#216      26 min 46 sec
Tailings tidy up: How bioremediation can repair the damage done by mining

Biogeochemist Dr John Moreau and botanist Dr Augustine Doronila discuss how contaminated mining sites can be rehabilitated with the help of a biological approach using plants and bacteria. Presented by Dr Shane Huntington.

"There are at least 500 species of these plants, which, as a technical definition,  accumulate a certain metal to 1,000 parts per million, or micrograms per gram of plant tissue. But most of these metals are toxic, and concentrations of up to 10 or 100 PPM as a general rule of thumb. But they accumulate it into concentrations, which are, at times, higher than what is in the soil." -- Dr Augustine Doronila




Dr John Moreau
Dr John Moreau

Dr John Moreau received his BA/BA (Hons., 1994) and Masters degree (2001) from Arizona State University, and his PhD (2006) from the University of California - Berkeley. Moreau started his postgraduate training as a mineralogist/solid-state geochemist, but soon came to discover in his research a disproportionately large and important role for microbes in influencing key elemental cycles within the Earth’s crust. After undertaking intensive cross-training in microbiology and stable isotope geochemistry, he completed his doctoral research at Berkeley in 2006 with a publication in Science, studying the role of sulfur-cycling bacteria in the environmental fate of metals in mining-impacted environments.As a recipient of a prestigious U.S. National Research Council Postdoctoral Research Fellowship, Moreau investigated the biogeochemical behavior of mercury and the role of sulfate-reducing bacteria in producing the neurotoxin methylmercury.Recently moved to Australia, Moreau's research has expanded to studying certain processes involved in controlling groundwater chemistry (particularly the biogeochemistry of acidic waters and brines) and the natural evolution of subsurface energy resources. His work includes understanding geomicrobiological responses to CO2 sequestration and the potential for recycling carbon as methane. Part of this involves understanding the natural methane cycle in the Earth’s deep subsurface biosphere, and Moreau serves on the Australia-New Zealand Integrated Ocean Drilling Program Science Committee. Moreau is the two-time recipient of a University of Melbourne Early Career Researcher Award and a Selby Science Foundation Award. Moreau is a member of the Melbourne Energy Institute’s Bioenergy and Water research groups.

Publications

Dr Augustine Doronila
Dr Augustine Doronila

Dr Augustine Doronila, PhD, worked in Italy and Switzerland as a contract horticulturist from 1985-89. In 1989, Augustine moved to Curtin University of Technology, Western Australia working as a Senior Tutor and Research Associate for 12 years with the the Department of Environmental Biology, where he was involved in post mining land rehabilitation with different mining and extractive industries. He has coordinated ca. 50 contract research and monitoring projects. He then took his Doctoral studies at the School of Botany, University of Melbourne in 2001 on phytoremediation of arseniferous gold mine tailings. He is currently working as a research fellow with the environmental and analytical chemistry research group at the School of Chemistry, University of Melbourne and undertakes research on arsenic and mercury bioavailability and food chain transfer, heavy metal bioavailability, metal hyperaccumulation in plants, soil chemistry and plant nutrition, restoration ecology and post mining reclamation.

Publications

Credits

Host: Dr Shane Huntington
Producers: Eric van Bemmel, Kelvin Param
Associate Producer: Dr Dyani Lewis
Audio Engineer: Gavin Nebauer
Voiceover: Nerissa Hannink
Series Creators: Kelvin Param & Eric van Bemmel

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VOICEOVER 
Welcome to Up Close, the research talk show from the University of Melbourne, Australia. 
SHANE HUNTINGTON I’m Shane Huntington, thanks for joining us.  Our energy and material-hungry lifestyles rely heavily on the mining of a variety of materials in vast quantities.  Unlike in the search for gold during the gold rushes on the 19th century, metals and other materials are now extracted from highly automated processing of large amounts of earth. In many cases, the yields are low, and the processing required results in toxic by-products, exacting a considerable environmental toll on the land and water in and around the mining sites.  Much research has been conducted on the remediation of these contaminated sites, and more recently, also on the potential benefits of controlled extraction from these sites.  Today on Up Close, we are joined by two researchers who are working on distinct methods of bio-remediation; that is, the use of biological processes to clean up the toxic waste and contamination left over from mining.   Dr John Moreau is a bio-geochemist in the School of Earth Sciences at the University of Melbourne, and Dr Augustine Doronila is a botanist working in the department of Chemistry, also at the University of Melbourne.  Welcome to Up Close, John and Augustine.

