Study On The Toxicity Threshold Of Cadmium On Ipomoea Aquatica

The toxic effects and the toxicity threshold of cadmium to Ipomoea aquatica were studied by both soil culture experiments in greenhouse and field experiments in order to provide a basis for establishing regional soil environmental quality standards.The main results are as follows:1. Six different soils added with different levels of Cd were used for the field experiment. The EC10 (on the basis of 0.1 mol.L-1 CaCl2-extractable Cd) of the biomass of above-ground parts, the biomass of roots, root length and plant height of water spinach were 0.04-1.26 mg.kg-1,0.36-1.68 mg.kg-1,0.9-3.05 mg.kg-1 and 0.19-2.07 mg.kg-1, respectively. The same kind of EC10 on different soils and different kinds of EC10 on the same soil all varied greatly. The sensibility to Cd toxicity of the growth indices for Ipomoea aquatica varied greatly, showing the biomass of above-ground parts> the biomass of roots> root length> plant heigh.2. Twelve kinds of soils were used in the greenhouse pot experiment. The EC10 values of the biomass of above-ground parts and roots, and root length were 0.0012-7.34 mg.kg-1、0.01-15.35 mg.kg-1 and 0.10-15.20 mg.kg-1, respectively. The EC10 of the root length was better than the others to be the indicator of toxic effects of Cd to Ipomoea aquatica in the greenhouse experiment.3. Both the field and pot experiments showed that irrespective of growth index and soil type, EC10 values based on different available soil Cd always increased in the order of water-soluble cadmium< CaCl2-extractable Cd< DTPA-extractable Cd. The EC10 values based on CaCl2-extractable Cd and DTPA-extractable Cd varied less than those based on water-soluble Cd. The EC10 based on DTPA-extractable Cd was better than that basaed on CaCl2-extractable Cd in the greenhouse pot experiment.