Micro-nano plastics make other pollutants more dangerous to plants and intestinal cells

(Press-News.org) Micro- and nanoscale plastic particles in soil and water can significantly increase how much toxic chemicals plants and human intestinal cells absorb, according to two new studies from Rutgers Health that raise fresh concerns about food safety from plastic pollution.

The first study in NanoImpact found that lettuce exposed to both nanoscale plastic particles and common environmental pollutants such as arsenic took up substantially more of the toxic substances than plants exposed to the pollutants, alone confirming the risks of polycontamination of our food chain. A companion study in Microplastics journal showed similar effects in human intestinal tissue.

The combination of both studies suggests micro and nano plastics, the byproduct of fragmentation of plastics in the environment over time, could be creating a dangerous cycle of contamination: making plants absorb more toxic chemicals that we might then eat, while making our bodies more likely to also absorb both those toxins and the plastics themselves and increasing risks for diseases, especially for susceptible populations. 

"We’ve already put about 7 billion metric tons of plastics into the environment that keep breaking apart," said Philip Demokritou, director of the Nanoscience and Advanced Materials Center at Environmental Occupational HealthSciences Institute at Rutgers University and senior author of both studies. "They pollute everything around us – the water we drink, the food we eat, the air we breathe."

Using a cellular model of the human small intestine, coupled with a lab-based gastrointestinal apparatus that simulates the digestive system, the researchers found that nano-size plastic particles increased the absorption of arsenic by nearly six-fold compared with arsenic exposure alone. The same effect was seen with boscalid, a commonly used pesticide, said the researchers from Rutgers, the Connecticut Agriculture Experiment Station (CAES) and New Jersey Institute of Technology (NJIT).

The relationship, moreover, worked both ways: The presence of these environmental pollutants also significantly increased the amount of plastic absorbed by the intestinal tissue, with plastic uptake roughly doubling when toxins were present.

"We know nanoscale materials can bypass biological barriers," said Demokritou, the Henry Rutgers Chair and professor in nanoscience and environmental bioengineering at the Rutgers School of Public Health and the Rutgers School of Engineering. "The smaller the particles, the more they can bypass biological barriers in our bodies that protect us."

For the other paper, the researchers exposed lettuce plants to two sizes of polystyrene particles – 20 nanometers and 1,000 nanometers – along with arsenic and boscalid. They found the smaller particles had the biggest impact, increasing arsenic uptake into edible plant tissues nearly threefold compared to plants exposed to arsenic alone.

The effects occurred in both hydroponic systems and more realistic soil conditions. Using advanced imaging and analytical techniques, the researchers showed the plastic particles themselves were also accumulating in plant tissues, with the smaller particles more likely to move from roots into shoots.

Micro and nanoplastics come from the slow breakdown of larger pieces of plastic in the environment.

"Even if we stop today producing plastics or using plastics, we have plenty of plastic waste unfortunately out there," Demokritou said.

The research was part of a larger USDA-funded project examining food safety issues related to micro and nanoplastics. The scientists said more research is needed to understand the long-term implications and to develop potential solutions.

"We need to stick with the ‘three-R’ waste hierarchy – reduce the use of plastics, reuse, recycle," Demokritou said. "For areas where you cannot apply these three Rs, like in agriculture where so much plastic is used for weed control and other things, use biodegradable plastics."

The researchers are developing new biodegradable materials that could replace conventional plastics and methods to better detect and measure plastic particles in food and water. However, they said preventing further contamination needs to be a priority.

"It's not that technically we cannot address some of these issues," Demokritou said. "But it will definitely be a challenge to retain all the benefits from this very useful material while reducing the harms that it does. There are social and economic obstacles related to plastic production and use to overcome.”

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