Evasion of Gaseous Elemental Mercury from Forest and Urban Soils Contaminated by Historical and Modern Ore Roasting Processes (Idrija, Slovenia)

Abstract

Considerable amounts of gaseous elemental mercury (Hg0) can be released into the atmosphere from Hg-enriched substrates, such as those from former mining areas, posing a potential environmental threat. In this work, Hg0 fluxes at the soil–air interface under natural vegetation covers were measured in various locations within the Idrija Hg mining area (Slovenia) and its surroundings. Sites were selected in order to compare Hg0 fluxes from both forest soils heavily impacted by historical ore roasting and urban soils characterised by a different degree of Hg enrichment due to the natural occurrence of Hg in rocks or recent mining and roasting processes. Replicate measurements at each site were conducted using a non-steady state flux chamber coupled with a real-time Hg0 analyser (Lumex RA-915M). Moreover, topsoil samples (0–2 cm) were analysed for Hg total concentration and speciation. Cinnabar was the predominant Hg form in almost all the sites. Despite Hg0 being undetectable in soils using thermo-desorption, substantial emissions were observed (70.7–701.8 ng m−2 h−1). Urban soils in a naturally enriched area showed on average the highest Hg0 fluxes, whereas relatively low emissions were found at the historical roasting site, which is currently forested, despite the significantly high total Hg content in soils (up to 219.0 and 10,400 mg kg−1, respectively). Overall, our findings confirm that shading by trees or litter may effectively limit the amount of Hg0 released into the atmosphere even from extremely enriched soils, thus acting as a natural mitigation.

A Novel Solution to Avoid Mercury Emissions Produced by Highly Contaminated Demolition Debris in Mining Site

“…In this regard, the importance of this problem has led to a vast scientific bibliography on this topic, as it is very complex to define a unique approach. Some of the topics studied in the last few decades are: mercury (Hg) concentration in soil and water in contaminated sites [4][5][6][7]; emission rates of Hg into the atmosphere and the distribution of contamination surrounding sites contaminated with mercury [8][9][10][11][12][13][14][15][16][17]; development of emission models to analyze the potential risks related to Hg contamination [18][19][20]; influence of contamination on people's health, either from a general perspective [21,22] or more specific studies on human diseases [23][24][25]; occupational risks related to the work in these areas [26,27]; and…”

“…Once these mine soils have been physically and chemically stabilized, the common next step is the successful establishment of a plant cover. The vegetation cover (or with other materials) of Hg-contaminated materials can strongly limit the reemission of this element to the atmosphere [7,16]. On the other hand, plants favor the ecological development of the ecosystem, enhance the fertility of the soil, and contribute to the stabilization of soil in open pits and slopes [41].…”

“…The analysis presented here is focused on the remediation using physical methods of the mercury contamination produced via gaseous mercury emissions from the demolition debris of a former metallurgical plant. A peculiarity of this metal is the high volatility of its elemental form (Hg 0 ), which is easily released into the atmosphere from natural surfaces after the reduction in oxidized forms (Hg 2+ ) that are dominant in terrestrial and aquatic environments [16]. For this purpose, a novel solution is presented, consisting of covering the contaminated debris (capping) with by-products of the industry, which implies the reuse of these by-products and their revaluation in the context of a circular economy.…”