Comparison of the ability of wheat, clover and rapeseed in phytoremediation of cadmium from soils for reducing heavy metal stress

Introduction Heavy metals, as one of the most important factors contaminating natural environments and agricultural ecosystems, are found in almost all industrial regions. Toxic effect of high concentration of heavy metals is also observed in plants. One of the specific characteristic of heavy metals which has high influence in occurrence of toxicity of heavy metals is their bioaccumulation. Heavy metals are not biologically inseparable and decomposable and remain in environment which finally threaten human health. Therefore, removing, or at least, reducing their concentration in agronomical systems is closely related to human health. Cadmium is a heavy metal which is an unnecessary element for plants and enter agronomical systems through pesticides usage. However, cadmium is easily absorbed by plant roots and its toxicity is 20 times more than that of other heavy metals. There are chemical, physical and biological methods for removal of heavy metals from agronomical soils. Phytoremediation is a low cost and environmental compatible method for heavy metal removal from soils. This research was aimed to compare the ability of wheat, clover and rapeseed for removal of cadmium from agronomical soils to achieve the goal of reduction of heavy metal for incoming crop in rotation.   Materials and methods The current research was conductedas3×3 factorial experiment based on randomized complete block design with three replications. The first factor was plant type including wheat, clover and rapeseed and the second factor was heavy metal concentrations including 0.0, 50 and 100 mg kg-1 soil. Soil samples were contaminated with cadmium concentrations of 0.0, 50.0 and 100 mg per kg soil. Experimental plots (with height and diameter of 40 cm) were filled with 10 kg contaminated soils. Four weeks after planting, all plants parts (including root and shoot) were harvested and oven dried at 75°C for 72 hours. Finally, cadmium concentration was determined in all plants.   Results and discussion  The highest cadmium uptake was observed in wheat under the concentration of 50 and 100 mg kg-1 soil. Increasing cadmium concentration from 50 to 100 mg kg-1 soil had not significant effect on the ability of wheat, clover and rapeseed for cadmium uptake from soil. Plants with high biomass are capable for more heavy metals uptake which is line with the findings of this research where wheat with higher biomass removed more cadmium from soil in comparison with clover and rapeseed. However, nonsignificant difference between clover and rapeseed for cadmium uptake was not compatible with this opinion where rapeseed produced higher biomass. Although different physical, chemical and biological methods are used for removal of heavy metals from soils, phytoremediation has the highest effect for removal of cadmium from soils.   Conclusion The current research confirmed the results of other experiments about the ability of phytoremediation for removal of cadmium from soil. Furthermore, the results revealed that wheat, in addition to its nutritional value, has a high ability for reduction of cadmium from contaminated soils and can be considered as a good crop in crop rotation programs.