Distribution of mercury in the atmosphere over Idrija, Slovenia

Idrija mine, the second largest mercury mine in the world, was in use since 1490. More than 107 000 tons of Hg were produced in its five centuries of history until 1990 when production was reduced to a few hundred kilos per year. The average recovery rate of mercury has been estimated to 73%; much of the remaining 27% was dissipated into the environment. In spite of present minimal levels of production, and only a few days of smelter operation per year, a real time survey with a mercury Zeeman analyser in a car showed relatively high mercury concentrations in the air. Amounts of 300--4000 ng Hg ^m-3 have been found around both the major sources of mercury vapour, the smelter and mine ventilation shaft -- while the amounts at the Old Place, at the City Museum, and near the Nikova-Idrijca confluence are of the order of 50 ng m^-3. Polluted air will be transported from those sources to a degree which depends on the weather conditions, mainly the direction and intensity of the wind. The high mercury contents in the air are not only due to anthropogenic sources (smelter and the ventilation shaft, dumps and smelter slag used in construction), but may also partly be natural as in the Pront area, where the outcropping bedrock contains native mercury.