More and more evidence is showing that microplastics in our blood could possibly cross the mammalian brain-hematogen barrier. Now, preliminary experiments are showing the potential impact they can have once there, by finding that weathered microplastics are much more toxic to human brain cells than fresh ones.

“The harmful effects of microplastics are particularly worrying because secondary microplastics entering the natural environment cause a more severe inflammatory response in the brain,” says biologist Sung-Kyun Choi from Daegu Gyeongbuk Institute of Science and Technology (DGIST).

We surrounded ourselves completely in plastic. We wear them, we communicate with them, we eat from them, we drink from them, we live in their coats, we travel with them and so on – 390 million tons of plastic were produced in 2021 alone. Each of these multiple sources emits fragments known as microplastics, not only after they are destroyed, but throughout their lifetime.

When these small parts are exposed to elements such as rain, wind and sunlight, they change shape and structure before returning to living bodies. Long before we’re born, we suck up dust from old pieces of plastic.

While previous research has tested the effects of newly produced plastic on our brain cells, DGIST biologist Hee-Yeon Kim and colleagues challenged them by using weathered particles instead. They carefully studied how our brain’s immune cells, microglia, responded to microplastics derived from weatherproof polystyrene, compared to “intact” cells of similar size.

Giving the mice weathered microplastics for seven days increased the levels of inflammatory particles in their blood. There was also increased cell death in the brain. The researchers then compared the weathered pieces of polystyrene to lab-grown human microglia.

Microglia, which make up 10 to 15 percent of brain cells, patrol our central nervous system looking for objects that shouldn’t be there. Not surprisingly, previous research by the team found that microparticles accumulated in the microglia of mice.

Kim and colleagues found that weathered microplastics affected proteins involved in converting sugar into energy and increased their expression in microglial cells 10-15 times more than in control cells. They also increased the concentration of proteins involved in the death of brain cells by 5 times.

The team suspects this may be due to changes that microplastics undergo when exposed to sunlight. Polystyrene absorbs ultraviolet waves, which makes the plastic more brittle and prone to breaking down. Kim and her team found that weathered polystyrene increases surface area and changes chemical bonds; two properties that affect their reactivity.

All this leads to an increased inflammatory response in brain cells – much more potent than that caused by uneroded microplastics tested at equivalent doses.

“We found for the first time that the plastic that enters the environment undergoes an accelerated decomposition process into secondary microplastics that can act as a neurotoxic substance, leading to increased inflammation and cell death in the brain,” explains Choi.

The results have so far only been seen in living mice and human tissue samples in the lab, but the fact that these pollutants can cause such profound changes once they reach brain tissue is a strong indication that they affect our brain health.

Although the experiments relied on small sample sizes and high microplastic concentrations to account for long-term microplastic accumulation, the researchers are now planning long-term studies with larger sample numbers and doses that better reflect environmental conditions over time to test their findings.

The results could come soon as fossil fuel companies invest billions of dollars this decade to further increase plastic production in the face of potential reductions in fuel use in response to climate change.

At most, this boom in plastics production is supported by government subsidies that use taxpayers’ own money. If our health is at stake, as research is increasingly suggesting, more attention will need to be paid to how we produce, use and dispose of plastic. Source