il mercurio nel sedimento

Sediments of the Marano and Grado Lagoon (Adriatic Sea, Italy) represent one of the world’s most major repositories of mercury (Hg). Its presence is a direct consequence of the historical mining activity in nearby Idrjia (Slovenia), as well as significant discharges from a chlor-alkali plant into the AussaeCorno river system, which connects to the lagoon. 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 work reported in this paper formed part of the multidisciplinary “MIRACLE” project, aimed at identifying areas at low risk of Hg bioaccumulation in commercial Manila Clams, an important part of the local economy in this region. The effect of resuspension on the cycling of inorganic mercury (IHg), reactive mercury (RHg) and methylmercury (MeHg) between the sediment and water columnwas investigated in a mesocosm study. Two experiments were conducted in October 2009 and September 2010 based on 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 mercury (THg), suggesting that the enhancement of methylation processes may occur. The findings reported in this paper may be useful for the local management of dredging and fishing activities, although mass balance calculations showed that the total flux of Hg species are trivial compared to lagoon-wide processes.

The “MIRACLE” Project was established in order to assess the feasibility of clam farming and high levels of sediment mercury (Hg) contamination coexisting in the Marano and Grado Lagoon, Italy. This lagoon has been subjected to Hg input from both industrial waste (chlor-alkali plant) and long-term mining activity (Idrija mine, NW Slovenia). One of the subtasks of the “MIRACLE” Project was to determine the historical evolution of Hg accumulation in the lagoon’s bottom sediments. Thirteen 1-m deep sediment cores were collected from the subtidal and intertidal zones, plus one in a saltmarsh, all of which were then analyzed for total Hg content and several physicochemical parameters. Sedimentation rate assessments were performed by measuring short-lived radionuclides (excess 210Pb and 137Cs). For most of the analyzed cores, natural background levels of Hg were observed at depths of 50-100 cm. In the eastern area, Hg contamination was found to be at its maximum level at the core top (up to 12 μg g
-1) as a consequence of the long-term mining activity. The vertical distribution of Hg was related to the influence of the single-point contamination sources, whereas the grain-size variability or organic matter content seemed not to affect it. In the western area, Hg content at the surface was found not to exceed 7 μg g
-1 and contamination was recorded only in the first 20-30 cm. Geochronological measurements showed that the depositional flux of Hg was influenced by anthropogenic inputs after 1800, when mining activity was more intense. After 1950, Hg in the surface sediment, most remarkable in the centralwestern sector, seemed to also be affected by the discharge of the Aussa River, which delivers Hg from the chlor-alkali plant. In 1996, Hg mining at Idrija ceased, however the core profiles did not show any subsequent decreasing trend in terms of Hg flux, which implies the system retaining some “memory” of contamination. Thus, in the short term, a decrease in Hg inputs into the nearby Gulf of Trieste and the lagoon seems unlikely. A preliminary rounded-down gross estimate of total Hg “trapped” in the lagoon’s sediments amounted to 251 t. Such a quantity, along with the complexity of the lagoon ecosystem, suggests that an in toto reclamation of the sediments at the lagoon scale is unfeasible, both economically and environmentally.

The existence of mining tailings in Idrija (Slovenia) and their subsequent transportation via the Isonzo River has been the primary source of mercury (Hg) in the northern Adriatic Sea for almost 500 years, making the Gulf of Trieste and the adjacent Marano and Grado Lagoon two of the most contaminated marine areas in the world. A further, more recent, contribution of Hg has been added by the operation of a chlor-alkali plant (CAP) located in the drainage basin flowing into the Lagoon. On the basis of previous research, as well as new data obtained from the “MIRACLE” project (Mercury Interdisciplinary Research for Appropriate Clam farming in a Lagoon Environment), the spatial distribution of Hg and its relationships with methylmercury (MeHg), organic matter and several geochemical parameters in surface sediments were investigated. The predominant and long-term impacts of the cinnabar-rich Isonzo River particulate matter in the Lagoon surface sediments are evident and confirmed by a decreasing concentration gradient from east (>11 mg g
1) to west (0.7 mg g
1). Hg originated from the CAP is only significant in the central sector of the Lagoon. Hg is primarily associated with fine-grained sediments (

