Interactive effects of microplastics and typical pollutants on the soil-plant system: a mini-review

Although research on microplastics (MPs) interactions with other soil pollutants is increasingly becoming available, most studies do not consider risks to soil fertility or plant growth. This review aims: 1) to summarize the results of current studies on interactions between MPs, heavy metals, and organic pollutants, and 2) subsequently evaluate risks to the soil-plant nexus. Available-literature shows that polypropylene, polyethylene and polylactic acid increase cadmium (Cd) bioavailability and subsequently reduce root growth.Such effects are not evident in sandy or clay soils due to the formation of CdCO3 and iron-oxide by altered bacterial communities that stabilize Cd contamination. Chronic instead of short-term exposure to polystyrene in copper (Cu) - polluted soils decreases crop yield. With coexistence of MPs and lead (Pb) in soil, the uptake of Pb in crops increases, causing altered malondialdehyde content and superoxide dismutase and guaiacol peroxidase activities. Moreover, co-toxicity of polystyrene or polytetrafluoroethylene with arsenic (As) decreases root biomass, photosynthesis rate and the chlorophyll-a content. In alkaline soil, polyvinyl-chloride could decrease the bioavailability of MeHg due to changes in the abundance of Proteobacteria, and Firmicutes. We also found strong interactions between MPs and organic pollutants. Polystyrene decreases negative impacts of sulfamethazine on bacterial diversity, and structure in soil. Polyethylene, polyvinyl-chloride and polystyrene have a strong adsorption capacity for 17β-estradiol.This implies that 17β-estradiol toxicity can be reduced by these MPs. At low concentrations, polyethylene, polypropylene, and polystyrene have low affinity to diazepam. In conclusion, serious ecological risks are associated with MPs and other pollutants' interactions to soil-plant system.