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.
