropogenically influenced and polyaromatic hydrocarbon (PAH)-contaminated soil with (Nbs) or without (N) bio-stimulation with calcium ammonia nitrate, NH4NO3 and KH2PO4 and the commercial surfactant Iveysol, plus two naphthalene-enriched communities derived from both soils (CN2 and CN1, respectively). Using a metagenomic approach, a total of 52, 53, 14 and 12 distinct species (according to operational phylogenetic units (OPU) in our work equivalent to taxonomic species) were identified in the N, Nbs, CN1 and CN2 communities, respectively. Approximately 10 out of 95 distinct species and 238 out of 3293 clusters of orthologous groups (COGs) protein families identified were clearly stimulated under the assayed conditions, whereas only two species and 1465 COGs conformed to the common set in all of the mesocosms. Results indicated distinct biodegradation capabilities for the utilisation of potential growth-supporting aromatics, which results in bio-stimulated communities being extremely fit to naphthalene utilisation and non-stimulated communities exhibiting a greater metabolic window than previously predicted. On the basis of comparing protein expression profiles and metagenome data sets, inter-alia interactions among members were hypothesised. The utilisation of curated databases is discussed and used for first time to reconstruct ‘presumptive’ degradation networks for complex microbial communities.

Biodegradation of Oil Tank Bottom Sludge using Microbial Consortia

We present a rationale for the selection of a microbial consortia specifically adapted to degrade toxic components of oil refinery tank bottom sludge (OTBS). Sources such as polluted soils, petrochemical waste, sludge from refinery-wastewater plants, and others were used to obtain a collection of eight microorganisms, which were individually tested and characterized to analyze their degradative capabilities on different hydrocarbon families. After initial experiments using mixtures of these strains, we developed a consortium consisting of four microorganisms (three bacteria and one yeast) selected in the basis of their cometabolic effects, emulsification properties, colonization of oil components, and degradative capabilities. Although the specific contribution each of the former parameters makes is not clearly understood, the activity of the four-member consortium had a strong impact not only on linear alkane degradation (100%), but also on the degradation of cycloalkanes (85%), branched alkanes (44%), and aromatic and sulphur–aromatic compounds (31–55%). The effectiveness of this consortium was significantly superior to that obtained by individual strains, commercial inocula or an undefined mixture of culturable and non-culturable microorganisms obtained from OTBS-polluted soil. However, results were similar when another consortium of four microorganisms, previously isolated in the same OTBS-polluted soil, was assayed.

Analysis of soil washing effectiveness to remediate a brownfield polluted with pyrite ashes.

Soil in a brownfield contaminated by pyrite ashes showed remarkably high concentrations of several toxic elements (Hg, Pb, Zn, Cu, Cd, and As). Initially, we assessed various physical, chemical and mineralogical properties of this soil. The data obtained, and particularly multivariate statistics of geochemical results, were useful to establish the predominant role of the soil organic matter fraction (6%) and iron oxyhydroxides in the binding of heavy metals and arsenic. In addition, we studied the viability of soil washing techniques to reduce the volume of contaminated soil. Therefore, to concentrate most of the contaminants in a smaller volume of soil, the grain-size fraction below 125 microm was treated by hydrocycloning techniques. The operational parameters were optimized by means of a factorial design, and the results were evaluated by attributive analysis. This novel approach is practical for the global simultaneous evaluation of washing effectiveness for several contaminants. A concentration factor higher than 2.2 was achieved in a separated fraction that contained less than 20% of the initial weight. These good yields were obtained for all the contaminants and with only one cycle of hydrocycloning. Hence full-scale soil washing is a plausible remediation technique for the study site.

Multivariate study of trace element distribution in the geological record of Roñanzas Peat Bog (Asturias, N. Spain). Paleoenvironmental evolution and human activities over the last 8000 cal yr BP

Trace element concentrations in the Roñanzas peat bog record reveal a contribution of natural processes but the influence of anthropogenic factors predominates in the last two millenniums, particularly aerosol deposition linked to mining and industrial activities in northern Spain. We observed that the Roñanzas record can be considered a preserved environment, suitable to search for local (<50 km), regional (50-150 km) and/or long-distance human activity fingerprinting, specifically that related to the deposition of heavy metals such as Pb, Zn and Hg. We also carried out a multivariate statistical study in order to clarify the geochemical behavior of trace and major elements. Our study design represents a novel approach to assign natural vs. human contributions in peatlands. Therefore, synergies obtained by the simultaneous study of multivariate statistics and enrichment factors allow robust conclusions about paleoenvironmental evolution and human activities. Anthropogenic influence has also been reported in similar records in other parts of Europe, thereby suggesting large-scale sources for atmospheric pollution. However, here we revealed remarkable particularities, such as the association of Cd, Zn and Pb, mainly linked to regional and local factors (mining and more recently the metallurgical industry), whereas we propose that the occurrence of Hg is associated with a combination of regional factors and global atmospheric pollution.

