Behaviour of Metal(loid)s at the Sediment-Water Interface in an Aquaculture Lagoon Environment (Grado Lagoon, Northern Adriatic Sea, Italy)

The cycling of metal(loid)s at the sediment\u2013water interface (SWI) was evaluated at two selected sites (VN1 and VN3) in an active fish farm in the Grado Lagoon (Northern Adriatic, Italy). In situ experiments using a transparent benthic chamber and the collection of short sediment cores were performed, to investigate the behavior of metal(loid)s in the solid (sediments) and dissolved (porewaters) phases. Total and labile concentration of metal(loid)s were also determined in sediments, to quantify their potential mobility. Comparable total concentrations were found at both sites, excluding As, Mn, Pb and V, which were higher at VN3. Metal(loid) porewater profiles showed a diagenetic sequence and a close dependence with redox (suboxic/anoxic) conditions in the surface sediments. Positive diffusive fluxes along with benthic fluxes, particularly at the more oxic site, VN1, were found for almost all metal(loid)s, indicating their tendency to migrate towards the overlying water column. Despite sediments at two sites exhibiting high total metal(loid) concentrations and moderate effluxes at the SWI, the results suggest that they are hardly remobilized from the sediments. Recycling of metal(loid)s from the SWI would not constitute a threat for the aquatic trophic chain in the fish farm

Correction to: Concentration of mercury in human hair and associated factors in residents of the Gulf of Trieste (North‑Eastern Italy)

The Gulf of Trieste (Northern Adriatic Sea, Italy) is the coastal area of the Mediterranean Sea most highly contaminated by mercury (Hg) due to fluvial inputs from the Isonzo/Soča River system, draining over 500 years’ worth of cinnabar extraction activity from the Idrija mining district (Western Slovenia). The aim of this research is to investigate the concentration of Hg in hair samples taken from the general population of the Friuli Venezia Giulia (FVG) Region coastal area, as a marker of chronic exposure to Hg. Three hundred and one individuals — 119 males and 182 females — were recruited by convenience sampling in Trieste in September 2021. An amount of approximately 100 mg of hair was collected from the occipital scalp of each participant to measure the respective Hg concentrations (expressed as mg/kg). Moreover, participants completed a self-report questionnaire collecting extensive socio-demographic and life-style information. A multiple linear regression analysis was employed to investigate factors associated with increased levels of Hg concentration in hair. A mean Hg concentration in hair of 1.63 mg/kg was found, slightly above the 1.0 mg/kg threshold recommended by the WHO for pregnant women and children, although still well below the no observed adverse effects level (NOAEL) of 10 mg/kg. Among respondents, 55.6% showed a Hg concentration in hair > 1 mg/kg, 22.9% > 2 mg/kg, and 2 participants exhibited Hg levels > 10 mg/kg. The adjusted mean hair Hg level increased in those subjects who reported a preference for shellfish/crayfish/mollusks (RC = 0.35; 95%CI: 0.16; 0.55), whereas it decreased in those who reported a preference for frozen fish (RC = -0.23; 95%CI: − 0.39; − 0.06). Though a risk alert for Hg exposure for coastal residents from FVG is deemed unnecessary at this time, it is recommended that pregnant women limit their ingestion of locally caught fish to < 4 servings/month

Fluxes of settling sediment particles and associated mercury in a coastal environment contaminated by past mining (Gulf of Trieste, northern Adriatic Sea)

Purpose: As the result of historical mining at Idrija (Slovenia), mercury (Hg) contamination in the Gulf of Trieste (northern Adriatic Sea) is still an issue of environmental concern. The element has been conveyed into the coastal area by the Isonzo/Soča River inputs of freshwater and suspended particles for centuries. This research aims to investigate the occurrence of Hg bound to the settling sediment particles (SSP) in the coastal water and to assess the sedimentary Hg fuxes. Methods: Settling sediment particles were collected at four sites located in the innermost sector of the Gulf, a shallow and sheltered embayment where the accumulation of fine sediments is promoted. Six sampling campaigns were performed under different environmental conditions in terms of discharge from the Isonzo River and 12 sediment traps were installed in the upper and bottom water column for SSP collection. Settling sediment particles (SSP) were collected approximately every 2 weeks and analysed for grain size and total Hg. Results: Settling sediment particles (SSP) consisted predominantly of silt (77.7±10.1%), showing a concentration of Hg ranging overall between 0.61 and 6.87 µg g−1. Regarding the daily SSP fuxes, the minimum (7.05±3.26 g m−2 day−1) and the maximum (92.4±69.0 g m−2 day−1) values were observed under conditions of low and high river discharge, respectively. The daily Hg fluxes displayed a notable variability, up to an order of magnitude, both in the surface water layer (3.07–94.6 µg m−2 day−1) and at the bottom (11.3–245 µg m−2 day−1), reaching the maximum values following periods of high river flow. Conclusions: The Isonzo River inputs of suspended particulate matter continue to convey Hg into the Gulf of Trieste, especially following river flood events, which represent one of the most relevant natural factors affecting the variations of the Hg flux in the investigated area

