Release of trace elements during bioreductive dissolution of magnetite from metal mine tailings: Potential impact on marine environments

Adverse impacts of mine tailings on water and sediments quality are major worldwide environmental problems. Due to the environmental issues associated with the deposition of mine tailings on land, a controversial discussed alternative is submarine tailings disposal (STD). However, Fe(III) bioreduction of iron oxides (e.g., magnetite) in the tailings disposed might cause toxic effects on coastal environments due to the release of different trace elements (TEs) contained in the oxides. To study the extent and kinetics of magnetite bioreduction under marine conditions and the potential release of TEs, a number of batch experiments with artificial seawater (pH 8.2) and a marine microbial strain (Shewanella loihica) were performed using several magnetite ore samples from different mines and a mine tailings sample. The elemental composition of the magnetite determined in the tailings showed relatively high amounts of TEs (e.g., Mn, Zn, Co) compared with those of the magnetite ore samples (LA-ICP-MS and EMPA analyses). The experiments were conducted at 10 °C in the dark for up to 113 days. Based on the consumption of lactate and production of acetate and aqueous Fe(II) over time, the magnitude of Fe(III) bioreduction was calculated using a geochemical model including Monod kinetics. Model simulations reproduced the release of iron and TEs observed throughout the experiments, e.g., Mn (up to 203 μg L−1), V (up to 79 μg L−1), As (up to 17 μg L−1) and Cu (up to 328 μg L−1), suggesting a potential contamination of pore water by STD. Therefore, the results of this study can help to better evaluate the potential impacts of STD

