From the top of the tallest mountain to the depths of the ocean floor, this planet of ours is now pretty much covered in a thin layer of plastic. Tiny fragments of the stuff abound in the water we drink, the condiments we flavor our food with, and the air we breathe. They have even been found in our blood.

Which makes it a little less surprising – though no less worrying – that a new study, set to be published in the journal Science of the Total Environment, has found microplastic pollution deep in the lung tissue of living humans for the first time.

“Microplastics have previously been found in human cadaver autopsy samples,” lead author Laura Sadofsky, Senior Lecturer in Respiratory Medicine at Hull York Medical School said in a statement. “[T]his is the first robust study to show microplastics in lungs from live people.”

The research used lung tissue samples from living patients who were undergoing surgical procedures as part of their routine care – though the surgeons at the nearby Castle Hill Hospital in East Yorkshire made sure to send the team healthy samples rather than the actual bits patients were going under the knife for.

Out of 13 lung samples, a staggering 11 contained microplastics, with the most common types being pieces of PET, used to make drinks bottles; polypropylene, used for plastic packaging and pipes; and resin, often used as an adhesive or sealant.

“We did not expect to find the highest number of particles in the lower regions of the lungs, or particles of the sizes we found,” Sadofsky said.

“It is surprising as the airways are smaller in the lower parts of the lungs and we would have expected particles of these sizes to be filtered out or trapped before getting this deep.”

Interestingly, the only samples that had escaped microplastic infiltration came from female donors. The team think this might be due to men having larger lungs, and therefore larger airways – but given the small size of the study, they say that more investigation is needed before they can draw any firm conclusions.

And with their study now set for publication, those future studies should now be possible. Humans are bombarded with microplastics pretty much every day of their lives – potentially starting from before they’re even born – but the effects of this constant exposure is as yet unknown in detail. With their new paper, though, Sadofsky and her colleagues have produced more than just a worrying indictment of how ubiquitous microplastic pollution has become – they’ve made an important first step towards figuring out what all this plastic pollution is doing to the world.

“This data provides an important advance in the field of air pollution, microplastics and human health,” Sadofsky said.

“The characterization of types and levels of microplastics we have found can now inform realistic conditions for laboratory exposure experiments with the aim of determining health impacts.”