Mercury distribution in environmental matrices (water, air, sediment) at former mining sites: the case study of the “Argento Vivo” mine (Levigliani, Apuan Alps)

Abstract: The toxicity of mercury in its various forms is a widespread issue in a framework of steadily increasing anthropization and global change. Although its pervasiveness in the environmental matrices (air, water, sediment) is a cause of great concern, a comprehensive understanding of mechanisms and processes that regulate its spread and diffusion is still a challenge. In this regard, abandoned or disused mining sites are certainly of interest, as the release of Hg into the environment may continue even decades after the end of excavation, processing, and production works. In Tuscany, besides the well-known and most productive areas of Monte Amiata, other mining sites have been exploited in the Apuan Alps since the Middle Ages, where Hg-rich ore deposits belonging to the Apuan Metamorphic Complex occur (Dini et al., 2001). One of the oldest mining excavations is the native mercury and cinnabar “Argento Vivo” mine of Levigliani, consisting of (i) a series of tunnels and descending galleries of various sizes and lengths, which are partially included in tourist tours, and (ii) an external area dedicated to the processing of the extracted material. The present study focuses on the characterization and quantification of mercury dispersed in air, water, and sediments in and around the mining area, with the aim to evaluate the environmental impact. Two surveys (March and June 2021) were carried out to highlight possible variability associated with the different seasonal conditions. The GEM (Gaseous Elemental Mercury) measurements, performed using a Lumex RA-915M portable analyzer, highlighted that the highest concentrations (up to 16,500 ng/m3 ) were recorded, as expected, at the furnace located in the external processing area, while the galleries showed values ranging from a few dozen up to 3,651 ng/m3 . The noticeable variations of GEM concentrations (even an order of magnitude) inside the galleries between the two measurement periods were probably due to the higher humidity and ventilation in June than in March. Up to 22 water samples (each survey), from the downstream water courses up to the Versilia River, were analyzed for dissolved Hg concentration using a Lumex RA-915M equipped with a RP-92 attachment. 17 sediment samples (collected in March) from the mine and surrounding areas, were dried, grinded, and homogenized, and let interacting with CO2 -saturated water. The leachate was analyzed by ICP-MS after centrifugation, whilst the sediment by AAS. The results showed that the contamination mainly affects the water and the leachates pertaining to the mining area (up to 3.6 and 31.3 µg/L, respectively), while downstream the mine the Hg concentrations were even <10 ng/L and <0.1 µg/L, respectively, i.e., well below the Italian law limit (1 µg/L). The more polluted sediments (up to 1,100 mg/kg) were those collected into the galleries, although only 5 more distal samples were characterized by Hg contents below the limit for residential use (1 mg/kg).