Transferfactors (TF) are commonly used to describe the availability of trace elements or heavy metals to plants; calculated as the concentration of the trace element in the plant divided by its concentration in the soil (Lübben and Sauerbeck, 1991; Kloke, 1988). The factor is strongly dependent on the plant species, the element and several soil prosperites as pH and organic matter soil (Lübben and Sauerbeck, 1991; Kloke, 1988). Three areas of lead-zinc-mining in Germany (near Freiburg i.Br., Clausthal-Zellerfeld and Siegen) were compared to two german non-polluted reference areas (near Nürnberg). To describe the Cd-uptake and its availability to the orchid Epipactis helleborine correlation-analyses and TF-calculations (Cd in the orchid root/ mobile Cd from the soil) were used.
Orchids growing on heaps of ore mining (34 samples) as well as those of the reference locations (28 samples) and refering soils were collected in spring 1990 (growing phase of the orchid) and in summer 1990 and 1991 (flowering phase of the orchid). After washing, the plant-samples were dried (exiccator) and then pressure digested (7 h, 150°C). The air-dried soil samples were treated with NH4NO3 1M to extract the mobile Cd-fraction of the soil (DIN V 19730), which is supposed to be available to the orchids. The soil-pH (pHCaCl2) was measured (Ulrich et al., 1984). Dichromosulfur-acid was used to determine the organic matter content of the soil (Gaudette et al., 1974).
At non-polluted areas a very highly significant, narrow positive correlation between the Cd-content of the orchid-roots and the extractable Cd from the soil (r = 0.80***) indicates that this ammoniumnitrate-extractable Cd represents the Cd-fraction, which is available to the orchid. At the polluted areas only a highly significant, distinct positive correlation (r = 0.52**) was found.
TF for Cd-uptake of Epipactis helleborine from polluted and non-polluted areas display the same dimension; 23-390 (polluted) and 58-371 (non-polluted). Most TF are below 200, there are only few plants, which show factors above this range. This indicates an equilibrium between the extractable mobile Cd-fraction of the soil and the Cd-content of the orchid-roots. This equilibrium is neither much influenced by the soil-pH nor the amount of the organic matter in the soil though both soil prosperities affect the solubility of Cd in the soil. Nevertheless at non-polluted areas little decrease of TF at high pHCaCl2 can be noticed. The influence of the pHCaCl2 on the TF at polluted areas depends on the different soil material and probably on Cd-speciation. Samples from Freiburg show strong variation of their TF but little differences in the soil-pH measured. The TF of the other polluted areas remain the same level while the pH is strongly varying.
At polluted areas it seems that a low amount of organic matter in the soil supports the Cd-uptake of Epipactis
helleborine. Samples with little amount of organic matter show high TF and vice-versa. This dependence however is not clear. The main factor for the Cd-uptake of the orchids and the equilibrium stabilizing is the mobile Cd-fraction of the soil. If there is more Cd in the soil available the uptake of the Cd into the orchid roots is proportional, not depending on either the sampling season or the degree of pollution.
The authors thank Prof. Dr. Schramel and his working-group (GSF-Researchcenter, Munich) for support, helpfull discussion and advice.
Gaudette, H.E., Flight, W., Toner, L. & Folger, D., J. Sed. Petrol. 44, 249-253 (1974).
Kloke, A., Handbuch der Altlastensanierung (Franzius, V., Wolf, K., Brandt, E., eds.) (Decker's Berlin, 1988).
Lübben, S. & Sauerbeck, D., Berichte aus der Ökologischen Forschung 6, 180-223 (1991).
Ulrich, B., Meiwes, K.-J., König, N. & Khanna, P.K., Der Forst und Holzwirt 11, 278-286 (1984).