JOHN MOREAU
Thank you.

AUGUSTINE DORONILA 
Yes, good morning, Shane. 

SHANE HUNTINGTON 
John, I'd like to start with you. What are some of the waste products associated with mining of minerals, and how are these products typically dealt with?

JOHN MOREAU
Sure. Probably the most well-known and nefarious waste product would be acid mine drainage, but it's a common misperception that it's the acid that's the more serious problem.  In fact, it's usually the toxic metals that accompany the release of the acid, such as copper, arsenic, mercury, lead, even zinc to some degree.

SHANE HUNTINGTON 
Is it not possible to simply put these materials back into the mines from whence they came? 

JOHN MOREAU
Well, that would be lovely, but no, I think it's not very possible because these materials diffuse and disperse easily into the ecosystems, and they have a quite significant impact because their toxicity levels only require very, very small concentrations.  So, we really have to find other ways to essentially remove them from natural waters and soils.

SHANE HUNTINGTON 
So, when you're mining, you're pulling these materials out in fairly large quantities.  Where are they actually placed at that point, near or around the mine?  Or, are they just dumped?

JOHN MOREAU
No, no.  You can't dump these things anymore.  I think that went out about a hundred years ago, fortunately. Most responsible mining companies - that is, mining companies that hope to make a profit - really address their environmental requirements, and they do a pretty well-regulated job these days of sequestering these materials physically into tailings, dams - essentially, physical restrictions, containment facilities that are designed to hold them.  But they're not perfect systems - rain falls on these materials and percolates through the sediments and soils, and carries some of the waste products into the soil or the ground water surrounding these facilities. And that's where it becomes a problem that the mining companies are seeking new ways to try to manage. 

SHANE HUNTINGTON 
It seems to me as though this is far from being a closed system, so there must be expectations that there would always be some sorts of contamination from these tailing stems.

JOHN MOREAU
There are sort of minimum regulatory limits, and they do depend partly on the use for groundwater and soils in the affected regions.  No, of course, they're not closed systems - there are probably few closed systems in nature, at least in the earth's surface environments. 

SHANE HUNTINGTON 
Is it possible to due the sort of mining that we need, perhaps with reduced profit margins, in a way that can completely avoid these nasty problems, or is it just not feasible given the quantities of earth we're talking about? 

JOHN MOREAU
Well, we like to think that it's a challenge to make it more feasible, and to adapt technologies like bio-remediation, which we consider to be a green technology to essentially allow the mining industry to continue doing what it's doing, which needs to happen in order for people to have iPhones like the one on the table right next to you there, and still maintain or reduce their ecological footprint.

SHANE HUNTINGTON 
Why is it, John, that the metal ions and other toxic substances we're talking about here are so problematic to humans and plant life and the biosphere in general?

JOHN MOREAU
Well, quite simply, because in the last three and a half billion or so years of the evolution of life on this planet, we just haven't adapted to be able to deal with these metals.  That's true for us just as it's true for microorganisms.  These metals have highly deleterious or negative impacts on essentially our proteins, which comprise our enzymes, which allow us to do all sorts of good stuff like obtain energy from food, breathe - you know, the basic vital functions. 

SHANE HUNTINGTON 
Now, interestingly, following on from that, bacteria, we find, grows pretty much anywhere in any environment. How is it that it's so different from us in that case, and it's so easily able to adapt to these otherwise toxic environments to many life forms?  
JOHN MOREAU
Well, that is true.  Bacteria are present everywhere.  There are no sterile environments on the earth's surface, or near surface.  Basically, any environment below about 120 degrees Celsius probably contains some bacteria, and to answer your second question, I think that's still an ongoing topic of research; how bacteria have evolved and maintained the capacity - physiologically, metabolically - to deal with metals that would be highly toxic to higher organisms.  Many of these bacteria have actually become specialist in this process or this functionality, and we call them extremophiles.  In a sense, microorganisms that are adapted to extreme conditions - not in temperature or in Ph or acidity in this case, but in concentrations of heavy metals.  
SHANE HUNTINGTON 
Now, obviously, this gives us a potential opportunity to look at cleaning up some of these mine sites with these particular organisms.  How would we actually go about that? 

