Osmium in environmental samples from Northeast Sweden: Part I. Evaluation of background status

Osmium (Os) concentrations and 187Os/188Os isotope abundance ratios are presented for sedimentary materials, soils, humus, plants, mushrooms, mosses and lichens collected in the vicinity of the town of Luleå, Northeast Sweden, the data for biological specimens being the first reported. Contributions from sampling and varying exposure time to the observed environmental variability were evaluated. Sedimentary materials (from both fresh and brackish water) are most elevated in radiogenic 187Os, followed by inorganic soil horizons, mushrooms and humus. The Os isotopic compositions of plants, mosses and lichens are much less radiogenic, with mean 187Os/188Os lying within a relatively narrow 0.3–0.6 range. Significant temporal variations in Os concentrations and isotopic compositions of plant samples are attributed to integrative uptake of airborne Os with non-radiogenic composition. Measured Os concentrations in biological matrices increase in the order: small shrub leaves (blueberry and lingonberry) ≤ spruce needles ≤ mushrooms ≤ tree leaves ≤ pine needles < mosses ≪ lichens. The concentrations found in three different species of plant were used to provide the first estimates of gaseous osmium tetroxide (OsO4) in the environment. Though the Os content of samples from Northeast Sweden does not differ significantly from matrix-matched international reference materials (not certified for Os) of abiotic origin, the estimates of gaseous OsO4 concentrations are roughly an order of magnitude higher than have been reported for particle-bound Os in other studies. The pronounced spatial variations between relatively closely situated sites in mean 187Os/188Os ratios for samples of the same species (presumably with the same dominating uptake mechanism) point to the presence of different local Os sources. This study therefore demonstrates that emissions of Os from automobile catalytic converters are not the only source of contemporary environmental contamination.