Dimensional characterisation of potentially toxic elements present in soil is of crucial importance for determining their actual impact on the environment and understanding the role played by colloidal particles in mobilising pollutants. Recently, a number of measurement determinations have been available for this purpose; nevertheless a single technique is often not exhaustive enough to completely determine particle size distribution and element concentration. The present work concerns the investigation of mercury in soil samples collected from a polluted industrial site. The analytical approach here proposed makes use of sedimentation field flow fractionation (SdFFF) instrumentation coupled off-line to a cold vapour generation electrothermal atomic absorption spectroscopic (CV-ETAAS) technique to achieve the complete Hg characterisation in colloidal soil fractions. In the investigated samples the results demonstrated a predominant presence of Hg in the fraction between 400 and 700 nm. The apparent relation between concentration of Hg and organic matter (O.M.) content in the soil samples seems to be not related to Hg sorbtion to soil O.M. but rather to the presence of colloidal mercuric sulphides particles which size is likely to be controlled by the occurrence of dissolved O.M. This research pointed out how relatively high levels of mercury in the original soil samples can become even more alarming if concentrated in the submicronic fraction.
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