Sediment dynamics and pollutant mobility in rivers

PAPER ON SEDIMENT DYNAMICS AND POLLUTANT MOBILITY AVAILABLE ONLINE.

The European Sediments Research Network (SEDNET) has made available for download a paper entitled "Sediment Dynamics and Pollutant Mobility in Rivers: An Interdisciplinary Approach" by U. Forstner. The document is available in pdf format (402 Kb) from the following web address. http://www.sednet.org/materiale/Forstner_2.pdf.


Ulrich Förstner
Department of Environmental Science and Technology, University of Technology of Hamburg-Harburg,
Eissendorferstr, Hamburg, Germany

Abstract

Characteristic dynamic features of sediment-related processes in rivers include dramatic effects of stormwater events on particle transport, rapid and far-reaching effects of sulphide oxidation during resuspension, and biological accumulation and potential release of toxic chemicals. Pollutant mobility is the net result of the stabilizing and mobilizing effects in both hydraulic and chemical fields. In practice, emphasis has to be given to fine-grained sediments and suspended matter as these materials exhibit large surface areas and high sorption capacities. Organic materials are highly reactive. Degradation of organic matter will induce oxygen depletion and might enhance formation of flocs and biofilms. Study of variations of sediment and water chemistry should predominantly include changes of pH and redox conditions, competition of dissolved ions and processes such as complexation by organic substances. Major questions relate to the potential reduction of sorption sites on minerals and degradation of organic carrier materials. All these processes will influence solution/solid equilibrium conditions
and have to be studied prior to modelling the overall effects of pollutants on the water body and aquatic ecosystems. With respect to handling and remediation of contaminated river sediments, either in-place or excavated, a chemical and biological
characterization of the material, of the (disposal) site and of the long-term processes is crucial. Passive techniques (e.g. in situ stabilization, subaqueous capping) provide economic advantages as there are no operation costs following their installation.
However, the success of these ecological and geochemical engineering approaches is mainly based on an in-depth knowledge of the underlying processes.

Tannery wastewater treatment - origin, composition, treatment process

source
Naturgerechte Technologien, Bau- und Wirtschaftsberatung (TBW) GmbH, Frankfurt
(Germany), April 2002

Treatment of Tannery Wastewater.pdf

Manufacturing of leather, leather goods,
leather boards and fur produces numerous
by-products, solid wastes, high amounts of
wastewater containing different loads of
pollutants and emissions into the air. The
uncontrolled release of tannery effluents to
natural water bodies increases health risks
for human beings and environmental
pollution. Effluents from raw hide
processing tanneries, which produce wet-blue,
crust leather or finished leather
contain compounds of trivalent chromium
(Cr) and sulphides in most cases. Organic
and other ingredients are responsible for
high BOD (Biological Oxygen Demand)
and COD (Chemical Oxygen Demand)
values and represent an immense
pollution load, causing technical problems,
sophisticated technologies and high costs
in concern with effluent treatment.

Comparison of different advanced oxidation process to reduce toxicity and mineralisation of tannery wastewater

Bundeswehr - Plenartagung im Bundestag

An folgende Politiker des Bundestages wurde die folgende Mail versendet:

SPD:	Franz.Muentefering@bundestag.de
CDU/CSU	Angela.Merkel@cducsu.de
Bündnis 90/Die Grünen	Katrin-Dagmar.Goering-Eckardt@bundestag.de Krista.Sager@bundestag.de
FDP	Wolfgang.Gerhardt@bundestag.de
PDS	Petra.Pau@bundestag.de Gesine.Loetzsch@bundestag.de

Sie beraten am 23. September im Rahmen der verteidigungspolitischen Kernzeitdebatte im Bundestag über die „Zukunftsfähigkeit der Bundeswehr“.

Heute gilt es mehr denn je Prioritäten zu setzen, für nachhaltige Bildung, eine leistungsfähige Wirtschaft und eine sozial gerechte Umgestaltung der sozialen Sicherungssysteme, usw. usf. viele existentielle Aufgabenstellungen lassen sich nennen, für die es schwierig ist die finanziellen Mittel bereit zu stellen.

