Evaluation of cadmium accumulation and absorption of micronutrient elements in lettuce (Lactuca sativa L.) under cadmium chloride stress

The high mobility and solubility of cadmium pose a serious threat to the health of humans and other organisms. There are no signs of toxicity when cadmium metal accumulates in the tissues of plants and enters the human food chain. Cadmium transfer rates from vegetables to the human diet depend on their accumulation. Thus, inorder to investigate heavy metal absorption by lettuce, this research evaluated the levels of cadmium accumulating in various lettuce organs.

The seeds of lettuce (Lactuca sativa Linn) were cultivated in autoclaved pots containing perlite and cocopeat (with a ratio of 2 to 1). The pots were kept under greenhouse conditions of 25±1 (day temperature) and 20±1 (night temperature) and light/dark conditions were placed. About three weeks after the plants reached the three-leaf stage, the seedlings were treated with cadmium chloride in 3 replicates. Four concentrations (0, 30, 60 and 90 μg/g perlite) were used every 3 days. After 5 stages of treatment and 28 days after cultivation, the third leaf of the plants was used for the studies.

Cadmium increased lettuce's phenol, flavonoid and antioxidant content significantly as compared to the control sample. Furthermore, by increasing the concentrations of cadmium, lettuce showed an increase in total protein, soluble sugar, free amino acids, proline, malondialdehyde, and hydrogen peroxide as compared to the control sample. Due to the increasing amount of cadmium applied to lettuce plants, an increase in the amount of cadmium in the roots was greater than in the aerial parts.

In general, the results of this research indicated that lettuce is a cadmium accumulating plant with the ability to accumulate heavy metals in its roots and aerial parts. Contaminated with heavy metals, it seems necessary to protect the health of consumers.