Geochemical investigations of Hg in urban soil of Idrija town

The presented research deals with urban area of Idrija (3 km2, 6000 inhabitants), where the world's second largest mercury (Hg) mine is situated. The mine was under exploitation for 500 years, leaving behind highly... [ view full abstract ]

The presented research deals with urban area of Idrija (3 km2, 6000 inhabitants), where the world's second largest mercury (Hg) mine is situated. The mine was under exploitation for 500 years, leaving behind highly contaminated surrounding soils. On the basis of systematic soil sampling (9 soil samples per km2, 45 sampling sites, two depths 0-10 cm and 10-20 cm) Hg properties were examined. After aqua regia digestion, the contents of Hg (ARS Hg) were measured. Using Hg thermal desorption Hg binding forms were identified. After water leaching test, water-soluble Hg fractions and after simulated stomach acid extraction, bioaccessible Hg fractions were estimated using ICP-MS. Spatial distribution of Hg properties was examined using GIS software. Regarding all samples, Hg ranged from 7 to 1550 mg/kg. Two binding forms were identified: matrix-bound Hg and cinnabar (HgS). The maximum of 1.2 % of ARS Hg was estimated to be water soluble and the maximum of 3.3 % of ARS Hg was estimated to be gastric bioaccessible. According to national guidelines, the investigated soil is critically polluted with mercury. This raises concern, because investigated soil is often used for vegetable gardening by the local population. Extremely high levels were detected near identified mercury sources (rocks containing mercury ore, mercury ore residue dumps and old roasting sites). Water-soluble Hg may lead to elevated Hg concentrations in edible plants or groundwater, gastric bioaccessible Hg may lead to elevated concentrations of Hg in the target vulnerable groups of population (children and gardeners), who often undergo hand-to-mouth exposure.