Determination of gaseous elemental mercury (GEM) emissions by a non-stationary static accumulation chamber. The case study of Portoscuso (South-West Sardinia)

This work describes the methodology based on a non­statonary statc accumulaton chamber used for measuring the GEM emissions at the soil­atmosphere interface in some residental and agricultural areas of the Portoscuso Municipality (South­West Sardinia). Afer a preliminary risk assessment of soil contaminaton, the investgated areas highlighted potental significant human health risks for volatlizaton pathways related to total Hg content in the soil. The aim of this study is to use the GEM emission rate to estmate indoor and outdoor human exposure according to the specific use of the areas. Acceptable GEM emissions (AGEM), i.e. maximum emissions associated with an acceptable human exposure and health risk, were defined accordingly and compared with measured ones. The measured GEM emissions probably consttute the sum of two contributons: • a real flux of GEM “through the soil­atmosphere interface”. This flux is originated by the presence of sources (both natural and/or related to potental contaminaton) in the first meters of depth and is regulated by mainly advectve mechanisms; • a component produced “at the soil­atmosphere interface”, as a response to the acton of UV radiaton on divalent Hg (II) in soil partcles. In this study the contributon of each of these two components has not been evaluated; however the main results showed, at the scale of the single sample representatve area (Thiessen polygon), few values (8 out of 163, about 5%) exceeding the AGEM values for the indoor scenario. These results are poorly indicatve of a real unacceptable risk, given their extremely punctual extent not representatve of a long­term human exposure. Conversely, GEM emissions for each macroarea showed a general compliance with acceptable thresholds emission (AGEM) computed for both outdoor and indoor scenarios. Further investgatons will be aimed at discriminatng the two components that originate the measured GEM flux values.