JOHN MOREAU
Well, that's right.  It's probably no surprise that many of these organisms have been enriched or selected for in areas where they are subjected to these types of conditions for extended periods of time.  So, in a mine site that has a contamination problem, for example, you might expect to find bacteria that have adapted to be able to tolerate certain high levels of particular toxic metals, and perhaps, more usefully, do something with those metals that will remove them, effectively, from being bioavailable to higher organisms.  So, an example would be bacterium that precipitates arsenic as a mineral from groundwater so that it's not available to cattle or livestock that would drink the groundwater otherwise. 

SHANE HUNTINGTON 
Talk us through how this sort of processing would occur in a typical mine site.  You essentially somehow have to introduce the bacteria, and then extract it at some point.  How would you go about that? 

JOHN MOREAU
Well, that is one way that we could go about doing it, but actually, we would prefer to work with what we have in situ, in nature; that is, to stimulate or artificially enhance the activity of the bacteria that are already present in the soils, sediments and groundwater, so that we don't have to introduce anything foreign.  There are obvious concerns with doing that - we don't quite know how they'll proliferate or impact the natural environment. So, we look for organisms that are already there and adapted to the conditions, but perhaps not doing their natural activity at levels that we would like to see.  An example of that might be cyanide, for example, gets produced, and cyanide breaks down products from the gold mining industry.  There are natural bacteria in soils and groundwater that are capable of degrading those toxins, but we need to help them do it at a rate that's going to be useful to us at human time-scales. 

SHANE HUNTINGTON 
John, are bacteria that are able to do this in such a thriving way, in such high cyanide environments, are they able to tolerate other sorts of environments as well, or do you find that you have one bacteria good for one particular contaminant, and you can't sort of duplicate that?

JOHN MOREAU
It's interesting.  The answer is yes, and no, I suppose.  There are some bacteria that can overlap into other uninhabitable or inhospitable environments - an example would be, bacteria that are well adapted to high temperature also tend to be well adapted to acidity, high acidity.  But there are other groups of bacteria that are, for example, highly tolerant of high salt concentrations, and that's pretty much all they can do.  So, what you're really asking in a sense is, how has this ability to tolerate extreme conditions evolved throughout the history of life, and whether those evolutions have been convergent or divergent; whether there are commonalities to different groups of organisms, or whether they've sort of become specialist over the last three and a half billion years or so.

SHANE HUNTINGTON 
You mentioned before the scaling-up of how quickly the bacteria does the job that we're asking it to do.  How do you go about influencing the bacteria to work in a different way, to expand its capacity? 

JOHN MOREAU
Well, in nature, most bacteria don't live under thriving conditions.  They are usually eking out in existence, kind of on the edge of their ability to earn a living, if you will, and things that are missing tend to be micronutrients like iron.  Sometimes carbon sources are limiting.  So, what we try to do is figure out, what are the missing ingredients or the ingredients that are present in very low quantities, and augment them so that the bacteria are essentially able to do what they would naturally do more efficiently.

SHANE HUNTINGTON 
I'm Shane Huntington, and you're listening to Up Close.  In this episode, we're talking mine site contamination and what to do about it with bio-geochemist Dr John Moreau, and botanist Dr Augustine Doronila.  Augustine, let's move now to plants, which is your area of expertise, and the use of plants for remediation of contaminated soils.  How is it that some plants are able to grow in these contaminated soils, while so many others would simply die? 

