METALS like gold, silver, platinum, copper, tin and iron are mined mostly in the mountains or below ground. Mining can potentially damage ecosystems or pollute water bodies if done improperly or irresponsibly. This is the reason why mining is a sensitive environmental issue. But now, there is an alternative way to safely "mine" some metals from a very unusual source -- plants!
There are plants called hyperaccumulators which are known to take up metals into their stems, leaves and even seeds without being poisoned. Why do these plants "eat" and accumulate metals in their bodies? One possible explanation is for self-defense against their natural enemies like herbivores.
An example of a hyperaccumulator is Pycnandra acuminate. According to Wikipedia, It is a rainforest shrub, endemic to New Caledonia, and is adapted to the nickel-rich ultramafic soils found there. It absorbs nickel from the soil and concentrates it within the plant to a concentration of up to 25 percent nickel citrate as dry weight of the sap, which is blue in color due to the nickel content.
In the Philippines, a shrub called Rinorea niccolifera was discovered in Zambales by Dr. Edwino Fernando of the University of the Philippines Los Baños (UPLB) as a plant that accumulates nickel up to 18,000 ppm in its leaves without itself being poisoned. The UPLB team has already discovered more than 20 new hyperaccumulator species in the country. There are only about 450 species of known hyperaccumulator plants in the world.
Extracting the accumulated metals in these plants is called phytomining. According to kiwiscience.com, the first phytomining experiments were carried out by Larry Nicks and Michael Chambers at the US Bureau of Mines, Reno, Nevada using the nickel (Ni) hyperaccumulator Streptanthus polygaloides. It was found that a yield of 100 kg/ha of sulphur-free Ni could be produced. Farming these hyperaccmulators and harvesting their metal-rich biomass is called "agromining."
Hyperaccumulators are also used to clean mining sites, or other contaminated sites. This process is called phytoremediation. While phytomining is relatively new, the use of plants for phytoremediation has been going on for many years. When I was managing a wastewater treatment plant many years ago, I was told that water hyacinths can absorb metals in water and soil. This was actually proven by research.
Hyperaccumulators can even be used even to clean up nuclear sites. After the Hiroshima, Fukushima, and Chernobyl nuclear accidents, sunflowers were planted on the contaminated land to help absorb toxic metals and radiation from the soil. Sunflowers were used near Chernobyl to extract radionuclides cesium 137 and strontium 90 from contaminated ponds.
Another reason why we should plant trees.
March 12, 2020
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