Federico Floreani

Lagoons are transitional ecosystems characterized by high natural variability in terms of salinity, oxygenation, and nutrient availability, which creates complex ecological conditions and a delicate biological balance. This variability often results into low ecological quality indices, therefore discriminating between natural and anthropogenic stress remains a challenge, particularly when using benthic foraminifera as bioindicators. The Marano and Grado Lagoon (northern Adriatic Sea, Italy) is a shallow coastal system generally considered well preserved, despite long-standing human activities and historical mercury contamination in its eastern sector. This study presents investigations of living benthic foraminifera and integrates modern assemblage analysis with sediment core data. The assemblage is dominated by Ammonia tepida , Haynesina germanica , Aubignyna perlucida , and Cribroelphidium gunteri , which are positively correlated with total organic carbon, while Ammonia parkinsoniana , Quinqueloculina spp., and agglutinated taxa are mainly related to salinity. Shell deformities, especially in Ammonia spp. and C. gunteri , are widespread. Cluster analysis evidenced three main assemblages: urban ( Haynesina germanica dominant), inner ( H. germanica with Aubignyna perlucida dominant) and the outer lagoon ( A. parkinsoniana dominant) biotopes, with reduced ecological quality in the inner sectors. A sediment core was used to explore the potential impact of recent anthropogenic disturbances. The deformation index exhibits increasing trend since the mid-18th century, before the major anthropogenic impacts, suggesting a predominantly natural control. Overall, results indicate that the moderate ecological status of the inner lagoon is mainly driven by natural stress, in agreement with the ‘estuarine quality paradox’, although intensified anthropogenic use may have influenced sensitive species distributions.

A key aspect for the evaluation of environmental and health risk associated with mercury (Hg) contamination is the assessment of its speciation, which can influence the mobility and bioavailability of this element in the environment. The evaluation of Hg speciation in soils and sediments of contaminated sites is commonly based on selective sequential extraction (SSE) methods, which, however, have certain disadvantages: they do not allow for a specific removal of Hg species, are generally time-consuming and characterised by a low reproducibility. An easy-to-use alternative to SSE may be represented by thermo-desorption (TD) technique, where different Hg species can be identified according to their specific release temperature during a gradual heating. The aim of this study was to evaluate the potential application of TD for the risk assessment associated with Hg occurrence in alluvial soils at some sites in the Friuli-Venezia Giulia Region (NE Italy) affected by past Hg inputs related to mining and, to a lesser extent, industrial activities. At each site, surface and deep soil samples (n≥12) were collected and analysed for total Hg concentration and Hg speciation through TD. Speciation analyses were performed by means of a Hg atomic absorption spectrometer (Lumex RA915M) coupled with a pyrolysis attachment (PYRO-915+). This setup allows for a continuous monitoring of Hg released during the sample heating. Calculations of risk associated to Hg volatilisation, leaching, and ingestion were performed using the relative amount of non-cinnabar (non-α-HgS) compounds determined through TD, considered as potentially mobile. Results were then compared with those obtained through the application of a SSE method commonly used for the assessment of Hg speciation in the investigated area. Almost all samples analysed through TD showed the occurrence of non-mobile red cinnabar (α-HgS), confirming the remarkable legacy of the mining source. Generally, although a slightly higher abundance of potentially mobile Hg forms was obtained through TD than SSE, the calculated risk resulted “acceptable” (hazard index < 1) using data from both techniques. Besides, it must be stressed that calculation performed through TD data are based on a larger number of samples, thus providing a greater representativeness of the mobility of the Hg species and associated risk in the investigated area. Considering also the good reproducibility of data obtained through TD and its celerity and accuracy in Hg species discrimination, the proposed approach could be considered as a valid and relatively low expensive tool for risk assessment at Hg contaminated sites. This is especially true for sites such as former Hg mining areas characterised by the occurrence of α-HgS, easily discriminable through TD.

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.

Portable X-ray fluorescence (pXRF) is one of the main geochemical techniques employed in multi-elemental analysis screening for contaminated sites management. As the confidence of pXRF analyses are matrix-specific, efforts are made to provide studies of pXRF quality on different geochemical datasets, focusing on less investigated elements such as mercury (Hg) and antimony (Sb), to help both new and experienced users. The analysis of environmental solid samples from two decommissioned mining sites in NE Italy, characterised by Pb-Zn and (Hg-rich) Cu-Sb ore deposits, were prepared with two different protocols and compared with traditional destructive analyses. Sample composition was found strictly dependent to the occurrence of false positives and overestimation at low concentrations. In contrast, milling the sample did not produce major variations in the overall quality. Lead (Pb), Sb, and Zn reached the definitive data quality in at least one of the two datasets. Consequently, as far as a thorough QA/QC protocol is followed, pXRF can rapidly produce chemical data that is as accurate as that produced by destructive standard laboratory techniques, thus allowing to identify potential sources of contamination that could be reprocessed for the extraction of valuable elements and mitigating the dispersion of contaminants and ecological or health risks.

Gaseous exchanges of mercury (Hg) at the water–air interface in contaminated sites strongly influence its fate in the environment. In this study, diurnal gaseous Hg exchanges were seasonally evaluated by means of a floating flux chamber in two freshwater environments impacted by anthropogenic sources of Hg, specifically historical mining activity (Solkan Reservoir, Slovenia) and the chlor-alkali industry (Torviscosa dockyard, Italy), and in a pristine site, Cavazzo Lake (Italy). The highest fluxes (21.88 ± 11.55 ng m⁻² h⁻¹) were observed at Solkan, coupled with high dissolved gaseous mercury (DGM) and dissolved Hg (THg_D) concentrations. Conversely, low vertical mixing and saltwater intrusion at Torviscosa limited Hg mobility through the water column, with higher Hg concentrations in the deep layer near the contaminated sediments. Consequently, both DGM and THg_D in surface water were generally lower at Torviscosa than at Solkan, resulting in lower fluxes (19.01 ± 12.65 ng m⁻² h⁻¹). However, at this site, evasion may also be limited by high atmospheric Hg levels related to dispersion of emissions from the nearby chlor-alkali plant. Surprisingly, comparable fluxes (15.56 ± 12.78 ng m⁻² h⁻¹) and Hg levels in water were observed at Cavazzo, suggesting a previously unidentified Hg input (atmospheric depositions or local geology). Overall, at all sites the fluxes were higher in the summer and correlated to incident UV radiation and water temperature due to enhanced photo production and diffusivity of DGM, the concentrations of which roughly followed the same seasonal trend.

The Marano and Grado Lagoon (Northern Adriatic Sea) has been affected by mercury (Hg) contamination coming from two sources, mining activity and discharges from a chlor-alkali plant (CAP). Sediments and water contamination have been previously well characterised, but little is known about the atmospheric compartment, where Hg is easily emitted and can persist for a long time as gaseous elemental mercury (GEM). In this work, atmospheric GEM levels and its spatial distribution over the lagoon were monitored at several sites by means of both continuous discrete instrumental measurements over several months and the determination of Hg bioaccumulated in lichens (Xanthoria parietina L.). Average GEM levels varied from 1.80 ± 0.74 to 3.04 ± 0.66 ng m⁻³, whereas Hg in lichens ranged between 0.06 to 0.40 mg kg⁻¹. In both cases, the highest values were found downwind of the CAP, but excluding this point, spatial patterns of Hg in the atmosphere and lichens reflected the concentration of this metal in the sediments of the lagoon, showing a decrease moving westward. These results could indicate that the lagoon acts as a secondary source of Hg into the atmosphere: future work is needed to characterise the quantity of releases and depositions at different environments inside the lagoon.