A plant test system for evaluating the toxicity of heavy-metal-contaminated soils has been developed and applied. It is based on both morphological (leaf area and plant fresh biomass) and physiological (photosynthetic performance and root peroxidase activity) responses of young cucumber plant (hybrid Levina) grown in excess heavy metals in the root media at controlled environment. The system allows classifying phytotoxicity of metal-contaminated media into five toxicity classes: nontoxic (I), slightly toxic (II), moderately toxic (III), strongly toxic (IV) and lethal (V). The system has been applied to evaluating the phytotoxicity of soil samples taken from the region of Pirdop, which are industrially contaminated with heavy metals, mostly by copper. The obtained results showed that the toxicity of the soil samples taken up to 1 km from the Cu-producing plant varied from lethal to moderately toxic.
Keywords: heavy metals, phytotoxicity, plant test system, photosynthesis, peroxidase activity.