Resumen
External pollution load in the Baltic Sea originates from urban, agricultural and industrial sources. Emissions of heavy metals have decreased substantially in the catchment area but the temporal trends are not always significant and differ with sample, area and pollutant. The most significant source of anthropogenic radioactivity in the Baltic Sea is fallout from the Chernobyl accident in 1986. Many factors affect the future development of pollutant concentrations including anthropogenic emissions, political decisions and changes in salinity, temperature and water currents, in eutrophication and oxygen status, in fisheries and in atmospheric deposition of pollutants. Large scale changes like eutrophication and climate change affect ecosystems in many ways, directly and indirectly, causing biological and abiotic effects. These factors are interrelated and difficult to predict. Measures aiming to enhance the ecological status of the Baltic Sea will certainly give positive results but this will take at least several decades.