By: Mary Ellen Ellis
Plants that clean contaminated soil are under study and actually being used already in some places. Instead of a massive cleanup that removes soil, plants can absorb and safely store those toxins for us.
Phytoremediation – Clean Up Soil with Plants
Plants absorb and use nutrients from soil. This extends to the uptake of toxins in the soil, providing us with a useful, natural way to clean contaminated land. Pollution from toxic metals to mine runoff and petrochemicals makes soil harmful and even unusable.
One way to deal with the problem is by brute force – simply remove the soil and put it somewhere else. Obviously, this has serious limitations, including cost and space. Where should the contaminated soil go?
Another solution is to use plants. Plants that can absorb certain toxins may be placed in areas of contamination. Once the toxins are locked in, the plants they can be burned. The resulting ash is light, small, and easy to store. This works well for toxic metals, which are not burned away when the plant is turned to ash.
How Can Plants Clean Soil?
How plants do this may vary depending on the species and toxin, but researchers have figured out how at least one plant absorbs a toxin without damage. Researchers in Australia worked with a plant in the mustard family, thale cress (Arabidopsis thaliana), and found a strain susceptible to poisoning by cadmium in soil.
From that strain with mutated DNA, they figured out that the plants without the mutation were able to safely absorb the toxic metal. The plants take it up from the soil and attach it to a peptide, a small protein. They then store it in vacuoles, open spaces inside cells. There it’s innocuous.
Specific Plants for Contaminated Soil
Researchers have figured out specific plants that can clean up certain toxins. Some of these include:
- Sunflowers have been used to absorb radiation on the site of the Chernobyl nuclear disaster.
- Mustard greens can absorb lead and have been used on playgrounds in Boston to keep kids safe.
- Willow trees are excellent absorbers and store heavy metals in their roots.
- Poplars absorb a lot of water and with it can take in hydrocarbons from petrochemical pollution.
- Alpine pennycress, researchers have discovered, can absorb several heavy metals when soil pH is adjusted to be more acidic.
- Several aquatic plants take heavy metals out of the soil, including water ferns and water hyacinth.
If you have toxic compounds in your soil, contact an expert for advice. For any gardener though, having some of these plants in the yard could be beneficial.
This article was last updated on
Read more about Soil, Fixes & Fertilizers
Soil and Gardening in NYC
Some urban garden sites may have dangerous chemicals or pollutants in the soil. Contaminated soil can pose different health risks depending on the type of contaminants in the soil, the length of time you were exposed and your overall health. Young children are more likely to develop health issues from contaminated soil because they are still developing and are more likely to put soil in their mouths.
You can be exposed to chemicals or pollutants in contaminated soil by:
- Eating food grown in contaminated soil.
- Putting your hands in your mouth after touching contaminated soil.
- Breathing in dust from digging in contaminated soil.
Detox for Contaminated Soil
If your soil has been contaminated with heavy metals like arsenic and chromium in treated lumber or creosote in railroad ties, or with lead and arsenic from iron supplements, or if the contamination is from toxic pesticides like permethrin, MSMA, 2,4-D, Roundup, Sevin or petroleum spills, the solution is the same. No, digging the soil out and hauling it off is not the answer. That just moves the problem from point A to point B.
First, stop the contamination if it continues in any way. The violators need to be put on notice that they are responsible for the contamination and damage. Second, apply fine textured humates or activated charcoal. Fine textured zeolite can be mixed with the carbon products or applied separately. The rates of both products should be at least 20 lbs. per 1000 sq. ft.
The next step is to spray all the foliage and drench the soil in the problem area with Garrett Juice with orange oil (D-Limonene) added at 2 ounces per gallon of mix. The carbon products (humates, compost tea and charcoal) will tie up the contaminants Garrett Juice and orange oil stimulate the microbes to feed on and breakdown the toxic molecules. Liquid molasses is in the Garrett Juice mix but adding additional molasses to the Garrett Juice mixture will help speed up the decontamination process. Adding a beneficial microbe product will speed up the process even more.