Benthic nutrient cycling at the sediment-water interface in a lagoon fish farming system (northern Adriatic Sea, Italy)

Metabolism and carbon, oxygen, and nutrient fluxes (DIC, DOC, DO2, NO2 12, NO3 12, NH4+, PO4 3 12 and SiO4 4 12) were studied during three surveys at two sites (VN1 and VN3) located at a fish farm at theMarano and Grado Lagoon (northern Adriatic Sea), using an in situ benthic chamber. Field experimentswere conducted in July and October 2015 and March 2016 at a depth of approximately 2 m along the main channels of the fish farm.Water samples were collected by a scuba diver every 2 h in order to investigate daily fluxes of solutes across the sediment-water interface (SWI). Regarding the solid phase, Corg/Ntot and Corg/Porg molar ratios suggested an autochthonous marine origin of the organic matter and a minor preservation of P in the sediments, respectively; high values of sulphur (Stot) were also encountered (0.8\u20132%). The conditions at VN3 were mostly anoxic with high NH4 + levels (30\u20131027 \u3bcM) and the absence of NO3 12. Substantial daily patterns of all solutes occurred especially in autumn andwinter. On the contrary, fluxes at VN1were less pronounced. Usually, inverse correlations appeared between dissolved O2 and DIC trends, but in our systemthis was observed only at VN3 in autumn and accomplished by a parallel increase in NH4+, PO4 3 12 and SiO4 4 12 during intense nutrient regeneration. These results are significantly different than those reported for open lagoon environments,where nutrient regeneration at the SWI and in surface sediments is the primary source of nutrients available for assimilation processes, especially during the warmer period of the year when the natural nutrient input by fresh water inflows is limited. Due to the importance of this site for aquaculture, biodiversity and ecosystem services, useful suggestions have been provided from this study in order to improve the quality of this unique aquatic system

Concentration of mercury in human hair and associated factors in residents of the Gulf of Trieste (North-Eastern Italy)

The Gulf of Trieste (Northern Adriatic Sea, Italy) is the coastal area of the Mediterranean Sea most highly contaminated by mercury (Hg) due to fluvial inputs from the Isonzo/Soca River system, draining over 500 years' worth of cinnabar extraction activity from the Idrija mining district (Western Slovenia). The aim of this research is to investigate the concentration of Hg in hair samples taken from the general population of the Friuli Venezia Giulia (FVG) Region coastal area, as a marker of chronic exposure to Hg. Three hundred and one individuals - 119 males and 182 females - were recruited by convenience sampling in Trieste in September 2021. An amount of approximately 100 mg of hair was collected from the occipital scalp of each participant to measure the respective Hg concentrations (expressed as mg/kg). Moreover, participants completed a self-report questionnaire collecting extensive socio-demographic and life-style information. A multiple linear regression analysis was employed to investigate factors associated with increased levels of Hg concentration in hair. A mean Hg concentration in hair of 1.63 mg/kg was found, slightly above the 1.0 mg/kg threshold recommended by the WHO for pregnant women and children, although still well below the no observed adverse effects level (NOAEL) of 10 mg/kg. Among respondents, 55.6% showed a Hg concentration in hair > 1 mg/kg, 22.9% > 2 mg/kg, and 2 participants exhibited Hg levels > 10 mg/kg. The adjusted mean hair Hg level increased in those subjects who reported a preference for shellfish/crayfish/mollusks (RC = 0.35; 95%CI: 0.16; 0.55), whereas it decreased in those who reported a preference for frozen fish (RC = -0.23; 95%CI: - 0.39; - 0.06). Though a risk alert for Hg exposure for coastal residents from FVG is deemed unnecessary at this time, it is recommended that pregnant women limit their ingestion of locally caught fish to < 4 servings/month

