Biochar increases arsenic release from an anaerobic paddy soil due to enhanced microbial reduction of iron and arsenic

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 u...

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Published in:Environmental pollution (1987) 2017-01, Vol.220 (Pt A), p.514-522
Main Authors: Wang, Ning, Xue, Xi-Mei, Juhasz, Albert L., Chang, Zhi-Zhou, Li, Hong-Bo
Format: Article
Language:English
Subjects:
Adsorption
Arsenic - analysis
Arsenic functional gene
Arsenic release
Bacillus
Bacteria - metabolism
Biochar
Charcoal - chemistry
Fe-reducing bacteria
Ferric Compounds - metabolism
Genes, Bacterial
Ions - chemistry
Iron - chemistry
Oryza
Oxidation-Reduction
Oxides - analysis
Paddy soil
Plant Components, Aerial
Soil - chemistry
Soil Pollutants - analysis
Solutions
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Summary: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−1 in 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. [Display omitted] •Biochar was applied to an As-contaminated paddy soil to test its influence on As release under anaerobic condition.•Biochar enhanced As and ferrous Fe concentrations in soil solution, decreased soil As in amorphous Fe/Al oxide fraction.•Increased As release strongly correlated with increased ferrous Fe and decreased As in soil amorphous Fe/Al oxide fraction.•Relative abundance of Fe reducing bacteria and As reducing functional genes increased with biochar amendment. Biochar increases As release from paddy soils under anaerobic conditions due to enhanced microbial reduction of Fe and As.
ISSN:0269-7491
1873-6424
DOI:10.1016/j.envpol.2016.09.095