Mercury distribution and speciation in historically contaminated soils of the Isonzo River Plain (NE Italy)

Purpose Mercury (Hg) mining has negatively impacted the environmental quality of the entire Isonzo/Soča River basin (NE Italy and NW Slovenia), which suffers from a high degree of contamination. This study aims to expand the knowledge on Hg distribution in soils, assess the degree of contamination and apply statistical methods for management purposes. The Hg speciation in soils and the determination of gaseous elemental mercury (GEM) could be useful for an environmental risk assessment of the area. Materials and methods Surface and subsurface soil samples ( n = 262) were collected for total Hg and selective sequential speciation ( n = 36) following the ISO ( 2005 ) guidance for the determination of the pedo-geochemical background and background values for inorganic and organic substances in soils. Total Hg was measured according to the US-EPA 7473, and speciation was conducted following the five-step method proposed by Bloom et al. (Anal Chim Acta 479:233–248, 2003 ). GEM was measured during field-work operations. Statistical analysis was performed in order to have a preliminary evaluation of the whole dataset and distinguish the pedo-geochemical areas and differences between surface and subsurface Hg background levels for management purposes using EXCEL™ and PAST statistical programs. Results and discussion Total Hg concentrations ranged from the natural background (