Potential Effect of Biochar on Soil Properties, Microbial Activity and Vicia faba Properties Affected by Microplastics Contamination

Microplastics (MPs) contamination is an emerging issue globally; however, adverse impacts of MPs on soil, plants and microbial activity have not been intensively studied. In this study, the potential effect of different levels of MPs (1.5, 7.5, 15%) has been investigated on soil properties, plant properties (Vicia Faba) and microbial activities through a pot experiment. The effect of biochar (BC: 2%) to mitigate the adverse effects of MP has also been examined. Soil properties (pH, EC, OM, CaCO3 and some elements) have significantly differed due to contamination of soil by MPs as well as by adding BC to the soil. The pH and CaCO3 were significantly increased more than in the control, while EC, TDS, available P, Mn and Fe were significantly decreased lower than the control, which implies adsorption on microplastic. Plant properties, such as enzymes, chlorophyll and fresh and dry weight in roots, were adversely affected by MPs contamination; however, BC mitigated this effect, especially with low contamination levels of MPs. The fresh and dry weight of the shoot was not significantly affected by MPs. The cytogenetic analysis showed that the mitotic index was significantly reduced compared to the control (9.39%), while BC increased the mitotic index at 1.5% MPs (7.11%) although it was less than the control. The percentage of abnormalities of V. faba root tip cells under different levels of MPs was significantly increased more than the control; however, BC mitigated this effect, especially at 7.5% MPs. The total count of bacteria and fungi even in soil or in the rhizosphere area did not follow a clear trend; however, the effect of BC was clear in increasing their activities. Microbial biomass carbon and nitrogen were also significantly affected by MPs and BC. In this study, the BC level was low, however, it mitigated some adverse effects of MPs, especially at 1.5 and 7.5% of MPs. Thus, the BC could be promising in mitigating the negative impacts of MPs when applied with suitable levels that need more future studies.