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

The Isonzo river mouth has been the sourer of HE in the Gulf of Trieste (no rthern 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 0.06 4-30.38 mug g(-1); average 5.04 mug g(-1); median 3.10 mug g(-1), n = 80) a nd related size fractions in sediments of this coastal area were investigat ed in detail. The relationship between total Hg and the fine silt-clay (< 1 6 <mu>m) fraction has provided information on the hydrological and mineralo gical fractionation process affecting this element, when compared to other heavy metals associated with fluvial inputs. Mercury 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 ri ver mouth and the surrounding beaches. Within the sediments belonging to th e Gulf area, Hg is bound either to fine particles or adsorbed onto the surf ace of clay minerals and/or partially complexed by colloids and organic mat ter. Recent accumulation of Hg in a 70 cm long Pb-210 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 t hat the first 50 cm of sediment in the central sector of the Gulf of Triest e are noticeably contaminated, reaching a maximum of up to 25-fold above th e proposed natural regional background of 0.17 mug g(-1). The vertical tren d is well correlated to historical data of Hg extraction activity at the Id rija mine. (C) 2001 Elsevier Science Ltd. All rights reserved.