Do you ever drive by a gas station that’s fenced off and there are workers digging a huge hole in the ground?  That’s because tanks that hold the gas have leaked and contaminated the ground under the station.  Around the world there are thousands of sites where toxic chemicals have been spilt accidentally or dumped in the past and left.  Up until the 1970s it was widely believed that the soil would act like a natural filter and clean the chemicals so they wouldn’t do any harm.  We now know that this is not true, and that these chemicals can migrate down through microscopic cracks in the soil, finally reaching ground water.

For years people have come up with different ways to clean these toxic chemicals out of the groundwater.  Traditionally the water is either pumped out and cleaned, or a specially designed cleansing solution flushes the toxins out of the water.   Both of these techniques are limited by the difficulty of accurately locating and accessing the contaminated groundwater since it can be very deep in the ground.  Now there is a new idea of how to clean contaminated groundwater.

Dr. Denis O’Carroll from the University of Western Ontario, and who is currently a visiting academic at the University of New South Wales (UNSW) Water Research Lab, believes that the solution is in nanoparticles.  So what are nanoparticles?

I found a number of different definitions for nanoparticles but the easiest to understand is that they are the smallest unit that can still behave as a whole entity in terms of properties and transport.  Specifically, a nanoparticle is a particle that is between 1 and 100 nanometers.  One nanometer is equal to one billionth of a meter.  Basically a nanoparticle is a very small particle of something.  Some of the more common nanoparticles are carbon, gold, iron, and titanium, but there are many others.  Nanoparticles are helpful because, “particles of a material have a relatively larger surface area compared to their volume. The proportionally larger exposed surface can make nanoparticles much more chemically active.”  This means that a nanoparticle of carbon will act very different than say a golf ball sized sphere of carbon.

So how does this fit into cleaning up contaminated groundwater?  Dr. O’Carroll has been experimenting with using iron nanoparticles that are 500 to 5,000 times narrower than a human hair to help do the cleaning.  How this works is the nanoparticles are injected directly into the contaminated soil, and then they flow to the toxins.  I’ll let Dr. O’Carroll explain the rest since it’s way over my head.  After the nanoparticles flow to the toxins they, “initiate a redox reaction, whereby electrons are transferred between the particle and the pollutant. This reaction changes the oxidation state of the pollutant and diminishes its overall toxicity to safer levels”.  Got it?  I don’t, but I do understand that whatever the nanoparticles are doing the end product is cleaner water and soil.

With this type of technology the size of the nanoparticles is particularly important.  Because they are so small they are able to fit through microscopic channels that the water flows through in order to get to the toxins.  You can think of the channels as tunnels and the nanoparticles as cars; because the cars are small they drive right through the tunnels to their destination.  But if you tried to drive a big rig through the tunnel it would slam right into it and be destroyed.

Another benefit, and detriment, of iron nanoparticles is that they are not very mobile and they dissolve quickly.  This is a benefit because they are safe for the environment, but a detriment because if they can’t move around and dissolve too fast they don’t have time to attack the toxins.  To keep them from breaking down Dr. O’Carroll is experimenting with different formations of iron, and also with encapsulating the nanoparticles in an environmentally safe “rust-preventing polymer” which slows their breakdown and makes them more mobile.

This technology is very groundbreaking and it will be interesting to see what happens in the next couple of years.  As of me writing this Dr. O’Carroll has done two trials with the nanoparticles in containment sites in Canada and “significant degradation of the contaminants at both sites has been observed”.  He hopes that soon nanoparticles will be used throughout the world to help with cleaning contaminated sites so that they can be useful once again.