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 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:
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.
For more of Joe’s pieces, Read his posts here –>