1. Allen, H. E. and Chen, P. H., 1993: Environmental Progress 12, 284.
2. Assink, J. W.: 1988, in Wolf, K. et al. (eds.), Contaminated Soil, Kluwer Academic Publ., Dordrecht, The Netherlands, p. 861.
3. Br�mmer, G. W., Hornburg, V., Hiller, D. A.: 1991, Mitteilungen der Deutschen, Bodenkundlichen Gesellschaft 63, 31.
4. Cottenie, A., Verloo. M., Kiekens, L., Velghe, G. and Camerlynck, R.: 1982, Chemical analysis of plants and soils, Laboratory for Analytical Chemistry and Agrochernistry, State University of Ghent, p. 63.
5. Daley, S.: 1989, Environ. Sci. Technol. 23, 912.