First investigation of atmospheric mercury pollution around the chlor-alkali plant of Pieve Vergonte (Italian central Alps)

In this study, the gaseous elemental mercury (Hg0) in air and its bioaccumulation in lichens were investigated in a case study located in the Ossola valley, close to the town of Pieve Vergonte (Italian central Alps), which is heavily polluted by chlor-alkali industrial activity operating since 1915. Atmospheric Hg0 was measured by means of a portable mercury analyzer (Lumex RA-915+) during car surveys and at fixed locations in autumn 2018 and winter 2019. Surveys covered an area of about 10 km2, including the chlor-alkali plant external area and the town of Pieve Vergonte. Results highlight Hg0 concentrations in air always above the typical terrestrial background concentration in the Northern Hemisphere (~1.5-1.7 ng m-3). Maximum values observed are two order of magnitude higher than the background levels and were always measured in the vicinity of the chlor- alkali plant. Samples of lichens were collected around the same area to evaluate the long-term dispersion pattern of atmospheric Hg. Total Hg concentrations in lichens were measured using an Automated Mercury Analyzer (AMA254, FKV, Italy). Results show a North-South gradient of Hg accumulation along the Ossola valley, where northerly winds prevail. Hg concentrations range from 0.143 mg kg-1 d.w. in lichens collected North of the chlor-alkali plant to 0.624 mg kg-1 d.w in lichens collected South of the chlor-alkali plant.