Tag Archives: soil remediation

Let them (Rice University scientists) show you how to restore oil-soaked soil

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I did not want to cash in (so to speak) on someone else’s fun headline so I played with it. Hre is the original head, which was likely written by either David Ruth or Mike Williams at Rice University (Texas, US), “Lettuce show you how to restore oil-soaked soil.”

A February 1, 2019 news item on ScienceDaily on the science behind lettuce and oil-soaked soil,

Rice University engineers have figured out how soil contaminated by heavy oil can not only be cleaned but made fertile again.

How do they know it works? They grew lettuce.

Rice engineers Kyriacos Zygourakis and Pedro Alvarez and their colleagues have fine-tuned their method to remove petroleum contaminants from soil through the age-old process of pyrolysis. The technique gently heats soil while keeping oxygen out, which avoids the damage usually done to fertile soil when burning hydrocarbons cause temperature spikes.

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Lettuce growing in once oil-contaminated soil revived by a process developed by Rice University engineers. The Rice team determined that pyrolyzing oil-soaked soil for 15 minutes at 420 degrees Celsius is sufficient to eliminate contaminants while preserving the soil’s fertility. The lettuce plants shown here, in treated and fertilized soil, showed robust growth over 14 days. Photo by Wen Song

A February 1, 2019 Rice University news release (also on EurekAlert), which originated the news item, explains more about the work,

While large-volume marine spills get most of the attention, 98 percent of oil spills occur on land, Alvarez points out, with more than 25,000 spills a year reported to the Environmental Protection Agency. That makes the need for cost-effective remediation clear, he said.

“We saw an opportunity to convert a liability, contaminated soil, into a commodity, fertile soil,” Alvarez said.

The key to retaining fertility is to preserve the soil’s essential clays, Zygourakis said. “Clays retain water, and if you raise the temperature too high, you basically destroy them,” he said. “If you exceed 500 degrees Celsius (900 degrees Fahrenheit), dehydration is irreversible.

The researchers put soil samples from Hearne, Texas, contaminated in the lab with heavy crude, into a kiln to see what temperature best eliminated the most oil, and how long it took.

Their results showed heating samples in the rotating drum at 420 C (788 F) for 15 minutes eliminated 99.9 percent of total petroleum hydrocarbons (TPH) and 94.5 percent of polycyclic aromatic hydrocarbons (PAH), leaving the treated soils with roughly the same pollutant levels found in natural, uncontaminated soil.

The paper appears in the American Chemical Society journal Environmental Science and Technology. It follows several papers by the same group that detailed the mechanism by which pyrolysis removes contaminants and turns some of the unwanted hydrocarbons into char, while leaving behind soil almost as fertile as the original. “While heating soil to clean it isn’t a new process,” Zygourakis said, “we’ve proved we can do it quickly in a continuous reactor to remove TPH, and we’ve learned how to optimize the pyrolysis conditions to maximize contaminant removal while minimizing soil damage and loss of fertility.

“We also learned we can do it with less energy than other methods, and we have detoxified the soil so that we can safely put it back,” he said.

Heating the soil to about 420 C represents the sweet spot for treatment, Zygourakis said. Heating it to 470 C (878 F) did a marginally better job in removing contaminants, but used more energy and, more importantly, decreased the soil’s fertility to the degree that it could not be reused.

“Between 200 and 300 C (392-572 F), the light volatile compounds evaporate,” he said. “When you get to 350 to 400 C (662-752 F), you start breaking first the heteroatom bonds, and then carbon-carbon and carbon-hydrogen bonds triggering a sequence of radical reactions that convert heavier hydrocarbons to stable, low-reactivity char.”

The true test of the pilot program came when the researchers grew Simpson black-seeded lettuce, a variety for which petroleum is highly toxic, on the original clean soil, some contaminated soil and several pyrolyzed soils. While plants in the treated soils were a bit slower to start, they found that after 21 days, plants grown in pyrolyzed soil with fertilizer or simply water showed the same germination rates and had the same weight as those grown in clean soil.

