Evidence of soil microplastics inhibiting the germination of commercial coriander seeds under field conditions

Abstract

The environmental impacts of microplastics (MPs) and nanoplastics (NPs), and their occurrence in aquatic, terrestrial, and aerial biomes have engrossed global attention. Most impact assessment studies have majorly linked the ecological hazards of MPs with the leaching of their additives, and the sorption and transport of co-contaminants due to prolonged environmental exposure. However, it is unclear whether the fresh (unaged) polymers themselves could significantly impact the biota. In this study, we have reported the impacts of virgin polypropylene (PP), polyvinyl chloride (PVC), and polylactic acid (PLA) MPs (0%, 0.05%, 0.1%, and 0.5% w/w dry soil) on the germination of an agricultural herb, coriander (Coriandrum sativum L.), under outdoor (field pots) and indoor (greenhouse) conditions. We observed that all three polymeric MPs in the soil delayed the germination (60-100% inhibition up to day 7) and impacted the seedling length within the 30-day exposure. The inhibitory effect was higher in the field than in the greenhouse. PVC showed the highest inhibition of germination under both conditions, followed by PP and PLA. PLA impaired the root length of the seedlings more than PP and PVC. At 0.5% (w/w), all polymers showed significantly elevated levels of reactive oxygen species in the root tips than control, suggesting MP-induced oxidative stress as a potential mechanism behind the impaired germination and seedling growth. These results clearly indicated a potential decline in crop survival and productivity caused by virgin MPs. The findings proposed that the soil MPs could be a global threat to the plants and ecosystem succession.