The problem of heavy metals
The cultivation of soils in garden plots and increasing their fertility is directly related to the problem of obtaining environmentally safe fruit and vegetables. On the one hand, there is a technological need for the use of organic and mineral fertilizers, pesticides, on the other hand, there is an uncontrolled technogenic impact on the environment( soil and atmosphere) from industry and transport.
The saturation of the habitat of people with salts of heavy metals is a serious danger. These include: lead, zinc, copper, molybdenum, cadmium, cobalt, mercury, tin, etc. It should be noted that heavy metals, being in small quantities by trace elements, are part of many plant enzymes, but in high concentrations they accumulate and becometoxic to plants and humans. At the same time, physicochemical processes are violated in the soil, the qualitative composition of humus and the entire absorbing soil complex, including microbiological processes, accumulates toxic compounds, which ultimately leads to a decrease in soil fertility. The flow of heavy metals into plants depends on the acidity of the soil, the content of humus, the mechanical composition of the soil, the conditions of moistening, and other factors.
The main sources of heavy metals entering the environment are:
- emissions from ferrous and non-ferrous metallurgy, thermal power plants, and motor transport;
- chemical means of protection against pests and diseases;
- unconventional forms of fertilizers - sapropels, sewage sludge, composts from urban garbage and wastes of various industries,
Technogenic contamination of soils, plants and products is subject to a greater degree of personal and horticultural plots, as they are located in a suburban area or nearhighways. The plants grown here accumulate heavy metals and, depending on the degree of soil contamination, can reduce productivity. For example, yield losses of berry crops reach 80-95%.And of course, such products will contain heavy metals in hazardous quantities.
To address this issue, the horticulturist and gardener should take a reasonable position scientifically based application of chemical means. This applies, first of all, to the observance of recommended doses of fertilizers and pesticides, as well as their forms.
The difficulty of releasing soils from the excess of heavy metals is aggravated by the fact that they persist in the soil for a long time, despite the extremely slow processes of natural self-purification. Experiments of the All-Russian Selection and Technological Institute of Horticulture and Nursery have shown that the "cunning" of heavy metals lies behind the fact that to a certain level of their content in the soil( for example, lead on strawberries and cadmium on the currant) there are no negative symptoms in appearanceplants. Even, on the contrary, there is a more "magnificent" growth of these plants. However, if the level of soil contamination with lead is 500 mg / kg, which is safe for strawberries, the berries were unfit for consumption for hygienic reasons.
The problem of reducing the supply of toxic substances to plants can be solved through multifaceted complex measures. Currently, all the known methods of detoxification( liberation) of soils contaminated with heavy metals can be divided into three groups.
1. Radical
A) Complete removal of contaminated soil and replacement with "clean" or specially treated. Reception is used for local contamination in a limited amount.
B) Transition to growing plants in protected soil( to prevent atmospheric emissions from entering the soil).
2. Biological
A) Using the adaptive capabilities of plants. For example, those that do not accumulate heavy metals in edible parts, or those that are relatively resistant to them. Thus, currants and raspberries suffer less from excess lead, strawberries and currants from excess copper, cherries from excess cadmium.
B) The use of plant-concentrates of heavy metals for the regular removal of their aboveground and underground masses, as well as special microorganisms that absorb heavy metals and thereby make them inaccessible to plants.
B) Use of "metal-resistant" varieties. The assessment of black currant varieties by the accumulation of heavy metal salts in berries showed, for example, in the grade Minai Shmyrev, a decrease in the content of zinc and copper by a factor of 10 compared to the grade Ershistaya, and of nickel and lead by 3 and 14 timescompared with the variety of Orlovia.
3. Physicochemical
Techniques affect the mobility of heavy metals and exclude them from the biological circuit or convert them into readily soluble and mobile forms. These include:
A) Washing of contaminated soil, for example, calcium nitrate or the introduction of soluble iron salts( ferric chloride) to remove from the soil copper, cadmium, chromium, manganese, nickel.
B) Change in soil acidity( up to optimum for each crop) by liming and increasing the humus content to reduce the toxicity of heavy metals due to their binding to organometallic complexes inaccessible to plants.
B) Application of mineral fertilizers( in rational doses).Their effectiveness in many ways depends on the content of humus in the soil. A peculiar "bar", passing through which sharply increases the return on mineral fertilizers, is 2%.Therefore, for the replenishment of humus in the soil, regular application of organic fertilizers is necessary, remembering that on an average on soddy-podzolic soils, an increase in the humus content by 0.1% gives a dose of 1 kg / m2.
Balanced nutrition of plants with the help of mineral fertilizers, in addition to the direct function of ensuring the vital activity of plants, also affects the behavior of heavy metals.
Thus, the introduction of nitrogen fertilizers reduces the toxicity of lead, copper and arsenic;phosphoric fertilizers - lead, copper, cadmium, nickel and zinc;Potassium fertilizers( in high doses) - radiocesium.
D) Detoxification of soil contaminated with heavy metals, using natural and artificial sorbents. Among the tested and effective sorbents are zeolite tuffs( 5% of the mass of the soil), lime( 1 kg / m2), peat( 20 kg / m2), which completely eliminate phytotoxicity and quality deviations of currant and strawberry. A number of sorbent meliorants based on zeolite tuffs and sapropel( Nara-1, Nara-2 and others) show an increase in the detoxification effect by several times in both mono- and complex soil contamination with cadmium, lead, copper.
Thus, most of the above methods are aimed at increasing soil fertility.
And therefore it can be considered proven that the more fertile the soil, the less heavy metals and other toxic substances can enter the plants and the purer the product from them.