“We knew we had a process that effectively cleans up oil-contaminated soil and restores its fertility,” Zygourakis said. “But, had we truly detoxified the soil?”

To answer this final question, the Rice team turned to Bhagavatula Moorthy, a professor of neonatology at Baylor College of Medicine, who studies the effects of airborne contaminants on neonatal development. Moorthy and his lab found that extracts taken from oil-contaminated soils were toxic to human lung cells, while exposing the same cell lines to extracts from treated soils had no adverse effects. The study eased concerns that pyrolyzed soil could release airborne dust particles laced with highly toxic pollutants like PAHs.

”One important lesson we learned is that different treatment objectives for regulatory compliance, detoxification and soil-fertility restoration need not be mutually exclusive and can be simultaneously achieved,” Alvarez said.

Here’s a link to and a citation for the paper,

Pilot-Scale Pyrolytic Remediation of Crude-Oil-Contaminated Soil in a Continuously-Fed Reactor: Treatment Intensity Trade-Offs by Wen Song, Julia E. Vidonish, Roopa Kamath, Pingfeng Yu, Chun Chu, Bhagavatula Moorthy, Baoyu Gao, Kyriacos Zygourakis, and Pedro J. J. Alvarez. Environ. Sci. Technol., 2019, 53 (4), pp 2045–2053 DOI: 10.1021/acs.est.8b05825 Publication Date (Web): January 25, 2019

Copyright © 2019 American Chemical Society

This paper is behind a paywall.

Nanoremediation to be combined with bioremediation for soil decontamination

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There’s a very interesting proposal to combine nanoremediation with bioremediatiion (also known as, phytoremediation) techniques to decontaminate soil. From a June 10, 2016 news item on Nanowerk,

The Basque Institute of Agricultural Research and Development Neiker-Tecnalia is currently exploring a strategy to remedy soils contaminated by organic compounds containing chlorine (organochlorine compounds). The innovative process consists of combining the application of zero-iron nanoparticles with bioremediation techniques. The companies Ekotek and Dinam, the UPV/EHU-University of the Basque Country and Gaiker-IK4 are also participating in this project known as NANOBIOR.

A June 10, 2016 Elhuyar Fundazioa news release, which originated the news item, provides more detail about the proposed integration of the two techniques,

Soils affected by organochlorine compounds are very difficult to decontaminate. Among these organochlorine compounds feature some insecticides mainly used to control insect pests, such as DDT, aldrin, dieldrin, endosulfan, hexachlorocyclohexane, toxaphene, chlordecone, mirex, etc. It is a well-known fact that the use of many of these insecticides is currently banned owing to their environmental impact and the risk they pose for human health.

To degrade organochlorine compounds (organic compounds whose molecules contain chlorine atoms) present in the soil, the organisations participating in the project are proposing a strategy based on the application, initially, of zero-iron nanoparticles [also known as nano zero valent iron] that help to eliminate the chlorine atoms in these compounds. Once these atoms have been eliminated, the bioremediation is carried out (a process in which microorganisms, fungi, plants or enzymes derived from them are used to restore an environment altered by contaminants to its natural state).

The bioremediation process being developed by Neiker-Tecnalia comprises two main strategies: biostimulation and bioaugmentation. The first consists of stimulating the bacteria already present in the soil by adding nutrients, humidity, oxygen, etc. Bioaugmentation is based on applying bacteria with the desired degrading capability to the soil. As part of this process, Neiker-Tecnalia collects samples of soils contaminated by organochlorine compounds and in the laboratory isolates the species of bacteria that display a greater capacity for degrading these contaminants. Once the most interesting strains have been isolated, the quantity of these bacteria are then augmented in the laboratory and the soil needing to be decontaminated is then inoculated with them.

Bank of effective strains to combat organochlorines

The first step for Neiker-Tecnalia is to identify bacterial species capable of degrading organochlorine compounds in order to have available a bank of species of interest for use in bioremediation. This bank will be gathering strains collected in the Basque Country and will allow bacteria that can be used as a decontaminating element of soils to be made available.

