Changing elemental uptake of radish seedlings grown in Cd and Pb polluted smectite substrates

Radish seedlings were grown for one month in a smectite substrate under controlled laboratory conditions. The purpose was avoiding as much as possible side effects such as heterogeneity of natural soils, as well as fertilizer and atmospheric supplies. One set of seedlings was watered at the beginning of the survey with plain deionized water, whereas the others were with the same water containing Cd or Pb at 0.5 and 1 mg/L concentrations, to quantify the impact of these metal pollutions on the plants. Significant changes were observed in the uptake of the seedlings watered with the contaminated solutions: Na and K uptakes decreased, whereas those of Al, Fe, Ca and Mn increased. Changes were also detected in the uptake of some rare earths and trace elements after watering with Cd or Pb contaminated solutions. The most concerning uptakes are for the pollutants Cd and Pb that increase by about 795 and 1240 times, respectively, in the contaminated seedlings, suggesting a high tolerance by the radishes for these two metals. The overall increasing elemental uptakes result from replacement of an ion exchange process during growth in the unpolluted substrate by an ion complexation process in the case of growth in the polluted substrate. ence of a significant Eu anomaly and disappearance of the Gd anomaly in the rare-earth distribution patterns of the contaminated radishes were necessarily induced by organic activity; they also explain the suggested changing uptake process. Rare-earth element distributions represent therefore an efficient tracer to evaluate how much soil pollution by a given metal potentially affects the uptake process of plants, and to postulate that some types of metal pollution, Cd and Pb here, affect specific functions of enzymes and/or of bacterial micro-organisms.