Effects of hypoxia on biogeochemical cycling of nutrients and trace elements in a stratified estuarine system (Gulf of Trieste, northern Adriatic Sea)

Estuaries can be thought as a sedimentary trap leading to the accumulation of potentially toxic trace elements (PTEs) in sediments. However, biogeochemical processes at the sediment-water interface (SWI) may also be responsible for the release of dissolved PTEs and nutrients in the overlying water column affecting the water quality. The estuarine system of the Timavo River (Gulf of Trieste, northern Adriatic Sea) is a semi-closed aquatic environment where a long-lasting oxic-hypoxic interface along the water column occurred due to the scarce water circulation in the innermost sector. To prevent bloom-forming and potential production of toxins and off-flavours, artificial mixing has been provided with a bubble plume installation connected to pressurised air and built on the sediment surface aiming at reoxygenating the water column. The aim of this research was to evaluate the behaviour of PTEs (As, Cr, Hg, Fe, Mn, Ni, Pb, V) and nutrients (NO3, NO2, NH4 and SRP) along the water column and at the SWI before (June) and during (September) the activation of the forced aeration system. Water samples were collected at different depths along the water column, in situ benthic chamber experiments were performed at the SWI and short sediment cores were sampled to investigate both the sediment and porewater. Dissolved oxygen decreased along the water column, especially in June when hypoxia (2.29 mg/L) and reductive conditions (58 mV) were observed at the bottom resulting in increasing dissolved PTE and nutrient concentrations. Accordingly, a gradual oxygen depletion was observed in the benthic chamber testifying to intense organic matter remineralisation processes. Moreover, the highest concentrations of dissolved PTEs in porewater were restricted to the top of the sedimentary sequence, especially in June when hypoxic conditions may promote PTE and nutrient effluxes from the sediment to the water column

Importance of a tidal flat-saltmarsh system as a source-sink of mercury in a contaminated coastal lagoon environment (northern Adriatic Sea)

Saltmarshes are important constituents of marine-coastal transitional environments that provide several services to the ecosystem. Due to anthropogenic activities, several contaminants are increasingly introduced into these environments where are disperse and can accumulate in the saltmarsh sediments. The Marano and Grado Lagoon (northern Adriatic Sea) is affected by Hg contamination, which mainly coming from historical regional mining activities (Idrija, western Slovenia) and, subordinately, from more recent industrial input due to a chlor-alkali plant. Several studies have also demonstrated the Hg contamination of saltmarsh sediments and halophyte vegetation that cover them. Moreover, saltmarshes not only trap contaminated sediments, but can act as a secondary source of contamination. This work aims at determining the potential role of the tidal flat-saltmarsh (TF-S) system as a sink or secondary source of Hg in this coastal lagoon in relation to the chemical-physical processes leading their remobilisation. The main objective was to understand the role played by periodic flow of tide in a TF-S pilot site in terms of transport, accumulation and release of Hg. Tidal flows and water chemistry were measured at the mouth of a principal tidal creek which collect the waters of a dense channel network draining a 5.5-ha tidal flat-saltmarsh system. Tidal fluxes were estimated by combining discrete hourly tidal flow measurements with weighted measurements of particulate (PHg) and dissolved (DHg) mercury obtained by water samples. The highest values of DHg and PHg were recorded during ebb tide and the quantitative fluxes estimated for all parameters highlighted a tendency for metal to be exported from the TF-S system due to the tidal flows in ebb tide conditions. The results obtained for the PHg fluxes, in particular, are in agreement with those observed on a macro-scale at one of the lagoon tidal inlets considering an annual mass-balance of PHg performed via several water column sampling campaigns. A simple estimation provides a negative sedimentary budget for the TF-S system, which loses PHg towards the main lagoon channel during a tidal semi-cycle thus confirming other evidence of serious morphological deterioration of this critical coastal environment

Mobility and fate of Thallium and other potentially harmful elements in drainage waters from a decommissioned Zn-Pb mine (North-Eastern Italian Alps)

