L. Tobler

Rare earth elements in soil and in soil-grown plants

Concentrations of the rare earth elements (REEs) La, Ce, Nd, Sm, Eu, Gd, Tb, Yb and Lu were determined in leaves of 6 plant species (Norway spruce, silver fir, maple, ivy, blackberry, and wood fern), and in pertinent soils and soil extracts, also taken from the same site. The distribution of the individual REEs in plants showed little or no agreement with that in the soil or the soil extracts. Ce had a negative anomaly with respect to the soil in all plants. The REE distribution patterns of fir and spruce were almost identical, but differed profoundly from that of the other species. In most cases, concentration ratios between species were a smooth function of the atomic number of the REE. Very similar results were obtained at 2 additional sites.

Deposition of 134,137Cs from Chernobyl fallout on Norway spruce and forest soil and its incorporation into spruce twigs

Abstract The aims of the present research are to describe the amounts, and the variation with time, of 134 Cs and 137 Cs in spruce-twigs ( P. abies karst. ) and in the soil of a spruce forest in Switzerland following deposition of the Chernobyl fallout. The activity of the twigs was subdivided into 3 compartments: the activity on their surfaces (i.e. the activity which can be removed from the twigs along with their natural wax coating), the activity incorporated into the needles and, finally, the activity incorporated into the wood. These compartments were separately sampled 6 times over a period from 54 to 233 days after the Chernobyl incident. Twigs which sprouted in two successive years (1985, 1986) were sampled and were found to show different behaviours. The activities associated with the 1986 twigs were roughly constant with time, while those of the 1985 twigs decreased exponentially, with half-lives around 150 days. The mean activity associated with 1 g (dry) of 1985 twigs is 724 mBq 137 Cs g −1 , of which 58% is incorporated into the twig wood, 17% into the needles and 25% associated with the adhering aerosol. 137 Cs on the surface of the needles was found to be water-insoluble. It is believed to be strongly adsorbed on to the soil-derived fraction of the aerosol residing on the needle surface and thus provides a tracer for studying the behaviour of natural aerosols on such surfaces. The same soil profile was measured before and after the Chernobyl incident, allowing direct comparison between nuclear weapons and Chernobyl fallout. The latter is mainly (56%) stored in the litter layer, with only 4% below a depth of 13 cm; it has penetrated into the soil to a much lesser extent than weapons fallout. The forest soil inventory of 137 Cs showed 2600 Bq m −2 from nuclear weapons fallout and 6200 Bq m −2 from Chernobyl. The 134 Cs/ 137 Cs activity ratio of the Chernobyl fallout was found to be 0·58 ± 0·01; the activity ratios in the different compartments investigated prove that incorporation of Cs into spruce occurred exclusively by uptake through the needles. A rough estimate indicates that in a spruce forest the activity stored in the twigs is half that stored in the soil.

THE ACCUMULATION OF THE RARE EARTH ELEMENTS AND OF SCANDIUM IN SUCCESSIVE NEEDLE AGE CLASSES OF NORWAY SPRUCE

The endogenous concentrations of Sc, La, Ce, Sm, Eu, Tb, Yb, and Lu were determined by neutron activation analysis in up to five successive needle age classes of Norway spruce (Picea abies). Trees from nine sites over different bedrocks were sampled individually. Concentration values found are generally much lower than those reported in the literature. This is attributed to the careful removal of any aerosols or soil particles from the needle surface prior to analysis. The concentration of each element increases linearly with the needle age class, i.e., the accumulation can be characterized by just one parameter, the yearly increment. This pattern is followed at small as well as at large concentrations. The accumulation behavior of the investigated elements is identical to that of Si. The relative concentrations of the rare earth elements (REE) in the needles are similar to those in the earth crust. There are significant correlations between the individual REE and between Sc and La.

Multivariate interpretation of the foliar chemical composition of Norway spruce (Picea abies)

Twenty-four chemical elements were analysed by INAA, ICP-AES and CN in needles of Norway spruce (Picea abies (L.) Karst.). Branches were sampled from 54 trees on eight sites in Switzerland and South Germany. From each tree, twigs were sorted into the most recent four or five age classes and their needles analysed separately. All measured concentrations could be considered as log-normally distributed and statistical analyses were, therefore, performed on logarithms. Variance components were estimated by maximum likelihood and compared between elements. Non-essential elements varied more than essential nutrients (Mn was an exception). The sites and the age of the needles were the most important sources of variance. The interaction between site and age, the individual tree, the sampled branch and the residual variance were usually much smaller sources of variance. The effects of the most significant factors – site and age – were further described by principal components and cluster analyses. Mineral elements either increased or decreased with the age of the needles according to their mobility in the phloem. Two different components were identified in the effect of the sites: a geochemical component linked to soil pH and a climate component linked to altitude, temperature and precipitation. Multivariate statistics are discussed as a tool for the interpretation of complex interaction patterns between element concentrations in plants.