Deshalb muß auf Militärausgaben verzichtet werden !!!


soll die Bundeswehr in eine in aller Welt einsetzbaren Interventionsarmee umgerüstet werden. Laut Minister Struck sind für neue Waffen bis 2010 45 Milliarden Euro, bis 2014 sogar 110 Milliarden Euro vorgesehen. Dabei handelt es sich vor allem um Waffensysteme, die die Kampffähigkeit in weit entfernten Regionen ermöglichen sollen.

Richtig ist: die Sicherheitslage hat sich grundlegend gewandelt. Krieg ist darauf jedoch die falsche Antwort.

Setzen Sie sich mit uns dafür ein, daß der Rüstungshaushalt jährlich um 5 % gesenkt wird. Das eingesparte Geld sollte meiner Ansicht nach für soziale Leistungen, eine sinnvolle Energiepolitik und zur Förderung ziviler Konfliktbearbeitung eingesetzt werden.

T. Sobisch

bezeichnender Weise erhielt ich nur von den beiden Abgeordneten der PDS eine Anwort
von der Grünen Fraktion wurde einige Tage danach eine Antwortmail versendet.

Rede von Dr. Gesine Lötzsch, MdB

Anrede,

im Antrag der Regierungsfraktionen zur Transformation der Bundeswehr findet sich eine Passage die ich nur unterstützen kann – nämlich folgende: „ Der grundlegend veränderte Auftrag und die Transformation der Bundeswehr müssen von einem breiten gesellschaftlichen Konsens getragen werden. Dieser Bedarf einer breiten sicherheits- und friedenspolitischen Debatte in Politik und Gesellschaft.“
Wo aber wird diese breite sicherheits- und friedenspolitische Debatte in Politik und Gesellschaft geführt?
In welcher Frage haben Sie in der Gesellschaft einen Konsens in der Sicherheits- und Friedenspolitik erreicht?
Sie wissen, daß eine Mehrheit der Bundesbürger den militärischen Einsatz der Bundeswehr in Ex-Jugoslawien und in Afghanistan abgelehnt hat und immer noch ablehnt.
Es gibt auch eine Mehrheit in der Bevölkerung, die keine Auslandseinsätze der Bundeswehr will, sondern Konfliktprävention und verstärkte Bekämpfung der Ursachen von Terror und Gewalt.
Die Bundesregierung regt diese Diskussion nicht an, nein, sie verweigert sich dieser Diskussion hartnäckig.
Sie schickt die Bundeswehrsoldaten von einem Krisenherd zum nächsten und setzt das Leben von Soldaten leichtfertig aufs Spiel.
Aus der Bundeswehr ist zu hören, daß die Sicherheitspolitik als „Gefechtsfeldtourismus“ bezeichnet wird.
Die Bundesregierung hat kein sicherheitspolitisches Konzept: Das letzte Weißbuch, das eine Konzeption der Bundeswehr enthielt, wurde 1994 von der Regierung Kohl vorgelegt, also vor 10 Jahren.
Seitdem hat sich einiges grundsätzlich in der Welt verändert.
Der ehemalige BM für Verteidigung Scharping hatte bereits für 2001 ein Weißbuch angekündigt, nun soll es – Ihrem Antrag nach - 2005 kommen.
Auch das bestätigt unseren Eindruck, daß Sie die Bundeswehr in Krisengebiete dieser Welt schicken, ohne die Folgen zu bedenken – das ist gefährlicher Aktionismus.
Das wird besonders deutlich, wenn man sich die fehlende Strategie der Bundesregierung in Afghanistan anschaut.

Niemand weiß, wo Bin Laden sich aufhält, die alten Herrschaftsstrukturen sind in den Regionen bestehen geblieben, der Drogenhandel blüht, die Bundeswehr schaut weg.

Afghanistan lebt nicht in Frieden und ist weit von einer funktionierenden Demokratie entfernt.

Die Bundesrepublik läuft Gefahr, in Afghanistan in einen lang andauernden, blutigen und extrem kostspieligen Konflikt verwickelt zu werden.

Der derzeitige Präsident der USA, George W. Bush, hat bereits erklärt, daß er kein Ende des Krieges gegen den Terrorismus sieht.

Ich glaube in dem Punkt stimmt er mit Bin Laden überein.

