The influence of different factors on heavy metals migration in “soil-plant” system
The level of human impact on the environment is continually increasing, which leads to a chemical contamination of soil with heavy metals. Lead and cadmium are the most toxic heavy metals for living organisms. Thus, the treatment of a soil with the extraction of heavy metals excess is a very urgent task. Phytoremediation is a process to clean the soil from toxins through cultivation of crops, which are able to extract and accumulate harmful substances in a biomass. And this process is a biological cycle. However this modern rapidly developing biotechnology does not possess sufficient knowledge of the nature of the processes.
The aim of this investigation is to establish the regularity of lead and cadmium migration in the "soil-plant” system to extract these metals from contaminated soils.
In the first phase of the work we tried to establish the linking between the level of human impact on soil ecosystem of natural springs and the properties of plants that grow around the territory of the springs. It was concluded that an increase in the extent of human impact on the ecosystem can be measured by the increase in the proportion of ruderal species in the overall composition of the plant families, by stand ruderal plants density, by a significant increase of lead and cadmium in plants.
In the second part of our investigation we tried to establish the influence of different levels of soil contamination on the plants ability to grow and accumulate lead and cadmium in a biomass. Therefore we took plants from different kinds and families. We studied the mechanical and physical-chemical properties of soil. The most resistant to the influence of lead compounds from the soil are oats and mustard. A double decline of their biomass in comparison with a control sample takes place at the concentration of lead which is 70-80 times greater than, for example, for rye.
It is known that the introduction of acids into the soil increases the mobility of heavy metals due to the formation of complexes soluble in water. Thus metals transfer from soil to a plant rises. Therefore, in the third part of our experiment, we decided to examine the effects of different chemical properties of acids (succinic, maleic, acetic, acroleic acids) on the lead and cadmium migration in the "soil-plant" system. All of these acids, except acrylic, are used in food, agricultural, pharmaceutical industry.
The acids reduce the growth of plants in comparison with a control sample. Perhaps the plants are exposed to the adverse effects of acidity or the transition of heavy metals.
Maleic acid showed the least phytotoxic effect of all analyzed acids and contributed significantly to an increase in the transition of heavy metals in plants. Therefore, it will be used in our further studies. In order to neutralize soil acidity, the dolomite flour was used. Trilon B was selected as an activator of plant growth as well. At this moment, the results of the last stage are being analyzed.