Coupled effects of microplastics and heavy metals on plants: Uptake, bioaccumulation, and environmental health perspectives

Microplastic pollution has severe ecological and environmental concerns because of its enormous production and discharge in natural ecosystems worldwide. Microplastics interact with heavy metals and metalloids like arsenic, chromium, copper, cadmium, and lead in soil and can cause detrimental effects on soil structure and microbial activities and subsequently impact the plants and human health. This article focuses on microplastic translocation from soil to plants together with heavy metals. Microplastic exposure impacts biomass, photosynthetic activity, chlorophyll content, root and shoot length in the plants through apoplastic and symplastic pathways. Microplastics can also indirectly affect the plant growth by changing soil nutrient content and microbial community structure. At the same time, microplastics can absorb heavy metals and increase phytotoxicity in plants. However, the current knowledge about the coupled effect of heavy metals and microplastics bioaccumulation in plants is limited. It is postulated that heavy metals and microplastics collectively impact the chlorophyll content, photosynthetic activity, and induction of reactive oxygen species in plants. This work also outlines the environmental health perspectives based on microplastic and heavy metals toxicity and provides a guideline for future research on the coupled effects of heavy metals and microplastics on plants and humans.