Amendment-assisted reduction of lead and cadmium risks in calcareous soil: integrated assessment using DTPA, SBRC and...

Reducing soil heavy metal health risks, via the use of immobilizing agents, can be challenging in high pH, calcareous soils. A contaminated calcareous soil (pH = 8.04, total Cd = 6.34, total Pb = 387 mg kg^-1) was amended with soluble phosphate, bentonite or lime and incubated for 360 d. Then, lead (Pb) and cadmium (Cd) bioavailabilities (RBA) were assessed using a mouse model, heavy metal bioaccessibilities (BAC) were assessed using the Solubility Bioaccessibility Research Consortium, and diethylenetriaminepentaacetic acid (DTPA)-extractable soil heavy metals were determined. Phosphate and lime amendments significantly reduced DTPA-Pb and Cd concentrations. All three amendments significantly decreased Pb and Cd BAC in the gastric phase. Phosphate amendment resulted in 16.0% lower Cd-RBA using liver + kidney as endpoints. The bentonite amendment resulted in 39.9% lower Pb-RBA using liver as an endpoint, and 43.4 and 56.4% lower Cd-RBA using liver and bone Cd as endpoints, respectively. The lime amendment resulted in 27.6 and 25.0% lower Pb- and Cd-RBA using liver and liver + kidney as endpoints, respectively. However, the bentonite and lime amendments resulted in significantly greater bone Pb concentrations and Pb RBA using bone as an endpoint. Significant, positive correlations were found between DTPA-Pb and Pb-RBA using liver as an endpoint, between DTPA-Pb and gastric Pb BAC, and between Pb- and Cd-RBA and BAC. Results indicated that phosphate, bentonite and lime can be used to reduce Cd health risks in metal-contaminated calcareous soils, metal RBA can be potentially predicted using a DTPA extraction and metal BAC results, and may help reclaim heavy metal contaminated, calcareous soils.