Determination of methylmercury in sediments by steam distillation/aqueous-phase ethylation and atomic fluorescence spectrometry

A method is described for the determination of methylmercury in natural sediment samples using steam distillation followed by aqueous phase derivatisation and gas chromatography-atomic fluorescence spectrometry. Recoveries of methylmercury spikes to wet sediments were >95% except for an industrially-contaminated, sulfidic sediment (76% recovery). The method precision was typically <10% relative standard deviation for unspiked sediment samples having methylmercury concentrations ranging from 0.6 to 76 ng/g. The detection limit was approximately 0.01 ng/g for 1 g of wet sediment. The method was assessed for artefactual methylation of added inorganic mercury spikes (1-10 mu g) Artefactual methylation ranged from unmeasurable to 0.05% of added inorganic mercury in one tropical lake sample. The results obtained with the proposed procedure for two reference sediment materials were significantly lower than literature reported values obtained by nitrogen-assisted distillation and were comparable with data obtained using low artifact producing solvent extraction procedures. Method throughput of the steam distillation step was four to five samples per hour which represents a considerable improvement over existing distillation methods. (C) 2000 Elsevier Science B.V. All rights reserved.