The potential impact of decommissioned mining areas on the quality of water resources is an issue of major concern for local communities. Acid mine drainage resulting from hydrolysis and oxidation of metal sulphides associated with mineral veins or mining wastes is often responsible for leaching large amounts of potentially harmful elements (PHEs) in solution, which can be dispersed into the surrounding environment and affect the quality of the recipient water bodies. The aim of the present study was to investigate the geochemical properties of the mine drainage waters at the decommissioned Salafossa mine (North-Eastern Italian Alps), to highlight anomalous concentrations of PHEs outflowing from the currently flooded galleries and to elucidate their speciation. In spite of the Zn-Pb sulphides still present in the body ore, there is no evidence of acid drainage waters from the mine galleries as a result of the buffering effect produced by carbonate host rocks. Due to their high mobility, however, Zn and Tl are present in solution mostly in ionic form. Conversely, the less mobile Pb, is referably partitioned in the solid phase. Additionally, the oxidising conditions of the drainage waters also allow the precipitation of some PHEs (As, Cd, Pb, Tl, Zn) in the form of Fe-Mn oxy-hydroxides and carbonates, which accumulate at the bottom of the mine galleries as fine \u201csediments\u201d or concretions. Drainage waters inside the mine were found to be highly enriched in Zn (up to 16 mg L\u20101), Fe (up to 5 mg L\u20101) and Tl (up to 260 \u3bcg L\u20101). Their concentrations, however, are partially diluted in the mine due to a mixing with less mineralised waters before being discharged into the Piave River, the major tributary downstream from the mining area. Although drainage waters are still characterised by high concentrations of Tl (about 30 \u3bcg L\u20101) at their outflow, dilution in the Piave River seems to be the only natural process mitigating the impact of PHEs within the drainage basin

The effects of resuspension on the fate of Hg in contaminated sediments (Nal\uf3n estuary, Spain)

Sediments of the Nal\uf3n estuary (Cantabrian Sea, Spain) are important repositories of mercury as a direct consequence of the runoffs from the historical Hg mining activity developed in the Nal\uf3n river basin. Previous studies have shown that sediment acts as secondary source of Hg species to the overlying water column in natural conditions. However, evidence for the effects of resuspension on the dynamics of Hg species is still lacking. The effect of resuspension on the cycling of inorganic mercury (IHg) and methylmercury (MeHg) between the sediment and water column was investigated in a mesocosm study. Two experiments were conducted in July 2017 based on unaltered material collected from sites heavily impacted by Hg and periodically subjected to dredging activities. Designed to mimic the resuspension of particles, both experiments revealed that the release of Hg species from the solid to the dissolved phase became negligible quickly after the event. MeHg values did not change according to total dissolved mercury (THg), suggesting that the enhancement of methylation processes may occur during this processes. The results reported in this research may be useful for the local fishing activities and environmental management, as well as for planning dredging activities on the area in order to decrease potential impacts on the aquatic environment

Ciclo biogeochimico del mercurio in un ambiente lagunare modificato dall'attivit\ue0 di vallicoltura (Laguna di Grado)

