Mercury and methylmercury contamination in Mytilus galloprovincialis from Taranto Gulf (Ionian Sea, Southern Italy): Risk evaluation for consumers
Introduction
In the marine environment, levels of contaminants have been increasing over the last decades, as a consequence of anthropogenic activities. Pollutants are potentially accumulated in organisms and sediments, and subsequently transferred to man through the food chain. Coastal zones, particularly near large urban centres, are of concern as they receive the largest exposure to chemical contamination, due to source proximity.
Contamination of marine organisms with toxic chemicals, such as, mercury has become intensively studied in recent years, due to the fact that mercury and its compounds are persistent, toxic, tend to bioaccumulate, and they pose human and ecosystem risks. Most of inorganic and organic mercury in aquatic environment appears to be bound to particles, colloids and high molecular weight organic matter (Horvat, 1977). The greater part of the mercury introduced into the coastal sea precipitates because of the very low solubility products of its compounds, and accumulates in the sediment which represents the principal sink. Due to bacterial activity, inorganic mercury in sediment may also be converted into the more toxic methylmercury. The methylmercury formed may readily dissolve in the water column and then could be taken up by the aquatic organisms and accumulated (Gagnon and Fisher, 1997). Methylmercury readily enters the aquatic food chain and it may be biomagnified as it accumulates in higher trophic levels and so the main pathway for mercury and methylmercury exposure in humans is seafood and fish consumption.
The relatively shallow waters in the Gulf of Taranto (Ionian Sea, Southern Italy), yield large numbers of mussels. Mar Piccolo basin represents a coastal marine ecosystem example, whose biological balances have been modified step by step, in relation to the anthropic development and, in particular, to the big industry settlement (iron and steel factory, petroleum refinery and shipyard). For these intense anthropogenic impacts, Taranto city has been identified as an “Area of High Environmental Risk” (Law n.349/1986). Later on, the Law n.426/1998 classified it as “Site of National Interest” including the site in the “National Project of Environmental Restoration”.
The Mar Piccolo basin is located in the Northern area of the Taranto town, Italy. It is an inner, semi-enclosed basin (surface area of 20.72 km2), with lagoon features, divided into two inlets, called first and second inlet, which have a maximum depth of 13 and 8 m, respectively. Tidal range does not exceed 30–40 cm. The scarce hydrodynamism and the low water exchange with the nearby Mar Grande basin determine, mainly in summer, a high water stratification. Mar Piccolo basin is influenced by urbanization, by harbour activities, by aquaculture and commercial fishing. The main problems of environmental impact are: nine pipes discharge sewages, the shipyard of the Italian Navy with its dry-docks (located in the first inlet), the largest mussel farm distributed in both the inlets, the fishing-boat fleet localized in the first inlet and small rivers and freshwater springs which drain the surrounding agricultural soils in the basin.
Mussels production in the Mar Piccolo is about 30,000 t/y. Only a part of the locally harvested seafood is used for home consumption, while most is exported to European Economic Community countries, in particular to Spain.
The aim of this work was to determine the concentration of total mercury (THg) and methylmercury (Me-Hg) in the mussels collected at 10 sites from Mar Piccolo, in order to investigate contamination level and public health risks associated with consuming mussels harvested from these areas. Moreover the goal of this study was also to estimate the weekly intake and compare it with the provisional tolerable weekly intake (PTWI) recommended by the European Food Safety Autority (EFSA, 2004).
Section snippets
Sampling of mussels
Mussels (Mytilus galloprovincialis Lam.) were collected in 10 stations of the Mar Piccolo of Taranto, seven stations in first inlet and three in the second inlet (Fig. 1). The Food and Agricultural Organisation recommendations for sampling, handling and specimen storage as described in the FAO Fisheries Technical Paper (1976), were followed. One hundred mussels of similar length (4–5 cm long, commercial size) were collected at the same intertidal depth.
Mussels of the same size were selected to
Total mercury in mussel
Table 2 showed mean values of THg and Me-Hg concentrations, together with the percentages of methylmercury to total mercury in analysed mussels. THg values in the mussels ranged from 0.236 to 0.559 μg g−1 d.w.. THg concentrations in mussels collected in the first inlet (stations 1–7) ranged from 0.236 to 0.559 μg g−1 d.w., with an average value of 0.386 μg g−1 d.w. while THg concentrations in the mussels of the second inlet (stations 8–10) ranged from 0.262 to 0.370 μg g−1 d.w., with an average value of
Conflict of Interest
The authors declare that there are no conflicts of interest.
Acknowledgment
The authors thank Mrs. Cristina Annichiarico for her collaborations with experimental activities.
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