title: Chemodynamics of chromium reduction in soils: implications to bioavailability.
abstract: Chromium toxicity in soils can be mitigated by reduction of Cr(VI) to Cr(III) which is influenced by the presence of free Cr(VI) species in soil solution, and the supply of protons and electrons. In this study, the effects of Cr(VI) adsorption (i.e. availability of free Cr(VI) species in soil solution), soil pH (i.e. supply of protons) and three electron donor carbon sources [black carbon (BC), chicken manure biochar (CMB) and cow manure (CM)] on the reduction of Cr(VI) to Cr(III) in soils were investigated. The results indicated that the rate of Cr(VI) reduction decreased with an increase in Cr(VI) adsorption and soil pH, which is attributed to decreased supply of free Cr(VI) ions and protons, respectively. Among the three different amendments tested, BC showed the highest rate of Cr(VI) reduction followed by CM and CMB. Furthermore, addition of BC, CM and CMB decreased the bioavailability of Cr(VI) in contaminated soils. The high efficiency of BC on Cr(VI) reduction was due to the electron donor's functional groups such as phenolic, hydroxyl, carbonyl and amides. The study demonstrated that free form of Cr(VI) ions in soil solution and carbon amendments enriched with acidic functional groups favored the reduction of Cr(VI), thereby mitigating its bioavailability and toxicity in contaminated soils.
authors.affiliation: Centre for Environmental Risk Assessment and Remediation, Building-X, University of South Australia, Mawson Lakes, South Australia 5095, Australia; Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, PO Box 486, Salisbury, South Australia 5106, Australia.
authors.forename: Girish
authors.initials: G
authors.lastname: Choppala
authors.forename: Nanthi
authors.initials: N
authors.lastname: Bolan
authors.forename: Balaji
authors.initials: B
authors.lastname: Seshadri
mesh_terms: D000327:Adsorption; D001682:Biological Availability; D002244:Carbon / Q000737:chemistry; D002606:Charcoal / Q000737:chemistry; D002857:Chromium / Q000737:chemistry* / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry; D006368:Helianthus / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008372:Manure; D010084:Oxidation-Reduction; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D008372:Manure; D012987:Soil; D012989:Soil Pollutants; C540010:biochar; D002857:Chromium; D002606:Charcoal; C074702:chromium hexavalent ion; C000499:ferric oxide; D002244:Carbon
keywords: Adsorption; Bioavailability; Black carbon; Hexavalent chromium; Reduction