The combining of the application of zero-iron nanoparticles and bioremediation constitutes a significant step forward in the matter of soil decontamination; it offers the added advantage of potentially being able to apply them in situ. So this methodology, which is currently in the exploratory phase, could replace other processes such as the excavation of contaminated soils so that they can be contained and/or treated. What is more, the combination of the two techniques makes it possible to reduce the decontamination times, which would take much longer if bioremediation is used on its own.

There is a NANOBIOR webpage here.

For the curious I have two 2012 posts that provide some very nice explanations by Joe Martin, then a Master’s student in the University of Michigan’s Public Health program,: Phyto and nano soil remediation (part 1: phyto/plant) and Phyto and nano soil remediation (part 2: nano).

Natural nanoparticles and perfluorinated compounds in soil

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The claim in a Sept. 9, 2015 news item on Nanowerk is that ‘natural’ nanoparticles are being used to remove perfluorinated compounds (PFC) from soil,

Perfluorinated compounds (PFC) are a new type of pollutants found in contaminated soils from industrial sites, airports and other sites worldwide.

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In Norway, The Environment Agency has published a plan to eliminate PFOS [perfluorooctanesulfonic acid or perfluorooctane sulfonate] from the environment by 2020. In other countries such as China and the United States, the levels are far higher, and several studies show accumulation of PFOS in fish and animals, however no concrete measures have been taken.

The Norwegian company, Fjordforsk AS, which specializes in nanosciences and environmental methods, has developed a method to remove PFOS from soil by binding them to natural minerals. This method can be used to extract PFOS from contaminated soil and prevent leakage of PFOS to the groundwater.

Electron microscopy images show that the minerals have the ability to bind PFOS on the surface of the natural nanoparticles. [emphasis mine] The proprietary method does not contaminate the treated grounds with chemicals or other parts from remediation process and uses only natural components.

Electron microscopy images and more detail can be found in the Nanowerk news item.

I can’t find the press release, which originated the news item but there is a little additional information about Fjoorkforsk’s remediation efforts on the company’s “Purification of perfluorinated compounds from soil samples” project page,

Project duration: 2014 –

Project leader: Manzetti S.

Collaborators: Prof Lutz Ahrens. Swedish Agricultural University. Prof David van der Spoel, Uppsala University.

Project description:

Perfluorinated compounds (PFCs) are emerging pollutants used in flame retardants on a large scale on airports and other sites of heavy industrial activity. Perfluroinated compounds are toxic and represent an ultra-persistent class of chemicals which can accumulate in animals and humans and have been found to remain in the body for over 5 years after uptake. Perfluorinated compounds can also affect the nerve-system and have recently been associated with high- priority pollutants to be discontinued and to be removed from the environment. Using non-toxic methods, this project develops an approach to sediment perfluorinated compounds from contaminated soil samples using nanoparticles, in order to remove the ecotoxic and ground-water contaminating potential of PFCs from afflicted sites and environments.

The only mineral that I know is used for soil remediation is nano zero-valent iron (nZVI). A very fast search for more information yielded a 2010 EMPA [Swiss Federal Laboratories for Materials Science and Technology] report titled “Nano zero valent iron – THE solution for water and soil remediation? ” (32 pp. pdf) published by ObservatoryNANO.

As for the claim that the company is using ‘natural’ nanoparticles for their remediation efforts, it’s not clear what they mean by that. I suspect they’re using the term ‘natural’ to mean that engineered nanoparticles are being derived from a naturally occurring material, e.g. iron.

Abakan makes good on Alberta (Canada) promise (coating for better pipeline transport of oil)

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It took three years but it seems that US company Abakan Inc.’s announcement of a joint research development centre at the Northern Alberta Institute of Technology (NAIT), (mentioned here in a May 7, 2012 post [US company, Abakan, wants to get in on the Canadian oils sands market]), has borne fruit. A June 8, 2015 news item on Azonano describes the latest developments,

Abakan Inc., an emerging leader in the advanced coatings and metal formulations markets, today announced that it has begun operations at its joint-development facility in Edmonton, Alberta.

