NATURAL BACKGROUND CONCENTRATIONS OF RARE-EARTH ELEMENTS IN A FOREST ECOSYSTEM

After preconcentration by extraction with 1-(2-pyridylazo)-2-naphthol and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, rare-earth elements were quantitatively determined by atomic emission spectrometry/inductively coupled plasma in various plant species (Betula alba, Pinus sylvestris, Vaccinium vitis-idaea, Vaccinium myrtillus, Deschampsia flexuosa, Polytrichum sp. and Sphagnum sp.) and soil horizons of a natural forest ecosystem in northwest Germany. Natural background reference concentrations of lanthanide elements in the plant materials investigated were (mg kg-1 dry wt): La, 0.15-0.25; Ce, 0.25-0.55; Pr, 0.030-0.060; Nd, 0.1-0.25; Sm, 0.02-0.04; Eu, 0.005-0.015; Gd, 0.030-0.060; Tb, 0.005-0.015; Dy, 0.025-0.05; Ho, 0.005-0.015; Er, 0.015-0.030; Tm, 0.0025-0.005; Yb, 0.015-0.030; Lu, 0.0025-0.005; and Y, 0.15-0.25. The concentration of lanthanides accumulated by Sphagnum sp. is greater by a factor of three than that concentrated by the other plants investigated. The plant/soil ratio (transfer factor) was between 0.04 and 0.09. For the reference materials NIST 1572 (Citrus Leaves), NIST 1573 (Tomato Leaves), NIST 1575 (Pine Needles), IAEA SL 1 (Lake Sediment), IAEA Soil 7, and BCR 261 (Rye Grass), indicative values for rare-earth elements are given.