Distribution of Al and Heavy Metals in Bulk Soil and Aggregates at Three Sites Contaminated by the Emissions of a Central Slovak Al Smelter

Abstract

Organic layers, bulk soil, and aggregates of A and B horizons were sampled at 3 locations along a forested (Fagus sylvatica L.) slope near an Al smelter at microsites affected and not affected by stemflow. Soil properties (pH, texture, ECEC, BS, SOC) were determined and Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in the mineral soil samples were partitioned into 7 fractions. High total concentrations of Cd (0.87–1.34 mg kg^-1), Cu (26.1–53.3), Mn (800–4200), Ni (9.7–32.0), Pb (91.5–108.8), and Zn (95.5–148.4) in the organic layers indicated atmospheric contamination. Decreasing Cd, Cu, Ni, and Zn concentrations as distance to the smelter increased identified the smelter as the point source. The concentrations of heavy metals in the mineral soil were low: Cd: 0.06–0.23 mg kg^-1, Cu: 3.8–15.4, Mn: 100–800, Ni: 1.4–5.9, Pb: 23.9–49.6, and Zn: 11.3–44 which may be explained by low pH and sorption capacity and may additionally be affected by probably high fly ash and F inputs. Lower strongly bound heavy metal percentages in the A than in the B horizons although pH was the same indicated that airborne metals were less strongly bound than lithogenic ones. The stocks of lithogenic metals were lower, those of airborne metals were higher at microsites affected than not affected by stemflow. This probably is the result of enhanced leaching of lithogenic metals due to the higher water flux and of additional atmospheric metal input due to the collecting effect of the bark. The heavy metal concentrations in bulk soil are up to 80% higher than in aggregates indicating that deposited heavy metals are bound preferentially to interaggregate soil material.