Stefano Covelli

Mercury contamination of coastal sediments as the result of long-term cinnabar mining activity (Gulf of Trieste, northern Adriatic sea) ☆

Abstract 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 the length 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 the fine silt-clay ( 210 Pb 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 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 in contaminated coastal environments; a case study : the Gulf of Trieste

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, originating from the Soca river, that drains the cinnabar deposits of the worlds 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. Mercury 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.

Mercury and methylmercury in the Gulf of Trieste (northern Adriatic Sea)

The distribution, sources and fate of mercury (Hg) in the water column of the Gulf of Trieste (northern Adriatic Sea), affected by the Hg polluted river Soca/Isonzo for centuries draining the cinnabar-rich deposits of the Idrija mining district (NW Slovenia), were studied in terms of total and dissolved Hg, reactive Hg, total and dissolved methylmercury (MeHg), mesozooplankton Hg and MeHg, and sedimentation rates of particulate Hg. Higher total Hg concentrations in the surface layer were restricted to the area of the Gulf in front of the river plume expanding in a westerly direction. Higher concentrations in bottom water layers were the consequence of sediment resuspension. Dissolved Hg exhibited higher concentrations in the surface layer in the area in front of the river plume. Higher bottom concentrations of dissolved Hg observed at some stations were probably due to remobilization from sediments, including resuspension and benthic recycling. The relationship between dissolved Hg in the surface layer and salinity showed nonconservative mixing in June 1995 during higher riverine inflow and nearly conservative mixing in September 1995 during lower riverine inflow. Both mixing curves confirm the river Soca/Isonzo to be the most important source of total and dissolved Hg, which are significantly correlated, in the Gulf. Reactive Hg is significantly correlated with dissolved Hg, indicating that the majority of dissolved Hg is reactive and potentially involved in biogeochemical transformations. The higher total MeHg in the bottom layer is the result of remobilization of MeHg from sediments including benthic fluxes. Strong seasonal variation of sedimentation rates of particulate Hg was found during a 2-year study in the central part of the Gulf. These variations followed those of total sedimented matter, indicating that sedimented Hg is mostly associated with inorganic matter. About a 2.5-fold higher fluxes of particulate Hg were observed at the depth of 20 m relative to 10 m which is attributed to bottom sediment resuspension. Temporal variability of mesozooplankton Hg and MeHg is the consequence of biomass and species variations, and grazing behaviour. From the preliminary Hg mass balance it appears that the Gulf is an efficient trap for total Hg and a net source of MeHg.

Heavy metal contamination in sediments of an artificial reservoir impacted by long-term mining activity in the Almadén mercury district (Spain)

Sediments from the Castilseras reservoir, located downstream on the Valdeazogues River in the Almadén mercury district, were collected to assess the potential contamination status related to metals(oids) associated with river sediment inputs from several decommissioned mines. Metals(oids) concentrations in the reservoir sediments were investigated using different physical and chemical techniques. The results were analyzed by principal component analysis (PCA) to explain the correlations between the sets of variables. The degree of contamination was evaluated using the enrichment factor (EF) and the geoaccumulation index (Igeo). PCA revealed that the silty fraction is the main metals(oids) carrier in the sediments. Among the potentially harmful elements, there is a group (Al, Cr, Cu, Fe, Mn, Ni, and Zn) that cannot be strictly correlated to the mining activity since their concentrations depend on the lithological and edaphological characteristics of the materials. In contrast, As, Co, Hg, Pb, and S showed significant enrichment and contamination, thus suggesting relevant contributions from the decommissioned mines through fluvial sediment inputs. As far as Hg and S are concerned, the high enrichment levels pose a question concerning the potential environmental risk of transfer of the organic forms of Hg (mainly methylmercury) from the bottom sediments to the aquatic food chain.

Oxygen, carbon, and nutrient exchanges at the sediment–water interface in the Mar Piccolo of Taranto (Ionian Sea, southern Italy)

