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Sulphur-oxidising bacteria isolated from deep caves improve the removal of arsenic from contaminated harbour sediments
Abstract
Acidophilic S-oxidising bacteria isolated from sulphur-rich deep caves (Frasassi, Italy), characterised by relatively low temperature, were tested for their ability to mobilise (semi-)metals from contaminated sediments. Sediment samples from two commercial Italian seaports were used to set up bioleaching experiments. The effect of different growth substrates was also investigated. Our experiments revealed that S-oxidising bacteria isolated from Frasassi caves have a high potential to remove As from contaminated marine sediments, as never reported before. Although As solubilisation efficiency was quite low (i.e. about 30%), only a small amount of As was associated with non-residual fractions of the sediment. On the contrary, the solubilisation efficiencies of Zn and Ni (20% and 10%, respectively) were lower than those previously obtained by the use of other acidophilic bacteria and mainly influenced by the experimental conditions rather than by the presence of the S-oxidising bacteria. Results presented here open new perspectives in bioleaching applications for the remediation of contaminated sediments. Indeed, microbial strains adapted to relatively low-temperature environments could improve sediment bioleaching at temperature regimes where mesophilic and thermophilic strains are not favoured. Such strains could be exploited for developing selective bioremediation procedures for sediments contaminated with As, to be applied in multistep biotreatment processes.
... These microorganisms were determined to be used in the construction of bio-concretes, crack healing in concretes, and soil bioremediation. In addition, diverse enzyme activities revealed in cave isolates can serve industrial uses with low energy spending [11,22,24,25]. Wastes bioremediation potentials were detected also in cave isolates [5,25]. ...
... In addition, diverse enzyme activities revealed in cave isolates can serve industrial uses with low energy spending [11,22,24,25]. Wastes bioremediation potentials were detected also in cave isolates [5,25]. ...
Microorganisms are distributed everywhere even on the extreme environments such as caves. The underground surfaces are minerals rich and the life in there is found to be related to both biotic and abiotic factors. Since the cycle of these minerals is insured by the chemolithotrophs living in there. In addition, caves are also considered as important reservoirs of bioactive compounds. However, caves are entered for different reasons. Some of cavers are of scientific research, some of them are for recreational reasons like sports and simple cave visits. All these activities are thought to impacts on the visible mat and invisible colonies of microorganisms through mechanical force or importing exogenous microorganisms. This study summarizes the different impacts which can be caused by the different human activities in caves. Finally, perspective of the conservation of cave microbial structure are suggested for the further uses of caves.
... This process involves a critical approach aimed at introducing or increasing the microbial population with degradation capabilities. In addition to this approach, other studies using microorganisms such as bacteria, fungi and microalgae focused on bioleaching (dissolving metallic cations from insoluble ores through biological oxidation and complexation processes, which is an innovative and low-carbon technology for metal extraction) [13,41], biotransformation (altering the valence states of metals to modify their mobility, bioavailability, and toxicity, including reduction and oxidation processes, methylation and demethylation, and hydrogenation) [19,123], bioaccumulation (active process in which microorganisms transport metals into their intracellular space and sequester them with proteins and peptide ligands, acting as a storage system) [1,108,77], and finally, bioprecipitation (metal precipitation occurring when metals react with extracellular polymers or microbial metabolite-derived anions such as sulphides or phosphates) [94,127]. ...
... In addition, Whiffin (2004) successfully manufactured the first biocemented sand column using bacteria, which opened a new era for manipulating the engineering characteristics of geomaterials using biological methods. Various biotreated methods have been developed to tackle geotechnical problems (Decho 2010;, for example, biocementation to improve soil strength and reduce erosion and seepage Gomez et al. 2018a;Nassar et al. 2018;Li et al. 2019;Montoya et al. 2019;Wu et al. 2019b;Xiao et al. 2022c), biodesaturation to enhance liquefaction resistance (Rebata-Landa and Santamarina 2012; He et al. 2013O'Donnell et al. 2017a;Nakano 2018;O'Donnell et al. 2019;Mousavi and Ghayoomi 2021;Wang et al. 2021a), bioclogging or biosealing (Davis et al. 2009;Mitchell et al. 2010Mitchell et al. , 2013Phillips et al. 2013a, b;DeJong et al. 2016;Phillips et al. 2018;Kirkland et al. 2020), and the bioremediation of heavy metal and oil pollution in soil and water (Davis et al. 2003;Wang and Chen 2006;Keimowitz et al. 2007;Beolchini et al. 2009;Wang and Zhao 2009;Luo and Gu 2011;Zhao et al. 2015;Beolchini et al. 2017;Cheng and Shahin 2017;Cornu et al. 2017;Li et al. 2017b;Qi et al. 2018;Shapiro et al. 2018;Naguib et al. 2019;Asta et al. 2020;Rolando et al. 2020). Biotreatment in this study is within the scope of microbially induced calcium carbonate precipitation (MICP). ...
Microbially induced calcium carbonate precipitation (MICP) has attracted great attention recently for its ability to improve the mechanical properties of soils. Calcium carbonate (CaCO3) precipitates that formed at the contact points and on the surface of particles or in the pore space of soil matrixes could increase the bonding strength, friction, and interlocking resistances due to the enhancement of the interparticle bonds, particle roughness, and packing density, and therefore, greatly improve the macroscopic performances of biocemented soils that were subjected to external loading. Strength is one of the key factors when determining the application of biotreatments in geotechnical engineering during the construction and operation periods. This study presented a systematic, objective, and extensive review of the strength of biocemented soils that was based on previous research. The improvement characteristics were comprehensively investigated under compression, tension, and static and cyclic shear conditions, for unconfined compressive (UCS), splitting tensile (STS), yielding, shear, and cyclic resistance strengths. Particle scale regimes were elaborated to interpret the improvement mechanism in the biotreatment and failure modes in biocemented specimens under external loading. Furthermore, the challenges of biocementation were discussed, and future investigations were envisioned. © 2022 This work is made available under the terms of the Creative Commons Attribution 4.0 International license,.
... In light of this, Behera et al. (2014) isolated 75 SOB from high sulfurcontaining environments. In two different investigations, in 2016 and 2017, researchers also isolated 24 bacteria from acid mine drainage and black shale and acidophilic SOB from sulfur-rich deep caves of Frasassi, Italy respectively (Sajjad et al., 2016;Beolchini et al., 2017). Pb and Cd tolerant SOB were also isolated by using a thiosulfate medium from different samples collected from various environments by Ashraf et al. (2018). ...
Aims:
The present investigation was carried out to isolate, screen and characterize potential sulfur-oxidizing bacteria (SOB) isolated from mustard field's soil.
Methods and results:
A total of 130 bacteria were isolated and after screening five maximum sulfate-producing isolates were optimized for culture conditions. The incubation time of 48 h was found optimum for all bacterial isolates and 30°C was the best temperature for the growth of SSD11, SSR1 and SSG8 whereas 35°C for SSF17. The pH 8 was found best for all four isolates except SSF17 (6 pH). Media having glucose as a carbon source and ammonium sulphate as an N-source were producing maximum sulphate. The isolates SSF17, SSR1 and SSG8 were identified as Burkholderia cepacia (accession no. MT559819), Enterobacter cloacae (accession no. MT559820) and Klebsiella oxytoca (accession no. MT372097), respectively, on the basis of morphological, biochemical and molecular characterization. The isolates were also found to increase N and S uptake efficiently in both wheat and mustard crops.
Conclusion:
This study strongly concludes that SOB isolated from the mustard field can oxidize sulfur in vitro and in vivo conditions. The three best isolates come out of the study were identified as Burkholderia, Enterobacter and Klebsiella strains. Also, inoculation of SOB increased the uptake of S and N nutrient in mustard and wheat crops and thus may be proved as an important plant growth-promoting bacteria having the biofertilization capability.
Significance and impact of the study:
As we know, our soil is continuously deteriorating day by day due to excessive utilization and immoderate use of chemical fertilizers. The SOB could minimize the application of chemical fertilizers thus reducing environmental deterioration by improving soil health in sustainable agricultural practices.
... In sulfuric acid dissolution, hydrogen sulfide (H 2 S) gas rises from rock fissures (narrow openings of rocks, commonly found in tectonically active areas) and reacts with atmospheric oxygen to form sulfuric acid (H 2 SO 4 ) that dissolves the carbonate rock to form caves (Palmer, 1991;Northup and Lavoie, 2001). Furthermore, decomposition of organic matter by microorganisms can be a source of sulfuric acid dissolution (Beolchini et al., 2017). ...