Il progetto \ue8 basato su uno studio multidisciplinare nella Valle Noghera, una delle poche valli da pesca rimaste ancora attive nella Laguna di Grado, nella quale \ue8 stato riscontrato il bioaccumulo del mercurio (Hg) in alcune specie ittiche d\u2019interesse commerciale. La pericolosit\ue0 del Hg \ue8 legata alla sua forma organica pi\uf9 tossica, il metilmercurio (MeHg), perch\ue9 facilmente bioaccumulabile lungo la rete trofica acquatica. L\u2019attivit\ue0 di ricerca sperimentale ha permesso di approfondire i processi e le dinamiche coinvolgenti questo metallo nell\u2019ecosistema vallivo, dal sedimento all\u2019acqua fino al biota, valutando gli input lagunari e gli output vallivi del Hg in forma disciolta e particellata. Dapprima \ue8 stata eseguita una caratterizzazione geochimica e geocronologica del sedimento. \uc8 stata determinata sia la concentrazione del Hg totale nei sedimenti superficiali e di fondo per definirne la distribuzione spaziale sia un\u2019analisi speciativa mediante pirolisi per individuare le tre principali forme chimiche con le quali si presenta; al fine di identificare la percentuale di Hg facilmente rimobilizzabile e potenzialmente \u201cpericolosa\u201d per la rete trofica. Successivamente, sono stati scelti due siti studio in due canali principali dove poter eseguire esperimenti stagionali in situ volti a valutare sia la mobilit\ue0 del metallo che dei nutrienti, poich\ue9 indicatori dello stato trofico del sistema vallivo. La scelta dei siti \ue8 avvenuta a seguito della registrazione, in ciascuno, dei parametri chimico-fisici dell\u2019acqua misurati in continuo da una sonda multiparamertrica per un periodo di circa un mese. Individuati i siti, la mobilit\ue0 del Hg totale, MeHg e dei nutrienti all\u2019interfaccia acqua-sedimento \ue8 stata indagata impiegando una camera bentica in situ e raccogliendo carote di sedimento superficiale, sottoposte poi ad estrusione in atmosfera inerte per estrarne le acque interstiziali. Lo scopo era calcolare rispettivamente i flussi bentici (reali) e diffusivi (istantanei) all\u2019interfaccia acqua-sedimento per valutare l\u2019eventuale biodisponibilit\ue0 del Hg per il biota e lo stato di trofia in relazione alla variabilit\ue0 stagionale. Ultimo step, sempre negli stessi due siti, sono state eseguite delle misure in continuo di Hg elementare gassoso all\u2019interfaccia acqua-aria per stimare l\u2019entit\ue0 di evasione attraverso il calcolo di flussi orari. Infine, sono state investigate le interazioni del metallo con la componente ittica, sia in specie allevate a fine commerciale sia in specie che pascolano libere in valle. La comprensione del ciclo biogeochimico del Hg in questo ambiente fortemente modificato dall\u2019uomo ha permesso di suggerire interventi ingegneristici e buone pratiche gestionali atte a mitigare l\u2019influenza di questo metallo sul biota.The research project is based on a multidisciplinary study in the Val Noghera, one of the few fish farms still active in the Grado Lagoon where mercury (Hg) bioaccumulation was found in some species of commercial interest. The level of risk with regards to Hg is due to its more toxic organic form, methylmercury (MeHg), because it is easily bioaccumulable along the aquatic trophic chain. The experimental research activity was focused on investigating the processes and dynamics involving Hg in the fish farm ecosystem (sediment, water column and biota), evaluating lagoon input and fish farm output of Hg in dissolved and particulate form. Initially, a geochemical characterisation of the sediment was performed to determine the total Hg concentration in the surface and bottom sediments in order to define its spatial distribution. Secondly, the three main Hg chemical forms were identified by pyrolysis in order to establish which is the easily remobilisable Hg percentage potentially dangerous to the food chain. Subsequently, two study sites were selected in two main channels in order to perform in situ seasonal experiments to evaluate the mobility of Hg and nutrients which are indicators of the fish farm trophic state. The two sites were previously chosen on the basis of the different chemical-physical parameters of waters measured in continuum by a multiparameter probe for a period of approximately one month. The mobility of the total Hg, MeHg and nutrients at the sediment-water interface (SWI) was investigated at each site using an in situ benthic chamber and collecting short sediment cores, which were extruded in inert atmosphere to extract porewaters. The aim was to estimate benthic (real) and diffusive (instantaneous) fluxes, respectively, at the SWI to evaluate the Hg bioavailability to the biota and the trophic state of the system in relation to the seasonal variability of the chemico-physical water column parameters. Next, water samples were collected at three different channel depths at the same sites: surface, middle and bottom. The aim was to determine the dissolved Hg and Methyl-Hg as well as nutrients along the water column in order to identify possible concentration gradients. Once Hg concentrations at the SWI and along water column were determined continuous measurements of gaseous elemental Hg (GEM) at the water-air interface were carried out in order to estimate the GEM hourly fluxes. Finally, the interaction between Hg and biota (fish) was investigated. Total Hg concentration was determined both in fish of commercial interest and in the same species that live freely in fish farm environment. The understanding of Hg biogeochemical cycling in this environment strongly modified by human activities has opened the path to suggest new plans, mostly engineering, and good management practices to mitigate the influence of this metal on the biota, thus improving the quality of this system