Potential of marigold (Calendula officinalis), ornamental cabbage (Brassica oleracea) and amaranthus (Amaranthus retroflexus) for phytoextraction of cadmium from the soil

Soil contamination by heavy metals is a serious environmental challenge and can cause problems for human and animal health globally. Most of remediation techniques to eliminate contamination from soils are very costly and deteriorate soil physical and chemical properties. The use of ornamental plants with high biomass and uptake is an innovative, economical and environmentally friendly way to remediate urban and industrial sites polluted by heavy metals. The purpose of this study was to investigate the ability of the marigold, ornamental cabbage and amaranthus to remediate cadmium contaminated soils in Zanjan province under greenhouse conditions.

The present study was conducted as a factorial experiment in a completely randomized design. Experimental treatments included three types of plant (marigold (Calendula officinalis), ornamental cabbage (Brassica oleracea) and amaranthus (Amaranthus retroflexus)) and soil cadmium levels (2.2, 12.2, 27.2, 57.2, 77.2 and 102.2 mg Cd/kg soil) which were used in triplicate.

The results indicate that high concentrations of cadmium in soil were toxic to plants and decreased the fresh and dry weight of the shoot and root. The highest level of soil cadmium (102.2 mg Cd/kg soil) decreased the fresh weight of the shoot in the marigold, ornamental cabbage and amaranthus by 77, 69 and 62%, respectively, when compared to the control (zero cadmium) treatment. Also, the concentration of cadmium of the shoot in the marigold, ornamental cabbage and amaranthus, when the soil cadmium level was 102.2 mg Cd/kg soil, increased by 39.88, 21.75 and 46 times, respectively, compared to the control (zero cadmium) treatment. The maximum amount of cadmium uptake for whole plant biomass was measured for marigold and ornamental cabbage when soil cadmium level was 77.2 mg Cd/kg soil, but the highest uptake for amaranthus was calculated in treatment with 102.2 mg Cd / kg soil. The lowest cadmium uptake was also observed in the control treatment. Translocation factors for cadmium in studying plants were higher than one and at the highest soil cadmium level (102.2 mg cadmium per kg soil), the calculated translocation factors of plants were in the order of marigold > amaranthus > ornamental cabbage respectively. The shoot bioaccumulation factor at the soil cadmium concentration of 102.2 mg Cd/kg soil was in the order of marigold > amaranthus > ornamental cabbage. The order of bioaccumulation factor for root at the soil cadmium concentration of 102.2 mg Cd/kg soil was amaranthus > ornamental cabbage > marigold.

The results showed that the translocation factor in the studied plants (marigold, ornamental cabbage and amaranthus) was more than one and the concentration of cadmium in dried tissues of aerial parts was more than 100 mg/kg. Therefore, these plants can be classified as metal accumulator plants in terms of cadmium uptake and translocation and are suitable for remediation of cadmium contaminated soils.