Abstract
A critical appraisal of single-step extraction procedures of chromium species from soil was done in terms of their selectivity towards Cr(III) and Cr(VI) species. Samples of natural mineral and organic soil and samples of soil enriched with different chromium compounds of various solubility (in liquid or solid form) were used to simulate contamination of soil by liquid and solid wastes. The efficiency of extraction of Cr(III) and Cr(VI) species with various reagents, e.g. acetic acid, chelating agents (EDTA, DTPA) or inorganic salts (phosphates and carbonates), was evaluated on the basis of recovery results obtained for enriched samples. None of used reagents allow for quantitative extraction of added Cr(III) form. Procedures based on extraction of soil with Na2CO3 at room and elevated temperature (90–95 °C) were suitable for extraction of Cr(VI) species from mineral soil, whereas for organic soil, the procedure based on extraction with Na2CO3 at room temperature was recommended. The developed extraction procedures were validated using certified reference material (CRM 041 soil) and applied for analysis of contaminated soil samples. The studies showed that the physical state of waste, initial form and oxidation state of chromium and soil properties influenced the final chromium species and their mobility in soil, which have an impact on contamination of environment. The analysis of contaminated soil samples from a tannery area showed that the share of Cr(VI) was very low (only 0.8–4.5%) despite the high total content of chromium, which confirmed that chromium was present in immobile forms.
Highlights
Chromium occurs in the environment mostly in two species, i.e. as a trivalent (III) and hexavalent (VI) form
The mass of chromium extracted from mineral and organic soil spiked with different trivalent and hexavalent compounds of chromium was determined, and recoveries were calculated (Table 2)
The efficiency of chromium extraction was higher from organic soil (0.3–13% of its total content) than from mineral soil (0.3 to 4.4%) (Fig. 1c)
Summary
Chromium occurs in the environment mostly in two species, i.e. as a trivalent (III) and hexavalent (VI) form. It was shown that Cr(III) plays a key role in chromium allergy and causes DNA damage in cell-culture systems (Vincent 2010). Chromium can enter the environment both from natural and anthropogenic sources, e.g. via electroplating, leather tanning and the textile industries (Avudainayagam et al 2003; Johnson et al 2006; Unceta et al 2010; Dhal et al 2013). Anthropogenic emission of chromium to the atmosphere is substantial and was estimated at 336 t in the European Union in 2013 (EEA Technical report 2015), 2700–2900 t in the USA and 21,000 t in China in 2009 (Cheng et al 2014).
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