Caves are extreme, often oligotrophic, environments that house diverse groups of microorganisms. Many of these microbes can perform microbiologically induced carbonate precipitation (MICP) to form crystalline secondary cave deposits known as speleothems. The urease family is a group of enzymes involved in MICP that catalyze the breakdown of urea, which is a source of energy, into ammonia and carbonate. Carbonate anions are effluxed to the extracellular surface of the bacterium where it then binds to environmental calcium to form calcium carbonate which then continues to grow in crystal form. Here, we studied bacterial communities from speleothems collected from the Iron Curtain Cave (ICC) in Chilliwack, B.C., Canada, to characterize these organisms and determine whether urease-positive (U+) bacteria were present in the cave and their potential impact on speleothem formation. The ICC is a carbonate cave located on the northside of Chipmunk Ridge, presenting a unique environment with high iron content sediment and limestone structures throughout. With six pools of water throughout the cave, the environment is highly humid, with temperatures ranging between 4 and 12°C depending on the time of year. Ninety-nine bacterial strains were isolated from popcorn (PCS) and soda straw (SSS) speleothems. These isolates were screened for urease enzymatic activity, with 11 candidates found to be urease-positive. After incubation, species-specific crystal morphologies were observed. Popcorn speleothem provided more bacterial diversity overall when compared to soda straw speleothem when examined under a culture-based method. Nearly twice as many U+ isolates were isolated from popcorn speleothems compared to soda straw speleothems. The U+ candidates were identified to the genus level by 16S rRNA analysis, and two isolates underwent whole-genome sequencing. Two novel species were identified as Sphingobacterium sp. PCS056 and Pseudarthrobacter sp. SSS035. Both isolates demonstrated the most crystal production as well as the most morphologically dissimilar crystal shapes in broth culture and were found to produce crystals as previously observed in both agar and broth media. The results from this study are consistent with the involvement of urease-positive bacteria isolated from the ICC in the formation of cave speleothems. 16S rRNA sequencing revealed a diverse set of microbes inhabiting the speleothems that have urease activity. Whole-genome sequencing of the two chosen isolates confirmed the presence of urease pathways, while revealing differences in urease pathway structure and number. This research contributes to understanding microbial-associated cave formation and degradation, with applications to cave conservation, microbiota composition, and their role in shaping the cave environment.
Among fundamental research questions in subterranean biology, the role of subterranean microbiomes playing in key elements cycling is a top-priority one. Karst caves are widely distributed subsurface ecosystems, and cave microbes get more and more attention as they could drive cave evolution and biogeochemical cycling. Research have demonstrated the existence of diverse microbes and their participance in biogeochemical cycling of elements in cave environments. However, there are still gaps in how these microbes sustain in caves with limited nutrients and interact with cave environment. Cultivation of novel cave bacteria with certain functions is still a challenging assignment. This review summarized the role of microbes in cave evolution and mineral deposition, and intended to inspire further exploration of microbial performances on C/N/S biogeocycles.
Heavy metal contamination is a worldwide concern and a challenge to resolve due to the toxicity poses a significant threat to all living organisms in the environment. Phytoremediation is an environmental-friendly approach to alleviate heavy metal contamination in the soil. Combining the plant and beneficial bacteria inoculant to remediate soil heavy metal is known as bacterial inoculant-assisted phytoremediation. Beneficial bacteria facilitate plant metal uptake by mobilizing the heavy metals in the soil and enhancing plant vigor. The inoculant formulations can be prepared as liquid, granules or powders. Nonetheless, the effective interaction between plant and bacteria is not promised in unsterilized soil, thus affecting the phytoremediation efficiency. The development of bacterial inoculants for phytoremediation and the effects of the inoculants in soil are overlooked in current research studies. Therefore, an ample understanding of the bacterial inoculant-assisted phytoremediation concept is pertinent to circumvent the limitations. This article discusses the relationship between beneficial bacteria inoculant and plant in different techniques of phytoremediation, recent advances in developing bacterial inoculants for phytoremediation and the fate of the inoculants in soil. The provided information in this article generates more insights on the optimization works, which ultimately leading to the possible field application.
In the last few decades, challenges of the aquatic environment have been dramatically changed in terms of magnitude of disturbances or types of hazards, along with the rise of new scientific and technological opportunities. In addition to the traditional (legacy) chemicals like metals or organic chemicals (including PAHs, PCBs and dioxins), emerging pollutants such as endocrine disruptors (EDCs), pharmaceuticals and microplastics are examples of worrying stressors for health of aquatic organisms and ecosystems. These compounds, introduced by different environmental sources and having a wide distribution, are absorbed by several species causing potential deleterious effects. The challenges of such pollutants will be discussed focusing on (i) new detection strategies, (ii) mode of action, (iii) ecological risk assessment and (iv) implementation of mitigation actions, to reduce the contaminant impact in terms of health care costs and maintenance of biodiversity. Sustainable and ecologically compatible methods and strategies for the reclamation of aquatic sediments contaminated with organic pollutants and toxic metals will also be described. Such knowledge will foster the reduction of use or release of many hazardous substances, together with providing insights on the early warning detection of chemical harmful agents within an environmental monitoring and security application program. Based on this knowledge, in this review we attempted to describe the approaches that are taken by research groups with different backgrounds operating at Università Politecnica delle Marche.
Nature is bountiful of living biota which ranges from 3 to 50 million and one-third of global biodiversity exists in India. Since prehistoric times, humans have exploited microorganisms for their own use. The Earth’s subsurface presents one of the finest promising locations to look for microbial life and the distinctive lithologies that life leaves behind. Studies on microbial diversity are hampered not only by the technical ability to assess the species numbers but also by the high heterogeneity of the environment, with its changing temporal and spatial microhabitats. Moreover, natural products are for the most part a booming source of drug leads. Regardless, their application in innovation of new drug has fallen out of favour. Not more than 10% of the planet’s biodiversity has been under trial for biological property; a lot of functional natural compounds are pending innovation. The test is how to get in touch with this natural chemical diversity. In this aspect, research on caves is the utmost need of the hour to increase our acceptance of the means of biological adjustment to severe circumstances, the relations involving organisms and minerals, the function of inorganic matter in diverse dark ecosystems and the evolution and speciation of biological schemes under acute circumstances, progressing to a range of biotechnological uses. In the present chapter, a handful of the important caves around the world are described, together with an analysis of the potential health effects from the microbes inhabiting such ecosystems. Needless to emphasise, such type of study spanning over length and breadth of India is the urgent need of the hour, which hopefully would unravel many of the microbes of biotechnological importance. Suggestions for potential investigations are highlighted to promote going with the flow from qualitative research to additional experimentations.
This review presents developments and applications in bioleaching and mineral biooxidation since publication of a previous mini review in 2003 (Olson et al. Appl Microbiol Biotechnol 63:249-257, 2003). There have been discoveries of newly identified acidophilic microorganisms that have unique characteristics for effective bioleaching of sulfidic ores and concentrates. Progress has been made in understanding and developing bioleaching of copper from primary copper sulfide minerals, chalcopyrite, covellite, and enargite. These developments point to low oxidation-reduction potential in concert with thermophilic bacteria and archaea as a potential key to the leaching of these minerals. On the commercial front, heap bioleaching of nickel has been commissioned, and the mineral biooxidation pretreatment of sulfidic-refractory gold concentrates is increasingly used on a global scale to enhance precious metal recovery. New and larger stirred-tank reactors have been constructed since the 2003 review article. One biooxidation-heap process for pretreatment of sulfidic-refractory gold ores was also commercialized. A novel reductive approach to bioleaching nickel laterite minerals has been proposed.
Sediment contamination in coastal areas with high anthropogenic pressure is a widespread environmental problem. Metal contaminants are of particular concern, since they are persistent and cannot be degraded. Microorganisms can influence metal mobility in the sediment by several direct and indirect processes. However, the actual fate of metals in the environment is not easily predictable and several biogeochemical constraints affect their behaviour. In addition, the geochemical characteristics of the sediment play an important role and the general assumptions for soils or freshwater sediments cannot be extended to marine sediments. In this paper we analysed the correlation between metal mobility and main geochemical properties of the sediment. Although the prediction of metal fate in sediment environment, both for ex-situ bioleaching treatments and in-situ biostimulation strategies, appears to require metal-specific and site-specific tools, we found that TOM and pH are likely the main variables in describing and predicting Zn behaviour. Arsenic solubilisation/increase in mobility appears to correlate positively with carbonate content. Cd, Pb and Ni appear to require multivariate and/or non-linear approaches.
Metal sulfide oxidation is an important process in the past and present global biogeochemical sulfur cycles. In this process, various sulfur compounds, namely elemental sulfur, polysulfides, thiosulfate, polythionates, sulfite, and sulfate, are generated in different environments. The formation of the sulfur compounds depends on the mineralogy of the metal sulfide and the geochemical conditions in the environment, mainly the pH and the presence of different oxidants. Metal sulfide oxidation can be described by two different pathways: the thiosulfate mechanism and the polysulfide mechanism. Microorganisms play a crucial role in the oxidation of intermediate sulfur compounds, which are formed by the chemical dissolution of the metal sulfides. Under oxic and acidic conditions (e.g., in sulfidic mine waste or in acid sulfate soils), microorganisms oxidize Fe(II) to Fe(III), which serves as an oxidant for the metal sulfides and for most of the intermediate sulfur compounds. Additionally, microorganisms may catalyze the oxidation of intermediate sulfur compounds to sulfate. Under oxic and pH-neutral conditions (e.g., in carbonate-buffered sulfidic mine waste or at the surface of marine sediments) the metal sulfides are chemically oxidized by molecular oxygen via a Fe(II)/Fe(III) shuttle to the metal (hydr)oxide, intermediate sulfur compounds, and sulfate. Microorganisms oxidize the intermediate sulfur compounds to sulfate and, at low partial pressure of molecular oxygen, may catalyze Fe(II) oxidation. Under anoxic and pH-neutral conditions (e.g., in marine sediments), metal sulfides and intermediate sulfur compounds are oxidized either chemically by MnO2 or by microorganisms using nitrate as an electron acceptor.