Herr Struck erklärt gern, daß die deutschen Interessen am Hindukusch verteidigt werden.

Aber warum definiert niemand öffentlich, worin die deutschen Interessen bestehen?

Was Afghanistan betrifft, sind mir nur die Interessen der USA und der afghanischen Warlords und Drogenschmuggler bekannt.

Die Bundesregierung glaubt sich bei Bush rechtfertigen zu müssen für die Nicht-Beteiligung am Irak-Krieg und verkauft den USA den Afghanistan-Einsatz als Kompensationsgeschäft.

Aber wir müssen uns gar nicht für die Nicht-Teilnahme am Irakkrieg bei der US-Regierung entschuldigen oder rechtfertigen.

Der Krieg gegen den Irak ist illegal, wie Kofi Annan, festgestellt hat, also bedarf es keiner Kompensationsgeschäfte.

Aber ich will noch auf einen anderen Punkt eingehen.

Sie fordern im Punkt 5 Ihres Antrages, daß Standortentscheidungen nach militärischen und betriebswirtschaftlichen Kriterien getroffen werden müssen und transparent zu machen sind.

Da habe ich schon eine Frage an die Grünen: Müßten nicht auch ökologische Kriterien eine Rolle bei Standortentscheidungen spielen, und wie stellen Sie sich einen transparenten Entscheidungsprozeß unter Einbeziehung der Betroffenen vor?

Ich erinnere Sie nur an das Bombodrom in Wittstock.

Die Grünen und die lokale SPD haben sich vor den

Wahlen in Brandenburg gegen das Bombodrom ausgesprochen.

Jetzt sind die Wahlen vorbei und die Bürger fragen sich natürlich, was aus dem Engagement der Politiker geworden ist.

Ich kann nur allen Bürgern, die sich für eine freie Heide engagieren, versichern, daß die PDS nach der Wahl wie vor der Wahl gegen das Bombodrom mit den Bürgern gemeinsam kämpfen wird.
<> Abschließend will ich die Positionen der PDS zusammenfassen:

Wir lehnen weltweite Einsätze der Bundeswehr ab. Die Bundeswehr ist für die Landesverteidigung da und wir halten auch gar nichts von Bundeswehreinsatz im Innern.

Die Zahl der Berufs- und Zeitsoldaten kann auf 100 000 reduziert werden.

Wir sind gegen jede Art von Zwangsdiensten und dazu gehören Wehrpflicht und Zivildienst.

Bei Standortschließungen muß die Bundesregierung ein Konversionsprogramm für die betroffenen Regionen vorlegen und aus dem Rüstungsetat finanzieren.

Und natürlich fordern wir den Verzicht bzw. Abbruch von Rüstungsprojekten, die weltweiten Militäreinsätzen dienen.

Das wäre die Richtung für die Transformation der Bundeswehr.

Zusammensetzung nichtionischer Tenside - HLB-Wert-Emulsionsstabilität / nonionic surfactant composition - HLB value - emulsion stability

Contribution/Beitrag

DECHEMA/GVC Jahrestagungen 2004 - 12. - 14. 10. Karlsruhe www.jt2004.de
14th Ostwald Kolloquium "Fluids at interfaces and in pores: phase transitions and related phenomena" 22-23. 11. 2004 Berlin Conference programm

Effect of nonionic surfactant composition and concentration on the optimum HLB value for emulsion stability

The HLB concept has long proved to be a useful tool for emulsifier selection.

The HLB value is a measure of the overall polarity of the emulsifier, irrespective of its composition – a single surfactant, a binary mixture or a mixture with a broad distribution. On the other hand, it is well established that the geometry of the surfactant molecules and their packing density in the adsorption layers has a marked influence on type and stability of the emulsions. Therefore, besides the overall HLB value surfactant composition and concentration should also have an important effect. Though, this is consistent with practical experience related in-depth studies are rare. Therefore, the influence of composition and concentration on emulsion stability was investigated for the system water – paraffin oil choosing ethoxylated isotridecanols and their mixtures as emulsifiers.

A multisample technique based on analytical centrifugation was used for an accelerated study of creaming and of separation of oil and water phases as function of temperature. Not only information on the extent of phase separation was obtained but also the kinetics were directly measured in-situ.