Abakan’s subsidiary, MesoCoat Inc., along with the lead project partner, Northern Alberta Institute of Technology (NAIT) will embark on an 18-month collaborative effort to establish a prototype demonstration facility for developing, testing and commercializing wear-resistant clad pipe and components. Western Economic Diversification Canada is also supporting this initiative through a $1.5 million investment toward NAIT. Improvements in wear resistance are expected to make a significant impact in reducing maintenance and downtime costs while increasing productivity in oil sands and other mining applications.

A June 4, 2015 Abakan news release, which originated the news item, provides more detail about the proposed facility, the difficulties encountered during the setup, and some interesting information about pipes,

Abakan shipped its CermaClad high-speed large-area cladding system for installation at the Northern Alberta Institute of Technology’s (NAIT) campus in Edmonton, Alberta in early 2015. Despite delays associated with the installation of some interrelated equipment and machinery, the CermaClad system and other ancillary equipment are now installed at the Edmonton facility. The Edmonton facility is intended to serve as a pilot-scale wear-resistant clad pipe manufacturing facility for the development and qualification of wear-resistant clad pipes, and as a stepping stone for setting-up a full-scale wear-resistant clad pipe manufacturing facility in Alberta. The new facility will also serve as a platform for Abakan’s introduction to the Alberta oil sands market, which, with proven reserves estimated at more than 169 billion barrels, is one of the largest oil resources in the world and a major source of oil for Canada, the United States and Asia. Since Alberta oil sands production is expected to increase significantly over the next decade, producers want to extend the life of the carbon steel pipes used for the hydro-transportation of tailings with harder, tougher coatings that protect pipes from the abrasiveness of tar-like bituminous oil sands.

“Our aim is to fast-track market entry of our wear-resistant clad pipe products for the transportation of oil sands and mining slurries. We have received commitments from oil sands producers in Canada and mining companies in Mexico and Brazil to field-test CermaClad wear-resistant clad pipe products as soon as our system is ready for testing. Apart from our work with conventional less expensive chrome carbide and the more expensive tungsten carbide wear-resistant cladding on pipes, Abakan also expects to introduce new iron-based structurally amorphous metal (SAM) alloy cladding that in testing has exhibited better performance than tungsten carbide cladding, but at a fraction of the cost.” Robert Miller stated further that “although more expensive than the more widely used chrome carbide cladding, our new alloy cladding is expected to be a significantly better value proposition when you consider an estimated life of three times that of chrome carbide cladding and those cost efficiencies that correspond to less downtime revenue losses, and lower maintenance and replacement costs.”

The costs associated with downtime and maintenance in the Alberta oil sands industry estimated at more than $10 billion a year are expected to grow as production expands, according to the Materials and Reliability in Oil Sands (MARIOS) consortium in Alberta. The development of Alberta’s oil sands has been held up by the lack of materials for transport lines and components that are resistant to the highly abrasive slurry. Due to high abrasion, the pipelines have to be rotated every three to four months and replaced every 12 to 15 months. [emphasis mine] The costs involved just in rotating and replacing the pipes is approximately $2 billion annually. The same is true of large components, for example the steel teeth on the giant electric shovels used to recover oil sands, must be replaced approximately every two days.

Abakan’s combination of high productivity coating processes and groundbreaking materials are expected to facilitate significant efficiencies associated with the extraction of these oil resources. Our proprietary materials combined with CermaClad large-area based fusion cladding technology, have demonstrated in laboratory tests a three to eight times improvement in wear and corrosion resistance when compared with traditional weld overlays at costs comparable to rubber and metal matrix composite alternatives. Abakan intends to complete development and initiate field-testing by end of year 2016 and begin the construction of a full-scale wear-resistant clad pipe manufacturing facility in Alberta in early-2017.

Given that there is extensive talk about expanding oil pipelines from Alberta to British Columbia (where I live), the information about the wear and tear is fascinating and disturbing. Emotions are high with regard to the proposed increase in oil flow to the coast as can be seen in a May 27, 2015 article by Mike Howell for the Vancouver Courier about a city hall report on the matter,

A major oil spill in Vancouver waters could potentially expose up to one million people to unsafe levels of a toxic vapour released from diluted bitumen, city council heard Wednesday in a damning city staff report on Kinder Morgan’s proposal to build a pipeline from Alberta to Burnaby [British Columbia].

