Investigating Hg dispersion in the environment: the experience from the abandoned mining area of Abbadia San Salvatore (Tuscany, central Italy)between research and remediation activitiesof natural and anthropic matrices.

The former mining area of Abbadia San Salvatore has been one of the most famous and technologically-advanced sites in the world for the extraction of Hg from cinnabar to produce liquid mercury. The mining edifices and structures represent an invaluable archeometallurgical treasure to be safeguarded and presently the remediation activities are going on with the aim to convert the whole surface (65 ha) into a historic museum and mining park. In 2008, when the Municipality of Abbadia San Salvatore became the owner of the mining concession, many efforts have been done to increase both the scientific knowledge and the remediation operations to improve the environmental quality of the mining site. In fact, the local authorities had to deal with edifices and buildings completely abandoned and invaded by vegetation. Moreover, numerous sites were (and partly are still) severely contaminated by mercury. Previous studies highlighted the presence of high Hg0 concentrations of the mining structures both outdoor and indoor as well as dissolved mercury in underground and surface waters and total and leachable mercury in soils. The most important achievements of this PhD thesis were mainly addressed to verify at which extent the contamination of mercury was tridirectionally affecting the surface- and ground-waters and the man-made materials inside the most contaminated building, i.e. those hosting the Gould furnaces. Two studies were made with the aim to investigate the interaction between the ASS mine and the environmental (natural and anthropogenic) matrices before the remediation. The results of a discontinuous monitoring of the Galleria Italia waters (from 2009 to 2020) that feed the Fosso della Chiusa creek were discussed since significant chemical variations were recorded and likely associated with the interaction of meteoric waters with the ore deposits as a function of the variable flow rate. Additionally, a specific investigation was dedicated to the waters, stream sediments and suspended solids of this small creek. The environmental matrices were collected at regular distances and the results evidenced the decreasing of As at the source and an enrichment in the sediments and suspended sediments. In the waters, a general increase in the three investigated phases (liquid, suspended and deposited) was observed for Hg. Moreover, the discharge of these two elements by the Fosso della Chiusa into the Pagliola river was calculated: 5.3 kg/yr for As and 2.1 kg/yr for Hg. It is remark that antimony almost behaved as a immobile element and its contribution was thus considered negligible. Additionally, a new methodological approach was tested to evidence the vertical distribution of gaseous mercury up to about 65 m above the urban center of Abbadia San Salvatore, which is spatially located close to the mining area. An instrumentation able to analyze Hg0 in a continuous mode was mounted on an octocopter which flew over the city center and the mining structures. The investigations carried out on the waters inside the former mining area allowed to define i) a geochemical and isotopic background, including Hg isotopes, of the water bodies in the mining area of Abbadia San Salvatore via a seasonal monitoring and ii) possible remediation activities (presently going on), through classical and new methodologies such as the use of a commercial product (named Capterall®) to understand whether the presence of dissolved mercury was to be reduced. The patented product was successfully applied to 3 differently-contaminated groundwaters from the mining area. A new procedure was also set up to estimate the release of GEM from any kind of material exposed to high Hg0 concentrations and, successively, a specific paint was tested to verify whether the GEM might be blocked to reduce air contamination of Hg0. A graphical abstract summarizing the main geochemical activities conducted during this 3-years long PhD thesis is reported in Fig. 1. The work in the former mining area of Abbadia San Salvatore is not over but I think that the investigations carried out during this PhD can help for future studies, hoping to see the local population and tourists to visit the new historic museum and mining park in a few years. When this is going to happen, I will be saying that my little contribution was useful.