Journal of Soil and Groundwater Environment (한국지하수토양환경학회지:지하수토양환경)

Korean Society of Soil and Groundwater Environment (한국지하수토양환경학회)
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pH Dependence of CH3Hg+-binding Sites in Humic Acid: An X-ray Absorption Study

pH에 따른 부식유기산의 메틸수은 결합 리간드 변화: X-선 흡수분석

  • Yoon, Soh-Joung (Mineral Resources Research Department, Korea Institute of Geoscience and Mineral Resources) ;
  • Bleam, William F. (Department of Soil Science, University of Wisconsin)
  • 윤소정 (한국지질자원연구원 광물자원연구실) ;
  • Received : 2011.12.16
  • Accepted : 2011.12.22
  • Published : 2011.12.31
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Abstract

Mercury accumulates in biota mainly as methylmercury. In nature, methylmercury shows high affinity to organic matter and $CH_3Hg^+$-organic matter complexation affects the mobility and bioavailabiity of methylmercury. In this study, we examined the methylmercury binding sites in an aquatic humic acid as affected by the pH condition using Hg $L_{III}$-edge extended X-ray absorption fine structure (EXAFS). We evaluated methylmercury binding humic ligands using methylmercury-thiol, methylmerury-carboxyl, and methylmercury-amine complexation models. When $CH_3Hg^+$-to-humic reduced sulfur ratio is 0.3, we found that most of $CH_3Hg^+$ binds to thiol ligands at pH 5 and 7. At pH 7, however, some carboxyl or amine ligand contribution is observed, unlike at pH 5 where $CH_3Hg^+$ almost exclusively binds to thiol ligands. The carboxyl or amine ligand contribution may indicate that some types of thiol ligands in the natural organic matter have relatively low complexation constants or acid dissociation constants compared to those of some carboxyl or amine ligands. Analysis results indicate that ~0.2 fraction of methylmercury binds to amine or carboxyl ligands and ~0.8 to thiol ligands at pH 7.

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References

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