Methodological considerations regarding the use of inorganic 197Hg(II) radiotracer to assess mercury methylation potential rates in lake sediment.
Methodological considerations on the determination of benthic methyl-mercury (CH(3)Hg) production potentials were investigated on lake sediment, using (197)Hg radiotracer. Three methods to arrest bacterial activity were compared: flash freezing, thermal sterilization, and gamma-irradiation. Flash freezing showed similar CH(3)Hg recoveries as thermal sterilization, which was both 50% higher than the recoveries obtained with gamma-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 (197)Hg(II) carry-over in the organic extraction and/or [(197)Hg]CH(3)Hg produced via abiotic reactions. Two CH(3)Hg extraction methods from sediment were compared: (a) direct extraction into toluene after sediment leaching with CuSO(4) 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.
Pérez Catán
Soledad
S
Laboratorio de Análisis por Activación Neutrónica, Comisión Nacional de Energía Atómica, Centro Atómico Bariloche, 8400 Bariloche, Argentina.
Guevara
Sergio Ribeiro
SR
Marvin-DiPasquale
Mark
M
Magnavacca
Cecilia
C
Cohen
Isaac Marcos
IM
Arribere
María
M
D001419:Bacteria / Q000378:metabolism; D019015:Geologic Sediments; D008631:Mercury Radioisotopes; D008767:Methylmercury Compounds / Q000378:metabolism*; D013696:Temperature; D014873:Water Pollutants / Q000378:metabolism*
D008631:Mercury Radioisotopes; D008767:Methylmercury Compounds; D014873:Water Pollutants