Einfluß der Zusammensetzung und Konzentration nichtionischer Tenside auf den HLB-Wert für optimale Emulsionsstabilität

Das HLB-Konzept hat sich seit langem als Werkzeug bei der Auswahl von Emulgatoren bewährt.

Der HLB-Wert repräsentiert die Gesamtpolarität des Emulgators, unabhängig von der Zusammensetzung – egal ob Einzeltensid, Mischung zweier Tenside oder Gemisch mit breiter Verteilung. Andererseits ist bekannt, daß die Geometrie der Tensidmoleküle and ihre Packungsdichte in den Adsorptionsschichten einen deutlichen Einfluß auf Typ and Stabilität der Emulsionen hat. Deshalb sollten neben dem summarischen HLB-Wert Tensidzusammensetzung and -konzentration einen wesentlichen Einfluß ausüben. Dies läßt sich anhand von Praxiserfahrungen bestätigen, jedoch gibt es hierzu kaum systematische Untersuchungen. Deshalb wurde der Einfluß von Zusammensetzung und Konzentration auf die Emulsionsstabilität für das System Wasser – Paraffinöl untersucht. Hierzu wurden in einem weiten HLB-Bereich (2 – 15) ethoxylierte Isotridecanole und deren Mischungen als Emulgatoren gewählt.

Die Emulsionsstabilität wurde mittels eines Schnellverfahrens basierend auf analytischer Zentrifugation untersucht (siehe Beispiel – Abbildung). Hierbei wurde für mehrere Proben gleichzeitig die Aufrahmung, Abscheidung von Öl- oder Wasserphase bei verschiedenen Temperaturen vermessen. Das Verfahren liefert nicht nur Informationen über das Ausmaß der Phasenseparation sondern ermöglicht in-situ die direkte Bestimmung der Kinetik der ablaufenden Prozesse.

Fig. Beispiel Öl-in-Wasser-Emulsion Entmischung

Nanoscience and technology: Opportunities and Uncertainties

Untitled Document

From the Royal Scociety

Our report on nanotechnologies - ‘Nanoscience and nanotechnologies: opportunities and uncertainties’ - was published on 29 July 2004. The report illustrates the fact that nanotechnologies offer many benefits both now and in the future but that public debate is needed about their development. It also highlights the immediate need for research to address uncertainties about the health and environmental effects of nanoparticles – one small area of nanotechnologies. It also makes recommendations about regulation to control exposure to nanoparticles. We hope that you find the report of interest, and welcome your feedback on it (see Send us your comments).

In order to make it easier and quicker to access, the main report has been split into chapters below. A pdf of the summary report – which contains the summary and recommendations of the main report – is also available. If you would like to receive a pdf of the main report (3,511 KB) or a hard copy of either the main or summary reports, please email nano@royalsoc.ac.uk or phone us on +44 (0)20 74512585.

The Opportunity Costs of the Iraq War - Project Billboard - Center for American Progress

The Opportunity Costs of the Iraq War - Project Billboard - Center for American ProgressProject Billboard and the Center for American Progress have released a major new analysis of the cost of the Iraq war, detailing exactly how the $144.4 billion pledged to date could have been spent on multiple projects to make America safer at home and stronger abroad. ....

role of fungi in the environment - geochemistry, metal accumulatuion

From the Bioremediation Discussion Group

Topic started by Len Walde


While testing plants for metal accumulation, we found a fungus, apparently

growing in some sort of symbiotic association. Upon assay, the plants

growing with the fungus, accumulated much more metal than the same plants

growing without it. One question might be: "Is it the fungus or the plants

doing the metals uptake?" --- What is going on here?


I would appreciate feedback, opinions, data and references to help me

understand this apparent anomaly. Note that I am an old Engineer and not a

microbiologist --- but learning ;-)

Many thanks for all contributions of knowledge.

Len


Contribution by Krishna Kishore Penugonda

That’s an interesting observation. I did work on sage brush plant on lead accumulation. I guess in your case Fungus is releasing some sort of biosurfactant which is making metal more soluble and plant is able to accumulate it. Most uptake is done by plant, not the fungus.

