Accumulation of heavy metals in the Oostriku peat bog, Estonia: Determination of binding processes by means of sequential leaching

The Oostriku peat bog (central Estonia) has been exposed to metal-rich groundwater discharge over a long period of time and has accumulated high concentrations of Fe (up to 40 wt-%), heavy metals (e.g. Pb, Zn, Mn, Cu), and As. In this study, the peat was characterised with respect to composition and metal content with depth. The peat pore water was analysed and compared to a spring water emerging at the site. Sequential extraction, using a Tessier scheme optimised for iron-rich sediments, was used to understand the relative roles of binding mechanisms involved in the retention of different metals in the peat. Significant difference in depth distribution was found between different metals bound in the peat, which was partly attributed to varying compositions of the peat with depth and different dominant binding mechanisms for different metals.