In the shallow environment, the nutrient and carbon exchanges at the sediment–water interface contribute significantly to determine the trophic status of the whole water column. The intensity of the allochthonous input in a coastal environment subjected to strong anthropogenic pressures determines an increase in the benthic oxygen demand leading to depressed oxygen levels in the bottom waters. Anoxic conditions resulting from organic enrichment can enhance the exchange of nutrients between sediments and the overlying water. In the present study, carbon and nutrient fluxes at the sediment–water interface were measured at two experimental sites, one highly and one moderately contaminated, as reference point. In situ benthic flux measurements of dissolved species (O2, DIC, DOC, N-NO3−, N-NO2−, N-NH4+, P-PO43−, Si-Si(OH)4, H2S) were conducted using benthic chambers. Furthermore, undisturbed sediment cores were collected for analyses of total and organic C, total N, and biopolymeric carbon (carbohydrates, proteins, and lipids) as well as of dissolved species in porewaters and supernatant in order to calculate the diffusive fluxes. The sediments were characterized by suboxic to anoxic conditions with redox values more negative in the highly contaminated site, which was also characterized by higher biopolymeric carbon content (most of all lipids), lower C/N ratios and generally higher diffusive fluxes, which could result in a higher release of contaminants. A great difference was observed between diffusive and in situ benthic fluxes suggesting the enhancing of fluxes by bioturbation and the occurrence of biogeochemically important processes at the sediment–water interface. The multi-contamination of both inorganic and organic pollutants, in the sediments of the Mar Piccolo of Taranto (declared SIN in 1998), potentially transferable to the water column and to the aquatic trophic chain, is of serious concern for its ecological relevance, also considering the widespread fishing and mussel farming activities in the area.

Morphoneotectonics and lithology of the eastern sector of the Gulf of Trieste (NE Italy)

ABSTRACT The paper aims to describe and map the geomorphological and lithological features of the Gulf of Trieste and its eastern coasts and to define its neotectonic behaviour by means of the analysis of the morphoneotectonic evidence. The final map, produced at a scale of 1:30,000, shows the outcome of field investigations carried out along the coast and the sea bottom and a detailed geomorphological classification of the coastline. Published and new data coming from the analysis of archaeological remains, geomorphological and sedimentological sea-level indicators and geophysical researches are discussed in order to provide a complete overview of the study area.

Occurrence and speciation of arsenic and mercury in estuarine sediments affected by mining activities (Asturias, northern Spain)

Sediments contaminated by Hg and As from two historical mining areas have been deposited in the Nalón estuary (Asturias, northern Spain) since 1850. Total mercury (Hgtotal) concentrations in the sediments range from 0.20 μg g-1 to 1.33 μg g-1, most of it in the form of sulphides. Concentrations of methylmercury (303.20-865.40 pg g-1) are up to two orders of magnitude lower than the concentration of Hgtotal. Total As concentration (Astotal) is enriched compared to the background level for the area. The relative abundance of As(V) on As(III) in the sediments ranges from 97.6% to 100%, whereas inorganic Hg accounts for more than 99% of the total Hg. The occurrence of the most toxic species, inorganic As(III) and organic methylmercury, seem to be related to redox conditions together with the amounts of sulphur which act as natural barriers which inhibit the biological and chemical speciation processes. Despite the high amounts of Hg and As present in the sediments, their transference to the water column appear to be limited thus converting sediments in an effective sink of both elements. Special attention should be paid to potential variations of the environmental conditions which might increase the element mobility and exchange between sediments and the water column.

Integrated environmental characterization of the contaminated marine coastal area of Taranto, Ionian Sea (southern Italy).

The Project RITMARE (la Ricerca ITaliana per il MARE—Italian Research for the sea) is one of the national research programs funded by the Italian Ministry of University and Research. RITMARE (2012–2016), coordinated by the National Research Council (CNR), and has involved an integrated effort of most of the scientific community working on marine and maritime issues. Within the project, different marine study areas of strategic importance for the Mediterranean were identified: among these, the coastal area of Taranto (Ionian Sea, southern Italy) was chosen for the presence of large industrial settlements and their impact on the marine environment. In particular, the research has been focused on the Mar Piccolo of Taranto, a complex marine ecosystem model important both from an ecological and social–economic points of view. In fact, water, sediments, and biota in the Mar Piccolo have been affected by a wide spectrum of anthropogenic pressures (among others, the most important iron and steel plant in Europe, the largest Italian Navy shipyard, an oil refinery, and shipbuilding activities) for decades. These stress factors have been responsible for a severe environmental contamination, mainly due to heavy metals, polycyclic aromatic hydrocarbons (PAHs), organic solvents, polychlorinated biphenyls (PCBs), and dioxin, with their consequent possible transfer to the aquatic trophic chain also considering the widespread fishing and mussel farming activities in this area. Within the project RITMARE, a task force of researchers composed of hydrogeologists, modellists, sedimentologists, geochemists, chemists, microbiologists, and biologists has contributed to elaborate a working conceptual model with a multidisciplinary approach useful to identify sources of anthropogenic stress, their impacts, and possible solutions of environmental remediation. Several topics have been addressed, among them: identification of sources of contaminants and anthropogenic pressures, distribution of contaminants, water mass circulation and sedimentary fluxes, biogeochemical cycling, bioaccumulation and biomagnification of contaminants, and risk analysis. All of them have been included in the conceptual model of the Mar Piccolo in order to provide the necessary input to a decision support system which should help in evaluating the correct mitigation strategies to be adopted. Therefore, this could be considered a comprehensive pilot study that may be applied to other shallow coastal environments with similar contamination issues. This special issue contains a collection of 22 publications. The review by Cardellicchio et al. (2015) introduces the state of knowledge on the Mar Piccolo, before the beginning of the RITMARE project, the ecological importance of this basin and its environmental issues. Two articles present the output of numerical modeling: the first by Zuffianò et al. (2015) defines the contribution of subaerial and submarine coastal springs to the hydrological dynamic equilibrium of the basin while De Pasca l i s e t a l . (2015) examine the ma in * Tamara Cibic tcibic@ogs.trieste.it