Microbial stratification in low pH oxic and suboxic macroscopic growths along an acid mine drainage.

Macroscopic growths at geographically separated acid mine drainages (AMDs) exhibit distinct populations. Yet, local heterogeneities are poorly understood. To gain novel mechanistic insights into this, we used OMICs tools to profile microbial populations coexisting in a single pyrite gallery AMD (pH ∼2) in three distinct compartments: two from a stratified streamer (uppermost oxic and lowermost anoxic sediment-attached strata) and one from a submerged anoxic non-stratified mat biofilm. The communities colonising pyrite and those in the mature formations appear to be populated by the greatest diversity of bacteria and archaea (including ‘ARMAN’ (archaeal Richmond Mine acidophilic nano-organisms)-related), as compared with the known AMD, with ∼44.9% unclassified sequences. We propose that the thick polymeric matrix may provide a safety shield against the prevailing extreme condition and also a massive carbon source, enabling non-typical acidophiles to develop more easily. Only 1 of 39 species were shared, suggesting a high metabolic heterogeneity in local microenvironments, defined by the O2 concentration, spatial location and biofilm architecture. The suboxic mats, compositionally most similar to each other, are more diverse and active for S, CO2, CH4, fatty acid and lipopolysaccharide metabolism. The oxic stratum of the streamer, displaying a higher diversity of the so-called ‘ARMAN’-related Euryarchaeota, shows a higher expression level of proteins involved in signal transduction, cell growth and N, H2, Fe, aromatic amino acids, sphingolipid and peptidoglycan metabolism. Our study is the first to highlight profound taxonomic and functional shifts in single AMD formations, as well as new microbial species and the importance of H2 in acidic suboxic macroscopic growths.

Comprehensive waste characterization and organic pollution co-occurrence in a Hg and As mining and metallurgy brownfield.

The abandonment of Hg-As mining and metallurgy sites, together with long-term weathering, can dramatically degrade the environment. In this work it is exemplified the complex legacy of contamination that afflicts Hg-As brownfields through the detailed study of a paradigmatic site. Firstly, an in-depth study of the former industrial process was performed to identify sources of different types of waste. Subsequently, the composition and reactivity of As- and Hg-rich wastes (calcines, As-rich soot, stupp, and flue dust) was analyzed by means of multielemental analysis, mineralogical characterization (X-ray diffraction, electronic, and optical microscopy, microbrobe), chemical speciation, and sequential extractions. As-rich soot in the form of arsenolite, a relatively mobile by-product of the pyrometallurgical process, and stupp, a residue originated in the former condensing system, were determined to be the main risk at the site. In addition, the screening of organic pollution was also aimed, as shown by the outcome of benzo(a) pyrene and other PAHs, and by the identification of unexpected Hg organo-compounds (phenylmercury propionate). The approach followed unravels evidence from waste from the mining and metallurgy industry that may be present in other similar sites, and identifies unexpected contaminants overlooked by conventional analyses.

A nanoremediation strategy for the recovery of an As-polluted soil

The present study investigates the impact of the nanoremediation treatment on soil recovery as evaluated by the development of barley plants. Highly As-polluted brownfield soil was treated with nanoscale zero-valent iron (nZVI) commercial suspension at two doses (1% and 10%). Barley plants were cultivated in treated and untreated soils in a growth chamber, and the As, Fe, and nutrients uptake were determined. The efficacy of As immobilization was evaluated according to the toxicity characteristics leaching procedure (TCLP) as well as using a sequential extraction procedure. The application of nZVI reduced the amount of As in the more available fractions and increased the amount of As in the residual fraction. The best immobilization results were obtained for the highest dose of nZVI (10%). In turn, the lower availability of As in nZVI-treated soils, particularly at the dose of 10%, stimulated the development of the barley plants and decreased the As uptake. Neither an important increase of available Fe nor negative impact on soil physico-chemical and biological properties were observed. Thus, our results show that the use of nZVI could be an adequate strategy to recover the land use in As polluted soils.

Optimisation of magnetic separation: a case study for soil washing at a heavy metals polluted site.

Sandy loam soil polluted with heavy metals (As, Cu, Pb and Zn) from an ancient Mediterranean Pb mining and metallurgy site was treated by means of wet high-intensity magnetic separation to remove some of the pollutants therein. The treated fractions were chemically analysed and then subjected to magnetic characterisation, which determined the high-field specific (mass), magnetic susceptibility (κ) and the specific (mass) saturation magnetisation (σS), through isothermal remanent magnetisation (IRM) curves. From the specific values of κ and σS, a new expression to assess the performance of the magnetic separation operation was formulated and verified by comparison with the results obtained by traditional chemical analysis. The magnetic study provided valuable information for the exhaustive explanation of the operation, and the deduced mathematical expression was found to be appropriate to estimate the performance of the separation operation. From these results we determined that magnetic soil washing was effective for the treatment of the contaminated soil, concentrating the majority of the heavy metals and peaking its separation capacity at 60% of the maximum output voltage.