Influence of sediment preservation on total mercury and methylmercury analyses

Estuarine and riverine sediments from four locations showing different sediment structures were analysed as fresh, thawed and lyophilised samples for total mercury (TotHg) and methylmercury (MeHg) concentrations, and results were compared to address effects of sample preservation on Hg speciation. TotHg was measured by cold Vapour atomic absorption spectrometry (CVAAS). MeHg was isolated by distillation and ion-exchange and analysed by cold vapour atomic fluorescence spectrometry (CVAFS) after preconcentration on a gold trap. No loss of TotHg nor MeHg due to lyophilisation was found. Concentrations of TotHg and MeHg respectively ranged from 92 to 267 ng g(-1) dw and 1.1 to 2.9 ng g(-1) dw in fresh samples, from 94 to 215 ng g(-1) dw and 1.1 to 2.8 ng g(-1) dw in thawed samples, and from 100 to 256 ng g(-1) dw and 1.2 to 3.1 ng g(-1) dw in lyophilised samples. Lyophilised samples showed better homogeneity and better MeHg analysis reproducibility compared with wet samples.