Methodological considerations regarding the use of inorganic ¹⁹⁷Hg(II) radiotracer to assess mercury methylation potential rates in lake sediment

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• 作者：Soledad Pé ; rez Catá ; n ; Sergio Ribeiro Guevara ; Mark Marvin-DiPasquale ; Cecilia Magnavacca ; Isaac Marcos Cohen ; Marí ; a Arribere
• 关键词：Mercury ; Mercury methylation ; ¹⁹⁷Hg tracer ; Lake sediment
• 刊名：Applied Radiation and Isotopes
• 出版年：2007
• 出版时间：September 2007
• 年：2007
• 卷：65
• 期：9
• 页码：987-994
• 全文大小：181 K

文摘

Methodological considerations on the determination of benthic methyl-mercury (CH₃Hg) production potentials were investigated on lake sediment, using ¹⁹⁷Hg radiotracer. Three methods to arrest bacterial activity were compared: flash freezing, thermal sterilization, and γ-irradiation. Flash freezing showed similar CH₃Hg recoveries as thermal sterilization, which was both 50 % higher than the recoveries obtained with γ-ray irradiation. No additional radiolabel was recovered in kill-control samples after an additional 24 or 65 h of incubation, suggesting that all treatments were effective at arresting Hg(II)-methylating bacterial activity, and that the initial recoveries are likely due to non-methylated ¹⁹⁷Hg(II) carry-over in the organic extraction and/or [¹⁹⁷Hg]CH₃Hg produced via abiotic reactions. Two CH₃Hg extraction methods from sediment were compared: (a) direct extraction into toluene after sediment leaching with CuSO₄ and HCl and (b) the same extraction with an additional back-extraction step to thiosulphate. Similar information was obtained with both methods, but the low efficiency observed and the extra work associated with the back-extraction procedure represent significant disadvantages, even tough the direct extraction involves higher Hg(II) carry over.