Biochar-impacted sulfur cycling affects methylmercury phytoavailability in soils under different redox conditions

Yongjie Wang, Yue Zhang, Yong Sik Ok, Tao Jiang, Peng Liu, Rui Shu, Dingyong Wang, Xinde Cao, Huan Zhong

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Recently, there has been increasing interest in reducing methylmercury (MeHg) phytoavailability using biochar, although the underlying mechanisms are not fully understood. By combining lab-scale batch incubation with pot and field validations, we demonstrate that biochar-impacted sulfur cycling in soils and MeHg-soil binding play key roles in controlling MeHg phytoavailability. (1) Under anoxic conditions, biochar-associated sulfate and biochar-facilitated microbial sulfate reduction enhanced the production of reduced inorganic sulfur species as acid-volatile sulfide (AVS) in soils by 122%, facilitating MeHg binding with soils and thus reducing MeHg phytoavailability. (2) In contrast, under oxic conditions, the reduced inorganic sulfur was oxidized (resulting in a 68–91% decrease in AVS), which released soil-bound MeHg and increased MeHg phytoavailability. The proposed mechanisms could explain the distinct effects of biochar amendment on MeHg bioaccumulation observed under anoxic (10–88% lower in rice grains) and oxic conditions (48–84% higher in wheat grains). Our results dispute the commonly held assumption that reduced MeHg phytoavailability under biochar amendment can be primarily attributed to MeHg-biochar binding. Therefore, the potential increased risk of MeHg in oxic soils following biochar amendment should be evaluated in more detail.

Original languageEnglish
Article number124397
JournalJournal of hazardous materials
Volume407
DOIs
Publication statusPublished - 2021 Apr 5

Keywords

  • Bioavailability
  • Mercury
  • Rice
  • Soil remediation
  • Wheat

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution
  • Health, Toxicology and Mutagenesis

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