Quantification of mercury in soils and sediments – acid digestion versus pyrolysis

Abstract

Mercury (Hg) pyrolysis techniques allow the differentation of Hg-binding forms in contaminated soils and sediments. However, data about reproducibility and accuracy of the results concerning quantification of single Hg-compounds and total Hg-concentrations are rare. Therefore the total mercury concentration of different contaminated soils and sediments determined by using a pyrolysis technique were compared to those obtained after aqua regia digestion and cold vapor atomic absorption spectroscopy Hg detection. Twenty replicates of four soil and two sediment samples containing different Hg-compounds were investigated by both methods. All samples were analyzed without any pretreatment. For most of the samples total Hg-concentrations determined by pyrolysis show lower values, and up to threefold higher relative standard deviation(s) (RSD) than those obtained after wet digestion. Soil samples containing specified Hg-compounds like metallic Hg (Hg⁰) or cinnabar (α-HgS) show by far higher RSD by means of both methods than samples containing only matrix-bound Hg-compounds. Single peak integration indicate that the distribution of Hg⁰ and cinnabar is usually heterogeneous resulting in RSD of up to 85%, whereas RSD of matrix-bound Hg-compounds were always distinctly lower. Besides the higher standard deviation the pyrolysis technique has been found to be reliable for screening contaminated soils and sediments due to the important additional information about occurring Hg-binding forms.