AUGUSTINE DORONILA 
Yes.  I suppose over the last 50 years, we've been discovering that there are a suite of plants, which are able to accumulate heavy metals to very extreme concentrations, and usually these are found in areas where there is a very high concentration of some of these metals, like some of the geological formations, which are essentially quite mineable because their minerals are in high concentrations.  So, if you like, these are experiments in evolution and natural selection, which have happened over millions of years.  Therefore, these communities have evolved in response to these very difficult soil conditions, and most likely also very difficult climatic conditions.  So, in one way, a lot of these are able to grow, but very slowly.  Just to give you a concrete example, we have a suite of about 500 plant species, which are known to accumulate nickel, for example.  Most of these are found in what are called ultramafic geological formations - in other words, outcrops of rock, which have very high magnesium and iron concentrations.  That's why they're called mafic - it's short for magnesium and iron.  In these crustal areas, certain metals have leeched out, so the ranges are quite different, but they're usually very high in nickel and chromium.  These metals are obviously quite toxic too, because of the oxidative stress, which occurs.  But we're finding out more and more that these places host these very unique plants - you know, when you think that there's probably about a quarter of a million species of plants known to humans at the moment, there's only 500 of these plant species which essentially have enough nickel to be comparable to the nickel content of your spoons and forks and your nickel plate and iron all around the place.  That's quite impressive.  But instead of poisoning themselves, they accumulate them, and, if you like, store them in parts of their tissues where they do not cause harm to their biochemical processes. 

SHANE HUNTINGTON 
When we look at some of these mining sites, where we're looking at extreme contamination, where the concentrations of some of these materials are extremely high - and in the case that John spoke about with the bacteria, the bacteria is already existing in these regions - but I can't imagine the plants existing in regions of such extreme contamination.  Are there locations where you're finding these plants where the levels are that high, or are we having to adapt the plants somehow, to take on such a big challenge as a mining contamination site?

AUGUSTINE DORONILA 
One of the things that we've understood is, these areas where historic mining has occurred - let's say, in the northern parts of England - they've realised that some of the plants that are naturally occurring pasture species, for example, have actually been subjected to this very intense form of natural selection, and populations of different common grass species, for example, in these tin and copper mines in the north of England actually are hosts to some very unique and highly adapted species of grasses, which can accumulate arsenic and copper.  In fact, these places are probably some of the best examples of natural selection in action, because modern mining has only occurred in the last 200 years, and you think, are these timeframes too quick to allow the conditions for plants to accumulate some of these toxic metals at such high concentrations?  Some very impressive studies on natural selection have been done on these areas, and demonstrated clearly that some of these processes can happen at such a very quick timeframe. 

SHANE HUNTINGTON 
Now, you're also working in one of these gold mining sites and using plants. 

AUGUSTINE DORONILA 
Yes, yes. 

SHANE HUNTINGTON 
How, or what role will the plants be playing in the cleanup of these mining sites?

AUGUSTINE DORONILA 
Well, essentially, we use this very thin green skin, if you like, as a very important role in stabilising these surfaces of essentially mined-out landscape, in which solid rock has been crushed up into dust. So, to create land forms like tailings dams or waste rock facilities - which, over geological time, will essentially erode because of exposure to wind and water - we need to have some binding force.  Essentially, if you are able to put the appropriate plant species, that can handle these quite challenging conditions - and fortunately, because the natural landscapes like some of these mining areas are also essentially semi-arid or very difficult Mediterranean conditions - our plants are already adapted to salt, exposure to extreme climate.  We are also finding that these adaptations to these generic forms of tough life are also the ones that confer then the ability to grow on these highly disturbed landforms.  And so, they stabilise the soils - you know, they put their roots in, and if you like, it's a form of bio-engineering, ecological engineering, where we bind these surfaces so they don't move all around the landscape and create conditions for exposure to harm from other conditions. 

SHANE HUNTINGTON 
We're talking about quite a long-term scenario here, then, aren't we?

AUGUSTINE DORONILA 
Yes, exactly.

SHANE HUNTINGTON 
With these plants staying on the site for extreme periods of time?

AUGUSTINE DORONILA 
Exactly, yes. 

SHANE HUNTINGTON 
Some of the plants that you work with are referred to as hyperaccumulators.  What is this, a hyperaccumulator, and how common are these found in nature?