A defined mesophile consortium including Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirilum ferriphilum was applied in bioleaching sediments contaminated with multiple heavy metals. Flask experiments showed that sulfur favored the acidification in the early stage while pyrite led to a great acidification potential in the later stage. An equal sulfur/pyrite ratio got the best acidification effect. Substrate utilization started with sulfur in the early stage, and then the pH decline and the community shift give rise to the utilization of pyrite. Solubilization efficiency of Zn, Cu, Mn, and Cd reached 96.1, 93.3, 92.13, and 87.65 %, respectively. Bioleaching efficiency of other elements (As, Hg, Pb) was not more than 30 %. Heavy metal solubilization was highly negatively correlated with pH variation. Logistic models were well fitted with the solubilization efficiency, which can be used to predict the bioleaching process. The dominant species in the early stage of bioleaching were A. ferrooxidans and A. thiooxidans, and the abundance of L. ferriphilum increased together with pyrite utilization and pH decline.
The production of end-of-life equipment, known as waste of electrical and electronic equipment (WEEE) or e-waste, is a direct consequence of the modern revolution of the electronic industry and of the constant evolution of technology. According to the United Nations Environment Programme (UNEP), a dramatic increase in the illegal import of e-waste, 200%-400% in South Africa and 500% in India, can be estimated for the period between 2017 and 2020 (Schluep et al. 2009). Organic and inorganic components in WEEE can cause environmental problems if not properly managed. Today, in the United States and Europe, the main WEEE management strategies are incinerators and landfills and these can represent a serious threat to the environment and human health, due to contaminant leaching in soils and ground waters, and to a release of potentially hazardous by-products in the atmosphere (Robinson 2009; Tsydenova and Bengtsson 2011). On the other hand, base (e.g. Cu) and precious metals (e.g. Au, Ag and Pd) in WEEE could be employed as raw materials, making WEEE an attractive secondary resource of valuable elements (Oguchi 2013). In the last decade, the scientific community and industrial research have made a significant effort in developing techniques for the recovery of metal components from WEEE, especially by pyrometallurgical and hydrometallurgical approaches. Nevertheless, such techniques may be extremely polluting and not environmentally sustainable (Korte et al. 2000; Mecucci and Scott 2002; Cui and Zhang 2008; Tsydenova and Bengtsson 2011). Biohydrometallurgical strategies, based mainly on the ability of microorganisms to produce leaching agents, are gaining increasing prominence in this field. For instance, the technique known in mining activities as bioleaching (i.e. biological leaching) is considered a novel approach for metal mobilisation from various types of solids (Beolchini et al. 2012). The main advantages of biohydrometallurgical methods would be low operating costs (due to a low energy input), reduced environmental impact and a general minimisation of the end product (Ehrlich 2001; C. L. Brierley 2010).
Snottites are extremely acidic (pH 0–2) biofilms that form on the walls and ceilings of hydrogen sulfide-rich caves. Recent work suggests that microbial communities including snottites and related cave wall biofilms accelerate cave formation by oxidizing sulfide to sulfuric acid. Therefore, we used full-cycle rRNA methods and metagenomics to explore the community composition and sulfur metabolism of snottites from the sulfidic Frasassi and Acquasanta cave systems, Italy. Acquasanta snottites were dominated by strains of Acidithiobacillus thiooxidans, with a smaller population of Ferroplasma sp. Frasassi snottites were also dominated by At. thiooxidans but with a more diverse community including relatives of ‘G-plasma’ (Thermoplasmatales), Acidimicrobium, and rare taxa. We identified diverse homologues of sulfide:quinone oxidoreductase (SQR) in the metagenomic datasets. Based on phylogenetic analysis, the numerically dominant At. thiooxidans populations have four different types of SQR, while Ferroplasma has two and Acidimicrobium and G-plasma each have one. No other genetic evidence for sulfur oxidation was detected for either Acidimicrobium or G-plasma, suggesting that they do not generate sulfuric acid. Our results confirm earlier findings that At. thiooxidans is the dominant primary producer and sulfide oxidizer in sulfidic cave snottites.
In coastal marine systems at high level of anthropization and socio-economic exploitation, like harbours, sediment represents a sink and a source for contaminants. Indeed, organic and inorganic pollutants coming from the water column are adsorbed and accumulated by sediment, as a consequence of natural processes occurring in all the aquatic systems. Unlike organic contaminants, metals cannot be degraded. Metal contamination in marine sediment is an environmental problem of high magnitude and, as a consequence, there is a need for environmentally friendly strategies. In this contest, biologically mediated leaching (bioleaching) may offer a solution. In the present work, bioleaching is applied on metal contaminated sediment coming from a marine harbour. Laboratory scale experiments were performed, at 10 g/L sediment content, in order to deepen the mutualistic interaction between chemolithotrophic Fe/S oxidizing bacteria, commonly applied in bioleaching strategies, and acidophilic heterotrophic Fe-reducing bacteria. Indeed, previous papers have partially investigated this aspect and offer some interesting insights. Here, the mutualism eventually occurring is better investigated, in view of the understanding of the processes involved during bioleaching, where the interaction metal-bacteria-sediment appears to be of central importance. Target metals were those mainly relevant in the sediment sample: arsenic (48 +/- 2 ppm), chromium (140 +/- 50 ppm), cadmium (1.8 +/- 0.5 ppm) and zinc (1030 +/- 70 ppm). During the experiment, other investigated responses were pH, microbial abundances and iron speciation. At the end of the experiment, Zn and Cd were the main solubilized metals, while Cr and As were scarcely removed from the sediment. Data about iron speciation also suggested that mutualism between chemolithotrophs and heterotrophs occurred, despite the presence of a complex environmental matrix such as marine sediment.
Bioleaching of metal sulfides is performed by a diverse group of microorganisms. The dissolution chemistry of metal sulfides follows two pathways, which are determined by the mineralogy and the acid solubility of the metal sulfides: the thiosulfate and the polysulfide pathways. Bacterial cells can effect this metal sulfide dissolution via iron(II) ion and sulfur compound oxidation. Thereby, iron(III) ions and protons, the metal sulfide-attacking agents, are available. Cells can be active either in planktonic state or in forming biofilms on the mineral surface; however, the latter is much more efficient in terms of bioleaching kinetics. In the case of Acidithiobacillus ferrooxidans, bacterial exopolymers contain iron(III) ions, each complexed by two uronic acid residues. The resulting positive charge allows an electrostatic attachment to the negatively charged pyrite. Thus, the first function of complexed iron(III) ions is the mediation of cell attachment, while their second function is oxidative dissolution of the metal sulfide, similar to the role of free iron(III) ions in non-contact leaching. In both cases, the electrons extracted from the metal sulfide reduce molecular oxygen via a redox chain forming a supercomplex spanning the periplasmic space and connecting both outer and inner membranes. In this review, we summarize some recent discoveries relevant to leaching bacteria which contribute to a better understanding of these fascinating microorganisms. These include surface science, biochemistry of iron and sulfur metabolism, anaerobic metabolism, and biofilm formation. The study of microbial interactions among multispecies leaching consortia, including cell-to-cell communication mechanisms, must be considered in order to reveal more insights into the biology of bioleaching microorganisms and their potential biotechnological use.
More than 100 cultures of acidophilic Fe(II)- and/or sulfur-oxidizing microorganisms from mine waste dumps in 10 different countries all over the world have been maintained in liquid media in the BGR-strain collection for many years. Our 16S rDNA analysis showed that most of the cultivated Fe(II)-oxidizers belong to four genera: Acidithiobacillus, Acidimicrobium, "Ferrimicrobium" and Leptospirillum. All analyzed Acidithiobacillus strains were identified as At. ferrooxidans. The Leptospirillum strains were affiliated with L. ferriphilum or L. ferrooxidans. The Gram-positive strains related to Acidimicrobium or "Ferrimicrobium" were phylogenetically more diverse than the strains of the genera Acidithiobacillus and Leptospirillum and fell into three separate clusters. While several strains could be identified as syngeneic (16S rDNA) with "Ferrimicrobium acidiphilum", two other 16S rDNA clusters were distantly related and might represent new species or even new genera. In addition, one new Sulfobacillus strain and one new Alicyclobacillus strain could be identified. Furthermore several strains related to Acidiphilium acidophilum have been detected and form one 16S rDNA cluster.
