A new study has discovered that microplastics, the tiny plastic particles less than five millimeters in length, are now contaminating edible plants, including vegetables.
The findings, published in the journal Nature Sustainability, shed new light on the possibility of food chain transfer of microplastics; meaning if they are getting into our crop plants, they are also getting into our meat and dairy.
This raises obvious concerns about growing crops on fields contaminated with wastewater treatment discharge or sewage sludge, a process that could introduce microplastics into the food chain. It also raises the key question of how microplastics affect human health, a question for which there is as yet no clear answer.
Microplastics are already ubiquitous throughout the ocean, in our seafood and salt.
Most microplastics are emitted to the terrestrial environment and accumulate in large amounts in soil. In addition, secondary particles are formed by the degradation of plastics. Wastewater, an important source of water for agricultural irrigation, also contains small-sized microplastics.
For decades, scientists believed that plastic particles were simply too large to pass through the physical barriers of intact plant tissue. But the new study disproves this assumption.
“Cracks at the emerging sites of new lateral roots of lettuce and wheat crops can take in MPs from the surrounding soil and water. Those MPs can then be transferred from the roots up to the edible parts of the crop,” said Luo Yongming of the Chinese Academy of Sciences (CAS), the study’s lead author.
Scientists already knew that particles as tiny as 50 nanometers in size could penetrate plant roots. But Luo’s group revealed that particles about 40 times that size can get into plants as well.
The microplastics identified in this study were spherical plastic particles up to two micrometers in size with a small degree of mechanical flexibility. These features allowed the microplastics to squeeze into the small apoplastic space of plant root cells.