There is an enourmous amount of metal-contamined, non-ferrous soils all around our globe. The concept of soil pollution has been around for decades, and it became one of our biggest problems next to other vital global issues. It is greatly harmful for the plants thereby for us too. Unfortunately, in the last few years, the amount of metal-contamined soils have drastically increased.
A research about Arundo in a non-ferrous mining and smelting area was carried out in Southern China, in which there is a confirmation that Aroundo Donax (giant reed) is one of the best, most sustainable, and profitable perennial energy crop on the market right now.
What does metal-contamined soil means, and why is it dangerous?
In China, nearly 2 million hectares of soil has been contamined by Cd (Cadmicum) and Pb (lead). Anthropogenic (human) activities such as the expandation of heavily polluting and rapidly growing industrial areas, mining, using pesticides, firing, smelting, were the main reasons why lots of tillable soils are ruined, and became marginal lands. However, metal-contamined soils are a subclass of soil pollution, because it means that the soil contains toxic heavy metals such as lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), mercury (Hg), and nickel (Ni).
Metal-contamined soils are as dangerous for humans as they are for plants. Soil is called the „kidney” of planet Earth, our home. The toxic heavy metals can trickle through the soil and get to our water supply, which is not infinite. In addition a few of the metals listed above can cause cancer and other health problems.
How can plants remediate metal-contamined soil?
Phytoremediation is a bioremediation process that uses various types of plants to remove, transfer, stabilize, and/or destroy contaminants in the soil. There are several different types of phytoremediation mechanisms. For instance, plant roots absorb the contaminants along with other nutrients and water, this is called Phyto-accumulation. Or there is a nother type of phytoremediation called: Phyto-degradation – In this process plants actually metabolize and destroy contaminants within plant tissues. Also there is a very unique type of phytoremediation, and it is named Phyto-volatilization, and in this process, plants take up water containing organic contaminants and release the contaminants into the air through their leaves.
How was the Chinese research carried out?
The research was carried out by the Central South University of China. They planted 1 plant/m2 in a 140m2 plot in heavily metal-contamined soil. Sampling sites were chosen in the immediate vicinity of mine tailings or smelting areas to make the research much more accurate. Every July between 2013-2017 they collected the plants, and the soil samples to find out more later in the laboratory. In total 174 samples were collected. 87 Arundo samples, and 87 potential metal-contamined soil samples.
Soil samples were dried at room temperature in the lab, and sieved successively for heavy metal analysis, whilst the Arundo samples were washed with distilled and tap water. The leaves, and stems were kept under 4°C for biochemical analysis and then dried in 105°C and 60°C successively. They went under a heavy metal analysis too. After that, soil samples were digested in a microwave digester (MDS-8G, Xinyi Company) from 130°C to 220°C. When it cooled down, the digested solution was filtered into a 50 Ml volumetric flask. The Cd (Cadmicum) and Pb (lead) contentracions in the digested solutions were measured by atomic absorption spectometry (AAS-6800).
Afterwards they made measurements on the Arundo itself: cellulose, chlorophyll content were measured by applicating several acids to the plants. Thenceforth the plants went under an analysis to show genetic comparisons amongst ecotypes, and the DNA samples were extracted from the giant reed using the E.Z.N.A.® plant DNA kit.
Results and conclusion
In the typical mining and smelting area of southern China the soil organic matter content was at a minimum of 1.74 g/kg and a maximum of 43.8 g/kg. The minimum soil Ph 2.5 and the maximum was 9.59. 525 mg/kg was the maximum and 47.3 mg/kg was the average Cd (Cadmicum) content of the. For Pb (lead) The maximum and average soil Pb content was 57164 mg/kg and 2828 mg/kg.
The maximum and average content of Cd (Cadmicum) in Arundo samples were 57164 mg/kg and 2828 mg/kg, and the maximum and average content of Pb (Lead) in Arundo samples were 111 and 12.3 mg/kg.
So in conclusion, the amount of Cd (Cadmicum) in soil was decreased by 7% and the amount of Pd (lead) in soil also decreased by 1.22%. Overall, these results are mindblowing, and one’s should consider using Arundo (Giant Reed) for phytoremediation uses too, next to other countless profitable uses such as: Biomass, Bioethanol, Biofuel, Furnitures.