Heavy metals contamination of post-mining mounds of former iron-ore mining activity

Abstract

The main question of the present study is how much are the former post-mining mounds (PMM) - the ancient remnants of mining of a provisional nature located in forest areas-contaminated by heavy metals (HM). To investigate if the PMM contain HM, we collected 15 soil samples from PMM and, for comparison, 15 from the surroundings - all these samples (30) were collected from a depth of 5–30 cm by soil auger. To find how deep the contamination of HM goes, we did 4 soil profiles to the depth 100 cm in four randomly selected PMM. In every soil profile, 4 soil samples were collected (16 soil profile samples). In total, 46 soil samples were analysed. Concentrations of HM were measured using spectrophotometry. Our results indicate the following: (1) PMM are not much contaminated by HM - only two (Fe and Mn) from nine HM significantly exceed the limits - the order of abundance of the studied HM is as follows: Fe > Mn > Cr > Zn > Ni > Cu > Pb > Co > Cd; (2) PMM are more contaminated by heavy metals than their surroundings; (3) within PMM, overburden is much more contaminated by HM than paleosols; (4) the rate of penetration of HM into the depth of the soils (into paleosols) is reduced due to the properties of the overburden of PMM.