We know microplastics are a big environmental problem and that they can now be found almost everywhere, including our food and water — and inside our bodies. But just how harmful are they? Since it’s a problem we’ve only recently started to realize, we don’t know yet — but the data is coming in, and it doesn’t look too good. At least in a petri dish, microplastics have the potential to cause significant damage to human cells in the laboratory, a new study found.

The study is the first to quantify the levels of microplastics (plastic particles measuring less than five millimeters) that may lead to harmful effects in human cells.

“This is the first-time scientists have attempted to quantify the effects of the levels of microplastics on human cells using a statistical analysis of the available published studies,” Evangelos Danopoulos, lead author and PhD student, said in a statement. “We are seeing reactions including cell death and allergic reactions as potential effects.”

Not only are microplastics everywhere already, but the contamination is expected to rise as plastic production and use around the world also increase. Within a century, the ecological risks of microplastics could be widespread in ecosystems across the world. So researchers are trying to understand just how dangerous these microplastics really are.

Exposure and contamination

Humans have two main routes of exposure to microplastics: ingestion and inhalation; we either ingest or inhale microplastics — and concerningly, both seem to be widespread. The presence of microplastics has been verified in human lung tissue, placenta, and colectomy samples.

Danopoulos and his team first reviewed a set of 17 previous studies that looked at the toxicological impact of microplastics on human cell lines. This allowed them to compare the level of microplastics consumed by people through polluted seafood, table salt, and drinking water with the level at which damage is caused to human cells.  

They found that four specific types of harm to human cells (cell death, damage to cell membranes and allergic response) were directly caused by the microplastic that people eat. The study also showed that microplastics with an irregular shape cause more cell death than spherical ones. Most laboratory studies focus on spherical ones. At the levels already found inside human bodies, these particles seem to be causing significant cellular damage.

“Our analysis of the data showed that cell viability depends on the shape of the microplastics. Irregularly shaped microplastics, which are the majority found in the environment, are more hazardous than spherical,” Danopoulos said. “So far, most toxicology studies have been testing spherical microplastics. There needs to be a shift.”

For the researchers, the findings show that we are eating microplastics at levels consistent with harmful effects on our cells, which could then trigger other health effects. Nevertheless, he highlighted the high level of uncertainty regarding how ingested microplastics are excreted from the body – crucial to better understand the true risk that microplastics pose to our health.

The study was published in the Journal of Hazardous Materials.