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 sed iment samples using steam distillation followed by aqueous phase derivatisa tion 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 t ypically <10% relative standard deviation for unspiked sediment samples hav ing 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 (1-1 0 mu g) Artefactual methylation ranged from unmeasurable to 0.05% of added inorganic mercury in one tropical lake sample. The results obtained with th e proposed procedure for two reference sediment materials were significantl y lower than literature reported values obtained by nitrogen-assisted disti llation 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 imp rovement over existing distillation methods. (C) 2000 Elsevier Science B.V. All rights reserved.