Me. Hines et al., Mercury biogeochemistry in the Idrija River, Slovenia, from above the mineinto the Gulf of Trieste, ENVIR RES, 83(2), 2000, pp. 129-139
The Idrija Mine is the second largest Hg mine in the world which operated f
or 500 years. Mercury (Hg)-laden tailings still line the banks, and the sys
tem is a threat to the Idrija River and water bodies downstream including t
he Soca/Isonzo River and the Gulf of Trieste in the northern Adriatic Sea.
A multidisciplinary study was conducted in June 1998 on water samples colle
cted throughout the Idrija and Soca River systems and waters and sediments
in the Gulf Total Hg in the Idrija River increased >20-fold downstream of t
he mine from <3 to > 60 ng liter(-1) with methyl mercury (MeHg) accounting
for similar to 0.5%, Concentrations increased again downstream and into the
estuary with MeHg accounting for nearly 1.5% of the total. While bacteria
upstream of the mine did not contain mercury detoxification genes (mer), su
ch genes were detected in bacteria collected downstream. Benthic macroinver
tebrate diversity decreased downstream of the mine. Gulf waters near the ri
ver mouth contained up to 65 ng liter(-1) total Hg with similar to 0.05 ng
liter(-1) MeHg. Gulf sediments near the river mouth contained 40 mu g g(-1)
total Hg with MeHg concentrations of about 3 ng g(-1), Hg in sediment pore
waters varied between 1 and 8 ng liter(-1), with MeHg accounting for up to
85%, Hg methylation and MeHg demethylation were active in Gulf sediments w
ith highest activities near the surface. MeHg was degraded by an oxidative
pathway with >97% C released from MeHg as CO2. Hg methylation depth profile
s resembled profiles of dissolved MeHg. Hg-laden waters still strongly impa
ct the riverine, estuarine, and marine systems, Macroinvertebrates and bact
eria in the Idrija River responded to Hg stress, and high Hg levels persist
into the Gulf. Increases in total Hg and MeHg in the estuary demonstrate t
he remobilization of Hg, presumably as HgS dissolution and recycling, Gulf
sediments actively produce MeHg, which enters bottom waters and presumably
the marine food chain. (C) 2000 Academic Press.