In presenting the report, deputy city manager Sadhu Johnston outlined scenarios where exposure to the chemical benzene could lead to adverse health effects for residents and visitors, ranging from dizziness to nausea to possible death.

“For folks that are on the seawall, they could be actually struck with this wave of toxic gases that could render them unable to evacuate,” said Johnston, noting 25,000 residents live within 300 metres of the city’s waterfront. “These are serious health impacts. So this is not just about oil hitting shorelines, this is about our residents being exposed to very serious health effects.

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  • Kinder Morgan’s own estimate is that pipeline leaks under 75 litres per hour may not be detected.

While I find the presentation’s hysteria a little off-putting, it did alert me to one or two new issues, benzene gas and when spillage from the pipes raises an alarm. For anyone curious about benzene gas and other chemical aspects of an oil spill, there’s a US National Oceanic and Atmospheric Administration (NOAA) webpage titled, Chemistry of an Oil Spill.

Getting back to the pipes, that figure of 75 litres per hour puts a new perspective on the proposed Abakan solution and it suggests that whether or not more and bigger pipes are in our future, we should do a better of job of protecting our environment now. That means better cladding for the pipes and better dispersants and remediation for water, earth, air when there’s a spill.

Nano-pesticides or nanopesticides or nano pesticides

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It’s the spelling that’s driving me nuts. In the last year it seems to have gotten quite higgledy piggledy and so we have this salad of one word, two words, and hyphenated words for anything  prepended by nano.  I hope it settles soon but in the meantime, here’s an Aug. 12, 2013 news item on Azonano concerning nano-pesticides,

Research is urgently needed to evaluate the risks and benefits of nano-pesticides to human and environmental health. Melanie Kah and Thilo Hofmann from the Department of Environmental Geosciences of the University of Vienna recently performed an extensive analysis of this emerging field of research.

The results were published June 6th in the internationally recognised journal “Critical Reviews in Environmental Science and Technology”. The study presents the current scientific state of art on nano-pesticides and identifies direction priorities for future research.

The University of Vienna June 20, 2012  press release, which originated the news item (I’ll explain the one year gap later in this posting), describes some of the concerns raised in the study,

Nano-pesticides encompass a great variety of products, some of which are already on the market. The application of nano-pesticides would be the only intentional diffuse input of large quantities of engineered nano-particles into the environment. Innovation always results in both drawbacks and benefits for human and environmental health. Nano-pesticides may reduce environmental contamination through the reduction in pesticide application rates and reduced losses. However, nano-pesticides may also create new kinds of contamination of soils and waterways due to enhanced transport, longer persistence and higher toxicity.

The current level of knowledge does not allow a fair assessment of the advantages and disadvantages that will result from the use of nano-pesticides. As a prerequisite for such assessment, a better understanding of the fate and effect of nano-pesticides after their application is required. The suitability of current regulations should also be analyzed so that refinements can be implemented if needed. Research on nano-pesticides is therefore a priority for preserving the quality of both the food chain and the environment.

Here’s a link to and a citation for the paper,

Nano-pesticides: state of knowledge, environmental fate and exposure modeling: Melanie Kah, Sabine Beulke, Karen Tiede and Thilo Hofmann. Critical Reviews of Environmental Science and Technology, Volume 43, Issue 16, 2013 , pages 1823-1867 DOI: 10.1080/10643389.2012.671750

http://www.tandfonline.com/doi/abs/10.1080/10643389.2012.671750

There was a 2012 version of this paper posted, which was when the press release was originally written and posted at the University of Vienna website, but June 2013 is when the paper was officially published. It is behind a paywall but thankfully one of the authors, Melanie Kah, gave Katy Edgington an interview about the study for Edgington’s June 26, 2012 article on scienceomega.com,

“Although some research is ongoing, one application that is fairly well-developed involves the injection of nanoscale zero-valent iron particles into groundwater to degrade certain contaminants. This is an example of something that is still under development but which is already being applied, as the technique is currently in use on a large scale in the United States.” [says Kah]

A project is underway in the department which aims to help make the technique more widely applicable, and another – at the complete opposite end of the scale in terms of its development – is looking at a potential application for carbon nanotubes.

