Without exceeding the limits: industrial soil rich in Zn and Cd has no effect on purslane and lettuce but promotes geranium growth

The aims of the study were (a) the assessment of growth and physiological response of a weed/alternative crop (purslane), an ornamental plant (geranium) and an edible vegetable (lettuce) to Zn- and Cd-contaminated industrial soil and (b) the investigation of the possible exclusion or accumulation process of these plants concerning Zn and Cd, evaluating thus their phytoremediation potential. Both Zn and Cd concentrations increased significantly in all three plant species in the contaminated soil compared to the uncontaminated control. Metal soil-to-plant transfer coefficient was lower in the first soil compared to control, indicating slower metal uptake with increased metal concentrations in soil. Geranium exhibited a growth promotion along with a better photosynthetic performance in the industrial soil. Purslane displayed an altered architecture and a more massive old leaf cohort, but its overall growth remained unaffected by increased [Zn] and [Cd], similarly to lettuce. No effects on PSII photochemical efficiency and photosynthetic pigments of all studied species were recorded. We conclude that metal uptake by plants remained within the limits of favorable growth and metal bioavailability was determined by (a) the fact that metals were deposited over long periods and were thus strongly retained by soil colloidal phases and (b) Cd/Zn antagonism. The results highlight the importance of soil history component in shaping heavy metal behavior, determining thus their bioavailability.