Calcium amendments affect heavy metal bioavailability in acidic and calcareous soils

Assessing the effects of calcium-containing amendments on heavy metal availability in metal-polluted, varying pH soils, is essential for remediation purposes. An acidic and a calcareous heavy metal-polluted soils were amended with lime (calcium hydroxide), calcium nitrate or calcium chloride, and then, heavy metal bioavailability was assessed using the metal hyperaccumulator Sedum plumbizincicola along with a DTPA extraction, a soil bioavailability index. Lime amendment resulted in decreased soil DTPA-extractable heavy metal concentrations in both soils (54.5 and 15.7% lower than the control in the acidic and calcareous soil, respectively), increased plant yield and decreased shoot accumulation of most metals. Calcium nitrate and calcium chloride amendments resulted in elevated soil pH in the acidic soil while those resulted in decreased pH in the calcareous soil, both resulting in decreased plant yield and elevated plant shoot heavy metal concentrations in both soils. The calcium chloride amendment also resulted in elevated soil DTPA-extractable Cd, Zn and Mn concentrations (32.5–350% greater than the control) and elevated shoot Cd, Zn and Mn concentrations (11.1–351%) in both soils. Choosing the correct calcium amendment for heavy metal-contaminated soils, while considering soil pH, is obviously important for successful remediation purposes.