Geochemical baselines in relation to analytical methods in the Itä-Uusimaa and Pirkanmaa regions, Finland

Abstract

ABSTRACT Geochemical baselines of As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, V and Zn concentrations were investigated for two Finnish regions (Ita-Uusimaa and Pirkanmaa) using different determinations based on separate analytical methods: (1) total concentrations based on X-ray fluorescence (XRF) spectrometry or strong acid leach; and (2) ‘near-total’ concentrations determined using aqua regia extraction (ISO 11466) and/or concentrated nitric acid leaching (US EPA 3051A). The geology of the Ita-Uusimaa region is dominated by late-orogenic plutonic rocks, while the bedrock in Pirkanmaa contains arc-type volcanic and sedimentary rocks and turbiditic greywackes. Topsoil (0–25 cm) and subsoil samples that were analysed represent the most common mineral soil parent material types of the study regions: sandy soils, glacial till and clayey soils. The normative mineral composition of the samples was estimated using the NORMA model. The regional baseline as an estimate of the upper limit of background variation was defined in two study areas from acid-leachable concentrations. Baselines concentrations of As, Co, V and Zn exceed the Finnish soil contamination trigger values in the study areas. Regional baselines defined for one region could not be applied in another test region. Statistical tests were carried out to indicate the significance of the differences between studied baseline concentrations determined using aqua regia extraction and concentrated nitric acid leaching. The differences were found to be highly significant for As, Pb and Sb while for Cd, Co, Cr, Ni and Zn the two analytical methods were comparable. The ratios between total and ‘near-total’ (aqua regia or nitric acid-extractable) concentrations reveal higher total concentrations determined by XRF spectrometry compared to acid-leachable contents for most inorganic elements. Lead and Cr show the lowest extractability using aqua regia, while Cu was most extractable using acid leaching. According to normative mineralogy, the levels of several trace elements determined by near-total, partial methods are controlled by the abundance of micas, goethite and hydrous Al silicates. In topsoil, organic carbon correlated with Hg, Pb and Cd concentrations.