Bioextraction/Phytostabilization – Helping Nature Do Her Thing Part 2
Fascinating experiments in Nigeria change our plans for growing lead out of the soil. Enjoy!
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I am Mason Olonade and this is Jìgìjìgì: Africulture Podcast. Here we believe building a healthy soil builds a healthy soul, so we share strategies for how to do both. To do both we ask two questions: How do you grow while you grow Kale, Collards, Tomatoes, and Melons. And why, do you think, the healthiest soils are Black?
Bioextraction and Phytostablization – Helping Nature Do Her Thing, Part 2
Just as plants move nutrients from the soil through roots to shoots, tubers, leaves, and seeds, so it goes for pollutants.
Before I continue with this episode I must emphasize the importance of soil testing. When Mandela and I grew down at Nu Ray Research Garden we learned that approximately 1/4th of the land was contaminated with high levels of lead.
It wouldn’t be a big problem for us because we are healthy and young, but for children and older folks it is not advised to consume anything that grows in a lead contaminated soil.
So what do you do with the soil you have, that may be contaminated or polluted? Like most answers to most questions, it depends. In the Master Gardener class I took the instructor told us that a particular place in DC was previously a military dumping ground, and so, the school had to get the soil excavated and replaced because of the arsenic contamination.
This may be an outlying example but in our case, the lead came from house paint illegally dumped during a housing renovation. These contaminants don’t go anywhere, unlike nutrients that can be leached away, contaminants leach within the soil, within our bodies, unless we do something about them.
If we had the time to experiment with our contaminated soil I would absolutely try my Black Thumbs at phytoremediation and growing the lead out of the soil.
My original plan would be to utilize the phytoextractive properties of plants and the chelant EDTA or Ethylenediaminetetraacetic acid. The EDTA, in solution with water will alter the chemistry of the soil and of the lead polluted therein to maximize the plants extraction potential.
Think of EDTA’s extraction assistance like using soap to clean a greasy dish. The soap doesn’t break up the grease but what it does is break is the surface tension of water. Breaking the surface tension changes the way water interacts, chemically, with lipids and fatty acids. Water no longer is slippery and fat no longer floats. Soap makes water an incredibly destructive force and allows it to shear the grease into smaller and smaller droplets that can be rinsed away.
EDTA works similarly. It solubilizes the lead into solution, much like salt or sugar into hot water. From this the EDTA-Lead solution will be phytoextracted from the soil into the plant.
At this stage we deepen our “depends.” Meaning, depending on the specific plant chosen, the lead may go to a different place within that plant. Each of these locations further deepens the depends, especially if greater concentrations are stored in the roots.
In that case, concentrations would be too high for phytoextraction. We would need to grow plants and trees to phytostabilize the lead and lock it out of absorption into plants or elsewhere in the soil. Similar levels to the lead that we experienced would be perfect for phytoextraction. In phyotoextraction the lead moves into the roots then to the leaves, or aerial parts of the plant. At that point the plant would be harvested and dumped at a hazardous waste facility. With certain pollutants, plants can be grown and then fermented and filtered into bio-ethanol, pyrolized into charcoal, or burned and their ashes harvested for valuable minerals. However, our case wold be similar to the authors Abioye et al, at the Federal University of Technology Minna in Nigeria. They reported in a 2013 research article that “the more available pool of lead was translocated from the roots to seeds and stem in that order.” The plant they chose for their study was Glycine max or Soybean. They stated further “it is a legume and, therefore, has the additional advantage of fixing nitrogen in the soil.”
While reading this paper I was struck by their observation. “It could be possible that some of the lead could have escaped into the atmosphere. USEPA reported that heavy metals (when mopped up by the plants) have the ability to escape into the atmosphere which could be in line with this finding.”
What was the finding? The soil test showed that after just three days, and then even more so after 12 weeks of remediation, the concentrations of lead in the soil were less than they were after initial pollutant introduction. In the 25ppm or 20mg/kg lead contaminated soils, the residual lead concentration was 2.13mg/kg after just 3 days of growth. 9.38x less lead after 3 days of growth. Marvelous results. Indeed I was marveled by a 2018 article published in the Journal of Environmental Engineering that changes my original plan. The article authored by Adejuno et al is titled “Compost and Biochar-assisted phytoremediation potentials of Moringa oleifera for remediation of lead.” This paper counters my previous plan with this paragraph. “It is remarkable to note that compost enhanced plant lead accumulation and translocation from roots to shoots. This finding may establish compost as an alternative natural chelate to enhance phytoextraction. Complexing agents, such as EDTA, citric acid, tartrate have been added to metals contaminated soils to increase metals accumulation in plants targets for phytoremediation. However, costs of the chemicals to the environment are the drawbacks of this approach. Hence, the use of controlled amount of compost to enhance Pb extraction is hereby proposed as an alternative method to clean up Pb contaminated soils.”
The authors close the article by saying, “The shoot of M. oleifera yielded a higher mass than its root, and the Pb concentrations in the root was higher than that in the shoot, suggesting that M. oleifera plant has the potential to provide vegetation cover for phytostabilization of lead contaminated soils. Groundnut shell biochar performed best in soil immobilisation of Pb and limited the uptake of Pb by M. oleifera. Therefore, this combination has the potential for phytostabilisation of Pb in contaminated soils. Lead uptake by M. oleifera, was enhanced by the compost. Sunflower-poultry manure compost, in combination with M. oleifera, can be proposed for phytoexraction of Pb- contaminated soils. The combination of sunflower-poultry manure compost and M. oleifera plant may be a promising phytoexraction technology for reclamation of lightly Pb contaminated soils, while phytostabilisation of highly Pb contaminated soil may be achieved using groundnut shell biochar in combination with M. oleifera plant. Compost and biochar amendments, fast-growing and Pb tolerant moringa oleifera plant may be proposed for reclamation of lead contaminated soil.”
This research is exactly why we are so excited to share it! Even we learn by providing and sharing new information with you, our loving sibling of the soil. To think that previous techniques that we’ve discussed here can not only build your soil, but clean soil is tremendously fascinating.
I’ve taken a deep interest in a different Yoruba Proverb. Isu wa lowo e, one wa lowo e. The yam is in your hand, the knife is in your hand. Everything you need to feed yourself, to sustain yourself, my sibling of the soil, is already within your grasp. Quite literally, the yam can filter our Zn and Cd from the soil, and then be fermented, producing bio-ethanol.
Share Jigijigi with your friends, family and your closely related siblings of the soil. Leave us a 5 star review wherever you listen to and we will say then as we say now, Asante Sana, Medase Pa, Modupe O. Thank you for listening to Jìgìjìgì