Plant leaves absorbed microplastics and nanoplastics directly from the air, with the particles subsequently entering the food chain through herbivores and crops consumed by humans, a new study found.
Microplastics are defined as plastic particles measuring up to 5 millimetres in diameter, while nanoplastics are even smaller, less than 1,000 nanometres.
The study, published in the journal Nature, showed that plastic particles entered leaves through multiple pathways, including surface structures such as stomata and the cuticle.
The research was conducted by scientists from Nankai University’s College of Environmental Science and Engineering, the University of Massachusetts Amherst, the Chinese Academy of Sciences’ Research Center for Eco-Environmental Sciences, Northeastern University, and the Beijing Academy of Agriculture and Forestry Sciences.
Stomata are small pores formed by specialised cells, while the cuticle is a protective membrane coated in wax, which makes it particularly conducive to absorbing microplastics.
“Once inside the leaf, microplastics move through spaces between plant cells and can also accumulate inside tiny hair-like structures, called trichomes, on the surface of leaves,” said an article explaining the research.
The study also found that microplastics could travel through the plant’s water and nutrient transport systems to reach other tissues. However, trichomes that are hair-like appendages on cells acted as ‘sinks’ that trapped external particles, thereby limiting the transport of plastics from leaves to roots.
“Given that leaves are a key part of the food chain, microplastic particles that accumulate here can easily pass to herbivores and crop leaves, both of which can be directly consumed by humans,” the article noted.
The authors of the study demonstrated that this absorption occurred widely in outdoor environments. The concentration of plastic particles in plant tissues correlated with the concentration of plastics in the surrounding air.
The researchers reported that levels of microplastics — specifically polyethylene terephthalate and polystyrene — were 10 to 100 times higher in vegetables grown outdoors than those cultivated in greenhouses. Plants with longer growth periods and older outer leaves were found to contain higher concentrations than younger or inner leaves.
In one experiment, lettuce plants exposed to outdoor air in Tianjin, China, accumulated between 7 and 10 nanograms of polystyrene nanoplastics per gram of dry plant weight.
At sites with high airborne microplastic contamination, concentrations in plant tissue were found to be up to ten times greater than at cleaner sites.
The study highlighted the ecological and health risks of atmospheric plastic pollution, with airborne micro- and nanoplastics accumulating in plants and moving up the food chain. However, researchers cautioned that the full extent of the impact remains unclear.
The scientists called for further investigation into dietary exposure to plastics, the efficiency of microplastic absorption in the human gut and the degree to which these particles reach crucial internal organs.