Mercury mobility and bioavailability in soil from contaminated area

Abstract

The mobility and bioavailability of mercury in the soil from the area near a plant using elemental mercury for manufacturing thermometers, areometers, glass energy switches and other articles made of technical glass has been evaluated. Mercury has been determined by sequential extraction method and with additional thermo desorption stage to determine elemental mercury. The procedure of sequential extraction involves five subsequent stages performed with the solutions of chloroform, deionized water, 0.5 M HCl, 0.2 M NaOH and aqua regia. The mean concentration of total mercury in soil was 147 ± 107 μg g−1 dry mass (range 62–393), and the fractionation revealed that mercury was mainly bound to sulfides 56 ± 8% (range 45–66), one of the most biounavailable and immobile species of mercury in the environment. The fractions that brought lower contribution to the total mercury content were semi-mobile humic matter 22 ± 9% (range 11–34) and elemental mercury 17 ± 5% (range 8–23). The contributions brought by the highly mobile and toxic organomercury compounds were still lower 2.3 ± 2.7% (range 0.01–6.5). The lowest contributions brought the acid-soluble mercury 1.5 ± 1.3% (range 0.1–3.5) and water-soluble mercury 1.0 ± 0.3% (range 0.6–1.7). The surface layer of soil (0–20 cm) was characterized by higher mercury concentrations than that of the subsurface soil (60–80 cm), but the fractional contributions were comparable. The comparison of mercury fractionation results obtained in this study for highly polluted soils with results of fractionation of uncontaminated or moderately contaminated samples of soil and sediments had not shown significant statistical differences; however, in the last samples elemental mercury is usually present at very low concentrations. On the basis of obtained correlation coefficients it seems that elemental mercury soils from “Areometer” plant are contaminated; the main transformation is its vaporization to atmosphere and oxidation to divalent mercury, probably mainly mediated by organic matter, and next bound to humic matter and sulfides.