Effect of Mycorrhiza and Eggshell on Growth Parameters and Hazard Index of Basil (Ocimum basilicum L.) in Multi-metal Contaminated Soil

One of the serious problems of biological communities is environmental pollution caused by heavy metals due to increase of industrial activities regardless of environmental considerations. According to the nature of these contaminants and considerable persistence in environmental components, especially soil, modification of contaminated soils to mitigate the negative effects of these contaminants on plants as a food chain initiator, is necessary. Considering the importance of using waste to recover them and also the different reaction of mycorrhiza in the face of heavy metals, this study aimed to investigate the effect of eggshell and mycorrhiza on changes in hazard index in basil plant.

This experiment was conducted in factorial completely randomized design consist of soil factors (non-contaminated, contaminated), eggshell waste (0, 3 and 5% w/w) and mycorrhiza (non-inoculated, inoculated with combined Funneliformis mosseae and Rhizophagus irregularis) in 3 replications (36 experimental units). Basil (Ocimum basilicum L.) was selected as an experimental plant due to its high leaf area and production of suitable dry matter. Finally, growth parameters, concentrations of zinc, copper, lead and cadmium in the plant tissue, transfer coefficient, translocation factor, hazard quotient and hazard index of the plant were evaluated.

Increasing the level of soil pollution reduced the height of the shoot by 54% and the fresh weight of the shoot by 70%. The use of eggshell waste by 5% w/w as compared to the control treatment in contaminated soil caused 32% increase in plant shoot height and 16.5% increase in fresh shoot weight. In contrast, root inoculation increased shoot height by 25.7% and shoot fresh weight by 4.47%. A relatively similar trend was observed in case of shoot and root dry weight. Under soil contamination conditions, application of 5% of eggshell waste reduced the amount of zinc, copper and cadmium in the shoots of the plant by 11.7%, 4.16% and 16.7%, respectively. In contaminated soil, application of mycorrhiza caused a significant reduction in concentration of zinc, copper, lead and cadmium in the shoots by 33.8%, 2.87, 25.9% and 43.3%, respectively. In contaminated soil, the highest hazard index (2.14) was observed in the treatment without eggshell and not inoculation with mycorrhiza. Because of eggshell application at the rate of 5% and mycorrhiza inoculation, hazard index decreased by 14.9% and 36%, respectively. According to the results, the use of eggshell waste and mycorrhiza inoculation reduced the hazard index in the contaminated soil, which the effects were different according to the type of element. However, in the case of both treatments, according to the level of contaminants, the value of basil hazard index did not fall below the allowable level, so that in 5% eggshell treatment, the hazard index was 1.54 and in mycorrhiza inoculation treatment, 1.31 was reported. The lowest hazard index in contaminated soil (1.16) was observed in treatment of mycorrhiza inoculated along with 5% eggshell.

Basil cultivated in contaminated soil, despite the effectiveness of treatments in reducing the hazard index, was still at the risk of consumption. Considering the type and concentration of heavy metals in the optimal use of recycled materials such as eggshell waste as well as bioremediators such as mycorrhiza can be of particular importance.