The sensitivity of Brassica napus ssp. oleifera to cadmium (Cd) and lead (Pb) contamination at different pH of mineral and organic soils

In a model pot experiment, the influence of elevated levels of cadmium and lead in soils on rapeseed (Brassica napus L.) growth, development, biomass (g DM pot-1), cationic ratios (Cd2+:- Ca2+, Cd2+:Mg2+, Pb2+:Ca2+, Pb2+:Mg2+) and tolerance index Ti, has been examined. The tested soils were: two organic soils (acidic and neutral) and a mineral one with pH differentiated into neutral and acidic. The metals were spiked into soils in doses of 10 mg Cd kg–1 DM and 100 mg Pb kg–1 DM of soil. Under the applied doses, the sensitivity of rapeseed to Cd was higher than to Pb. The application of Cd caused visible symptoms of chlorosis on plant leaves and a statistically significant (p < 0.01, p < 0.05) decrease in aerial biomass. The influence of Pb on B. napus biomass yield was not significant. The soil type and its reaction differentiated the biomass of plants in the following decreasing order: mineral neutral > organic neutral > mineral acidic > organic acidic. The Cd added to soil increased the Cd2+:Ca2+ and Cd2+:Mg2+ ionic ratios, while Pb caused an increase in Pb2+:Ca2+ and Pb2+:Mg2+ ratios compared to the control. The significantly higher values for the above ions ratios were recorded in rapeseed roots rather than in shoots. The results showed a crucial role of the soil type in determining the milimolar ionic relations in B. napus plants. The plant was more vulnerable to chemical composition changes in contaminated treatments comparing to control when grown on mineral soils (both acidic and neutral) than on organic ones. The high Ti value proves generally low sensitivity of B. napus to soil Cd and Pb contamination.