PROSPECTS FOR MODELING THE BEHAVIOR AND FATE OF MERCURY, GLOBALLY AND IN AQUATIC SYSTEMS

The phenomena of cold condensation and fractionation of chemical contaminants on a global scale are discussed. The net result of these phenomena is that concentrations of certain atmospherically transported contaminants are higher than expected in the condensed, i.e. non gaseous media of water, soils, sediments and biota as a result of the temperature dependence of partitioning and transport phenomena. It is argued that the phenomena are best investigated by a combination of monitoring and modeling. This approach is illustrated in the form of a nine meridional segment model for hexachlorocyclohexane. It is suggested that this approach should be applied to Hand but this is not presently possible because of the lack of data on Hg species properties and conversion rates. Available data have been used to test the hypothesis that lower temperatures cause enhanced partitioning from the atmosphere to a lake ecosystem at low temperatures by compiling a three species model of an atmosphere-water-sediment-fish system at 25 degrees C and 0 degrees C. Preliminary results show that the effect of this drop in temperature is to cause increases in concentrations throughout the aquatic ecosystem of factors of three to four, other factors being equal. Thus it is likely that a comprehensive global model will show that Hg is subject to the global fractionation phenomenon. It is recommended that attempts be made to develop such a model.