Effects of nano- & microplastics on terrestrial plants are ubiquitous and widespread: a systematic review

Over the last years there has been significant research on the presence and effects of plastics in terrestrial systems. Here we summarize current research findings on the effects of nano- and microplastics (NMPs) on terrestrial plants, with the aim to determine patterns of response and sensitive endpoints. We conducted a systematic review (based on 78 studies) on the effects of NMPs on germination, plant growth and biochemical biomarkers. The majority of studies to date have used pristine polystyrene or polyethene particles, either in a hydroponic or pot-plant setup. Our results show that effects on plants are widespread. We noted similar responses among plant species, and between monocots and dicots to NMPs, except for consistent lower germination in dicots due to NMPs. Our results also highlight variation in sensitivity of endpoints to NMPs. During early development, germination and root growth are more strongly affected compared to shoot growth. NMPs induced similar adverse growth effects on plant biomass and length in the most tested plant species (lettuce, wheat, corn, and rice) irrespective of the polymer type and size used. Moreover, biomarker responses were consistent across species; chlorophyll levels were commonly negatively affected, while stress indicators (e.g., ROS or free radicals) and stress respondents (e.g., antioxidant enzymes) were consistently upregulated. Importantly, effects were commonly observed at environmentally relevant concentrations for most endpoints. These findings clearly indicate that NMPs have a wide ranging and ubiquitous impacts affecting plant performance. Importantly, most studies have been conducted under highly controlled conditions and with pristine plastics, raising the urgent need to test under more environmentally realistic condition to ensure the lab-based studies can be extrapolated to the field.