The Marano and Grado lagoon, one of the largest wetlands in the Mediterranean Sea, has been subject to mercury contamination by industrial and mining activities. This must be considered a severe threat for Manila clam harvesting, which is an important fishing and commercial activity in the area. Contamination levels and potential risk for human consumption both in reared and wild clams collected from the lagoon were assessed by analyzing total mercury (THg) and methylmercury (MeHg) contents. In addition, relationships between THg and MeHg in sediments and in the bivalves were investigated. Increased bioaccumulation of THg but not of MeHg with increasing size of wild clam populations was observed at most sites. Higher concentrations both of THg (605
210 ng g1 ww) and MeHg (147
37 ng g1ww) were detected in the eastern lagoon where the highest THg contents in sediments were observed as a consequence of the long-term supply of cinnabar rich suspended material from the Isonzo river. The variation of Hg content in seeded Manila clams during growth was monitored over a period of 18 months at two sites of the western sector of the lagoon. Results showed that the two areas were suitable for clam farming, with THg levels in reared bivalves always lower than the 0.5 mg kg1ww European Community limit. At the same time, as clams grew bigger in size, their THg and MeHg concentrations decreased, becoming lower than in the starting seeded pool. Reared clams resented lower THg (84
55 ng g1 ww) and MeHg (44.1
24.6 ng g1ww) content than wild clams of the same commercial size (>30 mm). Based on a precautionary approach, intake of Hg and MeHg with the estimated clam consumption does not seem to constitute a risk for human health in the studied area.

Total mercury (Hg) concentrations and Hg speciation were determined in bottom sediments of Marano lagoon to investigate the consequences of Hg phases on fish farms and shellfish cultivation areas. Mercury phases were separated into cinnabar (HgS) and noncinnabar compounds, via a thermo-desorption technique, in surface and core sediments; both of which had been contaminated by industrial wastes and mining activity residues. The former are due to an industrial complex, which has been producing cellulose, chlor-alkali and textil artificial fibres since 1940. Processing and seepage wastewaters, which were historically discharged into the Aussa-Corno river system and therefore into the lagoon, have been significantly reduced since 1984 due to the construction of wastewater treatment facilities. The second source is the Isonzo River, which has been the largest contributor of Hg into the northern Adriatic Sea since the 16th century due to Hg mining at the Idrija mine (western Slovenia). Red cinnabar (HgS) derived from the mining area is mostly stable and insoluble under current environmental conditions. In contrast, organically bound Hg, such as Hg bound to humic acids, has the potential to be transformed into bioavailable Hg compounds (for example, methylmercury). The presence of the two Hg forms permitted each Hg source to be quantified. It also allowed the areas with the highest risk of Hg contamination from Hg-rich sediment to be identified; thus potentially obverting the transfer of Hg from the sediment into the water column and eventually into living biota. The results show that Hg Enrichment Factors in bottom sediments exceed values of ten and cinnabar dominates the central sector near the main tidal channel where tidal flux is more effective. Non-cinnabar compounds were found to be enriched in fine grained material and organic matter. In fact, up to 98% of total Hg at the Aussa-Corno river mouth and in the inner margin of the basin occurred in an organic form. This evidence, combined with the high contents of total Hg (4.1-6.6 µg g-1 and EF > 10) measured in surface sediments, suggest that Hg in Marano lagoon is involved in biogeochemical transformations (e.g. methylation).

Il Bacino di Buso occupa l’area centrale della Laguna di Marano e Grado, situata nell’Adriatico settentrionale. Questi ambienti di transizione presentano un’alta vulnerabilità a causa del pesante impatto antropico dovuto alle attività industriali e agricole che gravano sul bacino lagunare. Inoltre, la laguna di Marano e Grado è stata interessata dal fallout radioattivo a seguito dell’incidente di Chernobyl nel 1986. All’interno del bacino lagunare sono state identificate alcune aree preferenziali di accumulo dei metalli pesanti presi in esame e di 137Cesio. Il grado di arricchimento di alcuni elementi in tracce (Hg, Cr, Zn, Ni e Cu) nei sedimenti attuali è stato confrontato con i tenori degli stessi nei sedimenti di età preindustriale. I tenori di Hg risultano fino a 18 volte superiori ai valori di background naturale. I profili di arricchimento per questo metallo nelle carote hanno evidenziato la persistente contaminazione nel tempo.

Il fiume Isonzo è la principale sorgente di mercurio (Hg) nel Golfo di Trieste (Mar Adriatico ). Un suo tributario, il fiume Idrijca, drena i terreni mercuriferi dell’area di Idria nella Slovenia occidentale. La prolungata attività estrattiva della miniera di Idria si è protratta per circa 500 anni, interrompendosi definitivamente nel 1996. Più di 5 milioni di tonnellate di roccia mineralizzata a Hg (cinabro) sono state escavate e si stima che solo il 73% del Hg ad esse associato sia stato recuperato. Per tale ragione non solamente il sistema fluviale Isonzo-Idrijca ma anche il Golfo di Trieste ha ricevuto e sta attualmente ricevendo elevate quantità di mercurio. Concentrazioni fino a 25-30 µg g-1 del metallo sono state riscontrate alla foce dell’Isonzo evidenziando un decremento esponenziale con la distanza dal punto sorgente verso il mare aperto. Il Hg è presente in forma detritica (cinabro) nei sedimenti siltoso-sabbiosi in prossimità della foce fluviale e nei lidi costieri ad essa adiacenti. Nell’area del centrale del golfo il Hg è associato alle particelle più fini, probabilmente assorbito sulla superficie dei minerali argillosi e/o parzialmente complessato dai colloidi e dalla sostanza organica. L’evoluzione storica della contaminazione da Hg nei sedimenti marini recenti è stata studiata attraverso l’analisi di dettagliato di quattro carote prelevate nel golfo. Il fattore di arricchimento (F.A.) calcolato per il Hg indica che i sedimenti nel settore centrale del Golfo di Trieste sono contaminati fino a 90 cm di profondità e fino ad un massimo di oltre 60 volte il tenore di background regionale per il metallo. L’andamento con la profondità si correla molto bene con i dati relativi all’attività estrattiva ad Idria, tanto da permettere la stima di tassi deposizionali indicativi, in almeno due carote (GT2 e AA1), ed il calcolo dei flussi di Hg nei sedimenti di fondo. Sebbene il flusso di Hg nei sedimenti sia diminuito durante gli ultimi 80 anni e l’attività mineraria si sia arrestata nel 1996, è da ritenere al momento che l’ambiente marino non possa ritornare in un periodo di tempo breve ad una situazione simile a quella originaria, pre-attività estrattiva, poiché gli apporti fluviali sono ancora caratterizzati da elevati tenori di Hg.

