Mercury in contaminated coastal environments, a case study: the Gulf of Trieste

Some general facts, uncertainties and gaps in current knowledge of Hg cycli ng 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, orig inating from the Sofa 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, t he Gulf is also a subject to industrial and sewage pollution. Due to deteri orating water quality in the Gulf these is a great concern that Hg can be r emobilized from sediments to the water column as well as enhance methylatio n rates which may consequently increase already elevated Hg levels in aquat ic organisms. The paper presents data from a recent study which aims to ass ess the extent of contamination of the Gulf of Trieste after the closure of the Hg mine. Mercury and methylmercury were measured in various environmen tal compartments (estuarine and marine waters, sediments, and organisms) du ring the period 1995-1997. Data obtained show that even 10 years after clos ure of the Hg mine, Hg concentrations in river sediments and water are stil l very high and did not show the expected decrease of Hg in the Gulf of Tri este. A provisional annual mercury mass balance was established for the Gul f of Trieste showing that the major source of inorganic mercury is still th e River Sofa (Isonzo) while the major source of methylmercury is the bottom sediment of the Gulf. (C) 1999 Elsevier Science B.V. All rights reserved.