The role of Mn and Fe oxides in risk elements retention in soils under different forest types

Abstract

Retention of four selected risk elements (SRE) – arsen (As), cadmium (Cd), lead (Pb), zinc (Zn) – by manganese (Mn) and iron (Fe) oxides in different forest soils was investigated. The abundance of oxides and the association between oxides and SRE were observed in 91 soil samples of different forests divided into 5 categories covering the variability of forests in the Czech Republic. The sequential extraction procedure was used for dissolution of Mn and Fe oxide fractions (MnOF and FeOF) separately and together with the associated elements. It was found that Mn associated with MnOF is significantly higher in deciduous forests. These differences were ascribed mainly to the higher pH and lower DOC (dissolved organic carbon) in deciduous forests. The association of SRE with MnOF declines in the order Cd » Pb › Zn › As and the association with FeOF in the order As ≈ Pb » Cd › Zn. Despite their relatively lesser occurrence, MnOFs were found to be very significant for retention of Cd. FeOF is strongly associated with As and Pb. The category of forest has been identified to influence the amount of SRE retained by oxides especially in two cases: (1) the category of forests on Fluvisols differs from the other categories; (2) the retention of Cd by MnOF or FeOF is larger in deciduous forests compared with coniferous forests.