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Water as a mild extractant of metals and metalloids from soil samples

Soil is a very complex component of an ecosystem and is highly exposed to potential input of the toxic substances. Soil is a very powerful reservoir of such substances due to its ability to bind various chemicals onto the surface of the soil particles. Trace metals and metalloids are amongst such substances. Potential hazard of an elevated presence of toxic elements in soil lies in the fact that chemical elements, in their various chemical forms, can enter food chain. The main input of the toxic elements into food chain is through their uptake by plants. An assessment of mobility and bioavailability of trace elements that are present in soil requires determination of those elements in soil samples by an appropriate methodology. The most of the methods for trace metals and metalloids analysis in the soils samples, that are described in the scientific literature and present in wide professional practice, consist of a transfer of the analytes into solution with subsequent quantification of the elements in the prepared solutions (extracts or digestates) by mean of some of the atomic spectrometric techniques. Furthermore, the most applied method of transferring of the metals and metalloids into solution includes digestion of the tested soil samples by aqua regia. Such an aggressive digestion medium do not simulate natural conditions in soil and, yielding too high concentrations of the elements in the digestates, does not allow to draw reliable conclusions about mobility of the analyzed elements in soil. Therefore, many researchers are occupied with developing and characterization of the methodologies that would be better in terms of making assessments of bioavailability of the elements of ecological interest. Namely, the use of mild extraction reagents is much more appropriate. This work describes the analysis of 27 selected chemical elements (Al, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Sr, Ti, Tl, V, and Zn) in three selected certified reference materials (CRM) for soil. The extraction of the elements from CRM samples was made by deionized water at room temperature. The reaction mixtures (~1 g soil sample / 10 mL H2O) were shaken on the orbital shaker for 24 h. The samples were filtered (0.45 μm), acidified (HNO3, supra pur, ψ = 1 %), and the concentrations of the selected elements in the prepared extracts were measured by inductively coupled plasma – atomic emission spectrometry (ICP-AES).

soil ; mild extraction ; trace elements ; major elements ; ICP-AES

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