Investigating the effect of lead and cadmium on absorption of high consumption nutrients on Glycyrrhiza glabra

Background and objectives: Toxicity of heavy metals and their accumulation in soil, plant and food chains is one of the main environmental and health problems. Among toxic heavy metals, cadmium and lead have received more attention due to their durability and stability in the environment. In this regard, the impact of these metals on valuable medicinal plants and forages that enter into the food chain through human and animal consumption is of particular importance. Glycyrrhiza glabra L. is an example due to its importance as a medicinal plant which its roots and rhizomes is used in pharmaceutical and food industries. The purpose of this study is to investigate the effect of heavy metals of lead and cadmium on the absorption of high consumption nutrients and also the accumulation of these elements in the tissues of the lichen plant. Methodology: This research was carried out in a completely randomized design with two treatments of lead and cadmium having 4 replicates and 6 concentrations level in pot culture method (total of 48 pots). Concentration levels were 0, 10, 20, 40, 80 and 160 (ppm) for cadmium and zero, 50, 100, 200, 400 and 800 (ppm) for lead. The concentrations used were based on the standards of metal concentrations in the soil and national of World Health Organization. The salts used to prepare the concentrations of the treatments were lead nitrate and cadmium nitrate (MERC). Pot’s beds were prepared with heavy metal salts solution of lead and cadmium. Above concentrations liquids were sprayed on the rhizomes already placed in the pots. Pots were kept in the greenhouse for 7 months under irrigation under prescribed care. Nutrients were used according to the results of soil decomposition to the optimal extent and without effect on pot treatments (as a spray on the plant itself). Finally, samples of soil and plant (above and underground organs) were prepared and transferred to the laboratory for acid digestion and extraction of lead and cadmium. To assess the plant's ability, TF, BCF and BAC indices were also used to assess the accumulation capacity of these elements. Results:  The results of the comparison of the mean of lead and cadmium in the studied concentrations showed that increasing the concentration of these two elements in the soil did not have a significant effect on the amount of potassium, sodium, magnesium, calcium and organic matter in the aerial and underground parts of the plant. While the increase in the concentration of cadmium in the soil has a significant negative effect on the amount of this metal in the air and underground organs and the amount of nitrogen in the aboveground parts. Also, the increase in lead concentration has a significant effect on the amount of this metal on both above and underground organs while the amount of phosphorus and nitrogen on above ground parts. The results of the studied treatments on the accumulation and transfer of cadmium and lead in Glycyrrhiza glabra L. showed that in all concentrations of cadmium treatments (except 20 ppm) the amount of TF for cadmium metal was less than 1 but the amount of BAC and BCF was greater than one. In the case of lead metal in all different concentrations of lead treatment except concentrations of 200 and 800 (ppm) the amount of transfer factor is greater than one, but the values of BAC and BCF for these two treatments are more than one. Therefore, Glycyrrhiza glabra L. has a good ability in lead metal extraction and cadmium metal stabilization. Conclusion: The results of the study on the accumulation and transfer of cadmium and lead in the lichen plant showed that the plant could play the role of stabilizing and extractive for these two heavy metals, respectively. As reaction of Glycyrrhiza glabra L.is is positive, it seems that if the contamination is high, the most absorption is occurred in shoots and stems of the plant. Usage of the plant therefore does not harm consumers but when cadmium is a contaminant because the root stabilizes it and direct use of the plant root as a medicine can be harmful.