Introduction

Heavy metals are natural constituents of the Earth's crust and are present in varying concentrations in all ecosystems. Human activity has drastically changed the biogeochemical cycles and balance of some heavy metals. Heavy metals are stable and persistent environmental contaminants since they cannot be degraded or destroyed. Therefore, they tend to accumulate in the soils, seawater, freshwater, and sediments. Excessive levels of metals in the marine environment can affect marine biota and pose risk to human consumers of seafood. Heavy metals are also known to have adverse effects on the environment and human health.

The main anthropogenic sources of heavy metals are various industrial sources, including present and former mining activities, foundries and smelters, and diffuse sources such as piping, constituents of products, combustion by-products, traffic, etc. Relatively volatile heavy metals and those that become attached to airborne particles can be widely dispersed on very large scales. Heavy metals conveyed in aqueous and sedimentary transport enter the normal coastal biogeochemical cycle and are largely retained within near-shore and shelf regions.

During the last 2-3 decades considerable attention has been given to problems concerning negative effects of heavy metals (HMs) on various ecosystems in different environmental media. Numerous field observations indicate a significant increase of HM concentrations in agricultural and forest soils as well as in marine and inland water sediments. This increase is frequently observed in remote areas thousands of kilometers away from major anthropogenic sources and can be explained by transboundary atmospheric long-range transport only. An assessment of the potential ecological and health risks associated with atmospheric fluxes of heavy metals requires an understanding of the relationships between sources of emission to the atmosphere and the levels of concentrations measured in ambient air and precipitation. In 1998 in Aarhus (Denmark) 36 Parties to the Convention on Long-Range Transboundary Air Pollution signed the Protocol on HMs. The Protocol is aimed at the at elimination, restriction on use, and reduction of HM emissions to the environment. The main tasks of EMEP in the field of heavy metals are to provide monitoring and modeling data on concentrations, depositions and transboundary fluxes of HMs over Europe.

In line with recommendations of the Steering Body and scientific Workshops the MSC-E model was compared with the most comprehensive scientific models for lead and cadmium. An integrated program for the intercomparison study of mercury models was developed and the third stage of it was realized in 2004. The intercomparison results for lead and cadmium showed that MSCE-HM model adequately reproduces the pattern of concentrations and deposition distributions both in individual grid cells and over the whole modeling region. It allowed to use the model on the operational basis for solving the problems challenging EMEP.

The work on assessment of HM environmental contamination was carried out in accordance with EMEP work plan.