Krishna


Contribution by Vestel B. Shirley, Laboratory Manager, School of Agriculture and Environmental Sciences at North Carolina A&T State University

Peel the fungus off the plant, digest with nitric acid, do elemental analysis.

There are spot tests that can be done for each metal group. Check with a

freshman chemistry book on qualitative analysis. The reagents are usually

common and much less expensive than buying an instrument.


Contribution by Louis DeFilippi, President, Louis DeFilippi, LLC

I would have said siderophore, not surfactant. In any case, see plain text from Chemistry World, May 2004. Please excuse any highlighting (couldn't figure out how to fix). Best wishes, Louis


It’s a fungi old world Fungi do more than rot fruit and veg: they have a profound role in geochemistry. Simon Hadlington explains In short While fungi are mainly known for their role in rotting down organic matter, they have a key role in the cycling of inorganic compounds, including nutrients and metals found in rocks and minerals Fungi can be found on rock surfaces where they can cause deterioration; they can also stabilise certain rock types by precipitating minerals within the rock structure Fungi can solubilize or insolubilize many toxic metals, making the organisms candidates for bioremediation cleaning up contaminated soil and water using biological agents

We’ve all had that sinking feeling when we reach for a juicy orange from the fruit bowl only to discover that it has a soggy patch of powdery blue-and-white mould growing on it. Fungi are ubiquitous and for obvious reasons are generally seen as agents of rot. And indeed they are fundamentally important in recycling organic matter at both the local and global level.

But fungi play a more subtle role in the cycling of elements. Their activity is not confined to matter made mainly from carbon and nitrogen; as well as rotting down animal and vegetable, they also interact intimately with mineral. Not only do fungi cycle important inorganic components of minerals, including metals, phosphorus and sulphur, they also play a role in breaking down the surfaces of rocks and even materials used in buildings in a process called bioweathering. And the ability of fungi both to solubilize and precipitate a range of metals in the environment (processes termed mobilisation and immobilisation), means that they could be potentially useful in bioremediation – the use of biological agents to clean up contaminated land and effluents.

In the Division of Environmental and Applied Biology at the University of Dundee, UK, Geoffrey Gadd and his colleagues Euan Burford and Marina Fomina are providing new insights into the part that microorganisms, including fungi, play in shaping the mineral world around us in the discipline known as biogeochemistry.

“The most important perceived environmental roles of fungi are as decomposer organisms,” says Gadd. “However, a broad appreciation of their role as agents of biogeochemical change is lacking, and apart from obvious connections with the carbon cycle they are frequently neglected within broader microbiological and geochemical spheres.” The role of fungi in mineral degradation

The interactions that occur between fungi and the inorganic components of the Earth’s surface mean that fungi play a significant, if often overlooked, role in the degradation of rocks and stones including building materials.

While rock substrates can be weathered by the mechanical action of the filamentous hyphae of fungi (growing hyphae can produce enough hydraulic pressure to split rock) chemical weathering is believed to be more important. This is an opinion shared by Gadd, who says that “microbes, including fungi, can produce chemical weathering of rocks and minerals through excretion of, for example, hydrogen ions, organic acids and metabolites. And even carbon dioxide produced during respiration can lead to carbonic acid attack on mineral surfaces. Biochemical weathering of rocks can result in changes in the micro-topography of minerals through pitting and etching of mineral surfaces, mineral displacement activities and even complete dissolution of mineral grains”.

But how do fungi colonise the surface of rock in a biologically inert and even hostile environment? The answer lies in the presence of other, hardier microbes that can survive in these extreme conditions. Once one particular organism gains a foothold, it provides the nutrients for others to follow. So-called poikilotrophic microorganisms can tolerate extreme micro-climatic conditions of little or no light, extreme pH values and little water. These organisms may also secrete polysaccharides into the environment forming a ‘biofilm’, which in turn can be colonised by other organisms, including fungi.

‘Inorganic rock substrates do not necessarily favour fungal growth, although the presence of organic and inorganic residues on mineral surfaces or within cracks and fissures may encourage proliferation of fungi and other microbes,’ says Gadd. ‘In addition, the waste products of algae and bacterial – or dead cells of these organisms – decaying plant material, dust particles, aerosols and animal faeces can all act as nutrient sources for fungi.’

