Study of metal mobility and phytotoxicity in bottom sediments that have been influenced by former mining activities in Eastern Slovakia

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The aim of this study was to determine the mobility of metals in contaminated sediments in the water reservoir Ružin No.I, which is situated on the Hornad and Hnilec Rivers (Eastern Slovakia). Bottom sediments are contaminated above all by heavy metals, namely As, Cu, Cd, Cr, Hg, Mn and Zn, which were alluvial into the reservoir from localities of former mining activities, and thus they represent ecological load mainly at the inputs into reservoir. The mobilities and solid-state distributions of As, Cd, Cr, Cu, Hg, Ni, Pb, Sb, and Zn ions in impoundment materials were investigated using a five-step sequential extraction procedure. The greatest quantity of Hg was released in the organic–sulfide fraction (F4), in the range of 75.2–87.6 % in both samples. The highest percentage of the total metal content for As, Cr, and Sb was between 82.0 and 94.6 % in the fifth step for both samples also. Cu and Pb were released in the greatest quantities in the third step in the reducible fraction, from 45 to 65.7 % in sample HN and up to 68–50 % in sample HR. High bioavailability was observed for copper, zinc, lead, and cadmium. Nickel, arsenic, antimony, and chromium were only extracted in the residue fraction and displayed low bioavailability. The bioavailability of the metals in the sediments followed the sequence: Cu > Hg > Pb > Cd > Zn > Ni > As > Cr > Sb. The sediment phytotoxicity was evaluated based on the germination of seeds and decreases in the root growth of the plant Sinapis alba. The percentage inhibition of seed germination was 8.9–41.1 % in the 2010–2011 HR samples and 9.1–45.1 % in the 2010–2011 HN samples, which was higher than the inhibition of root growth. In the majority of tested Sinapis alba seeds, the metals displayed no phytotoxic effect. This indicates that the Sinapis alba test still exhibited a strong tolerance to contaminated sediment as this plant species has developed distinct detoxification mechanisms.