Preliminary investigation of Hg in interstitial soil and free gases in a peripheral area of Mt. Etna, Sicily

Abstract

Mercury (Hg) is one of the most hazardous elements emitted into the atmosphere both from natural and anthropogenic sources. Volcanic emissions represent an important natural source of Hg in the environment known for its potential toxicity to many forms of life and for its long atmospheric residence time, which allows an efficient global distribution. My PhD project is framed within the broader context of the HERMES project (co-founded PRIN 2022) and involves the biogeochemical study of Hg on the Mt. Etna volcano. Specific aims include: determining Hg concentrations in soils and interstitial gases in soils; characterising the microbiota linked to the mercury cycle in soils; quantifying mercury emissions from the volcano’s peripherals emissions; quantifying atmospheric Hg deposition fluxes. Here we present preliminary data on the outgassing of Hg from soils collected using a Lumex® RA-915M (Zeeman atomic adsorption spectrometer) analyser within a wide concentration range (2 to 50,000 ng m-3). The instrument inlet port was equipped with a three-way valve and the gas was injected into the instrument using a 100-mL syringe. The first sampling campaigns were focused on some of the degassing areas around Mt. Etna, including some of the sites of the “Etnagas” CO2 monitoring stations network (INGV). With respect to the atmospheric background values (2-3 ng m-3) Hg concentration in free gases reached higher values between 264 - 9,913 ng m-3 in Salinelle, Aqua Grassa and Fondachello sites, highlighting an important flux of mercury to the atmosphere. Hg concentration in the interstitial gases in soils ranged from 28.7 to 57.5 ng m-3 in the Santa Venerina site and 52.8 to 100 ng m-3 in the Torre del Filosofo site. These preliminary results show that the contribution of peripheral and soil degassing with respect to the crater degassing is non-negligible and requires further investigations.