This study deals with laboratory-scale investigations to evaluate the efficiency of different chemical leaching agents (i.e. sulfuric, oxalic and citric acids) and bioleaching processes (based on different acidophilic bacterial strains) on the mobilisation of metals/semi-metals in contaminated harbour sediments. A simplified life-cycle assessment was also performed in order to compare the investigated strategies in terms of their main environmental impacts. The different chemical leaching agents provided different extraction efficiencies of toxic metals. Among the investigated chemical leaching agents, citric acid 0.5 M and sulfuric acid pH 2 were the most effective, with average mobilisation efficiencies of 30% for Zn and Cr, 40% for Ni, and 35 and 58% for As, under citric and sulfuric acid, respectively. Similar higher extraction efficiencies of metals were also observed in bioleaching experiments with the presence of ferrous iron. The life-cycle assessment revealed that treatments based on diluted sulfuric acid are a better option considering both resource requirements and emissions, leading to lower environmental impacts compared with the other treatment strategies. Overall results from this study provide new insights for the definition of the most efficient and environmentally friendly strategies to be used for dredged sediments contaminated with metals.
Spatial prioritization in conservation is required to direct limited resources to where actions are most urgently needed and most likely to produce effective conservation outcomes. In an effort to advance the protection of a highly threatened hotspot of marine biodiversity, the Mediterranean Sea, multiple spatial conservation plans have been developed in recent years. Here, we review and integrate these different plans with the goal of identifying priority conservation areas that represent the current consensus among the different initiatives. A review of six existing and twelve proposed conservation initiatives highlights gaps in conservation and management planning, particularly within the southern and eastern regions of the Mediterranean and for offshore and deep sea habitats. The eighteen initiatives vary substantially in their extent (covering 0.1-58.5% of the Mediterranean Sea) and in the location of additional proposed conservation and management areas. Differences in the criteria, approaches and data used explain such variation. Despite the diversity among proposals, our analyses identified ten areas, encompassing 10% of the Mediterranean Sea, that are consistently identified among the existing proposals, with an additional 10% selected by at least five proposals. These areas represent top priorities for immediate conservation action. Despite the plethora of initiatives, major challenges face Mediterranean biodiversity and conservation. These include the need for spatial prioritization within a comprehensive framework for regional conservation planning, the acquisition of additional information from data-poor areas, species or habitats, and addressing the challenges of establishing transboundary governance and collaboration in socially, culturally and politically complex conditions. Collective prioritised action, not new conservation plans, is needed for the north, western, and high seas of the Mediterranean, while developing initial information-based plans for the south and eastern Mediterranean is an urgent requirement for true regional conservation planning.
This review aims to present the current status of studies on geochemical (major minor and trace elements), biochemical (total organic carbon, total nitrogen, isotopic carbon composition, Bacteria, Archaea, phytopigments, proteins, carbohydrates, lipids, humic and fulvic acids), mineralogical (light and heavy minerals, clay minerals) and pollutant (trace metals, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pesticides, organic stannic compounds) parameters, grain-size composition and sediment-water interactions (early diagenesis and benthic fluxes) for the bottom sediments of the central and southern Adriatic Sea. The review highlighted gaps in or completeness of the parameters needed for research, of areas in which the parameters were investigated, as well as the interdisciplinary nature of the studies. In general, biogeochemical, mineralogical, grain-size and pollutant studies in the central and southern Adriatic Sea are restricted to limited areas, consider only single parameters without an interdisciplinary approach and, except for some more recent projects, are predominatly out of date. On the whole, there is a lack of an organised study concerning the various parameters for the entire central and southern Adriatic Sea and their evolution over time.
With increasing interest in the carbon cycle on arid land, there is an urgent need to quantify both soil organic carbon (SOC) and inorganic carbon (SIC) thus to assess various methods. Here, we present a study employing three methods for determinations of SOC and SIC in the Yanqi Basin of northwest China. We use an elemental analyzer for both SOC and SIC, the Walkley-Black method for SOC, a modified pressure calcimeter method for SIC, and a simple loss-on-ignition (LOI) procedure for determinations of SOC and SIC. Our analyses show that all three approaches produce consistently low values for SOC (1-14 g kg(-1)) and high values for SIC (8-53 g kg(-1)). The Walkley-Black method provides an accurate estimate of SOC with 100% recovery for most soil samples. The pressure calcimeter method is as accurate as the elemental analysis for measuring SIC. In addition, SOC and SIC can be accurately estimated using a two-step LOI approach, i.e., (1) combustion at 375°C for 17 hours to estimate SOC, and (2) subsequent combustion at 800°C for 12 hours to estimate SIC. There are strong linear relationships for both SOC and SIC between the elemental analysis and LOI method, which demonstrates the capability of the two-step LOI technique for estimating SOC and SIC in this arid region.
Modern commercial application of biohydrometallurgy for processing ores became reality in the 1950s with the advent of copper bioleaching at the Kennecott Copper Bingham Mine. Early application entailed dump leaching of low-grade, low-value, run-of-mine material. Dump bioleaching has evolved into a commercially accepted option for bioheap copper leaching of higher-grade, higher value ores. This commercial practice is exemplified by at least 11 mining operations. Paradoxically, application of biohydrometallurgy in the pretreatment of refractory gold ores began with processing high value concentrates, using biooxidation-tank processes and was followed by extension to processing low-grade, lower value ores in heaps. Now, bioleaching has been extended to the commercial extraction and recovery of cobalt. Even with the current success of biohydrometallurgical applications in the mining industry, the real potential of biotechnology in mining remains to be realized. As confidence in commercial bioprocessing grows and experience extends the application's knowledge base, innovations and new commercial practices will emerge. Near-term future commercial applications will likely remain focused on recoveries of copper, gold and possibly nickel. Recent technical advances show that very refractory chalcopyrite can be successfully bioleached. Processes for copper recovery from this mineral will include both heap and stirred-tank reactors. Next generation technologies for pretreatment of refractory gold ores will be based on use of thermophilic bacteria for sulfide oxidation. For biohydrometallurgy to commercially advance, the microbiologist must work cooperatively with the practitioners of the technology for mutual understanding of operational limitations and practical constraints affecting the microbiological component. q 2001 Elsevier Science B.V. All rights reserved.
A remediation process for heavy metal polluted sediment has previously been developed, in which the heavy metals are removed from the sediment by solid-bed bioleaching using sulfuric acid as a leaching agent arising from added elemental sulfur (S°). This process has been engineered with Weiße Elster River sediment (dredged near Leipzig, Germany), as an example. Here, six heavy metal polluted sediments originating from various bodies of water in Germany were subjected to bioleaching to evaluate the applicability of the developed process on sediment of different nature: each sediment was mixed with 2 % S°, suspended in water and then leached under identical conditions. The buffer characteristics of each sediment were mainly governed by its carbonate and Ca content, i.e., by its geological background, the redox potential and oxidation state depended on its pre-treatment (e.g., on land disposal), while the pH value was influenced by both. The added S° was quickly oxidized by the indigenous microbes even in slightly alkaline sediment. The microbially generated H2SO4 accumulated in the aqueous phase and was in part precipitated as gypsum. Significant acidification and heavy metal solubilization only occurred with sediment poor in buffer substances. With the exception of one sediment, the behavior in bioleaching correlated well with the behavior in titration with H2SO4. Since the content in carbonate seemed to be the most important factor deciding on the leachability of a sediment, oxic Weiße Elster River sediment was mixed with 2 % S° and 0 to 100 g/kg of ground limestone to simulate various buffer capacities, suspended in water and then leached. The lime did not inhibit microbial S° oxidation but generated a delay in acidification due to neutralization of formed H2SO4, where the pH only started to decrease when the lime was completely consumed. The more lime the sediment contained, the longer this lag period lasted, and the higher the pH and the lower the fraction of the solubilized heavy metals finally was. Since Cu requires stronger acidic conditions for its solubilization, it responded more sensitively to lime addition than Zn, Ni, and Cd. Heavy metal polluted sediment containing large amounts of carbonate may, in principle, also be remediated by bioleaching, but metal solubilization requires excessive amounts of the leaching agent and is thus uneconomical.
Highly acidic (pH 0-1) biofilms, known as 'snottites', form on the walls and ceilings of hydrogen sulfide-rich caves. We investigated the population structure, physiology and biogeochemistry of these biofilms using metagenomics, rRNA methods and lipid geochemistry. Snottites from the Frasassi cave system (Italy) are dominated (>70% of cells) by Acidithiobacillus thiooxidans, with smaller populations including an archaeon in the uncultivated 'G-plasma' clade of Thermoplasmatales (>15%) and a bacterium in the Acidimicrobiaceae family (>5%). Based on metagenomic evidence, the Acidithiobacillus population is autotrophic (ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), carboxysomes) and oxidizes sulfur by the sulfide-quinone reductase and sox pathways. No reads matching nitrogen fixation genes were detected in the metagenome, whereas multiple matches to nitrogen assimilation functions are present, consistent with geochemical evidence, that fixed nitrogen is available in the snottite environment to support autotrophic growth. Evidence for adaptations to extreme acidity include Acidithiobacillus sequences for cation transporters and hopanoid synthesis, and direct measurements of hopanoid membrane lipids. Based on combined metagenomic, molecular and geochemical evidence, we suggest that Acidithiobacillus is the snottite architect and main primary producer, and that snottite morphology and distributions in the cave environment are directly related to the supply of C, N and energy substrates from the cave atmosphere.
