Potential of Natural Clay Deposits to Prevent Cadmium Uptake by Canola

Stabilizing heavy metals in polluted soils is a method to prevent them from entering plants. Clay minerals are considered good sorbents for heavy metals due to their low cost, high abundance, easy manipulation and harmlessness to the environment. The objective of this study was to investigate the potential of clay deposits containing smectites and palygorskite to sorb cadmium and to reduce its movement into canola. Two selected deposits are located in the Isfahan Province. Physical and chemical characteristics of clay deposits were determined. The clay fraction was then separated from each deposit sample. This study showed that palygorskite was the dominant clay mineral in deposit sample 1 and smectites in deposit sample 2. These clays were then used as an amendment to plant growth medium. Pot experiment was carried out with canola (Brassica napus) as a test plant with 3 replicates. Treatments included three growth media: smectite + quartz sand, palygorskite + quartz sand and pure quartz sand (control treatment) under 3 Cd concentrations: 0, 2.5 and 7.5 ppm. Results obtained from the pot experiment indicated that deposits containing smectite and palygorskite were very useful in stabilizing cadmium in polluted soils and could prevent Cd from entering plant. Smectite clay mineral could retain a higher quantity of cadmium as compared to palygorskite. Plants in pots amended with smectite had a higher growth rate as compared to those in control and palygorskite amended pots. Cadmium accumulation in plant roots was much higher than that in shoot. Furthermore, the higher Cd concentration in growth media resulted in the higher amount of Cd uptake by the plant.