| Summary: | The expression Chemical Time Bombs refers to a chain of events resulting in the delayed and sudden occurrence of harmful environmental effects due to the mobilization of chemicals stored in soils and sediments in response to slow alterations in environmental conditions. This workshop was part of a series of workshops in which basic ideas were developed and regional awareness promoted. The International Workshop on Delayed Environmental Effects of Chemical Pollution with Focus on the Nordic Countries was held in Uppsala, Sweden on 14 and 15 September 1991. A brief account of the discussions and the main conclusions are presented here. It was concluded that the effects in Nordic countries could be extended to areas with similar climate and bedrock conditions. These include the northern parts of Canada and Russia, Scotland, Iceland and Greenland. Fundamentally, Chemical Time Bombs in the Nordic and other cold climate areas do not differ from those in warmer areas. Conditions specific to cold climate areas are generally a thin soil cover, extensive occurrence of peat, and prolonged periods of frost and snow cover. Processes determining the buildup and triggering of Chemical Time Bombs differ only in rate and intensity as far as they are dependent on temperature and daylight. Loads of contaminants identified as being specific to Scandinavia are Hg and potentially toxic organic outputs of papers mills which threaten inland water ecosystems, as well as the Gulf of Bothnia and the Baltic Sea ecosystems. Assessment of risks from Chemical Time Bombs is still in its infancy. Quantitative risk assessment models for the accumulation in soils and sediments of heavy metals and toxic organic pollutants are still lacking.
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