Wetland ecosystems maintain a fragile balance of soil, water, plant, and atmospheric components in order to regulate water flow, flooding, and water quality. Marginally covered in traditional texts on biogeochemistry or on wetland soils, Biogeochemistry of Wetlands is the first to focus entirely on the biological, geological, physical, and chemical processes that affect these critical habitats. This book offers an in-depth look at the chemical and biological cycling of nutrients, trace elements, and toxic organic compounds in wetland soil and water column as related to water quality, carbon sequestration, and greenhouse gases. It details the electrochemistry, biochemical processes, and transformation mechanisms for the elemental cycling of carbon, oxygen, nitrogen, phosphorus, and sulfur. Additional chapters examine the fate and chemistry of heavy metals and toxic organic compounds in wetland environments. The authors emphasize the role of redox-pH conditions, organic matter, microbial-mediated processes that drive transformation in wetlands, plant responses and adaptation to wetland soil conditions. They also analyze how excess water, sediment water, and atmospheric change relate to elemental biogeochemical cycling. Delivering an in-depth scientific examination of the natural processes that occur in wetland ecosystems, Biogeochemistry of Wetlands comprises a key perspective on the environmental impact of pollutants and the role freshwater and coastal wetlands play in global climate change.
Acidophilic microorganisms are distributed throughout the three domains of living organisms. Within the archaeal domain, both extremely acidophilic Euryarchaeota and Crenarchaeota are known, and a number of different bacterial phyla (Firmicutes, Actinobacteria, and Proteobacteria [α, β, and γ subphyla], Nitrospira, and Aquifex) also contain extreme acidophiles. Acidophilic microorganisms exhibit a range of energy-transforming reactions and means of assimilating carbon as neutrophiles. Entire genomes have been sequenced of the iron/sulfur-oxidizing bacterium Acidithiobacillus ferrooxidans and of the archaea Thermoplasma acidophilum, Picrophilus torridus, Sulfolobus tokodaii, and Ferroplasma acidarmanus, and more genome sequences of acidophiles are due to be completed in the near future. Currently, there are four recognized species of this genus that grow autotrophically on sulfur, sulfide, and reduced inorganic sulfur compounds (RISCs). Acidithiobacillus ferrooxidans is the most well studied of all acidophilic microorganisms and has often, though erroneously, been regarded as an obligate aerobe. In both natural and anthropogenic environments, acidophilic microorganisms live in communities that range from relatively simple (two to three dominant members) to highly complex, and within these, acidophiles interact positively or negatively with each other. In a study which examined slime biofilms and snotites that had developed on the exposed surface of a pyrite ore within the abandoned Richmond mine at Iron Mountain, the major microorganisms identified were Leptospirillum spp. (L. ferriphilum and smaller numbers of L. ferrodiazotrophum) and Fp. acidarmanus, Sulfobacillus, and Acidimicrobium/Ferrimicrobium-related species. Using a modified plating technique, the uncharacterized β-proteobacterium can be isolated in pure culture and shown to be a novel iron-oxidizing acidophile.
Bioleaching is a consolidated biotechnology in the mining industry and in bio-hydrometallurgy, where microorganisms
mediate the solubilisation of metals and semi-metals from mineral ores and concentrates. Bioleaching
also has the potential for ex-situ/on-site remediation of aquatic sediments that are contaminated with metals,
which represent a key environmental issue of global concern. By eliminating or reducing (semi-)metal contamination
of aquatic sediments, bioleaching may represent an environmentally friendly and low-cost strategy for
management of contaminated dredged sediments. Nevertheless, the efficiency of bioleaching in this context is
greatly influenced by several abiotic and biotic factors. These factors need to be carefully taken into account before
selecting bioleaching as a suitable remediation strategy. Here we review the application of bioleaching for
sediment bioremediation, and provide a critical view of the main factors that affect its performance. We also discuss
future research needs to improve bioleaching strategies for contaminated aquatic sediments, in view of
large-scale applications.
The effects of sulfur concentration on the bioleaching of heavy metals from the sediment by indigenous sulfuroxidizing bacteria were investigated in an air-lift reactor. Increasing the sulfur concentration from 0.5 to 5 g/l enhanced the rates of pH reduction, sulfate production and metal solubilization. A Michaelis-Menten type equation was used to explain the relationships between sulfur concentration, sulfate production and metal solubilization in the bioleaching process. After 8 days of bioleaching, 97-99% of Cu, 96-98% of Zn, 62-68% of Mn, 73-87% of Ni and 31-50% of Pb were solubilized from the sediment, respectively. The efficiency of metal solubilization was found to be related to the speciation of metal in the sediment. From economical consideration, the recommended sulfur dosage for the bioleaching of metals from the sediment is 3 g/l.
Pilot studies were carried out to evaluate different options for metal-polluted (Cd, Cr, Cu, Ni, Pb and Zn) sediment decontamination. Chemical and biological leaching tests were done in a 350-L capacity stirred-tank reactor. The use of short acidic sediment washing steps (pH 2.0-3.0) was not an efficient approach for metal removal. The addition of an oxidant agent during the first washing step resulted in a large increase of removal yields for Pb (53-76%), Cd (54-92%) and Zn (69-93%). However, other metals were not well leached from sediments: Cr (6-30%), Cu (0-34%) and Ni (1-16%). The bioleaching treatment, with or without chemical washing steps, allows very good removal yields for Cd (82-100%), Cu (44-70%) and Zn (80-87%). On the other hand, this method was not efficient to remove other metals like Cr (6-16%), Ni (12-21%) and Tb (14-33%). The metals solubilized by chemical and/or biological leaching techniques can be efficiently removed from solution by precipitation using lime.
The microbial populations in stirred-tank, mineral-processing bioreactors and in ore leaching heaps generally comprise several species. The presence of sulfur and iron as energy sources from most of their mineral substrates and the existence of gradients (chemical and physical) in their environments underlie the diversity in these populations. Many of the important organisms are well known and their relative proportions in the bioreactor populations of some pilot plants and commercial operations have been estimated. Generally, two or three species, specific to a particular temperature range, predominate in the various mixed cultures that exist in the bioreactors. The description of populations in ore leaching heaps has so far been mostly qualitative. Reasons for the coexistence of different species in these mixed cultures or populations are clearer in some cases than in others. Similarly, some of the features that give individual species a competitive advantage over others in mixed cultures have been revealed but others, particularly at elevated temperatures, remain to be defined.
A method for enumeration of viable numbers of Thiobacillus ferrooxidans using membrane filters on ferrous-iron agar is presented. Factors affecting colony production were the concentration and brand of agar, pH of the medium, and type of membrane filter. The results suggest that inhibition of T. ferrooxidans by agar is a result of the acid hydrolysis of agar, the main product of which is d-galactose. Colony development was suppressed by aged medium, by acid-hydrolysed agar and by 0.1% galactose. Sartorius and Millipore membrane filters were suitable for the experiments, whereas Oxoid MF-50 membranes virtually suppressed the production of colonies. The method was employed to follow growth of T. ferrooxidans in pH 1.3 medium. The viable cell numbers were correlated with 14CO2-fixation and ferrous iron oxidation. Generation time was 6 h 22 min with a yield of 2.2×1012 organisms/g atom Fe2+ oxidized. Growth of T. neapolitanus on thiosulphate medium was not affected by agar-type or membrane filters and yield of the organism was 1.5×1013 organisms/g molecule Na2S2O3 oxidized.
Bioleaching Xiangjiang River alkaline sediment contaminated by multiple heavy metals was investigated. Multiple metals in alkaline sediment possess significant toxicity to aquatic organisms or humans and will greatly inhibit bioleaching. The bioleaching method using autotrophic bacteria mixed with heterotrophic bacteria can solve this problem successfully. The experiment results showed that bioleaching efficiencies of Zn, Mn, Cu, and Cd were 95.2 %, 94.2 %, 90.1 %, and 84.4 %, respectively. Moreover, the changes of heavy metal concentrations in different fractions in contaminated sediment before and after bioleaching were analyzed by selective sequential extraction, and it was discovered that the main fractions of Zn, Mn, Cu and Cd after bioleaching are Fe-Mn oxide, organic associated form and a residual form. Its biotoxicity decreased greatly. The bioleaching heavy metals from sediment using autotrophic bacteria combined with heterotrophic bacteria can effectively improve the bioleaching efficiency and reduce toxicity.
The contamination of aquatic sediments with metals is a widespread environmental problem. Coastal aquatic ecosystems with low hydrodynamics need to be periodically dredged in order to maintain the navigation depth and facilitate sailing; consequently large volumes of contaminated sediments need to be managed. Conventional remediation strategies include in-place sediment remediation strategies (e.g. in situ-capping) and relocation actions; in particular, landfill disposal and dumping at sea are still widely applied. Both this options are becoming unsustainable, due to problems associated with contaminant transport pathways, the uncertainties about long-term stability under various environmental conditions, the limited space capacity, costs and environmental compatibility. Alternative approaches have received increased attention; treatment and reuse of contaminated sediments is politically encouraged, but its application is still very limited. Because of the potential human health and environmental impacts of contaminated sediment, different chemical treatments are conventionally applied for contaminated sediments before reuse in other environmental settings. Environmentally friendly techniques developed for soils and other environmental matrices have been investigated for applications with sediments. Biotechnological approaches are gaining increasing prominence in this field and they are often considered as a promising strategy for the eventual treatment of contaminated sediments. In this paper an overview of the main treatment strategies potentially available for sediment contaminated with metals is given, together with a brief overview of the issue associated with the problem of the sediment management.