To discuss this newsletter or any other topic, tune in Sunday 8am - 11am central time to the Dirt Doctor Radio Show . The call-in phone number is 1-866-444-3478 . Listen on the internet or click here to find a station in your area.
Please share this newsletter with everyone in your address book and all your friends on Facebook and Twitter to help me spread the word on organics.
P.S. Here is an overview about Organic Gardening .
Q: Should plants be removed (asparagus) before treating with the soil detox. P.D., Grandbury.
A: No - the liquids in my detox program function as excellent root stimulators.
Q: Twenty years ago, I built some raised beds and used old crossties for borders. I was an organic gardener, but I was ignorant about the chemicals with which the crossties were treated. I quit gardening 10 years ago, fell from grace on organic, and used chemical fertilizers on the yard. Now, I want to garden again, so I have dug up the crossties and hauled them away. How can I decontaminate the garden site? R.B., Marshall
A: The best product for cleaning the soil is Biogize-SD, an activated charcoal product. Zeolite is the second-best. Follow the label directions for Biogize or hire an organic landscape contractor to apply it.
SOIL DETOX FOR CONTAMINATED SOIL
Digging the soil out and hauling it off is not the answer. That just moves the problem from point A to point B.
If your soil has been contaminated from pesticides or petroleum spills, is contaminated with heavy metals like arsenic and chromium in treated lumber or creosote in railroad ties, or with lead and arsenic from iron supplements, the solution is basically the same.
First, stop the contamination.
Second, apply the activated charcoal product Biogize-SD. It’s very fine-textured and must be mixed with water to apply. Fine textured humates are the next best choice. Zeolite can be applied in a granular form if the budget allows.
The next step is to spray and/or drench the problem area with the Garrett Juice solution plus orange oil or D-Limonene at 2 ounces per gallon of mix. Activated charcoal will tie up the contaminants Garrett Juice and D-Limonene stimulate the microbes to feed on and breakdown the toxins. Liquid molasses is in the Garrett Juice mix but adding additional molasses to the Garrett Juice mixture will greatly help the decontamination process. Adding the microbe product called Bio S.I. will speed up the process.
Activated charcoal is widely used to decontaminate soils from a host of toxic compounds.
The North Carolina Cooperative Extension Service states in Using Activated Charcoal to Inactivate Agricultural Chemical Spills: “Activated charcoal is the universal adsorbing material for most pesticides.” Many golf courses use activated charcoal just for those unforeseen emergencies when fertilizers, pesticides, herbicides, insecticides, miticides and other disease control products are overused. Many agricultural growers use activated charcoal to decontaminate soils after heavy spraying of pesticides and fungicides, prior to reseeding. And many gardeners and homeowners use charcoal for localized soil contamination.
What do my soil test results mean?
- Ask whether metals were extracted using a strong acid.
- If so, you can compare your results directly to the levels reported in the OSU Extension publication EC 1616, Reducing Lead Hazard in Gardens and Landscapes.
- Also see Reducing Lead Hazard in Gardens and Landscapes for recommended gardening practices for different thresholds of lead in the soil.
- The sample test below shows levels of arsenic, cadmium, chromium, copper, lead, nickel and zinc in a homeowner’s soil.
- See the OSU Extension publication EC 1478, Soil Test Interpretation Guide, if you submitted a soil sample for plant nutrition.
How to Have Your Soil Tested
Many state laboratories test soil samples to make gardening recommendations. When the concern is lead, instead of a general soil test, ask for a screening test, which typically costs around $30.
Make sure the lab tests for the total lead content of your soil. Not all state laboratories will perform the required screening test, so you might have to send a soil sample to a lab in an adjacent state, as I did, or to a private lab.
To find a testing lab, consult your local or district extension agent or contact your state’s land-grant university. A lab can provide instructions on how to collect a sample of your soil. Lead can vary greatly even within small areas, so be sure to follow the recommendations for your site.
