Lead immobilization in simulated polluted soil by Douglas fir biochar-supported phosphate

Article Authors: Arwenyo Beatrice a d, Jac J. Varco b, Andrew Dygert b, Felix S. Atsar a, Sabrina Solomon a, Rooban Venkatesh K.G. Thirumalai c, Charles U. Pittman Jr. a, Todd Mlsna a


This study compared the lead (Pb2+) immobilization efficacy of biochar-supported phosphate to conventional in-situ heavy metal immobilization methods (with lime, neat biochar and phosphate). The biochar-supported phosphate was obtained by treating Douglas fir biochar (BC) with anhydrous calcium chloride and potassium dihydrogen phosphate. The amount of Pb2+ immobilized was determined by comparing the concentration of ammonium nitrate extractable Pb2+ lead from lead-spiked soil (without amendment) to that of a 30 d incubation with (a) lead-spiked soil plus 5% (wt./wt.) biochar supported-phosphate, (b) lead-spiked soil plus 5% (wt./wt.) untreated Douglas fir biochar, (c) lead-spiked soil plus 5% (w/w) lime and (d) lead-spiked soil plus 5% (wt./wt.) potassium dihydrogen phosphate. The control (lead-spiked soil without amendment) produced the largest quantity (96.08 ± 9.22 mg L−1) of NH4NO3-extractable Pb2+, while lead-spiked soil treated with 5% (wt./wt.) biochar-supported phosphate resulted in the lowest quantity of NH4NO3 extractable Pb2+ (0.3 ± 0.2 mg L−1). The mechanism for immobilization of Pb2+ by BP occurs at pH < 7 through dissolution of hydroxyapatite embedded in BP during modification, followed by precipitation of insoluble Pb10(PO4)6(OH)2. The residual lead fraction in the lead-spiked soil increased by 20.9% following amendment with BP. These results indicate that biochar-supported phosphate is a candidate to reduce lead mobility (bioavailability) in polluted soil. This amendment may lower Pb2+ uptake into plants while minimizing the potential for water contamination due to Pb2+mobility.

Bibliographical metadata

Journal Chemosphere
Volume 292
DOI 10.1016/j.chemosphere.2021.133355
Related Faculties/Schools

a bDepartment of Plant and Soil Sciences, Mississippi State University, Mississippi State, MS, 39762, USA
cInstitute for Imaging & Analytical Technologies, Mississippi State University, Starkville, MS, 39762, USA
dDepartment of Chemistry, Gulu University, P O Box 166, Gulu, Uganda