Bioreduction of iron (hydr)oxides from mine tailings under marine conditions

[eng] Mining industry faces environmental problems concerning waste management. Given the environmental issues associated with storage of mine wastes on land, one disposal option that has gained attraction is submarine tailings disposal (STD). This practice involves disposal of mine tailings under seawater through underwater pipelines. Discharged mine wastes may be geochemically altered by microbial communities that living in the seabed have an ecophysiology that is compatible with the mine tailings. These communities (e.g., Shewanella, Geobacter) would be able to reduce the structural Fe(III) of oxides and oxyhydroxides (henceforth referred to as (hydr)oxides) of iron contained in the tailings, leading to a release of Fe(II) and Trace Elements (TEs) into the marine environment. The present study aimed at understanding the reaction of bioreduction of iron (hydr)oxides that are contained in mine tailings and assessing the environmental impact of STD. For this purpose, different samples of iron (hydr)oxides and mine tailings were reacted in batch and column experiments in the presence of Shewanella loihica, a dissimilatory iron reducing bacteria. The release of Fe(II) and TE was monitored throughout the experiments, and the surface of the reacted oxides were examined. Geochemical simulations of the experimental data were used to quantify the extent of the overall reductive dissolution reaction. Furthermore, to understand the influence of aqueous iron in the ocean’s nitrogen cycle, a series of experiments were carried out with Fe(II) released from bioreduced iron oxides in the presence of nitrite. Results showed that Shewanella loihica bioreduces Fe(III) from the iron (hydr)oxides contained in the mine tailings under marine conditions. The dissolution process leads to a release of Fe(II) and TEs, which are harmful for the marine environment. It was deduced that the reactive surface area of the iron (hydr)oxides is a key factor in the bioreduction process as it provides available Fe(III) and available surface, on which Shewanella loihica attach for electron transferring. However, adsorption of some of released Fe(II) onto the surface leads to a decrease in the reactive surface area, which lowers the total available Fe(III), and to a transformation of the former oxide to a new biogenic phase containing Fe2+/Fe3+ (i.e. magnetite). Moreover, it was demonstrated that the Fe(II) released promotes a nitrite removal, interfering thus with the nitrogen cycle of the ocean. The nitrite removal was characterized using chemical and isotopic analyses, which allowed a better understanding of the mechanisms controlling the Fe(II)-N interaction and an identification of the source of nitrite reduction in the sea. From the results, it is inferred that STD can become a major environmental concern because (1) the Fe(II) released may lead to fertilization and eutrophication of disposal sites, resulting in an oxygen depletion and an expansion of the oxygen minimum zone and (2) the TEs released bioaccumulate in the environment and trophic webs, ultimately affecting human health and social economic development.[spa] La indústria minera s’encara a un problema de gestió dels residus produïts. Degut als problemes mediambientals que provoca l’emmagatzematge terrestre de les cues mineres, la deposició submarina de les cues (STD) és una opció que ha guanyat interès en els darrers anys. Aquesta pràctica implica el dipòsit dels residus al fons marí mitjançant canonades submergides des de les indústries mineres. Aquestes cues es poden veure afectades geoquímicament per les poblacions microbianes que viuen en el fons marí i que poden tenir una ecofisiologia compatible amb els residus. Aquestes comunitats (per exemple, Shewanella, Geobacter) poden bioreduir el ferro fèrric dels òxids i/o hidròxids continguts en els residus miners, alliberant Fe (II) i elements traça (TE) al medi marí. El principal objectiu d’aquest treball va ser entendre el procés de bioreducció dels òxids i hidròxids de ferro presents en els residus miners i avaluar les conseqüències mediambientals dels dipòsits de residus al fons marí. Per dur a terme aquest propòsit, es van fer experiments de tipus batch i de columna amb diverses mostres d’òxids i hidròxids de ferro i de residus miners, les quals van reaccionar amb Shewanella loihica, un bacteri desassimilatori del ferro capaç de dur a terme la dissolució reductiva del ferro. Es va monitoritzar l’alliberament de Fe(II) i de TEs, es van observar les superfícies dels sòlids reaccionats i es va fer un model geoquímic per quantificar la bioreducció. A més a més, per tal d’entendre millor la influència del ferro en el cicle del nitrogen de l’oceà es van dur a terme uns experiments batch on el ferro bioreduït interaccionava amb nitrit. Els resultats han demostrat que la Shewanella loihica pot bioreduir els òxids i/o hidròxids de ferro continguts en residus miners en condicions semblants a les del fons marí. Aquesta dissolució bioreductiva comporta l’alliberament de Fe(II) i de TEs que poden arribar a ser perjudicials per l’ambient. S’ha deduït que la superfície reactiva dels òxids i/o hidròxids é un factor clau en la bioreducció perquè proveeix Fe(III) per bioreduir i superfície perquè els bacteris transfereixin electrons.. Ara bé, l’adsorció de Fe(II) en la superfície comporta, per una banda, la disminució de la superfície reactiva i del Fe(III) disponible i, per altra banda, la formació d’una nova fase mineral biogènica que conté Fe2+/Fe3+, és a dir una transformació a magnetita També s’ha demostrat que el Fe(II) alliberat per la bioreducció pot interferir, amb el cicles biogeoquímic del nitrogen de l’oceà. Així, el Fe(II) bioproduït desencadena l’eliminació del nitrit en el mar. Aquest procés s’ha caracteritzat utilitzant anàlisis químiques i isotòpiques. Les dades isotòpiques han servit per entendre millor els mecanismes que regulen la interacció Fe(II)-nitrogen, i per identificar l’origen de la reducció de nitrit en el medi marí. A partir dels resultats obtinguts, es dedueix que el dipòsit de residus miners al mar (STD) és un problema mediambiental perquè (1) l’alliberament de Fe(II) pot provocar una fertilització i eutrofització dels llocs on es dipositin els residus amb una disminució de l’oxigen dissolt i una expansió de la zona mínima d’oxigen i (2) l’alliberament d’ETs pot provocar una bioacumulació d’aquests elements a les xarxes tròfiques. Tot plegat afecta no només l’equilibri d’altres cicles biogeoquímics a l’oceà sinó també la salut humana i l’economia de la societat

Dissimilatory bioreduction of iron(III) oxides by Shewanella loihica under 1 marine sediment conditions

