Mercury distribution in the krka river Estuary (Eastern Adriatic Coast)

Abstract

The investigation of the distributions of total and organic mercury was carried out in the water, sediments and mussels of the Krka River Estuary and the Kornati Archipelago (eastern Adriatic coast) during 1985–1987. The mercury content of the silt/clay sediment fraction (< 75 μm) was analyzed to reduce the influence of irregular sediment structure. The results obtained suggest that both the Krka River and the Kornati Archipelago are unpolluted by mercury. A slight increase in the mercury concentrations in the central part of the estuary points to the possibility of pollution by anthropogenic sources. The distribution of the concentration of reactive mercury (0.3–3.0 ng dm −3)in the unfiltered water followed the distribution pattern obtained for sediment. The portion of reactive versus total mercury in water was considerably lower in the freshwater surface layer (30–50%) than in the deeper saline water layer ( > 80% ) of the stratified Krka River Estuary. Mercury accumulation was observed at the interface of these two layers (at the halocline). The concentrations of mercury in mussels ( Mytilus galloprovincialis, Link.) (10–50 μg kg −1 wet wt.) were significantly affected by internal biological factors, and their distribution differed from the pattern observed for sediments and water. Despite the fact that organic mercury has been detected in sediments (≈0.5% of total) and the edible part of the mussels (13–65%), it has not for a certainty been established in water. A tendency to consider the Mediterranean as an area of higher ‘natural mercury levels’ has been challenged by the fact that the concentrations obtained are in the same range as those obtained for other unpolluted marine areas throughout the world.