A biological test system for the evaluation of the phytotoxicity of metal-contaminated soils.

The potential soil phytotoxicity in the surroundings of an old zinc smelter closed in 1966, was evaluated by a biological test system. This system is based on the analysis of shoot growth and (iso-) enzymes in leaves and roots of 2-week-old seedlings of Phaseolus vulgaris grown on soil samples under controlled environmental conditions. The biological data were presented in a phytotoxicity index, which allowed classification of the soil samples into four phytotoxicity classes. Comparison was made between the biological results and soil and plant metal content. The study revealed that more than 20 years after closure of the factory, the soils in its surroundings were still potentially phytotoxic. Zinc proved to be the most important, but not the only, phytotoxic element, as was shown by isozyme analysis and by the strong correlation between the biological data, the water soluble Zn fraction of the soil and leaf Zn content. The effect of contamination extended to a distance of more than 3 km from the industrial site in the direction of the prevailing wind.