Geochemical baselines
Sampling years: 2004–2005
Sample media: humus: concentrated nitric acid extraction from the <2 mm grain-size fraction; topsoil (0–25 cm) and subsoil: aqua regia extractable concentrations from the <2 mm grain-size fraction
Soil parent materials: sand 98 profiles, glacial till 102 profiles, clay 100 profiles
The Geological Survey of Finland (GTK) has studied geochemical baselines around the Helsinki Metropolitan Area (the municipalities or cities of Kirkkonummi, Vihti, Hyvinkää, Nurmijärvi, Järvenpää, Tuusula, Kerava and Sipoo) using topsoil, subsoil and humus samples collected in 2004–2005. The 300 sample profiles represented the most common mineral soil types of the region. Altogether, 98 sample pits were dug in sand and gravel formations, 102 profiles were investigated in glacial till and 100 in fine-grained sediments (clayey soil deposits). Aqua regia extraction was used for mineral soil samples and concentrated nitric acid for humus samples. In addition to element concentrations, pH and loss on ignition (LOI) were measured for both humus and mineral soil samples. Separate carbon measurements were taken from mineral samples. The aim of this study was to provide the regional environmental authorities with information on geological and diffuse anthropogenic geochemical baselines for different elements.
Concentrations of most of the elements studied showed large natural variation in different soil parent materials and humus. A good correlation was recorded between topsoil and subsoil concentrations, suggesting a geological origin for the distribution patterns. The concentrations of most trace elements, including heavy metals, were highest in fine-grained (clay) soil deposits. Concentrations of several trace metals such as copper, chromium and vanadium correlated with the clay fraction content in both topsoil and subsoil samples.
The organic matter content in minerogenic topsoil showed a good correlation with Hg, Ag, S, Pb and Cd, partly reflecting the atmospheric deposition and other anthropogenic input. The concentrations of carbon, sulphur, cadmium, mercury and lead were relatively high in the humus samples compared with the mineral soils.
Report:
Tarvainen, T. (toim.), Eklund, M., Haavisto-Hyvärinen, M., Hatakka, T, Jarva, J., Karttunen, V., Kuusisto, E., Ojalainen, J. & Teräsvuori, E. 2006. Alkuaineiden taustapitoisuudet pääkaupunkiseudun kehyskuntien maaperässä. Summary: Geochemical baselines around the Helsinki metropolitan area. Geologian tutkimuskeskus, Tutkimusraportti 163. http://tupa.gtk.fi/julkaisu/tutkimusraportti/tr_163.pdf
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