Growing plants on oil contaminated land
It is well known just how damaging oil can be to nature. It is also well known just how difficult it can be to clean up after a spill or contamination. Removing an oil spill or contamination from soil is hard and requires very different techniques to removing oil from water. A Lithuanian company, Biocentras, together with academic partners from Latvia and Lithuania developed a technique that has so far cleaned over 22,000 tons of soil without the need for potentially harmful chemicals or genetically modified technologies. This natural process transforms contaminated soil so that it can be used again for growing all kinds of plants.
With ever greater pressure on natural resources and legislation to protect all aspects of the environment, taking care of forests and natural landscapes is an important part of business. This importance is even clearer in the oil industry as the impact of spillage and contamination on nature can be severe.
The process of refining oil can create very high levels of contaminated soil. In the industry, this is known as 'sludge'. As might be imagined, this is different to a spill, which is hopefully a one-off event. Depending upon the situation, the soil can either be treated on location or removed and treated if it is in a sensitive area.
A Three Stage Process
A first part of the oil is washed out by using a water solution of biosurfactant, and subsequently separated. The collected oil can even be used again. The biosurfactant solution used in the washing process can be applied up to ten times and is easily biodegraded into a common natural compound.
The oil that is still bound in the soil can then be treated with specially selected micro-organisms to lower contamination concentration to a level when phytoremediation can start.
Phytoremediation consists of decreasing pollutant concentrations in contaminated soils, by growing plants able to degrade to an acceptable level or render harmless the contaminants in the soil.
In total, the process will take approximately one year, depending upon the severity of the contamination and the location. Location is an important factor in the process. As Monika Kavaliauske, manager at Biocentras, explains, "The bacteria used in the process lie dormant in negative temperatures, but then come to life as the temperature rises. However, some organisms can start to degrade oil at temperatures that are only a little more than is required to melt ice. In fact, it is much more effective in warmer climates." With much of the world's oil coming from hot countries, she understandably sees a positive future for the technology developed in the project.
A Natural Solution
Many of the existing solutions for this problem rely on chemicals. For highly contaminated soil, larger amounts of chemicals are required, meaning that the potential for side-effects on the surrounding environment are increased. Other solutions use genetically modified bacteria which have their own potential problems, including a lack of public trust.
In contrast, once the non-genetically modified bacteria have done their work, they simply die and become food to other forms of life. This provides a totally natural solution, known as biodegradation. The role of Biocentras is therefore one of optimising the use of the bacteria to provide the right amount and the best possible conditions. Not only is the process cleaner and more natural, but their internal studies suggests that it is one of the most efficient methods currently available.
The developed technology can be applied to soil contaminated by any concentration of oil or oil products. Usually biodegradation can be effective in 20 to 50 g/kg of pollution, and sometimes up to 100 g/kg. However, Biocentras manages to clean up oil sludge with up to 300 g/kg of pollutants.
The Role of EUREKA
EUREKA played an important role in this project. By helping Biocentras understand how international R&D should be performed, they renewed their laboratory which has led to an ongoing involvement in Europe's scientific and innovation markets.
This involvement includes working with partners based both in Lithuania and Latvia on this project. The Kaunas University of Technology in Lithuania provided assistance from their Environmental Engineering Institute and their Process Control Department, where they helped to optimise most of the treatment processes. While the Latvian State Institute of Wood Chemistry also played a role by participating in the development of the phytoremediation stage.
Currently, this technology is mainly in use in Lithuania. Biocentras has a number of smaller clients and one larger client -- an oil refinery -- which has enabled them to continue their testing and perfecting of the method. They have now successfully treated over 22,000 tons of soil.
Monika Kavaliauske sees the next phase of development as taking the process into the warmer, oil producing parts of the world. She says, "We have no clients in the Middle East and are actively looking for them. There are potential applications for most of the world and we are keen to develop it further."