AUGUSTINE DORONILA 
Like I said previously, we currently know that there are at least 500 species of these plants, which, as a technical definition, accumulate a certain metal to 1,000 parts per million, or micrograms per gram of plant tissue.  But most of these metals are toxic, and concentrations of up to 10 or 100 PPM as a general rule of thumb.  But they accumulate it into concentrations, which are, at times, higher than what is in the soil, so it's a hyper response, if you like - it's a hyperactive response. 

SHANE HUNTINGTON 
I'm Shane Huntington, and my guests today are Dr John Moreau and Dr Augustine Doronila.  We're talking about the science of bio-remediation, and how it's applied to cleaning up contamination of mine sites, here on Up Close.  Augustine, when we look at evolutionary - so, the drivers, with things like plants or animals or anything for that matter - there's usually something that leads to a particular biological item doing a certain thing.  In the case of plants taking on these heavy metals, I find it hard to see that it would just be so that they can grow in certain locations.  Is there another driver that has led to these evolutionary changes, so that they can take on such - you know, what are hundreds of times the normal toxicity levels of these metals?

AUGUSTINE DORONILA 
The current working hypothesis is that this adaptation to living in heavy metal-rich environments is, if you like, it confers an advantage on these species because, once the plant tissue is loaded up with metals, it's a challenge for herbivores to eat these plant tissues.  Therefore, by being able to reproduce, then they've occupied a niche, which is otherwise inaccessible to many other plant species.  A lot of these hyperaccumulating species are very slow growing, essentially because there's very few nutrients in these soils anyway.  But we're finding out that, if you grow these species in soils with a little bit of the metal, they will accumulate them to vast amounts anyway, but they can also respond in accumulating a lot of biomass.  But by growing in these difficult environments, all the other plant species that do not have the ability to tolerate the metals essentially drop off the race, because they just can't cope. 

SHANE HUNTINGTON 
It sounds to me like we should be using the plants to do the metal extraction for us.  Is that something that people are looking into?

AUGUSTINE DORONILA 
Yes.  This is one of the avenues, if you like, where we can use these plants in a process to clean up some of the other urban environments where we have accumulated metals, and clean them in a way which does not require a staggering amount of energy, because that is one of the problems with living in big cities - we tend to accumulate all these metals, because all these metals are useful for us in some form or other, to build our cities.  But then, due to the weathering processes, these metals do go into solution, and then perform their biologically damaging effects.  But if we are able to use plants in the form of - as we call phytoremediation - using plants to remediate metal or polluted and contaminated soils, then it could be a cost-effective way of doing that, because it's not a lot of rocket science.  If you use a plant that can polish off the metals - you go through an ergonomic cycle, for example, you harvest the plants and you burn it - you convert that calorific value into some sort of energy value, then you end up with ash, which is usually just a tenth of the original biomass.  Then, you can put that ash, which is laden with the metals in question, through a normal metallurgical extraction process. 

SHANE HUNTINGTON 
Now, you mentioned earlier that some of the concentration levels exceed what we would find in our cutlery.  

AUGUSTINE DORONILA 
Yes. 

SHANE HUNTINGTON 
Talk us through a couple of examples.  That seems extraordinary. 

AUGUSTINE DORONILA 
Yes.  We've found several species of tropical nickel hyperaccumulators in the Philippines, for example, and in New Caledonia, in which it was discovered that the sap of these woody shrubs and trees had up to 8 per cent nickel.  It's quite a staggering thing, to realise that a plant is able to just have a biochemical process to load up essentially sticky sap, which in one sense is a good way to reduce the release of these metals in a form which is damaging to the other plant tissues.

SHANE HUNTINGTON 
John, coming back to bacteria for a moment, is it likely that we'll be able to use those sorts of techniques for bacteria, to get to the point where we're almost mining with bacteria and extracting metals through the process of utilisation of bacteria?

JOHN MOREAU
Well, it's certainly already being tried.  The process of bio-recovery from mining waste streams is not just an active area of research, but there are pilot scale tests across the world in various mine sites, essentially with bioreactors, if you will, churning away trying to extract toxic metals out of acidic mine waste streams.  So, I think it will, perhaps, become eventually a feasible technique for low-level remediation.  It certainly would have to be augmented, I think, with other strategies, but with more research, I think we can actually increase the efficiency quite a bit.

