title: Biochar increases arsenic release from an anaerobic paddy soil due to enhanced microbial reduction of iron and arsenic.
abstract: Previous studies have shown that biochar enhances microbial reduction of iron (Fe) oxyhydroxide under anaerobic incubation. However, there is a lack of data on its influence on arsenic (As) release from As-contaminated paddy soils. In this study, paddy soil slurries (120 mg As kg-1) were incubated under anaerobic conditions for 60 days with and without the addition of biochar (3%, w/w) prepared from rice straw at 500 °C. Arsenic release, Fe reduction, and As fractionation were determined at 1, 10, 20, 30, and 60 d, while Illumina sequencing and real-time PCR were used to characterize changes in soil microbial community structure and As transformation function genes. During the first month of incubation, As released into soil solution increased sharply from 27.9 and 55.9 to 486 and 630 μg kg-1in unamended and biochar amended slurries, with inorganic trivalent As (AsIII) being the dominant specie (52.7-91.0% of total As). Compared to unamended slurries, biochar addition increased As and ferrous ion (Fe2+) concentrations in soil solution but decreased soil As concentration in the amorphous Fe/Al oxide fraction (F3). Difference in released As between biochar and unamended treatments (ΔAs) increased with incubation time, showing strong linear relationships (R2= 0.23-0.33) with ΔFe2+and ΔF3, confirming increased As release due to enhanced Fe reduction. Biochar addition increased the abundance of Fe reducing bacteria such as Clostridum (27.3% vs. 22.7%), Bacillus (3.34% vs. 2.39%), and Caloramator (4.46% vs. 3.88%). In addition, copy numbers in biochar amended slurries of respiratory As reducing (arrA) and detoxifying reducing genes (arsC) increased 19.0 and 1.70 fold, suggesting microbial reduction of pentavalent As (AsV) adsorbed on Fe oxides to AsIII, further contributing to increased As release.
authors.affiliation: Laboratory for Agricultural Wastes Treatment and Recycling, Institute of Agricultural Resources and Environment, Jiangsu Academy of Agricultural Sciences, Nanjing, Jiangsu, 210014, People's Republic of China.
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.affiliation: Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian, 361021, People's Republic of China.
authors.forename: Xi-Mei
authors.initials: XM
authors.lastname: Xue
authors.affiliation: Future Industries Institute, University of South Australia, Mawson Lakes, South Australia, Australia.
authors.forename: Albert L
authors.initials: AL
authors.lastname: Juhasz
authors.affiliation: Laboratory for Agricultural Wastes Treatment and Recycling, Institute of Agricultural Resources and Environment, Jiangsu Academy of Agricultural Sciences, Nanjing, Jiangsu, 210014, People's Republic of China.
authors.forename: Zhi-Zhou
authors.initials: ZZ
authors.lastname: Chang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu, 210023, People's Republic of China. Electronic address: hongboli@nju.edu.cn.
authors.forename: Hong-Bo
authors.initials: HB
authors.lastname: Li
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000032:analysis*; D001419:Bacteria / Q000378:metabolism*; D002606:Charcoal / Q000737:chemistry*; D005290:Ferric Compounds / Q000378:metabolism; D005798:Genes, Bacterial; D007477:Ions / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D012275:Oryza; D010084:Oxidation-Reduction; D010087:Oxides / Q000032:analysis; D035261:Plant Components, Aerial; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D012996:Solutions
chemical_list: D005290:Ferric Compounds; D007477:Ions; D010087:Oxides; D012987:Soil; D012989:Soil Pollutants; D012996:Solutions; C540010:biochar; D002606:Charcoal; C021024:ferric hydroxide; D007501:Iron; D001151:Arsenic
keywords: Arsenic functional gene; Arsenic release; Biochar; Fe-reducing bacteria; Paddy soil