Shewanella is a genus of marine bacteria capable of dissimilatory iron reduction (DIR). In the context of deep-sea mining activities or submarine mine tailings disposal, dissimilatory iron reducing bacteria may play an important role in biogeochemical reactions concerning iron oxides placed on the sea bed. In this study, batch experiments were performed to evaluate the capacity of Shewanella loihica PV-4 to bioreduce different iron oxides (ferrihydrite, magnetite, goethite and hematite) under conditions similar to those in anaerobic sea sediments. Results showed that bioreduction of structural Fe(III) via oxidation of labile organic matter occurred in all these iron oxides. Based on the aqueous Fe (II) released, derived Fe(II)/acetate ratios and bioreduction coefficients seem to be only up to about 4% of the theoretical ones, considering the ideal stoichiometry of the reaction. A loss of aqueous Fe (II) was caused by adsorption and mineral transformation processes. Scanning electron microscope images showed that Shewanella lohica was attached to the Fe(III)-oxide surfaces during bioreduction. Our findings suggest that DIR of Fe(III) oxides from mine waste placed in marine environments could result in adverse ecological impacts such as liberation of trace metals in the environment. © 2019 Elsevier LtdThanks are due to Javier García-Veigas, Eva Prats and Maite Romero (Scientific and Technical Services of the University of Barcelona) for technical assistance in the SEM-EDX and ICP-AES analyses, and to Jordi Bellés (IDAEA-CSIC) for technical assistance in the laboratory. We are indebted to Natàlia Moreno (IDAEA-CSIC) for her assistance in the XRD analyses. This study was funded by the Chilean Government through the Research Fund for Fishery and Aquaculture (Fondo de Investigación Pesquera y de Acuicultura; FIPA) of SUBPESCA , Project No. FIP 2015-11 and the Catalan Government through project 2017SGR 1733 . Appendix APeer reviewe

Dissimilatory bioreduction of iron (III) oxides by Shewanella loihica under marine sediment conditions

Shewanella is a genus of marine bacteria capable of dissimilatory iron reduction (DIR). In the context of deep-sea mining activities or submarine mine tailings disposal, dissimilatory iron reducing bacteria may play an important role in biogeochemical reactions concerning iron oxides placed on the sea bed. In this study, batch experiments were performed to evaluate the capacity of Shewanella loihica PV-4 to bioreduce different iron oxides (ferrihydrite, magnetite, goethite and hematite) under conditions similar to those in anaerobic sea sediments. Results showed that bioreduction of structural Fe(III) via oxidation of labile organic matter occurred in all these iron oxides. Based on the aqueous Fe (II) released, derived Fe(II)/acetate ratios and bioreduction coefficients seem to be only up to about 4% of the theoretical ones, considering the ideal stoichiometry of the reaction. A loss of aqueous Fe (II) was caused by adsorption and mineral transformation processes. Scanning electron microscope images showed that Shewanella lohica was attached to the Fe(III)-oxide surfaces during bioreduction. Our findings suggest that DIR of Fe(III) oxides from mine waste placed in marine environments could result in adverse ecological impacts such as liberation of trace metals in the environment

Geochemical and isotopic study of abiotic nitrite reduction coupled to biologically produced Fe(II) oxidation in marine environments

Estuarine sediments are often characterized by abundant iron oxides, organic matter, and anthropogenic nitrogen compounds (e.g., nitrate and nitrite). Anoxic dissimilatory iron reducing bacteria (e.g., Shewanella loihica) are ubiquitous in these environments where they can catalyze the reduction of Fe(III) (oxyhydr)oxides, thereby releasing aqueous Fe(II). The biologically produced Fe(II) can later reduce nitrite to form nitrous oxide. The effect on nitrite reduction by both biologically produced and artificially amended Fe(II) was examined experimentally. Ferrihydrite was reduced by Shewanella loihica in a batch reaction with an anoxic synthetic sea water medium. Some of the Fe(II) released by S. loihica adsorbed onto ferrihydrite, which was involved in the transformation of ferrihydrite to magnetite. In a second set of experiments with identical medium, no microorganism was present, instead, Fe(II) was amended. The amount of solid-bound Fe(II) in the experiments with bioproduced Fe(II) increased the rate of abiotic NO2− reduction with respect to that with synthetic Fe(II), yielding half-lives of 0.07 and 0.47 d, respectively. The δ18O and δ15N of NO2− was measured through time for both the abiotic and innoculated experiments. The ratio of ε18O/ε15N was 0.6 for the abiotic experiments and 3.1 when NO2− was reduced by S. loihica, thus indicating two different mechanisms for the NO2− reduction. Notably, there is a wide range of the ε18O/ε15N values in the literature for abiotic and biotic NO2− reduction, as such, the use of this ratio to distinguish between reduction mechanisms in natural systems should be taken with caution. Therefore, we suggest an additional constraint to identify the mechanisms (i.e. abiotic/biotic) controlling NO2− reduction in natural settings through the correlation of δ15N-NO2- and the aqueous Fe(II) concentration.This study was supported by projects CGL2017-87216-C4-1-R, CGL2017-82331-R and CEX2018-000794-S funded by the Spanish Ministry of Science and Innovation and AEI/FEDER funded by the European Union, and by MAG (2017 SGR 1733) financed by the Catalan Government. R. Margalef-Marti wishes to thank the Spanish Government for the Ph.D. grant BES-2015-072882. The authors are indebted to Jordi Bellés (IDAEA-CSIC), Natàlia Moreno (IDAEA-CSIC) and Xavier Alcové (SCTT-Barcelona University) for laboratory assistance and XRD analyses, respectively. The isotopic analyses were prepared at the MAiMA-UB research group laboratory and analyzed at the scientific and technical services of Barcelona University (CCiT-UB). We acknowledge Max Giannetta for his scientific discussions during the manuscript elaboration. We also wish to thank the Editor and three anonymous reviewers for their constructive comments that have improved the quality of the paper.Peer reviewe

