Influence of brown coal on limit of phytotoxicity of soils contaminated with heavy metals
Introduction
High concentrations of heavy metals such as copper, lead, zinc and cadmium, are accumulating in surface layers of soils situated, among other things, in influencing zones of industrial plants. The most contaminated with heavy metals area in Poland is in the south-west region of the country, particularly Legnicko-Głogowski district. Numerous researches conducted on areas neighbouring with Copper–Smelters “Legnica” and “Głogów” have shown the large accumulation of copper, lead, zinc and cadmium in surface layers of soils [1], [2], [3], [4], [5]. Maximum contents of copper and lead, measured within distance less than 1 km from the main emitter, amount to several grams per kilogram of soil. Despite considerable improvement of the air clarity in the last years, soil contamination with heavy metals in the region of mentioned smelters, does not change very much and it can be assumed that for many years it will be the potential threat to whole food chain, and also for ground and surface water and soil microorganisms [6], [7].
Listed metals belong to the group of very high degree of potential threat caused in the biological environment. In the aftermath of the biological accumulation of these metals in each element of the environment, they go to the highest link in the food chain [7]. There exist a few methods of coping with this problem. One of the most popular is phytoextraction—the use of pollutant-accumulating plants to remove metals or organic pollutants from soil by concentrating them in harvestable parts [8], [9], [10], [11], but it seems that the most efficient way to limit biological activity of heavy metals in soils is transferring them into forms hard accessible for plants. Such properties are possessed by organic matter, which can create organometallic relationships, so-called chelates, with heavy metals affecting their accessibility for plants, soil micro-organisms, as well as exerting an influence on metals potential transfer to the ground and surface water. The essential source of supplementing soils in organic matter can be brown coal or fertilizers made on its basis. The raw coal, as well as modified in different ways, delivers material with high degree of humification, relatively resistant to mineralization and with long-lasting activity [12], [13], [14], [15]. Very important advantage of the brown coal is his large resistance to decomposition. It causes that the single use of the brown coal holds raised content of the total coal in soil more than 10 years [16].
The paper determines the possibility of using the brown coal to limit phytotoxicity of soils contaminated with heavy metals. In the research there were used soils received from the area of the Copper–Smelter “Legnica” (I and II zone) and from the Experimental Field of Warsaw Agricultural University (SGGW) in Skierniewice. The soils from I and II zone were highly contaminated with heavy metals (mostly with copper and lead) while soil from Skierniewice had their raised content. Presented paper contains results of the pot experiment: chosen physicochemical and chemical properties of soils and plants properties. In the experience, in order to limit transfer of heavy metals from soils to plants there was used brown coal. For the purpose of examining phytotoxicity of soils and possibility of its limitation by using different doses of brown coal, each year different species of plants were tested.
Section snippets
Materials and methods
The research was made as the pot experiment in the vegetative hall of the SGGW Experimental Field in Skierniewice in years 2001–2003. The experiment was founded in vases of the Wagner type with 5 kg capacity, with four repetitions in completely random system. The experiment included fertilization with six combinations (0, 50, 75, 100, 150, and 175) [g of brown coal pot−1] for soil from I and II zone of the Copper–Smelter “Legnica” and four combinations (0, 50, 100 and 150) [g of brown coal pot−1] for
Results and discussion
Results received in the research showed that single use of the brown coal increasing doses improved properties of examined soils, particularly reaction, hydrolytic acidity, sorptive capacity and organic carbon. It had influence on decrease of solubility (mobility) of heavy metals compounds in soil, and consequently their phytoavailability. From the research it results that together with growth of the brown coal dose grew the sorptive capacity of examined soils (together with growth of
Conclusions
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The use of increasing doses of the brown coal caused following changes in chosen physicochemical properties of examined soils:
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Stabilization of the soils reaction during experiment duration, especially visible after use of highest doses of examined fertilizer.
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Decrease of hydrolytic acidity.
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Improvement of the sorptive properties of soils, and particularly growth of the sorptive capacity, the sum of alkaline cations and the degree of saturation of sorptive complex.
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Growth of the organic coal
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