Study of the effect of cadmium and polyvinyl chloride on the accumulation of microelements and some physiological traits of Koshia seedlings

Microplastics in the soil are polymer particles caused by human activities with different chemical compounds that affect plant growth by changing the biological diversity and physical and chemical characteristics of the soil. Cadmium is an unnecessary heavy metal with high pollution, and its excessive presence in the soil of agricultural areas and natural environments can damage the growth of crops by reducing the efficiency of photosynthesis and inhibiting the activity of antioxidant enzymes. Phytoremediation is an on-site cleaning method using green plants with high coverage to remove, destroy or separate pollutants such as cadmium from the environment. Koshia is a very adaptable herbaceous plant, resistant to salinity, drought and environmental stresses, which has a wide range of expansion due to its high adaptability in different climates. This study was conducted to investigate the potential of cadmium remediation by the Koshia plant in the conditions of soil contamination with cadmium and polyvinyl chloride microplastics and the extent of the plant's access to important nutrients in such conditions. The factorial experiment was carried out on the base of a completely randomized design in three replications in the research greenhouse of Crop Physiology, Faculty of Agriculture, Bu-Ali Sina University in 2022. The experimental treatments included polyvinyl chloride microplastic at three levels of zero, 0.1 and 1% by weight of soil and cadmium at two levels of zero and 10 mg kg-1 of soil. In this research, root dry weight, shoot dry weight, proline, total antioxidant capacity, free radical inhibition percentage and accumulation of cadmium, iron, copper, manganese and zinc elements in shoots were investigated. The results showed that increasing the concentration of cadmium to 10 mg in the soil and microplastic to 0.1 and 1% caused a decrease in root dry weight, shoot dry weight, iron, copper, manganese and zinc element concentration in Koshia seedlings. The combined effect of cadmium and microplastic significantly increased the amount of proline, the total antioxidant capacity, inhibition percentage of free radicals and cadmium. At the highest stress level (cadmium 10 mg and microplastic 1%), the dry weight of root and shoot was 1.10 and 5.60 g per plant, respectively. The highest amount of proline was obtained at a concentration of 10 mg kg-1 of cadmium and 1% soil microplastic, equivalent to 38.70 µmol g-1 fresh weight. In the treatment of 10 mg of cadmium, the amount of total antioxidant activity increased by 53.62 and 81.38%, respectively, with the increase of soil microplastics from zero to 0.1 and 1%. The inhibition percentage of free radicals also increased by 9.55% in the treatment of 10 mg of cadmium and 1% microplastic compared to the control. Also, at the concentration of 10 mg of cadmium in the soil, with the increase of soil microplastics from zero to 0.1 and 1%, the amount of cadmium in the shoot increased by 21.30 and 42.02%. At the highest level of stress, cadmium 10 mg and microplastic 1%, the amount of iron, copper, manganese and zinc elements in the shoot decreased to 24.13, 55.97, 39.88 and 47.93 mg kg-1 soil, respectively, compared to without microplastic (control), so that the highest negative effect was observed in copper, zinc, manganese and then iron, respectively. the results of this research showed that although the used concentrations of cadmium and polyvinyl chloride microplastics in the soil, caused a decrease in the absorption of important nutrients, a decrease in the growth and dry weight of the plant's shoot and root, the Koshia plant through absorption and the accumulation of cadmium in aerial parts have a good potential for plant remediation in cadmium and microplastics contaminated soils.