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Title: Solubility of lead and copper in biochar-amended small arms range soils: influence of soil organic carbon and pH

Author
item Uchimiya, Sophie
item BANNON, DESMOND - United States Army Center For Health Promotion And Preventative Medicine

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2013
Publication Date: 7/19/2013
Citation: Uchimiya, M., Bannon, D.I. 2013. Solubility of lead and copper in biochar-amended small arms range soils: influence of soil organic carbon and pH. Journal of Agricultural and Food Chemistry. 61:7679-7688.

Interpretive Summary: Biochar is produced by heating crop residues and other agricultural wastes in the absence of air. Biochar has received considerable interests from practitioners to solve various problems related to heavy metals, water retention, and low carbon content of soil. Soil will respond to biochar addition in dynamic way that will change in the time scales of months to years. Underlying principles need to be understood, in order to predict how soil will respond to biochar. This study measured soluble (readily available form to plants) lead and copper concentrations in 7 different contaminated soils amended with different biochars. The results indicated the predictable influence of soil property on the performance of biochar. In addition, biochar can be tailored to achieve desirable outcomes including the mitigation of off-site migration for toxic heavy metals.

Technical Abstract: In situ application of heavy metal stabilizing agents has in some cases increased the mobility of target metal contaminants. Mechanistic understandings are necessary to better predict (1) the dynamic short- and long-term response to soil amendments, and (2) the utility of biochars in nonremoval and removal remedial options. This study exposed seven small arms range soils with known TOC, CEC, pH, Pb content and speciation to consecutive equilibrations in weak acid and acetate buffer over 2 wk period. Biochars were designed to have abundant surface-bound carboxyl and phosphate ligands (PS800) or soluble P (700BL), and were compared with 350 and 500 °C cottonseed hull biochars (CH350 and CH500) and corncob flash carbonization charcoal (corn). In weak acid, the Pb stabilization ability of biochars progressively increased with repeated extraction. In acetate buffer, PS800 and 700BL stabilized Pb, while only PS800 stabilized Cu. Over the course of consecutive equilibrations, acidic, high TOC soil strongly retained Pb and Cu (nearly 100% residual), regardless of biochar amendment. To ensure complete retention of Pb and Cu in sandy soils, 10 wt% PS800 was required. In a striking contrast, CH350, CH500, and corn mobilized Pb and Cu in sandy soils. The results suggest that carboxyl and other specific surface ligands are necessary to complex (through inner-sphere coordination) and stabilize Pb and Cu under acidic pH in the presence of soluble ligand (acetate). On the other hand, biochar-born DOC likely mobilized heavy metals (especially Cu) by forming soluble complexes.