The Isonzo River mouth has been the source of Hg in the Gulf of Trieste (Northern Adriatic sea) since the sixteenth century, making this shallow basin one of the most contaminated marine areas in extent of time and amount of metal accumulated. The occurrence and behaviour of total Hg (range 0.064-30.38 µg g-1; average 5.04 µg g-1; median 3.10 µg g-1, n=80) and related size fractions in sediments of this coastal area were investigated in detail. The relationship between total Hg and fine silt-clay (< 16 µm) fraction has provided information on the hydrological and mineralogical fractionation process affecting this element, when compared to other heavy metals associated to fluvial inputs. Hg contents are very high along the littoral zone of the northern (Italian) sector where this metal is present in detrital form (cinnabar) in sandy-silty sediments near the river mouth and the surrounding beaches. Within the sediments belonging to the Gulf area, Hg is bound either to fine particles or adsorbed onto surface of clay minerals and/or partially complexed by colloids and organic matter. Recent accumulation of mercury in a 70 cm long 210Pb dated core, collected in the central part of the Gulf, was also compared to other heavy metals (Fe, Cr, Cu, Mn, Ni and Zn). A preliminary estimate of Hg enrichment shows that the first 50 cm of sediment in the central sector of the Gulf of Trieste are noticeably contaminated, reaching a maximum of up to 25 fold above the preliminary proposed natural regional background of 0.17 µg g-1. The vertical trend is well correlated to historical data of Hg extraction activity at the Idrija mine.

Mercury (Hg) concentrations and Hg phases were investigated in contaminated sediments and flooded soils in the drainage area of the Idrija Hg mine, Slovenia. The main aim of this study was the analytical separation and quantification of cinnabar (HgS) and noncinnabar Hg compounds in sediments contaminated by mining residues. Separation of Hg phases was performed by means of a solidphase-Hg-thermo-desorption technique complemented by selective extraction of organically bound Hg. Speciation measurements indicate the occurrence of two major Hg forms: cinnabar the primary ore and an unspecified group of matrix-bound, noncinnabar Hg compounds. The results show that Hg concentrations and dispersion of the two Hg phases within the river system depend on the distribution of different sediment grain size fractions. Accumulation of cinnabar predominately occurs in corse grained river sediments, where it constitutes on average more than 80% of total Hg (up to 1000 mg/kg) in present- and past day sediments. In contrast noncinnabar Hg was found to be enriched in areas where fine grained material was deposited reaching up to 40% of Hgtot (1-60 mg/kg) in flooded soils and up to 55% (

Some general facts, uncertainties and gaps in current knowledge of Hg cycling in coastal and oceanic environments are given. As a case study the Gulf of Trieste is chosen. The Gulf is subject to substantial Hg pollution, originatine from the Soca river, that drains the cinnabar deposits of the world’s second largest Hg mining area, Idrija, Slovenia. The Gulf belongs to one of the most polluted areas in the Mediterranean. Apart from Hg problems, the Gulf is also a subject to industrial and sewage pollution. Due to deteriorating water quality in the Gulf there is a great concern that Hg can be remobilized from sediments to the water column as well as enhance methylation rates which may consequently increase already elevated Hg levels in aquatic organisms. The paper presents data from a recent study which aims to assess the extent of contamination of the Gulf of Trieste after the closure of the Hg mine. Mercuri and methylmercury were measured in various environmental compartments (estuarine and marine waters, sediments, and organisms) during the period 1995-1997. Data obtained show that even 10 years after closure of the Hg mine, Hg concentrations in river sediments and water are still very high and did not show the expected decrease of Hg in the Gulf of Trieste. A provisional annual mercury mass balance was established for the Gulf of Trieste showing that the major source of inorganic mercury is still the River Soca-Isonzo.while the major source of methylmercury is the bottom sediment of the Gulf.