Geochemical baselines in the assessment of soil contamination in Finland

This study provides an overview on the development of the guidelines and legislation related to soil contamination in Finland, with the main focus on geochemical baselines. The use of geochemical baseline surveys in the assessment soil contamination in Finland and in some other countries is briefly discussed and the current practices in Finland are presented. Finally, the geochemical baselines in the assessment of soil contamination in Finland are outlined with suggestions for further applications and recommendations for future research needs. The growing demand to increase sustainable land management in urban areas has involved various applications of geochemical surveys. Soil contamination was acknowledged as a leading environmental problem in the industrialized countries in the 1980s. The Government of Finland highlighted the importance of studying the level of soil contamination in Finland in 1988. The practices and guidelines for the assessment of soil contamination have been further developed by the environmental authorities and other interest groups, and in 2007, a Government Decree on the Assessment of Soil Contamination and Remediation Needs (214/2007) was issued. According to the Government Decree (214/2007), the assessment of soil contamination shall be based on a site-specific estimate of the risks to human health and the environment. Three categories of soil screening values, the threshold value and the lower and the upper guideline value, are introduced in the Government Decree (214/2007). The threshold value is used as a trigger value, which if exceeded indicates the necessity for further investigations on potential contamination. The geochemical baseline concentration, however, is regarded as the assessment threshold in areas with a baseline concentration higher than the threshold value. The Government Decree (214/2007) refers both to the natural geological background concentrations of elements and the diffuse anthropogenic input with the term “geochemical baseline”. For estimating the regional or local baseline concentration the upper limit of geochemical baseline variation for potentially harmful elements can be used. Today, geochemical background information is available from national and regional geochemical mapping surveys, as well as from targeted geochemical baseline surveys, from which geochemical baseline mapping of sub-urban and urban areas has had a special focus on environmental applications and land use planning. The geochemical baseline studies provide information on baseline concentrations for remediation projects, land extraction, land use planning and other urban functions. Furthermore, they provide information for mineral exploration, for studies on the baseline status of the environment, as well as for environment impact assessment. The baseline information can also be applied in multidisciplinary studies such as the protection of human health. The main sample parent material used in the geochemical baseline studies is minerogenic soil. Both composite and single samples are used. Single samples are often used when the data are targeted for use in calculating statistics for different soil parent materials and land use patterns. The sampling depth in geochemical mapping is traditionally quite variable, but in urban geochemical baseline studies the main focus is on topsoil. In Finland, the guidelines are given for soil contamination analysis and they are also followed in geochemical baseline surveys. For determining the concentrations of inorganic elements, the samples are to be sieved to the <2 mm fraction following aqua regia extraction or strong nitric acid leach. Different gas chromatographic methods are recommended to be used to analyse organic compounds. For risk assessment purposes, as well as for tracing the origin of elevated concentrations, i.e. whether it is anthropogenic or geogenic, weaker extraction methods provide additional information to be applied in data analysis. The utilization of geochemical baseline information is important when assessing the possible soil contamination and remediation needs. Regional variation due to differences in the geological environment can be high and should be taken into consideration in contamination assessment. Various sampling materials may reveal different geochemical baseline levels. Finnish legislation supports the use of geochemical baseline information, and the Finnish national geochemical baseline database (TAPIR) provides end-users with nationally comparable and scientifically sound geochemical baseline data that enhance the rationality and transparency of decision-making.