Geochemical and isotopic study of abiotic nitrite reduction coupled to biologically produced Fe(II) oxidation in marine environments

Estuarine sediments are often characterized by abundant iron oxides, organic matter, and anthropogenicnitrogen compounds (e.g., nitrate and nitrite). Anoxic dissimilatory iron reducing bacteria (e.g.,Shewa-nella loihica) are ubiquitous in these environments where they can catalyze the reduction of Fe(III) (oxyhydr)oxides, thereby releasing aqueous Fe(II). The biologically produced Fe(II) can later reduce ni-trite to form nitrous oxide. The effect on nitrite reduction by both biologically produced and artificiallyamended Fe(II) was examined experimentally. Ferrihydrite was reduced byShewanella loihicain a batchreaction with an anoxic synthetic sea water medium. Some of the Fe(II) released by S. loihica adsorbedonto ferrihydrite, which was involved in the transformation of ferrihydrite to magnetite. In a second setof experiments with identical medium, no microorganism was present, instead, Fe(II) was amended. Theamount of solid-bound Fe(II) in the experiments with bioproduced Fe(II) increased the rate of abiotic NO2- reduction with respect to that with synthetic Fe(II), yielding half-lives of 0.07 and 0.47 d, respec-tively. The d18O and d15N of NO2- was measured through time for both the abiotic and innoculated ex-periments. The ratio of ε18O/ε15N was 0.6 for the abiotic experiments and 3.1 when NO2- was reduced by S. loihica, thus indicating two different mechanisms for the NO2-reduction. Notably, there is a wide rangeof the ε18O/ε15N values in the literature for abiotic and biotic NO2- reduction, as such, the use of this ratioto distinguish between reduction mechanisms in natural systems should be taken with caution.Therefore, we suggest an additional constraint to identify the mechanisms (i.e. abiotic/biotic) controllingNO2 reduction in natural settings through the correlation of d15N-NO2- and the aqueous Fe(II)concentration

Origin, accumulation and fate of dissolved organic matter in an extreme hypersaline shallow lake

Hypersaline endorheic aquatic systems (H-SEAS) are lakes/shallow playas in arid and semiarid regions that undergo extreme oscillations in salinity and severe drought episodes. Although their geochemical uniqueness and microbiome have been deeply studied, very little is known about the availability and quality of dissolved organic matter (DOM) in the water column.. A H-SEAS from the Monegros Desert (Zaragoza, NE Spain) was studied during a hydrological wetting-drying-rewetting cycle. DOM analysis included: (i) a dissolved organic carbon (DOC) mass balance; (ii) spectroscopy (absorbance and fluorescence) and (iii) a molecular characterization with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The studied system stored a large amount of DOC and under the highest salinity conditions, salt-saturated waters (i.e., brines with salinity > 30%) accumulated a disproportionate quantity of DOC, indicating a significant in-situ net DOM production. Simultaneously, during the hydrological transition from wet to dry, the DOM pool showed strong alterations of it molecular composition. Spectroscopic methods indicated that aromatic and degraded DOM was rapidly replaced by fresher, relatively small, microbial-derived moieties with a large C/N ratio. FT-ICR-MS highlighted the accumulation of small, saturated and oxidized molecules (molecular O/C > 0.5), with a remarkable increase in the relative contribution of highly oxygenated (molecular O/C>0.9) compounds and a decrease of aliphatic and carboxyl-rich alicyclic moleculesThese results indicated that H-SEAS are extremely active in accumulating and processing DOM, with the notable release of organic solutes probably originated from decaying microplankton under large osmotic stress at extremely high salinities