Speciation of Mercury in the Environment

Abstract

Despite a large number of investigations concerning the distribution of mercury in the aquatic environment, our understanding of the overall dynamics of environmental mercury is still unsatisfactory. This may be mainly because little information is available on the distribution of mercury in the methylated form that is more biologically available for aquatic organisms.

Hence, the work reported here was undertaken to establish a highly sensitive and reliable method for the determination of methylmercury as well as total mercury in various biological and non-biological environmental samples by the combination of dithizone extraction and ECD-gas chromatography. These samples include natural water containing mercury down to parts per trillion levels. The method for methylmercury is based on the fact that methylmercuric dithizonate in the final sample solution is converted into methylmercuric chloride as soon as it is subject to ECD-gas chromatography.

The differences in the composition of the samples determine the pretreatment of the sample for the highest extraction efficiency. Thus, the biological sample, suspended solids and sediment were treated with KOH in ethanol, whereas the water sample was treated with KMnO₄ and sulfuric acid. After pretreatment, methylmercury in the sample was extracted with dithizone in benzene and then back-extracted into alkaline Na₂S solution. The excess sulfide ions were removed by acidification with HC1 and purging with N₂ and methylmercury was re-extracted with a small portion of dithizone in benzene. The extract was washed with NaOH solution and subjected to the conventional ECD-gas chromatography.