“People have suggested that carbon nanotubes could be used to replace activated carbon, the material used worldwide to decontaminate water,” clarified Dr Kah. “It is suggested that carbon nanotubes have different properties which will complement activated carbon, but this is only at the laboratory scale so far.”

It is important to steer clear of making broad generalisations about the risks and benefits of nanopesticides as compared to conventional pesticides, Dr Kah emphasised. They cannot be considered as a single entity; rather each case must be taken on its own merits.

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In their review of the literature on the topic, the authors also discuss how the adequacy of existing legislation and regulation may be affected in light of the development of nanopesticides in various forms.

“I think it is far too early to propose any amendments to the current regulation,” Dr Kah stated. “It appears from our analysis that a lot of nanopesticides would be well covered by the European regulation on plant protection products because this regulation is very thorough; indeed it is probably the strictest in the world.”

I imagine that since the initial publication of the paper and the interview, there may have been a few changes to the paper and refinements to Kah’s ideas but the Edgington article does provides some interesting insight, especially if you don’t have access to the paper.

Phytoremediation, clearing pollutants from industrial lands, could also be called phyto-mining

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The University of Edinburgh (along with the Universities of Warwick and Birmingham, Newcastle University and Cranfield University) according to its Mar. 4, 2013 news release on EurekAlert is involved in a phytoremediation project,

Common garden plants are to be used to clean polluted land, with the extracted poisons being used to produce car parts and aid medical research.

Scientists will use plants such as alyssum, pteridaceae and a type of mustard called sinapi to soak up metals from land previously occupied by factories, mines and landfill sites.

Dangerous levels of metals such as arsenic and platinum, which can lurk in the ground and can cause harm to people and animals, will be extracted using a natural process known as phytoremediation.

A Mar. 4, 2013 news item on the BBC News Edinburgh, Fife and East Scotland site offers more details about the project and the technology,

A team of researchers from the Universities of Edinburgh, Warwick, Birmingham, Newcastle and Cranfield has developed a way of extracting the chemicals through a process called phytoremediation, and are testing its effectiveness.

Once the plants have drawn contaminated material out of the soil, they will be harvested and processed in a bio-refinery.

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A specially designed bacteria will be added to the waste to transform the toxic metal ions into metallic nanoparticles.

The team said these tiny particles could then be used to develop cancer treatments, and could also be used to make catalytic converters for cars.

Dr Louise Horsfall, of Edinburgh’s University’s school of biological sciences, said: “Land is a finite resource. As the world’s population grows along with the associated demand for food and shelter, we believe that it is worth decontaminating land to unlock vast areas for better food security and housing.

“I hope to use synthetic biology to enable bacteria to produce high value nanoparticles and thereby help make land decontamination financially viable.”

The research team said the land where phytoremediation was used would also be cleared of chemicals, meaning it could be reused for new building projects.

In my Sept. 28, 2012 posting I featured an international collaboration between universities in the UK, US, Canada, and New Zealand in a ‘phyto-mining’ project bearing some resemblance to this newly announced project. In that project, announced in Fall 2012, scientists were studying how they might remove platinum for reuse from plants near the tailings of mines.

I do have one other posting about phytoremediation. I featured a previously published piece by Joe Martin in a two-part series on the topic plant (phyto) and nano soil remediation. The March 30, 2012 posting is part one, which focuses on the role of plants in soil remediation.

Phyto and nano soil remediation (part 1: phyto/plant)

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One of my parent’s neighbours was a lifelong vegetarian and organic gardener. The neighbour, a Dutchman,  had been born on the island of Curaçao, around 1900, and was gardening organically by the 1940’s at the latest. He had wonderful soil and an extraordinary rose garden in the front yard and vegetables in the back, along with his compost heap. After he died in the 1980’s, his granddaughter sold the property to a couple who immediately removed the roses to be replaced with grass in the front and laid a good quantity of cement in the backyard. Those philistines sold the soil and, I imagine, the roses too.