This work describes the effect of weathering of fresh quenched municipal solid waste incinerator (MSWI) bottom ash on the mobility and leaching behavior of zinc (Zn). A sequential extraction procedure (SEP) was used to characterize the fractionation of zinc in the fresh and weathered MSWI bottom ash samples. It showed that the stable fraction of Zn, including organic matter bound fraction and residual fraction decreased from 62.4% to 30.9% during the weathering treatment, while the mobile fraction, including exchangeable fraction, carbonate bound fraction and Fe–Mn oxides bound fraction, increased from 37.6% to 60.1%. Furthermore, two standard leaching procedures, synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP), were carried out on the fresh and weathered samples. The leaching of Zn was attenuated with the weathering treatment in the SPLP procedure, but enhanced in the TCLP procedure. The SEP and TCLP results suggested that the weathering treatment could enhance the mobility of Zn, which was distinct from previous work.
Bioleaching strategies are still far from finding real applications in sediment clean-up, although metabolic mechanisms governing bioleaching processes have been deeply studied and can be considered well established. In this study, we carried out bioleaching experiments, using autotrophic and heterotrophic acidophilic bacteria strains, and worked with marine sediments characterized by different geochemical properties and metal concentrations and speciations. The solubilization efficiency of the metals was highly variable, with the highest for Zn (40%-76%) and the lowest for Pb (0%-7%). Our data suggest that the role of autotrophic Fe/S oxidizing bacteria is mainly associated with the production and re-cycling of leaching chemical species, mainly as protons and ferric ions. Metal solubilization appears to be more related to establishing environmental conditions that allow each metal or semimetal to remain stable in the solution phase. Thus, the maintenance of acid and oxidative conditions, the chemical behavior in aqueous environment of each metal species and the geochemical characteristics of sediment interact intimately to influence metal solubilization in site-specific and metal-specific way.
The microbial consortium in continuous-flow, stirred tank processes used to treat gold-bearing arsenopyrite concentrates in South Africa has become adapted to high concentrations of arsenic over several years. The dominant microorganisms, Acidithiobacillus caldus and Leptospirillum ferriphilum, were found to contain two sets of arsenic-resistance genes. One set was present in all isolates of a species irrespective of whether they were highly arsenic resistant or not, while a second, transposon-located set was present in only those strains that had been adapted to high concentrations of arsenic.The arsenopyrite treatment tanks from Tamboraque (near Lima, Peru) have not been inoculated with an arsenic-adapted consortium from South Africa. Isolation of a Leptospirillum ferrooxidans from the Tamboraque consortium allowed us to determine whether these microorganisms had acquired similar arsenic-resistance mechanisms as contained on the transposons in the highly arsenic resistant South African cultures. Several isolates of both L. ferriphilum and L. ferrooxidans from Europe as well as a “Leptospirillum ferrodiazotrophum” were also screened to detect whether they contained similar arsenic-resistance transposons even though they had not been selected for enhanced arsenic resistance.Transposons containing arsenic-resistance genes that were identical or closely related to those from South Africa were found in both L. ferrooxidans and L. ferriphilum isolates from South America and Europe. The widespread occurrence of arsenic-resistance transposons suggests that it should be possible to select for highly arsenic resistant biomining microorganisms from many different sources and therefore, unnecessary to use pre-adapted arsenic resistant consortia.
The solubility of arsenic (As) and heavy metals (Me) from two sediments with differing chemical characteristics and degrees of contamination was quantified by suspension leaching under both aerobic and anoxic conditions. Elemental sulphur (S°) was added as a substrate for the indigenous Thiobacillus spp. The objective of this study was to examine the effects of measures, which attempted to stimulateor to prevent the mobilization of the pollutants in the source material.By stimulating aerobic bioleaching with S°, up to 80% (660 mg/kg) of the As became soluble in a highly polluted lake sediment (Suesser See) in the form of arsenite and arsenate. Without the addition of S°, the As solubility ranged between 0.6 and 3.5 mg/kg. No toxic effects of As (III) on bacterial growth and microbial activity of the indige nous Thiobacillus spp. were observed. By comparison, the As solubility in an oxic sediment from the river Weisse Elster was low (max. 0.5 mg/kg), while the total Me solubility reached 60% (3.7 g/kg).The anaerobic leaching tests were performed under the conditions of a nitrogen atmosphere in a special vessel allowing the redox potential and the pH of the solution to be continuously recorded. In the lake sediment without adding S°, the As solubility increased temporarily; up to 9% of the total As became soluble, and As (III) was the dominant As soluble species (20 mg/kg). In the late leaching phase (—300 mV), the total soluble As decreased, and As (V) became the major soluble species (3.9 mg/kg). In the presence of S°, soluble As and Me were immobilized. The inhibition of As and Me release can be explained by fixation as insoluble sulphides, suggesting that immobilization was driven by dissimilatory sulphur reduction.The data indicatethat the availability of oxidizable sulphur and the oxidation state of the polluted material play an important role in assessing the release of arsenic and heavy metals, including anaerobic conditions. Attention has to be paid to the maintaining of strong anaerobic conditions in sulphur-rich materials in order to prevent the mobilization of pollutants.
Bioleaching is one of the feasible methods for the treatment of sediments contaminated with heavy metals. Effects of solid content, substrate (sulfur) concentration and pH on the performance of bioleaching process were investigated in this study. It was found that rates of sediment acidification and metal solubilization decreased with increasing solid content. Besides, sulfur concentration greater than 5 g/l was found to be inhibitory to bacterial activity and metal solubilization from sediment. It was concluded that a substrate concentration of 5 g/l in reactor was the optimum concentration for bioleaching process. It was also observed that solubilization of heavy metal from the sediment was highly pH-dependent. For all values of solid content and sulfur concentration tested, the efficiency of metal solubilization from sediment followed the order Cu>Zn>Pb>Cr. Keywords Bioleaching; contaminated sediment; heavy metal; solid content; sulfur concentration; thiobacilli
Phosphate and OH- are often used for the extraction of As and Se from soils, either as single extractants or as part of a sequential extraction scheme. However, the recovery of As and Se species and the integrity of the resulting solution speciation merit investigation. In this study the relative effectiveness of PO4 at 0.1 and 0.5 M and pH values of 3 and 6.7 and 0.1 M OH- to extract As(III), As(V), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), p-arsanilic acid (p-ASA), roxarsone (ROX), Se(IV) and Se(VI) sorbed to goethite and an amorphous Fe oxide were compared, and the speciation in the resulting extract was determined. The extent to which 0.1 M PO4 added to 0.25 M NH2OH·HCl or 0.175 M Na oxalate/0.1 M oxalic acid prevents readsorption of As(V) or Se(IV) to goethite during the dissolution of an amorphous Fe oxide was also assessed. Hydroxide was the most effective extractant for desorption of all species except As(III) from both oxide surfaces. Arsenite was extracted most efficiently by 0.5 M PO4 at low pH; however, amorphous Fe oxide exhibited a strong affinity for As(III) with a maximum of 18% of As(III) extracted by 0.5 M PO4 at pH 2.8. Partial oxidation of As(III) to As(V) occurred in all extractions where an Fe oxide solid phase was present, but only in the hydroxide extract in the absence of a Fe solid phase. Addition of 0.1 M PO4 to extractants used for the dissolution of the amorphous Fe oxide prevented the readsorption of As(V) and Se(IV) to goethite.
A study was conducted to assess the retention form of arsenic in soil and to evaluate the use of phosphate for releasing it from the soil. In this study, a loam soil was artificially polluted with arsenate at pH 5.5, which is one of the pH values at which maximum arsenic adsorption occurred. The soil was kept for 2.5 months under wet conditions to allow for stabilization. The soil was maintained under aerobic condition and losses of arsenic by volatilization were determined to be minimal. The soil was then sequentially extracted with a series of chemicals to identify the soil fractions in which the arsenic was bound. The percentage of arsenic found in the Fe bound-exchangeable, reducible-residual, Al bound exchangeable, residual, calcium bound exchangeable, and easily exchangeable forms was 31.6, 27.3, 25.2, 5.5, 4.9, and 4.7%, respectively. A batch experiment showed that at 20°C, 80% of the bound arsenic was removed by phosphate in the pH range of 5 to 7. A power function model was found to fit the data with a desorption rate constant of 402 mg/kg As h−1.
