Gaseous mercury fluxes from soils and health risk assessment at a coastal legacy industrial site

A reliable estimation of gaseous elemental mercury (GEM) re-emissions from soils at mercury (Hg)-contaminated sites represents a key aspect for a proper health risk assessment for the local population, which may be potentially exposed through inhalation. This study investigates GEM fluxes at the soil-air interface within an area impacted by past local industrial emissions of Hg (Portoscuso, Italy) through a non-steady-state flux chamber (accumulation chamber) coupled to a real-time GEM analyser. Several flux measurements (n = 163) distributed over 5 selected sub-areas were performed, providing good spatial representativeness. Calculated GEM emission rates were used to assess indoor and outdoor human exposure according to the specific use of each area (e.g. residential or agricultural) by comparing them with values corresponding to acceptable exposure. Substantial GEM emissions (3.54–3164 ng m−2 h−1) were observed for nearly all sampling points, with notable spatial heterogeneity partially related to meteorological factors and highest values mostly near the industrial complex. Comparable median fluxes were observed for urban settlements and arable areas (110 and 101 ng m−2 h−1, respectively), highlighting the impact of land-use on GEM volatilisation. Overall, GEM emissions were below the estimated acceptable GEM flux for the site (Hazard Index<1), with the exception of 8 points randomly distributed over the study area and not likely indicative of a real unacceptable risk related to legacy re-emissions from contaminated soils. These results indicate that the adopted approach can be useful for large-scale preliminary investigations of GEM fluxes in Hg-contaminated sites, allowing point anomalies to be detected through direct field measurements.