The range of rock types on which fungi have been found is impressive: limestone, soapstone, marble, granite, sandstone and quartz, for example. Even more remarkably, fungi have been found in extremely harsh environments, such as deserts.

Once established on a rock, fungi generally acidify their immediate environment by excreting protons, organic acids and carbonic acid. Laboratory experiments have shown that alkaline rocks are generally more susceptible to fungal attack than acidic rocks.

Different minerals tend to be attacked by specific groups of microbes, says Gadd. ‘Research has demonstrated that siderophore-producing fungi [iron-chelating species]can pit and etch microfractures in samples of olivine and glasses under laboratory conditions, and it has also been shown that both natural and man-made and antique medieval glass can be deteriorated by fungi.’

Fungi attack aluminosilicates and silicates, probably by producing organic acids, inorganic acids, alkalis and complexing reagents, although carbonic acid production may also be important. Burford says that among the most important silicate-attacking fungi are organic acid-producing species. ‘For example Aspergillus niger has been shown to degrade olivine, dunite, serpentine, muscovite and feldspar, among others. Penicillium expansum causes extensive degradation of basalt, while Penicillium simplicissimum and Scopulariopsis brevicaulis have been shown to release aluminium from alumosilicates.’

In some coniferous forests in Europe, weathering of rocks such as feldspars and the granite bedrock has been attributed to the production of oxalic, citric, succinic, formic and malic acids by various fungi. Going into more detail, Burford says that ‘fungal hyphal tips have been found to produce micro- to millimolar concentrations of these acids that could effectively dissolve calcium-rich feldspars at rates of up to 0.3 to 30 micrometers a year’.

Fungi can also attack rock surfaces through redox action on mineral constituents such as manganese and iron. ‘Desert varnish is an oxidised metal layer a few millimetres thick found on rocks and soils of arid and semi-arid regions and is believed to be of fungal and bacterial origin,’ says Fomina. ‘For example, fungi of the Lichenothelia genus can oxidise manganese and iron in metal-bearing minerals such as siderite – FeCO3 – and rhodochrosite – MnCO3, or from metals absorbed from rainfall or windblown dust and precipitate them as oxides.’ Similarly, the oxidation of Fe(II) and Mn(II) by fungi can cause dark layers, called patinas, to form on glass surfaces.

Fomina explains why limestone is especially vulnerable to bioweathering by fungi, and why certain types of fungi are known to known to colonise and degrade limestone. ‘Cavities in limestone provide a major habitat for these organisms, particularly in extreme environments such as cold deserts. The production of organic acids such as oxalic and gluconic acids is believed to play a major role in the biochemical degradation of limestone materials.’

Fungi are also known to degrade sandstone, a phenomenon attributed to the production of acids, including acetic, oxalic, citric, formic and tartaric, among others.

As well as mobilising metals from such rocks, fungi can also act to immobilise metals, that is, precipitate them from solution into a solid form, and this too has an effect on the geochemical profile of an environment. Gadd points out that ‘fungal biomass can provide a metal sink through either biosorption to cell walls, pigments and extracellular polysaccharides, intracellular accumulation and sequestration, or precipitation of metal compounds on to hyphae as secondary minerals’. The environment’s pH can influence the binding capacity of the fungal biomass, with a lower pH decreasing the binding capacity for metals such as copper, zinc and cadmium.

Fungi can cause the deterioration of carbonate minerals, such as limestone, dolomite and marble, but can also precipitate carbonates. According to Gadd ‘fungal filaments mineralised with calcite [CaCO3] together with whewellite [calcium oxalate monohydrate] have been reported in limestone and calcareous soils’. It is entirely possible that fungi play a prominent role in stabilising some limestone rock substrates. ‘Calcite formation by fungi may occur through indirect processes via the fungal excretion of oxalic acid and the resulting precipitation of calcium oxalate,’ adds Gadd. ‘For example oxalic acid excretion and the formation of calcium oxalate results in the dissolution of the internal pore walls of the limestone matrix, so that the solution becomes enriched in carbonate. During passage of the solution through the pore walls, calcium carbonate re-crystallises and this contributes to the hardening of the material.’