The presence of selected toxic heavy metals, such as cadmium (Cd), lead (Pb) and mercury (Hg), was investigated in fish and seafood products, namely, blue mussel, carpet shell clam, European squid, veined squid, deep-water rose shrimp, red mullet, European seabass, gilthead seabream, Atlantic cod, European hake, Atlantic bluefin tuna and swordfish so as to assess their human exposure through diet. Metals were detected by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) and hydride generation atomic absorption spectrometry (Hg-AAS). Measurements of Cd, Pb and Hg were performed by means of analytical methods validated in compliance with UNI CEI EN ISO/IEC 17025 [2005. General requirements for the competence of testing and calibration laboratories. Milano (Italy): UNI Ente Nazionale Italiano di Unificazione]. The exposure assessment was undertaken matching the levels of Cd, Pb and total Hg with consumption data related to fish and seafood products selected for this purpose. In order to establish human health implications, the estimated weekly intakes (EWIs) for Cd, Pb and Hg were compared with the standard tolerable weekly intakes (TWI) for Cd and provisional tolerable weekly intakes (PTWIs) for Pb and Hg stipulated by the European Food Safety Authority (EFSA) and the Food and Agriculture Organization/World Health Organization (FAO/WHO) Joint Expert Committee on Food Additives (JECFA). The found metal concentrations were largely below the maximum levels (MLs) established at the European Union level with the exception of Cd. This metal exceeded the MLs in squid, red mullet, European hake and Atlantic cod. Squid and blue mussel showed the highest Pb concentrations which accounted for 60% and 10% of the MLs, respectively. Highest Hg levels were found in predatory fish. The concentrations of Hg in swordfish, Atlantic bluefin tuna and red mullet accounted for 50%, 30% and 30% of the MLs, respectively. The EWIs for Cd, Pb and Hg related to the consumption of fish and seafood products by the median of the Italian total population accounted for 20%, 1.5% and 10% of the standard TWI for Cd as well as PTWIs for Pb and Hg, respectively. Furthermore, the EWIs estimated using consumption data concerning Italian consumers did not exceed the standard TWI and PTWIs, except for Cd at 95th percentile.
Des travaux pilotes ont été menés dans le cadre de cette recherche afin de tester différents scénarios de décontamination de sédiments pollués par plusieurs métaux lourds (Cd, Cr, Cu, Ni, Pb et Zn). Des essais de lixiviation chimique et biologique ont été réalisés en réacteur de 350 L. L'application de lavages acides (pH 2.0–3.0) des sédiments constitue une approche peu efficace pour l'enlèvement des métaux toxiques. L'ajout d'un agent oxydant lors du premier lavage augmente considérablement les rendements d'enlèvement du Pb (53–76 %), Cd (54–92 %) et Zn (69–93 %). Les autres métaux demeurent toutefois difficiles à extraire: Cr (13–30 %), Cu (11–34 %) et Ni (0–16 %). La biolixiviation seule ou en combinaison avec un ou deux lavages chimiques, représente une approche efficace pour l'élimination du Cd (82–100 %), Cu (44–70 %) et Zn (80–87 %). Par contre, cette technique présente peu d'intére̊t pour la réduction des teneurs en Cr (6–16 %), Ni (12–34 %) et Pb (14–33 %). Les métaux solubilisés par lixiviation chimique et/ou biologique peuvent être précipités efficacement lors de la neutralisation des effluents acides par une solution de chaux.
Microbial life in extremely low pH (<3) natural and man-made environments may be considerably diverse. Prokaryotic acidophiles (eubacteria and archaea) have been the focus of much of the research activity in this area, primarily because of the importance of these microorganisms in biotechnology (predominantly the commercial biological processing of metal ores) and in environmental pollution (genesis of ‘acid mine drainage’); however, obligately acidophilic eukaryotes (fungi, yeasts, algae and protozoa) are also known, and may form stable microbial communities with prokaryotes, particularly in lower temperature (<35°C) environments. Primary production in acidophilic environments is mediated by chemolitho-autotrophic prokaryotes (iron and sulfur oxidisers), and may be supplemented by phototrophic acidophiles (predominantly eukaryotic microalgae) in illuminated sites. The most thermophilic acidophiles are archaea (Crenarchaeota) whilst in moderately thermal (40–60°C) acidic environments archaea (Euryarchaeota) and bacteria (mostly Gram-positives) may co-exist. Lower temperature (mesophilic) extremely acidic environments tend to be dominated by Gram-negative bacteria, and there is recent evidence that mineral oxidation may be accelerated by acidophilic bacteria at very low (ca. 0°C) environments. Whilst most acidophiles have conventionally been considered to be obligately aerobic, there is increasing evidence that many isolates are facultative anaerobes, and are able to couple the oxidation of organic or inorganic electron donors to the reduction of ferric iron. A variety of interactions have been demonstrated to occur between acidophilic microorganisms, as in other environments; these include competition, predation, mutualism and synergy. Mixed cultures of acidophiles are frequently more robust and efficient (e.g. in oxidising sulfide minerals) than corresponding pure cultures. In view of the continuing expansion of microbial mineral processing (‘biomining’) as a cost-effective and environmentally sensitive method of metal extraction, and the ongoing concern of pollution from abandoned mine sites, acidophilic microbiology will continue to be of considerable research interest well into the new millennium.
Aquatic sediments are a known source of pollutants, but their impact on the quality of overlying waters is not easily quantified. Sediments are generally considered to behave as a sink for pollutants such as heavy metals in the aquatic environment, frequently acting as a source for their presence in waters, with implications for catchment management. This study aimed to calculate the contribution of sediments to metal levels in overlying waters, helping understand their role as a source of metals in river catchments. An aquivalence mass balance approach was modified to take into account both natural and anthropogenic influences and applied to assess sediment contribution in a reach of the River Yare in the UK. The rates of total metal transport from sediments to overlying waters were estimated to be 29.89 g d(-1) for cadmium (Cd), 1633.39 g d(-1) for lead (Pb), 8.29 g d(-1) for mercury (Hg) and 357.56 g d(-1) for nickel (Ni). The results from the case study demonstrated that sediments could be a significant source of metal emissions in river catchments. The calculations proposed in the paper could be useful in developing strategies for sediment management, not only to improve and/or maintain quality of sediments but also to inform the selection of measures of pollution control for the catchment.
Environmental studies on soil and sediment analysis are often based on the use of leaching or extraction procedures (e.g. single or sequential extraction procedures) which enable broader forms or phases to be measured (e.g. `bioavailable' forms of elements) and which are, in most cases, sufficient for the purpose of environmental policy. However, the lack of uniformity in the procedures used often hampers comparison of the results, owing to their `operationally defined' character. This implies that the `forms' of metals are defined by the determination of extractable elements, using a given procedure and, therefore, the significance of the analytical results is highly dependent on the extraction procedures used. The comparability of results can hence only be achieved if similar procedures are applied, which justifies efforts towards standardization. This article describes case studies of standardization approaches for single and sequential extraction procedures applied to soil and sediment analysis. In particular, the strategy followed by the Standards, Measurements and Testing program (formerly BCR) is fully described (feasibility study, interlaboratory studies and establishment of standardized protocols based on the results of tests and participants' experience).
Differential rates of plagioclase and K-feldspar weathering commonly observed in bedrock and soil environments are examined in terms of chemical kinetic and solubility controls and hydrologic permeability. For the Panola regolith, in the Georgia Piedmont Province of southeastern United States, petrographic observations, coupled with elemental balances and 87Sr/86Sr ratios, indicate that plagioclase is being converted to kaolinite at depths > 6 m in the granitic bedrock. K-feldspar remains pristine in the bedrock but subsequently weathers to kaolinite at the overlying saprolite. In contrast, both plagioclase and K-feldspar remain stable in granitic bedrocks elsewhere in Piedmont Province, such as Davis Run, Virginia, where feldspars weather concurrently in an overlying thick saprolite sequence. Kinetic rate constants, mineral surface areas, and secondary hydraulic conductivities are fitted to feldspar losses with depth in the Panola and Davis Run regoliths using a time-depth computer spreadsheet model. The primary hydraulic conductivities, describing the rates of meteoric water penetration into the pristine granites, are assumed to be equal to the propagation rates of weathering fronts, which, based on cosmogenic isotope dating, are 7 m/106 yr for the Panola regolith and 4 m/106 yr for the Davis Run regolith. Best fits in the calculations indicate that the kinetic rate constants for plagioclase in both regoliths are factors of two to three times faster than K-feldspar, which is in agreement with experimental findings. However, the range for plagioclase and K-feldspar rates (kr = 1.5 × 10−17 to 2.8 × 10−16 mol m−2 s−1) is three to four orders of magnitude lower than for that for experimental feldspar dissolution rates and are among the slowest yet recorded for natural feldspar weathering. Such slow rates are attributed to the relatively old geomorphic ages of the Panola and Davis Run regoliths, implying that mineral surface reactivity decreases significantly with time.Differential feldspar weathering in the low-permeability Panola bedrock environment is more dependent on relative feldspar solubilities than on differences in kinetic reaction rates. Such weathering is very sensitive to primary and secondary hydraulic conductivities (qp and qs), which control both the fluid volumes passing through the regolith and the thermodynamic saturation of the feldspars. Bedrock permeability is primarily intragranular and is created by internal weathering of networks of interconnected plagioclase phenocrysts. Saprolite permeability is principally intergranular and is the result of dissolution of silicate phases during isovolumetric weathering. A secondary to primary hydraulic conductivity ratio of qs/qp = 150 in the Panola bedrock results in kinetically controlled plagioclase dissolution but thermodynamically inhibited K-feldspar reaction. This result is in accord with calculated chemical saturation states for groundwater sampled in the Panola Granite. In contrast, greater secondary conductivities in the Davis Run saprolite, qs/qp = 800, produces both kinetically controlled plagioclase and K-feldspar dissolution. Faster plagioclase reaction, leading to bedrock weathering in the Panola Granite but not at Davis Run, is attributed to a higher anorthite component of the plagioclase and a wetter and warmer climate. In addition, the Panola Granite has an abnormally high content of disseminated calcite, the dissolution of which precedes the plagioclase weathering front, thus creating additional secondary permeability.
