INTERACTION BETWEEN PLANTS AND NANO- PLASTICS: PHYTOTOXICITY AND DEFENSE MECHANISMS

Abstract

Microplastics (MPs) and nano-plastics (NPs) pollution has become a challenge for terrestrial ecosystems. An important vector for the transport of microplastics (MPs) into agricultural soils is organic fertilizers, which pose human health concerns through the food chain. The present study aimed at quantification and characterization of MPs in 3 different types of composts i.e., MSW compost (MSWC), Leaf compost (LC) and Organic compost (OC), and their subsequent translocation to lettuce (Lactuca sativa) grown on contaminated composts. Moreover, exogenous application of nano-plastics via foliar and root pathways was carried out to understand the growth and physiological response of plant under NPs stress. The results revealed that the MP abundance ranged from 3810 – 16530 MPs/kg. MSWC had the highest abundance (16082 ± 632 MPs/kg), followed by LC and OC (6299 ± 1011 and 3680 ± 419 MPs/kg, respectively). MPs of <100 μm in size were most dominant in MSWC and LC. Fragments and fibers were the prevalent shape types, with white/transparent colored MPs being more abundant. Polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) were the dominant polymers. MPs accumulation revealed by SEM in the lettuce leaves was greatest in the lettuce plants grown on MSWC, followed by those grown on LC and OC, indicating that MSWC grown lettuce is not suitable for human consumption. The decrease in the growth (leaf length, number of leaves, leaf fresh and weights) and physiological (membrane stability index, relative water contents) parameters of lettuce was in line with the trend of MP accumulations. Whereas, the exogenously applied NPs densely accumulated in lettuce leaves and roots, indicating their uptake and translocation in plant. The NPs resulted in a significant decline in growth (leaf and root length, number of leaves, leaf and root fresh & dry weights) and physiological (membrane stability index, relative water contents) parameters via both foliar and root pathways. The biochemical parameters i.e., ROS and Antioxidant enzymes (SOD, CAT, POD) also reflected the stress and impact caused by NPs on plants. Hence, it is highly important to regulate the micro and nano-plastic contents in composts because it is a threat to plants and human health.