Myself, I’m not not a gardener but I have a strong appreciation for the necessity of good soil so, I’m pleased to repost a couple of pieces on soil remediation written by Joe Martin for the Mind the Science Gap (MTSG) blog. First here’s a little bit about the MTSG blog project and about Joe Martin.

I wrote about the MTSG blog in my Jan. 12, 2012 posting, which focussed on this University of Michigan project designed by Dr. Andrew Maynard for Masters students in the university’s Public Health program. Very briefly here’s a description of Andrews and the program from the About page,

Mind the Science Gap is a science blog with a difference.  For ten weeks between January and April 2012, Masters of Public Health students from the University of Michigan will each be posting weekly articles as they learn how to translate complex science into something a broad audience can understand and appreciate.

Each week, ten students will take a recent scientific publication or emerging area of scientific interest, and write a post on it that is aimed at a non expert and non technical audience.  As the ten weeks progress, they will be encouraged to develop their own area of focus and their own style.

…

About the Instructor.  Andrew Maynard is Director of the University of Michigan Risk Science Center, and a Professor of Environmental Health Sciences in the School of Public Health.  He writes a regular blog on emerging technologies and societal implications at 2020science.org.

As for Joe Martin,

I am a second year MPH student in Environmental Quality and Health, and after graduation from this program, I will pursue a Ph.D. in soil science.  My interests lie in soil science and chemistry, human health and how they interact, especially in regards to agricultural practice and productivity.

Here’s a picture,

Joe Martin, Masters of Public Health program, University of Michigan, MTSG blog

Joe gave an excellent description of nano soil remediation but I felt it would be remiss to not include the first part on phyto soil remediation. Here’s his Feb. 3, 2012 posting about plants and soil remediation:

Pictured: The Transcendent Reality of Life and the Universe.

Plants are awesome. It’s from them that we get most of our food. It’s from plants that many of our medicines originated, (such as Willow and aspirin). We raise the skeletons of our homes and furnish their interiors with trees. Most of our cloth is woven from plant fiber, (a statement I feel comfortable making based solely on the sheer weight of denim consumed each year in this country.) And although there is an entire world of water plants, all of the plants I listed above are grown in the soil*. How the individual soil particles cling to each other, how they hold water and nutrients, and how the soil provides shelter for the various macro and micro-organisms is as important to the growth of plants as sunlight.

But no matter how proliferative, no matter how adaptive plants are, there are still spaces inaccessible to them. A clear example would be the Saharan dunes or a frozen tundra plain. However, many of places where plants can’t survive are created by human activity. The exhaust of smelters provides one example – waste or escaped zinc, copper, cadmium, and lead infiltrate downwind soils and often exterminate many or most of the natural plants. Normal treatment options for remediating metal contaminated soils are expensive, and can actually create hazards to human health. This is because, like some persistent organic pollutants (the infamous dioxin is a great example), the natural removal of metals from soils often proceeds very slowly, if it proceeds at all. For this reason, remediation of metal soil often involves scraping the contaminated portion off and depositing it in a hazardous waste landfill. In cases of old or extensive pollution, the amount of soil can exceed thousands of cubic feet. In this process, contaminated dust can easily be stirred up, priming it to be inhaled by either the workers present or any local populations.

But it can be cousins of the evicted shrubs and grass which offer us the best option to undo the heavy metal pollution. In a process called phytoremediation, specific plants are deliberately seeded over the contaminated areas. These plants have been specifically chosen for the tendency to uptake the metals in question. (In some cases, this process is also used for persistent organic pollutants, like 2,3,7,8-TCDD, infamously known as dioxin.) These plants are allowed to grow and develop their root systems, but are also selectively mowed to remove the pollutant laden leaves and stems, and ultimately remove the contaminant from the soil system. Once the pollution level has descended to a sufficiently low level, the field may be left fallow. Otherwise, the remediating plants can be removed and the ground reseeded with natural plants or returned to agricultural, commercial, or residential use.

