Research Progress on Toxicological Effects of Microplastics-Heavy Metal Pollution on Plant-Arbuscular Mycorrhizal Fungi Symbiosis System.

In recent years, more and more attention has been paid towards the microplastics (MPs) in soil. However, not only microplastics but also heavy metals are present in the soil. The coexistence of microplastics and heavy metals in soil will affect plants growth and plant-fungi symbiotic system. Some studies have shown that the tolerance of plants to heavy metals is enhanced by plants-arbuscular mycorrhizal fungi (AMF) symbiotic system. However, the colonization of AMF in plant roots and the abilities of AMF to filter and chelate heavy metals would be affected by microplastics, thus affecting the accumulation of heavy metals in plants. The plasticizers, stabilizers, flame retardants, and other harmful substances, which can be toxic to plants and AMF, will be released along with the microplastics as they degrade. Furthermore, the sub-micron plastics and nano-plastics directly entered plant root, stem, leaf and fruit. Microplastics adhered to plant seeds and roots to affect plant germination and seedling growth, consequently altering the colonization of AMF on plant roots. Additionally, heavy metals are adsorbed by microplastics due to their characteristics of large surface area, strong hydrophobicity, and slow degradation. However, the influence factors of adsorption included the type of microplastics, heavy metals and environmental conditions. Microplastics will affect the soil physical and chemical properties, such as the soil pH, organic carbon, cation exchange capacity. Moreover, competitive adsorption of microplastics and soil particles for heavy metal ions will change the bioavailability of heavy metals and affect heavy metal accumulation in plants. Although numerous studies have been conducted on the co-contamination of microplastics and heavy metals, there is insufficient information regarding the impacts of co-contamination of microplastics and heavy metal on the plant-AMF symbiotic system. Therefore, this article provides a summary and some suggestions about effects of co-contamination of microplastics and heavy metals on plants and AMF for further studies. [ABSTRACT FROM AUTHOR]