Some Interactions in Plants Among Cadmium, Other Heavy Metals, and Chelating Agents

Four experiments were conducted under glasshouse conditions with either soil or solution culture to evaluate interactions of Cd among other mineral elements in plants when yields are decreased by Cd as can happen under conditions of contamination. Chelating agents were included in the study because of their uses in plant nutrition and because they are known to increase uptake and translocation differentially of trace metals. Bush beans (Phaseolus vulgaris L. var. ‘Improved Tendergreen’) were grown with 10⁻⁶, 10⁻⁵ and 10⁻⁴M Cd in solution culture. Vegetative yields were depressed in the presence of Cd; 10⁻⁴M produced the greatest reduction (61%). The Cd concentration in plants was roots > stems < leaves. All levels of applied Cd significantly depressed the Mn concentration in leaves, stems, and roots. ThL, was the most prominent interaction. In a test with Yolo loam soil (Typic Xerorthents, fine-loamy, mixed, slightly acid, thermic) with bush beans, Cd was applied at 0, 50, aud 100 μg Cd/g soil as CdS0₄. Each level was interacted with either NTA (nitrilotriacetic acid) EDTA (ethylenediamine tetraacetic acid) (100 μ/g soil) as Na salts. Yields were depressed substantially by 50 μ Cd/g soil only when chelating agents were also applied (36% for NTA and 48% for EDTA). The 100 μ Cd/g soil decreased yields only slightly without chelating agents (28%). Cadmium significantly decreased and Cu concentrations in leaves and overcame much of the tendency of the chelating agents to increase concentrations of Mn, Cu, and Fe in plants. Zinc was decreased only on the per plant basis with the highest applied level of (M with chelating agents. The Cd decreased the Ca and Mn concentrations in leaves of bush beans. Cadmium levels in the plants were increased by EDTA from 6 to 423 μ/g dry weight at the high Cd level. In another experiment with the same soil, diethylenetriamine pentaacetate acid (DTPA) (100 μ/g soil) increased take of Cd to 35 μ/g dry weight in bush beans. The interactions were similar to those with the other chelating agents. A leaf concentration of 15 μ Cd/g (dry weight basis) decreased yields of bush beans. With corn (Zea mays L. var. ‘Golden Bantam’) grown also in the same soil, the addition of 5% CaCO₃ decreased yield reduction due tn Cd by decreasing its uptake (by 64% for 200 μ Cd/g soll and 76% for 400 μ). A concentration of 219 μ Cd/g in corn shoots decreased yields. Caution in the use of metal chelates is indicated when soils contain significant levels of available Cd.