Assessment of heavy-metal contamination of floodplain soils due to mining and mineral processing in the Harz Mountains, Germany

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study area was assessed with respect to its heavy-metal load on the basis of the current guideline values. The heavy-metal loads of the soils in the study area have ranges of <0.2–200 mg kg⁻¹ for Cd, <10–30,000 mg kg⁻¹ for Pb, 7–10,000 mg kg⁻¹ for Cu and 50–55,000 mg kg⁻¹ for Zn. Mobility of the heavy metals was determined by extraction at different pH values. The acid neutralisation capacity (ANC_x) at these pH values was also determined to estimate the probability that the pH can drop to pH=x. The ANC values in the study area ranged from 6 to 3000 mmol H⁺ kg⁻¹, from −33 to 800 mmol H⁺ kg⁻¹ and from −74 to 160 mmol H⁺ kg⁻¹ for ANC_3.5, ANC_5.0 and ANC_6.2, respectively. Together with pedological data, the extraction experiments permit differentiation between soil units that have been placed in the same environmental hazard class on the basis of total heavy-metal loads.