As part of the quest to understand how microplastics in the environment affect the health of living creatures, researchers with the University of California have found that high levels of these pollutants have short-term impacts on lab mice, causing blood-sugar, liver and intestinal problems.

The test mice were fed a highly-concentrated solution of nanoparticles of a type of plastic called polystyrene; commonly used in food packaging, styrofoam and disposable plastic cutlery, polystyrene can be identified by its Resin Identification Code (RIC) 6, found in the product’s triangular recycling symbol. To exaggerate the effect these nanoplastics might have on the test animals, the amount administered to each mouse was equivalent to a 180-pound (80 kilogram) person ingesting 4.8 grams (a little over 1/6th of an ounce) of plastic each day for seven weeks—far higher than what one might be exposed to in our current environment.

The nanoplastic doses had a number of health impacts on the test animals: the bodies of the mice began to have trouble clearing glucose from their blood, a high blood-sugar state that can contribute to type-2 diabetes; they also had elevated levels of a molecular marker associated with liver problems—alanine aminotransferase (ALT)—suggesting that the plastics were injuring their livers. On top of all of this, the mice developed an increase in gut permeability that caused their intestinal walls to absorb materials that wouldn’t ordinarily be allowed into the bloodstream.

It should be noted that while the amount of plastic nanoparticles the mice were subjected to were far higher than what we would encounter in the environment, these pollutants are known to accumulate in the tissues of organisms, the effect of which is the subject of ongoing research.

For instance, there is concern over hormone-like compounds such as bisphenol A (BPA), used to make polycarbonate plastics (RIC-7), that might be among the micro and nanoplastics that may be accumulating in our bodies: although its effect has since been found to be tens of thousands of times weaker than estrogen, the potential for it to mimic the effects of the hormone have prompted Canada, the European Union and the United States to ban BPA from use in baby bottles.

“It is a possibility that micro-and nanoplastics are acting as vehicles for these chemicals,” remarked Angel Nadal, a physiologist at Spain’s Miguel Hernandez University, who was not involved with the study.

The work of the UC Davis research team is ongoing, studying the potential effects nanoplastics might have on other biological functions, such as kidney function.

“I feel like we’re there and we don’t know a lot about what these plastics are doing to us,” according to study lead and UC molecular physiologist Amy Parkhurst, who points out that “a lot is still unknown” about this pervasive environmental pollutant.