Phyto and nano soil remediation (part 2: nano)

For Part 2, I’ve included part of my original introduction (sans the story about the neighbour’s soil and a picture of Joe Martin):

I’m pleased to repost a couple of pieces on soil remediation written by Joe Martin for the Mind the Science Gap (MTSG) blog.

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 Master’s 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.

Here’s a bit more about 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 part 2: nano soil remediation or Joe’s Feb. 10, 2012 posting:

Last week I wrote about phytoremediation, and its potential to help us combat and undo soil contamination. But, like any good advanced society, we’re not pinning all our hopes on a single technique. A commenter, Maryse, alerted me to the existence of another promising set of techniques and technologies: nano-remediation.

For those who don’t know, nano-technology is a science which concerns itself with manipulating matter on a very small scale.  Nano-particles are commonly described as being between 100 nanometers (nm) to 1nm, though this is hardly a hard and fast rule. (For perspective, a nanometer is one one-millionth of a millimeter. If you aren’t inclined to the metric system, there are roughly four hundred million nanometers per inch.) On such micro-scales, the normal properties of compounds can be altered without changing the actual chemical composition. This allows for many new materials and products, (such as Ross Nanotechnology’s Neverwet Spray,) and for new applications for common materials, (using graphene to make the well-known carbon nanotubes).

When we apply the use of nano-scale particles to the remediation of contaminated soil, we are using nano-remediation. Unlike phytoremediation, this actually encompasses several different strategies which can be broadly classes as adsorptive or reactive. (Mueller and Nowack, 2010) The use of iron oxides to adsorb and immobilize metals and arsenic is not a new concept, but nano-particles offer new advantages. When I wrote “adsorb”, I was not making a spelling error; adsorption is a process by which particles adhere to the surface of another material, but do not penetrate into the interior. This makes surface area, not volume, the important characteristic. Nano-particles provide the maximum surface area-to-weight ratio, maximizing the adsorptive surfaces onto which these elements can attach. These adsorptive processes a very effective at binding and immobilizing metals and arsenic, but they do not allow for the removal of the toxic components. This may be less-than-ideal, but in places like Bangladesh, where arsenic contamination of groundwater poses major health risks, it may be just short of a miracle.

Reactive nano-remediation strategies focus on organic pollutants, and seem to work best for chlorinated solvents such as the infamous PCBs. Nano-scale zero valent iron, or nZVI, is the most widely explored and tested element used in these methods. The nZVI, or sometimes nZVI bound to various organic molecules like polysaccharides or protein chains, force redox reactions which rapidly disassemble the offending molecules.

There are other advantages to these nano-molecular techniques aside from the efficiency with which they bind or destroy the offending pollutants. In reactive remediation, the hyper reactivity nZVI causes it to react with other common and natural elements, such as dissolved oxygen in ground water, or nitrate and sulfate molecules, and in the process this inactivates the nZVI. While this forces multiple applications of the nano-particle (delivered in slurry form, through an injection well), it also prevents unused iron from drifting out of the treatment zone and becoming a pollutant itself. For adsorptive and reactive remediation techniques, that active nano-particles are injected into a well dug into or near the contaminated soil and/or groundwater. When injected as a slurry, the nano-particles can drift along with the flow of ground water, effectively creating an “anti-pollution” plume. In other formulations, the active mixture is made to flow less easily, effectively creating a barrier to filter spreading pollution or through which polluted ground water can be pulled.

There are health risks and concerns associated with the production and use of nano-particles, so some caution and validation is needed before its used everywhere. However, there has already been some successes with nano-remediation. The example of PCB remediation with nZVI is taken from great success the US Air Force has had. (PCB contamination is a legacy of their use as fire-suppressants). Beyond this, while nano-remediation has not been widely applied on surface or near-surface soils, it does enable remediation in deeper soils normally only accessed by “pump-and-treat” methods, (which are expensive and can have decades-long time frames). When coupled with other techniques, (like phytoremediation), it does fit nicely into an expanding tool bag, one with which we as a society and species can use to reverse our impact on the planet, (and our own health).

Further Reading: There was no way for me to represent the full sum of nano-remediation, nevertheless nanotechnology, in this post. It has such potential, and is developing at such a rate that the attention it deserves is better measured in blogs (or perhaps decablogs). So if you are interested in nano-technology or nano-remediation, click through some of the links below.

List of popular blogs: http://www.blogs.com/topten/10-popular-nanotechnology-blogs/, including some very important ones on the health risks of nano-technology.

A cool site listing sites currently using nano-remediation: http://www.nanotechproject.org/inventories/remediation_map/, and another post from the same site dealing with nano-remediation [PEN webcast on site remediation]: http://www.nanotechproject.org/events/archive/remediation/

An excellent peer-reviewed article: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2799454/

Citation: Mueller C and Nowack B. Nanoparticles for Remediation: Solving Big Problems with Little Particles. 2010. Elements, Vol. 6. pp 395-400.

You can read about the other MTSG contributors and find links to their work here.

I have mentioned remediation before on the blog,

soil remediation and Professor Dennis Carroll at the University of Western Ontario in my Nov. 4, 2011 posting

remediation and a patent for Green-nano zero valent iron (G-nZVI) in my June 17, 2011 posting

groundwater remediation and nano zero valent iron (nZVI) at the University of California at Santa Barbara in my March 30, 2011 posting

site remediation and drywall in my Aug. 2, 2010 posting

remediation technologies and oil spills my May 6, 2010 posting

my March 4, 2010 posting  (scroll down about 1/2 way) which is a commentary on the Project for Emerging Nanotechnologies (PEN) webcast about site remediation in Joe’s list of resources

Thank you Joe for giving me permission to repost your pieces. For more of Joe’s pieces,  Read his posts here –>

2 thoughts on “Phyto and nano soil remediation (part 2: nano)

  1. Pingback: Phyto and nano soil remediation (part 2: nano) « FrogHeart - All about nano technology - NanoTechno.org

  2. Pingback: NanoRem: pollution, nanotechnology, and remediation « FrogHeart

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