Microbial activity can also make oxalate degrade, transforming it into carbonate, and finally resulting in calcite precipitating inside the pores. This in turn can close the pore system and hardens the parent material.

Metal ions can be reduced to their elemental form by fungal activity. So Ag(I) becomes elemental silver, selenate, Se(VI), and selenite, Se(IV), become elemental selenium, while tellurite, Te(IV), gives elemental tellurium. How fungi interact with minerals

Fungi can chemically alter their mineral environment in a number of ways. Metal ions can be mobilised by dissolving a range of metal compounds such as oxides, phosphates, sulphides or more complex mineral ores, or by desorbing them from exchange sites on clay minerals or organic matter. Different mechanisms are involved to do this.

‘Fungi can acidify their environment by proton efflux via H+-ATPases, maintenance of charge balance or as a result of respiratory carbon dioxide accumulation,’ says Burford. Once the environment is acidified, metals can be released from minerals by a number of routes, such as competition between protons and the metal in the mineral or in a metal–anion complex where, in the latter, the anion is protonated and so releases the free metal cation.

Certain fungi produce carboxylic acids, such as oxalic and citric acid, during their metabolism and these can form stable complexes with a large number of metals. ‘Many metal citrates are highly mobile and not readily degraded by microorganisms, and the presence of citric acid in soil may therefore enhance the solubility of metals’, explains Burford. ‘Oxalic acid can also act as a leaching agent for metals that form soluble oxalate complexes, including aluminium and iron.’

As well as acids, there are other metabolites that fungi can produce that can bind and remove metals in solution. Polysaccharides and pigments are examples of these metabolites, as well as specific iron-chelating compounds called siderophores. Precisely how ‘available’ the metals become will depend on the fate of the complexes in the soil.

‘Biomethylation is another way by which metals can become solubilized’, says Fomina, who goes on to explain the process: ‘A range of fungi can mediate methylation of metalloids like selenium and tellurium. Methyl groups are transferred to the metal and a given species may transform a number of different elements.’ The methylated metal compounds formed by these processes vary in their solubility, volatility and toxicity. For example, the methylated selenium compounds made in this way are volatile and can be lost to the atmosphere.

Another important process in metal mobilisation is redox transformation – the mobilisation of metals from metal-containing compounds by reduction and oxidation. ‘For example, oxidation of metal-complexing dimethylsulfide, dimethylsulfoxide or thiosulfate may increase metal availability if metal sulfates are formed,’ says Fomina. On the other hand, the solubilities of iron and manganese increase on reduction of Fe(II) to Fe(II) and Mn(IV) to Mn(II). Reduction of Hg(II) to Hg(0) results in the diffusion of elemental mercury out of cells.

As well as mobilising metals in the environment, fungi can also immobilise them. Paradoxically, while immobilisation results in a decrease in the external activity of the free metal species, it may shift the equilibrium and promote the release of more metal into the soil from bound or insoluble sources.

One of the most obvious processes that results in metal immobilisation is the binding interaction of metals with the surfaces of cells – a phenomenon called biosorption.

‘Fungal cell walls consist of about 80–90 per cent polysaccharide, with glycoproteins and some lipids,’ says Gadd. ‘The polysaccharide component includes microcrystalline fibrils of beta-linked polysaccharides, chitin, chitosan and beta-glucans. The chemical properties of the functional groups associated with fungal walls, including carboxyl, amine, hydroxyl, phosphate and sulfhydryl groups, provide the basis for the attraction of metals to cell walls.’ Pigments such as melanin can also strongly bind metals.

Immobilisation of metals and minerals can also occur by precipitation within cells or immediately outside them. This can happen if the organism produces or releases anions such as hydroxyl, sulphate, phosphate or carbonate from mineral substrates that can react with soluble metal cations in the environment.

