Plastics are not inert: they gradually break into fragments over time, forming micro- and then nanoplastics (i.e., particles <1 μm in size). Nanoplastics are found in drinking water and foods packaged in plastic. This reality suggests that humans may be ingesting appreciable quantities of nanoplastics to which the gut is highly exposed. Yet, we have a limited understanding of how nanoplastics affect digestive system health. Additionally, to date, studies on this topic have employed commercial particles, which often contain additives. In the study published in Environmental Science: Nano, the research team specifically examined how the guts and livers of mice were affected by polystyrene nanoplastics, employing model particles produced in the laboratory using a controlled process.
To this end, the team's chemists employed an additive-free process that they had developed themselves to synthesise 100% polystyrene nanoplastics. It was thus possible to focus on the specific effects of the polymer in particulate form. The particles were labelled with gold so that their presence in the bodies of the mice could be detected and quantified. The team's toxicologists exposed the mice to three doses of nanoplastics—0.1, 1, or 10 mg of nanoplastics per kg of body mass per day—which were added to the mice's drinking water for 90 days. The mice received one of two diets—a standard mouse diet or a "Western-style" diet (high fat + high sugar), and the impacts of the nanoplastics on the mice's guts and livers were examined.
Diet-dependent effects
It was found that exposure to low doses of polystyrene nanoplastics over the 90-day period had strong diet-dependent effects.
Gut barrier integrity was altered, an effect that was amplified in mice consuming the Western-style diet. Gut microbiota composition was also altered, an effect that was amplified in mice consuming the standard diet.
In the liver, exposure to low doses of nanoplastics disrupted fat metabolism regardless of diet, but glucose intolerance was more pronounced in mice consuming the Western-style diet. This effect was seen even though nanoplastics did not appear to cross the gut barrier. The above changes were associated with greater mass gain in the mice.
The study's results illustrate that low doses of nanoplastics without chemical additives can alter gut and liver function in a diet-dependent manner.