Trace metal pollution in freshwater sediments of the world’s largest mercury mining district: sources, spatial distribution, and environmental implications

PurposeThe Almadén mining district has suffered long-term extraction activity, and this has left significant areas of decommissioned mining liabilities. Nowadays, the uncontrolled runoff and related erosion and transport of trace metal-enriched soils and sediments affect the whole freshwater ecosystem. The goal of this study was to distinguish geogenic from mining-related sources of trace metals in freshwater sediments, to understand their dispersion in the watershed, and, finally, to evaluate the potential environmental implications for future corrective plans.Materials and methodsFreshwater surface sediment samples were collected from ten points along the main streams of the watershed (nine inside the mining district and one control point outside the district). Sediments were air dried and analyzed by different standard methods for pH, total major and trace element concentrations, total organic carbon, and grain size. In addition to the determination of the enrichment factor, a multi-statistical approach was applied involving discriminant analysis, Student’s t test, and Mann-Whitney U analysis.Results and discussionSediments inside the district contained high levels of major and trace elements with respect to the control point. The predominance of fine fractions in these sediment samples appears to be one of the most important factors that affects trace metal concentrations. Among the trace elements, not only Hg but also As, Pb, and Zn are discriminative geochemical markers, thus allowing the identification of the different mining sources and their individual or combined impact throughout the district. Furthermore, the high enrichment factors obtained for As, Hg, Pb, and Zn with respect to the local background values highlight the persistent and severe impact from the decommissioned mines on the freshwater surficial sediments and their potential geoavailable risk for aquatic organisms.ConclusionsThe geochemistry of freshwater sediments alone demonstrates that different contamination sources are recognizable within the mining district and these can be related to the specific decommissioned mines. In addition, the discrete sources can be clearly distinguished on the basis of the statistical analysis of the geochemical data. Despite the closure of the mines, stream sediments are still the main repository of trace metals within the district, and they are therefore a potential threat to the freshwater ecosystem.

Evaluation of mercury biogeochemical cycling at the sediment–water interface in anthropogenically modified lagoon environments

The Marano and Grado Lagoon is well known for being contaminated by mercury (Hg) from the Idrija mine (Slovenia) and the decommissioned chlor-alkali plant of Torviscosa (Italy). Experimental activities were conducted in a local fish farm to understand Hg cycling at the sediment-water interface. Both diffusive and benthic fluxes were estimated in terms of chemical and physical features. Mercury concentration in sediments (up to 6.81μg/g) showed a slight variability with depth, whereas the highest methylmercury (MeHg) values (up to 10ng/g) were detected in the first centimetres. MeHg seems to be produced and stored in the 2-3cm below the sediment-water interface, where sulphate reducing bacteria activity occurs and hypoxic-anoxic conditions become persistent for days. DMeHg in porewaters varied seasonally (from 0.1 and 17% of dissolved Hg (DHg)) with the highest concentrations in summer. DHg diffusive effluxes higher (up to 444ng/m2/day) than those reported in the open lagoon (~95ng/m2/day), whereas DMeHg showed influxes in the fish farm (up to -156ng/m2/day). The diurnal DHg and DMeHg benthic fluxes were found to be higher than the highest summer values previously reported for the natural lagoon environment. Bottom sediments, especially in anoxic conditions, seem to be a significant source of MeHg in the water column where it eventually accumulates. However, net fluxes considering the daily trend of DHg and DMeHg, indicated possible DMeHg degradation processes. Enhancing water dynamics in the fish farm could mitigate environmental conditions suitable for Hg methylation.