The degree to which anions can affect As mobility in subsurface environments depends on As speciation and fractionation in the soil. In this study, the fine soil fraction of an acidic soil was deliberately contaminated with arsenate (As(V)) and adequately aged for more than 220 days. A selective sequential extraction (SSE) scheme was developed to fractionate As in the soil into 6 fractions, while the influence of various anions on As mobility was assessed by evaluating its extractability by various salts such as Na3PO4, Na2CO3, Na2SO4 and NaCl. The variables of the extraction experiment were type of salt, salt concentration and reaction time. Fractionations of As in soil samples after extraction with the salts were also examined and the results compared against the initial As fractionation. The SSE results showed that the majority of the As was strongly adsorbed via surface complexation in the fine soil. A considerable amount of As was also associated with the exchangeable fraction, amorphous Fe oxyhydroxides, and the residual fraction. Abilities of the anions in mobilizing As bound in the fine soil followed the order of . Arsenic mobilization by was believed to be due primarily to a ligand exchange mechanism, through which the strongly bound As was replaced by the anion. Anion exchange might also contribute to the mobilization of As in this study. Increase in the concentration of the anions tested did not further mobilize As from the soil, with the exception of . The kinetics of As release in the solution could be best described by the Elovich model, which represents an exponential decrease in As desorption rate as more As was extracted from the soil.
In order to evaluate the effect of improved oxygen concentrations in overlying surface water on the redox status, sediment geochemistry and metal bioavailability in metal-polluted sediments a 54 days lab experiment with two different experimental treatments was conducted (90% and 40% O(2)). Changes in redox potential (Eh) in the sediment were monitored over time. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) and at 4 sediment depths (0-1, 1-4, 4-8 and 8-15 cm), acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured and metal release to overlying surface water was determined. Labile metal species in both water and sediment were measured using Diffusive Gradients in Thin films (DGT). Our results showed that elevated oxygen levels in overlying surface water led to an Eh increase in the sediment of the 90% O(2) treatment from 0 to ± 200 mV while AVS concentrations in the upper sediment layer decreased by 70%. Following AVS oxidation metal availability in the pore water was highly elevated after 54 days. However, Cu remained strongly bound to the sediment during the whole experiment. Only a limited metal release to the overlying surface water was noticed, which was due to the fact that SEM(tot) concentrations in the sediment did not yet exceeded AVS levels ([SEM(tot) - AVS]/f(OC) = 0) after 54 days. Additionally, adsorption on Fe and Mn hydroxides and particulate organic carbon also slowed down any potential metal release. Our results indicated that increasing oxygen concentrations due to general water quality improvements can enhance the mobility of trace metals which may result in the leaching of sediment-bound metals to overlying surface water, even in undisturbed watercourses.
We investigated the effects of Shewanella putrefaciens cells and extracellular polymeric substances on the sorption of As(III) and As(V) to goethite, ferrihydrite, and hematite at pH 7.0. Adsorption of As(III) and As(V) at solution concentrations between 0.001 and 20 μM decreased by 10 to 45% in the presence of 0.3 g L(-1) EPS, with As(III) being affected more strongly than As(V). Also, inactivated Shewanella cells induced desorption of As(V) from the Fe(III)-(hydr)oxide mineral surfaces. ATR-FTIR studies of ternary As(V)-Shewanella-hematite systems indicated As(V) desorption concurrent with attachment of bacterial cells at the hematite surface, and showed evidence of inner-sphere coordination of bacterial phosphate and carboxylate groups at hematite surface sites. Competition between As(V) and bacterial phosphate and carboxylate groups for Fe(III)-(oxyhydr)oxide surface sites is proposed as an important factor leading to increased solubility of As(V). The results from this study have implications for the solubility of As(V) in the soil rhizosphere and in geochemical systems undergoing microbially mediated reduction and indicate that the presence of sorbed oxyanions may affect Fe-reduction and biofilm development at mineral surfaces.
Process water and effluents from mining operations treating sulfide rich ores often contain considerable concentrations of metastable inorganic sulfur compounds such as thiosulfate and tetrathionate. These species may cause environmental problems if released to downstream recipients due to oxidation to sulfuric acid catalyzed by acidophilic microorganisms. Molecular phylogenic analysis of the tailings pond and recipient streams identified psychrotolerant and mesophilic inorganic sulfur compound oxidizing microorganisms. This suggested year round thiosalt oxidation occurs. Mining process waters may also contain inhibiting substances such as thiocyanate from cyanidation plants. However, toxicity experiments suggested their expected concentrations would not inhibit thiosalt oxidation by Acidithiobacillus ferrivorans SS3. A mixed culture from a permanently cold (4-6 °C) low pH environment was tested for thiosalt removal in a reactor design including a biogenerator and a main reactor containing a biofilm carrier. The biogenerator and main reactors were successively reduced in temperature to 5-6 °C when 43.8% of the chemical oxidation demand was removed. However, it was found that the oxidation of thiosulfate was not fully completed to sulfate since low residual concentrations of tetrathionate and trithionate were found in the discharge. This study has demonstrated the potential of using biotechnological solutions to remove inorganic sulfur compounds at 6°C and thus, reduce the impact of mining on the environment.
In the present study we have concerned ourselves with heavy metal pollution in aquatic systems, and found that a series of metals, many of which are toxic, have become accumulated in sediments associated with inland water bodies, estuaries and coastal zones. A comparison of the metal values found in the sediments, collected from various areas, reveals that in industrialized and urbanized areas, the metal enrichment must be ascribed to anthropogenic influences rather than to natural enrichment of sediments by geological weathering (as evidenced by the analyses of the lower sections of sediment profiles).
This study deals with bioremediation treatments of dredged sediments contaminated by heavy metals based on the bioaugmentation of different bacterial strains. The efficiency of the following bacterial consortia was compared: (i) acidophilic chemoautotrophic, Fe/S-oxidising bacteria, (ii) acidophilic heterotrophic bacteria able to reduce Fe/Mn fraction, co-respiring oxygen and ferric iron and (iii) the chemoautotrophic and heterotrophic bacteria reported above, pooled together, as it was hypothesised that the two strains could cooperate through a mutual substrate supply. The effect of the bioremediation treatment based on the bioaugmentation of Fe/S-oxidising strains alone was similar to the one based only on Fe-reducing bacteria, and resulted in heavy-metal extraction yields typically ranging from 40% to 50%. The efficiency of the process based only upon autotrophic bacteria was limited by sulphur availability. However, when the treatment was based on the addition of Fe-reducing bacteria and the Fe/S oxidizing bacteria together, their growth rates and efficiency in mobilising heavy metals increased significantly, reaching extraction yields >90% for Cu, Cd, Hg and Zn. The additional advantage of the new bioaugmentation approach proposed here is that it is independent from the availability of sulphur. These results open new perspectives for the bioremediation technology for the removal of heavy metals from highly contaminated sediments.
Thiobacillus ferrooxidans originally cultured on ferrous iron can adapt to grow on thiosulphate, tetrathionate, trithionate or sulphur in liquid media. In unneutralized cultures (initial pH 4–4.4) mean doubling times on thiosulphate were 8.5–13 h and on tetrathionate was about 10 h. In pH-controlled cultures, growth on thiosulphate commenced at pH values from pH 3.6–4.7, with no growth in media initially below pH 3.5 or above pH 4.8. On tetrathionate, growth commenced between pH 1.5–4.3, with no growth below pH 1.3 or above pH 4.4. Growth rate was maximal ( = 0.043 h-1) on thiosulphate at pH 3.6 and on tetrathionate at pH 2.5 ( = 0.05 h-1). Growth yields of about 5.9 g (210 mmoles CO2 fixed) and 9.8 g (350 mmoles CO2 fixed) dry wt per gram-molecule were obtained respectively on thiosulphate and tetrathionate. Bacteria grown on thiosulphate or tetrathionate could produce colonies on ferrous iron agar, but this ability declined on prolonged culture on sulphur compounds. All the cultures grown on various inorganic sulphur compounds were capable of re-adapting to growth on iron. This was investigated in detail. About 66–82% of iron-grown organisms readily produced colonies on tetrathionate, but only about 1 in 109 produced colonies on thiosulphate.