SHANE HUNTINGTON 
John, with regards to plants, obviously there's a range of mechanisms where these metals can be contained within the plant structure - whether it's in the cell walls, or the sap, or a range of other possibilities.  What's the analogue in bacteria?

JOHN MOREAU
Well, I suppose there are a couple of different ways.  There are so-called dissimilatory processes, by which the toxic metals, for example, would be sequestered into by-products of the bacterium's natural metabolism, that are not incorporated into the cell.  An example of that would be an anoxic environment - bacteria that have adapted to breathing sulphate in the way that we breathe oxygen produce a metabolic waste product called sulphide, which is actually extremely reactive with heavy metals, a number of metals, and the sulphide can precipitate those metals from waste streams or groundwater.  Precipitation is the process whereby metals that are in solution are removed from solution - by solution, I mean natural waters, groundwater, surface waters - by the process of forming a new mineral.  So, something that is dissolved becomes something that is solid, and the density of those solids, in many cases, tends to cause them to sink or precipitate out from that fluid.  So, the sulphide can precipitate or re-precipitate those metals from waste streams or groundwater as really the starting material.  They essentially re-precipitate the ore that was originally being mined - only the interesting thing about this ore that's re-precipitated in the bioremediation process is that it's usually concentrated greatly, to become almost 90 per cent or greater purity.  So, in some sense, it's a sort of a precursor to a cost-effective bio-recovery strategy for the metals as well.  You'll see around metals contaminated mine sites or other areas, often wetlands restoration strategies and wetlands creation strategies, because wetlands are naturally anoxic environments that foster the growth of sulphate-reducing bacteria.  Another strategy would be to actually allow the bacteria to accumulate the metals into their biomass, and that may actually be a sort of a self-terminating approach, because the metals may eventually kill the bacteria.  But we rely on the growth of biomass to outpace, effectively, the contamination of the biological system by that metal.  So, the bacteria, effectively, act as sponges, and they just suck up, if you will, the metals from solution, and precipitate them or absorb them to the cell walls, or into intracellular vesicles or cavities. Eventually, they will kill the bacterium, but again, we rely on sort of fostering the growth of biomass to outpace the influx of metals. 

SHANE HUNTINGTON 
Do you feel as though there is the possibility of completely decontaminating some of these sites, or is this beyond what we can do at the moment?

JOHN MOREAU
That's a big question.  I guess my intuitive answer would be to say probably not - probably some management needs to be done on the front end of the mining operations in the planning and the management strategies for the waste that will be generated.  But obviously, with a process and a sector of the economy like mining, which is going to continue for the foreseeable future - the mining of heavy metals and precious metals from the earth - we need to be working on alternative ways and cost-effective ways to mitigate the environmental waste that's generated from these operations, and bioremediation may be one of those means. 

SHANE HUNTINGTON 
Dr John Moreau, bio-geochemist from the School of Earth Sciences at the University of Melbourne, and Dr Augustine Doronila, botanist with the department of Chemistry, also at the University of Melbourne, thank you for being our guests on Up Close today, and talking about the science of bioremediation.

JOHN MOREAU
Thanks very much.

AUGUSTINE DORONILA 
Thanks very much, Shane.

SHANE HUNTINGTON 
Relevant links, a full transcript, and more info on this episode can be found at our website, at www.Up Close.unimelb.edu.au.  Up Close is a production of the University of Melbourne, Australia.  This episode was recorded on 20 September 2012.  Our producers for this episode were Kelvin Param and Eric van Bemmel. Associate Producer Dyani Lewis, Audio Engineer Gavin Nebauer.  Up Close is created by Eric van Bemmel and Kelvin Param.  I'm Shane Huntington.  Until next time, goodbye. 

VOICEOVER 
You've been listening to Up Close.  We're also on Twitter and Facebook.  For more info, visit www.Up Close.unimelb.edu.au.  Copyright 2012, the University of Melbourne. 


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