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Tips from the Compleat Gardener: Phytoremediators refresh the land


For months now it seems one cannot watch the news without seeing stories about floods, cars floating away, septic systems and toxic waste dumps all making contributions to the rushing water enroute to the rivers, the oceans of our communities, washing over formerly clean land, soaking in.

Eventually the waters will recede, homes will be cleaned, ruined things hauled away, but what about the land? The plant kingdom stands ready to help, an army of phytoremediators ready for deployment.

Phytoremediation is defined as the use of various plants to remove, transfer, stabilize or destroy contaminants in soil or water. Heavy metals have been in our environment since the beginning of mining and have steadily increased as the waste products of manufacturing and the exhaust from use of fossil fuels. Classic remediation involves removing contaminated soil to a landfill which is expensive and the contaminant persists just somewhere else. Putting certain plants to work is less expensive and fairly effective.

There are several methods through which phytoremediation occurs: phytoextraction, phytomining, phytostabilization, phytodegradation, phytovolitilization and phytostimulation. Different plants do different things to make our world cleaner and their use is getting increasingly more common.

Phytoextraction occurs when a plant draws a substance up out of the soil into its green structure. A plant that does this is called a p-accumulator and if it takes up a large amount of a contaminant a hyper-accumulator.

Certain common plants are excellent at drawing up heavy metals, such as the members of the mustard family, the braissicas, spinach, lettuce, turnips, carrots, radishes and zucchini to name a few.

If you are using these plants to clean the soil you would bring them to maturity, harvest and incinerate and the ash can yield enough of the metals to pay for the process. If you are eating these plants from an unknown source be aware what might be in the salad.

One of the best plants to have if radioactive waste is your problem is the annual sunflower, Helianthus annus, which also draws up arsenic and stores the contaminant in its roots. To remove it from the soil the plants should be uprooted and transferred to a radioactive containment area. White clover and corn are also accumulators of radioactive waste as well as members of the carrot or parsley family and the legumes. Another reason to know the source of your food.

Certain trees will also absorb radio nuclides; larch, sweet gum, (Liquidamber styraciflua), the tulip and the spruce, which stores it in the bark. I know that lichen often covering trees in the Northeast also is a major absorber of radioactive contamination. This was discovered when people who live on reindeer meat were found to have high levels in their bodies. In the regions affected by the Chernobyl nuclear disaster the lichen were found to contain high levels of radioactivity, the reindeer eat lichen and the cycle continues.

If the contaminant is an organic compound like pesticides and herbicides the willow family stands ready to help by absorbing, using some of the metals to feed microorganisms, which then degrade the toxin.

The willows have extensive root systems that filter water. The family name Salix, comes from the Celts sai lis, by water, and they grow best in wet places where they filter lots of water, a way to locate a river or stream in the wild. The bark was the original source of aspirin, salicylic acid .

Poplar trees are also good at phytoremediation, drawing in and transforming products perhaps used on nearby fields. Use the hedgerow for the working trees, they may not be the handsomest specimens or if given room can be quite elegant but they feed and shelter wildlife and remove toxins from the environment.

More to come.

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