Effect of surface contamination on results of plant analysis

Abstract Chemical analysis of plants is often done without paying attention to the ubiquitous natural presence of exogenous material on the plant surface. The analytical result will then be higher than the endogenous plant concentration. It is shown that this error can be related to three parameters: (i) the surface loading L, (ii) the enrichment factor (EF) of the exogenous material with respect to the soil, and (iii) the plant‐to‐soil concentration ratio (CR). These factors are considered for 19 essential and trace elements and the results indicate that the error can range from insignificant to disastrous. Experimental data are mostly for needles of spruce trees growing in a relatively clean surrounding, but the proposed relations can be extended to estimate the effect for other plant species and surroundings.

Aerosols deposited on spruce needles

The aerosols adhering to one year old spruce needles are investigated as for the mass deposited and as for the chemical composition. The method for the isolation of the material is presented. 33 elements are determined by neutron activation analysis. Precision, accuracy, sampling error and variation over 14 sites at the interior of woods are discussed. Chemical composition is compared to local topsoil and to local aerosols collected on filters.

Soil contamination of plant surfaces from grazing and rainfall interactions

Abstract Contaminants often attach to soil particles, and their subsequent environmental transport is largely determined by processes that govern soil movement. We examined the influence of grazing intensity on soil contamination of pastures. Four different grazing densities of sheep were tested against an ungrazed control plot. Scandium concentrations were determined by neutron activation analysis and was used as a tracer of soil adhesion on vegetation. Soil loadings (g soil kg −1 dry plant) increased 60% when grazing intensity was increased by a factor of four ( p = 0·003). Rain and wind removed soil from vegetation in the ungrazed control plots, but when grazing sheep were present, an increase in rain from 0.3 to 9.7 mm caused a 130% increase in soil contamination. Multiple regression was used to develop an equation that predicts soil loadings as a function of grazing density, rainfall and wind speed ( p = 0.0001, r 2 = 0.78). The model predicts that if grazing management were to be used as a tool to reduce contaminant intake from inadvertent consumption of resuspended soil by grazing animals, grazing densities would have to be reduced 2.5 times to reduce soil loadings by 50%.

The concentration of rare earth elements in plants and in the adjacent soils

La, Ce, Nd, Sm, Eu, Tb, Yb and Lu were determined in needles of age class 5 from 6 individual Norway spruce trees and in their soils. Measurements were done by neutron activation analysis with a group separation of the REE. Concentrations in spruce needles are among the lowest values reported for plant leaves. Concentrations show small variations between the soils, but large variations between the trees. The mean ratio plant/soil is about 5·10−3 forall REE except Ce. Needles have no Eu-anomaly and a strong negative Ce-anomaly with respect to the soil. In addition to the fractionation of the individual REE between trees and the soil, there is also a considerable fractionation between the trees.

Major and trace elements in spruce needles by NAA.

Concentrations of 23 elements in needles of Norway spruce (P. abies) have been determined at 47 sites. It is shown that a thorough removal of the aerosols sitting on the needles surface is necessary in order to get the inherent needle concentrations. Neutron activation was used to determine concentrations from 10−9 to 10−2 g/g. Irradiation and counting conditions are given. The essential elements, Ca, Cl, Cu, Fe, K, Mg, Mn, P, Zn, and the nonessential elements, Al, As, Ba, Br, Co, Cs, Hg, La, Na, Rb, Sb, Sc, Sr, and V, could be determined. The concentrations of most elements are about a factor of 6 smaller than the mean concentrations in land plants. Analytical reproducibility was much better than the variation among individual trees, and the variation within sites is smaller than among sites. In general, essential elements have smaller variations than nonessential elements. For some elements, variations between sites are owing to differences in the soil pH or the emission situation.

Variation of the rare earth element concentrations in the soil, soil extract and in individual plants from the same site

Samples of various types (spruce needles, blackberry leaves, soils, and soil extracts) have each been taken at 6 places from the same site. In addition, 4 whirls each from 2 spruce trees were sampled. Rare earth elements (REEs) were determined in these samples by neutron activation analysis with a chemical group separation. Variations between places were found to be small with soils and soil extracts, but large with plants. Variations between whirls were small. Plants neither reflected the soil nor the soil extract. Both plant species were dissimilar, but the logarithm of their ratio was a linear function of the atomic number of the REE. A negative Ce anomaly (with respect to soil) was found in both plant species.