A laboratory-incubated redox oscillation experiment to investigate Hg fluxes from highly contaminated coastal marine sediments (Gulf of Trieste, Northern Adriatic Sea)

The Legacy of the Idrija Mine Twenty-Five Years after Closing: Is Mercury in the Water Column of the Gulf of Trieste Still an Environmental Issue?

Mercury (Hg) contamination in the Gulf of Trieste (northern Adriatic Sea) due to mining activity in Idrija (Slovenia) still represents an issue of environmental concern. The Isonzo/Soča River's freshwater inputs have been identified as the main source of Hg into the Gulf, especially following periods of medium-high discharge. This research aims to evaluate the occurrence and distribution of dissolved (DHg) and particulate (PHg) Hg along the water column in the northernmost sector of the Gulf, a shallow and sheltered embayment suitable for the accumulation of fine sediments. Sediment and water samples were collected under unperturbed and perturbed environmental conditions induced by natural and anthropogenic factors. Mercury in the sediments (0.77-6.39 µg g-1) and its relationship to grain size were found to be consistent with previous research focused on the entire Gulf, testifying to the common origin of the sediment. Results showed a notable variability of DHg ( Collapse

Key Words

• mercury
• sediments
• suspended particulate matter
• water column

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MESH Headings

• Environmental Monitoring
• Geologic Sediments
• Mercury/analysis
• Mining
• Rivers
• Water
• Water Pollutants, Chemical/analysis

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Grants Collapse

Affiliation(s)

Elena Pavoni Dipartimento di Matematica e Geoscienze, Università Degli Studi di Trieste, Via Weiss 2, 34128 Trieste, Italy; (E.P.); (E.P.); (G.F.)
Elisa Petranich Dipartimento di Matematica e Geoscienze, Università Degli Studi di Trieste, Via Weiss 2, 34128 Trieste, Italy; (E.P.); (E.P.); (G.F.)
Sergio Signore Autorità di Sistema Portuale del Mare Adriatico Orientale-Porto di Trieste, Via Karl Ludwig Von Bruck 3, 34144 Trieste, Italy;
Giorgio Fontolan Dipartimento di Matematica e Geoscienze, Università Degli Studi di Trieste, Via Weiss 2, 34128 Trieste, Italy; (E.P.); (E.P.); (G.F.)
Stefano Covelli Dipartimento di Matematica e Geoscienze, Università Degli Studi di Trieste, Via Weiss 2, 34128 Trieste, Italy; (E.P.); (E.P.); (G.F.)

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Can Sediments Contaminated by Mining be a Source of Mercury in the Coastal Environment Due to Dredging? Evidence from Thermo-Desorption and Chemical Speciation

The sediments in the Gulf of Trieste (northern Adriatic Sea, Italy) are contaminated by mercury (Hg) due to historic mining which took place in Idrija (Slovenia). Despite many studies having been done regarding Hg, no information is available on the potential impact of dredging required along the main channel approaching the Port of Monfalcone. Sixteen surface sediment samples were collected along the channel to determine both total Hg concentration and chemical species using the thermo-desorption (TD) technique. Six samples were also chosen to apply a selective sequential extraction (SSE). The TD technique showed the maximum Hg release approximately at 260 and 335°C, corresponding to metacinnabar (β-HgS) and cinnabar (α-HgS), respectively. The SSE demonstrated that Hg was mainly associated with poorly soluble or insoluble compounds (98.7%). A resuspension event over a limited period of time can be considered of negligible impact to the water column due to the scarce Hg mobility from sediments.

Mercury geochemistry and microbial diversity in meromictic Glacier Lake, Jamesville, NY

Meromictic lakes are stratified lakes that typically stimulate phototrophic anoxic microbial metabolism, including the transformation of sulphur. Less studied are the transformations of mercury in these environments, and the microorganisms, which mediate these reactions. In order to further an understanding of redox species, mercury and microbial populations in meromictic lakes, we examined the geochemistry and microbiology of Glacier Lake in Jamesville, NY. We found an anoxic transition at a depth of 6 m, followed by active nitrate and sulphate utilization. A chlorophyll a maximum was located at 11 m, coinciding with peaks of several photoautotrophic microbial lineages and total mercury and methyl mercury. Via amplicon sequencing, the microbial population showed pronounced peaks of cyanobacteria at 10 m, Chlorobi at 12 m and Chloroflexi at 14 m. Sulphate-reducing bacteria were also most abundant between 10 and 14 m depth. A functional gene indicating the potential for the production of methyl mercury, hgcA, was detected at several depths in the lake. Our work suggests that in addition to the sulphur cycle, the cycling of mercury may be indirectly coupled with phototrophic processes in Glacier Lake.

Mobility of metal(loid)s at the sediment-water interface in two tourist port areas of the Gulf of Trieste (northern Adriatic Sea)

One of the main environmental issues affecting coastal marine environments is the accumulation of contaminants in sediments and their potential mobility. In situ benthic chamber experiments were conducted at two tourist ports (marinas) located in the Gulf of Trieste, one in Slovenia and one in Italy. The aim was to understand if and where recycling at the sediment-water interface (SWI) may affect metal(loid)s. Short sediment cores were also collected near the chamber to investigate the solid (sediments) and dissolved phases (porewaters). Both diffusive and benthic fluxes were estimated to elucidate the release of metal(loid)s at the SWI. Total element concentrations and their labile fractions were determined in sediments to quantify their potential mobility. The total element contents were found to be two orders of magnitude higher in the Italian marina than in the Slovenian one, especially for Hg (up to 1000 mg kg^-1), whereas the labile fraction was scarce or null. The opposite occurred in the Slovenian marina. Metal(loid)s in porewaters showed a clear diagenetic sequence and a close dependence upon the suboxic/anoxic conditions of sediments. The results suggest that although the sediments of the Italian marina exhibit the highest total metal(loid) concentration, these elements are scarcely remobilisable. Conversely, in the Slovenian marina, sediments seem to be comparatively more prone to release metal(loid)s at the SWI.