When it is applicable, phytoremediation offers a significant advantage over either restricted access, (a common strategy which amounts to placing a fence around the contaminated site and keeping people out), or soil removal. While the polluted grass clippings much still be treated as hazardous waste, the volume and mass of the hazardous material is greatly reduced. Throughout the process, the remediating plants also serve to fix the soil in place, reducing or preventing runoff and free-blowing dust. Instead of bulldozers and many dump trucks, the equipment needed is reduced to a mower which captures grass or plant clippings and a single dump truck haul each growing season. Finally, the site does not need to be reinforced with topsoil from some other region to return it to useable space. These last few advantages can also greatly reduce the cost of remediation.

The major disadvantages of phytoremediation are time and complexity. Scraping the soil can be done in a few months or less, depending on the size of the area to be remediated. Phytoremediation takes multiple growing seasons, and if the land is a prime space for development this may be unacceptable. Phytoremediation requires different plants for different pollutants or mixtures of pollutants. I chose the copper, zinc, lead, and cadmium mixture earlier in the article because in a study from 2005, (Herrero et al, 2005), they specifically attempted to measure the ability of rapeseed and sunflower to extract these metals from an artificially contaminated soil. The unfortunate reality is that each contaminant will have to be studied in such a way, meticulously pairing pollutants (or mixture of them) with a plant. Each of the selected plants must also be able to grow in the soil to be remediated. Regardless of type of contamination, a North American prairie grass is unlikely to grow well in a Brazilian tropical soil. For these reasons, phytoremediation plans must be individually built for each site. This is costly both in dollars and man hours. Furthermore, there is always the problem that some pollutants don’t respond well to phytoremediation. While copper, zinc, and cadmium have all been found to respond quite well to phytoremediation, lead does not appear to be. In the Herraro et al study, the plants accumulated lead, but did so in the roots. Unless the roots were dug up, this would not effectively remove the lead from the soil system. Unfortunately, lead is one of the most common heavy metal pollutants, at least in the U.S., a legacy of our former love for leaded gasoline and paint.

Despite these disadvantages, phytoremediation presents a unique opportunity to remove many pollutants. It is by far the least environmentally destructive, and in many cases may be the cheapest method of remediation. I am happy to see that it appears to be receiving funding and is being actively researched and developed, (for those who don’t pursue the reference, the Herraro article came from The International Journal of Phytoremediation.) In recent times, we’ve been hit with messages about expanding hydrofracking and the Gulf Oil spill, but perhaps I can send you into this weekend with a little positivity about our environmental future. The aggregated techniques and methods which can be termed “phytoremediation” have the potential to do much good at a lower cost than many other remediation techniques. That sounds like a win-win situation to me.

* I am aware that many of these crops can be grown aero- or hydroponically. While these systems do provide many foodstuffs, they are not near the level of soil grown crops, and can be comparatively very expensive. I chose not to discuss them because, well, I aspire to be a soil scientist.

1.) Herreo E, Lopez-Gonzalvez A, Ruiz M, Lucas Garcia J, and Barbas C. Uptake and Distribution of Zinc, Cadmium, Lead, and Copper in Brassica napus vr. oleifera and Helianthus annus Grown in Contaminated Soils. 2005. The International Journal of Phytoremediation. Vol. 5, pp. 153-167.

A note on photos: Any photos I use will be CC licensed. These particular photos are provided by Matthew Saunders (banana flower) and KPC (rapeseed) under an attribution, no commercial, no derivation license.  I originally attempted to link to the source in the caption, but wordpress won’t let me for some reason. Until I work that out, the image home can be found under the artist’s names a few sentences earlier. I believe this honors the license and gives proper credit, but if I’ve committed some faux pas, (which would not be a surprise), don’t hesitate to comment and correct me. And thanks to those who have done so in previous posts, its one of the best ways to learn.

Part 2: nano soil remediation follows.

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