Oxalate is an important component of many fungal interactions with the mineral environment. Most simple metal oxalates are insoluble. Calcium oxalate is commonly found in soils and leaf litter, occurring as the dihydrate, also known as weddellite, or the monohydrate, called whewellite. Crystalline calcium oxalate is formed by a number of fungi by excretion of oxalate and the precipitation of calcium. In this form, the compound represents an important reservoir of calcium and carbon within ecosystems. Consequences of fungal interactions

The fact that fungi interact with minerals has potentially important consequences for human activity. Microbes can colonise all types of building material, from plaster and plastic to metal and concrete. ‘This ability of fungi and other microorganisms to degrade concrete and other structures may have significant implications for the underground storage of nuclear waste,’ says Gadd. ‘In high-level nuclear waste disposal the bentonite buffer around the copper canisters is considered to be a hostile environment for most microbes due to the combination of radiation, heat and low water availability. But discrete microbial species can cope with each of these constraints.’ Interestingly, in the late 1990s fungi were seen growing extensively on the walls and other built structures in the inner part of the sarcophagus constructed around the fourth unit of the Chernobyl power plant after it was damaged 10 years earlier.

However, fungi might also be useful in mopping up metals and radionuclides in the environment. ‘Toxic metals in natural, industrial and agricultural soils are a risk to human health,’ notes Gadd. ‘Some of the processes by which fungi interact with metals could have potential for treatment of contaminated land as well as liquid effluents.’

For example the solubilization of toxic metals could provide a route for their removal from affected soils, whereas immobilisation could enable metal ions to be transformed into insoluble, more chemically inert forms.

‘These processes could be used in situ, but for fungi are possibly best suited for use in bioreactors where, for example, immobilised metal can be separated from soil components,’ says Gadd. ‘Living or dead fungal biomass and fungal metabolites have been used to remove metal species, compounds and particulates and even organometal compounds from solution. There has also been the use of extracellular ligands excreted by fungi, especially from Aspergillus and Penicillium species, to leach metals such as zinc, copper, nickel and cobalt from a variety of materials, including low-grade mineral ores.’

In addition, some fungi naturally associate with the roots of plants, forming a symbiotic relationship called a mycorrhiza, and these can be involved in the uptake and sequestration of metals by the plant. Such systems have potential for cleaning up contaminated soil in the overall process termed phytoremediation, where the metal is accumulated in plant tissues above the ground. Overall, Gadd suggests that the role of fungi in geochemistry is something that warrants greater attention. ‘It is clear that fungi have important biogeochemical roles in the biosphere but are frequently neglected within broader microbiological and geochemical research spheres, in contrast to bacteria,’ he says. ‘It is timely to draw attention to ‘geomycology’ and the interdisciplinary approach that is necessary to further understanding of the important roles that fungi play in the biogeochemical cycling of elements, the chemical and biological mechanisms that are involved, and their environmental and biotechnological significance.

‘To achieve a better understanding of fungal–mineral interactions, the development of experimental methods and techniques that reflect and interrogate environmental conditions more precisely is an urgent need.’

Simon Hadlington is a freelance science writer based in York; e-mail simon@hadlington.plus.com
References and further reading

• G M Gadd, E P Burford and M Fomina, Biogeochemical activities of microorganisms in mineral transformations: consequences for metal and nutrient mobility. J. Microbiol. Biotechnol., 2003, 13, 323

• E P Burford and G M Gadd, Geomycology: fungal growth in mineral substrata. Mycologist, 2003, 17, 98

• M Fomina, E P Burford and G M Gadd, Toxic metals and fungal communities. In: Fungi in Ecosystem Processes. Ed: J. Dighton. Marcel Dekker Inc, New York (in press)

• E P Burford, M Fomina and G M Gadd, Fungal involvement in bioweathering and biotransformation of rocks and minerals. Mineral. Mag., 2003, 67, 1127

• G M Gadd, Mycotransformation of organic and inorganic substrates. Mycologist (in press)



Comment:

A very nice overview indeed. Only to add the role of lichens as an important vehicle for fungi to colonize the inorganic and organic world.



Contribution by Sarabjeet Singh Ahluwalia

Hi Len Walde

Please explain in detail of your experimental protocol. What happens during metal uptake by the plants from the soil mycorrhiza plays a important role through the roots of the plants. So if you in doubtful you have to do material balance of metal available and uptake by plant (root, stem and leaves). Moreover it is not only fungus but some bacteria also do the transform the metal. Also let me know which metalyou are studying. There are few metals which undergo transformation/reduction.