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Microplastics are pretty much everywhere you look. These tiny pieces of plastic pollution, less than five millimeters across, have been found in human blood, breast milk, and placentas.

Yes, they are in our drinking water and the air we breathe. But they’ve also been found in regions of the planet that you might think of as pristine, such as the French Pyrenees, the Galápagos Islands, and even the Mariana Trench—the deepest part of the ocean. Most recently, we’ve heard that the recycling process can release tons of microplastics into the environment.

Given their horrifying ubiquity, it’s worth considering what we know about microplastics. What are they doing to us?

The short answer is: we don’t really know. But scientists have begun to build a picture of their potential effects from early studies in animals and clumps of cells.

This week, I came across a new study that looks at the impact microplastics might have on our immune cells. It is really difficult to do this kind of research in people—you can’t ethically inject a person with tiny bits of plastic, for a start. So the researchers looked at cells in a dish.

Specifically, they looked at macrophages—a type of white blood cell that kills foreign invaders and helps get rid of dead cells. Thierry Rabilloud at the French National Centre for Scientific Research and his colleagues investigated how macrophages responded to beads of polystyrene.

Tests revealed that some types of macrophages engulf the beads of plastic entirely. Others don’t. The cells that get loaded up with plastic behave differently, suggesting they may not work as well at providing protection from harmful bacteria and other invaders that might cause disease.

Rabilloud and his colleagues write that microplastics could have wider effects on the immune system more generally, as well as on the health of the body tissues that the particles infiltrate. 

One remaining question is what happens after the plastic is taken into our cells. It’s possible that our bodies can find a way to eliminate it. But if not, it could stick around for the rest of our lives, and damage or kill those cells it has infiltrated.

Microplastics could have other health consequences. You might remember a recent Tech Review article about some research into their effects on seabirds, for example. These poor animals are often exposed to a lot of plastic because garbage ends up floating about on the sea, degrading extremely slowly.

Here, bits of plastic can end up collecting various types of bacteria, which cling to their surfaces. Seabirds that ingest them not only end up with a stomach full of plastic—which can end up starving them—but also get introduced to types of bacteria that they wouldn’t encounter otherwise. It seems to disturb their gut microbiomes.

There are similar concerns for humans. These tiny bits of plastic, floating and flying all over the world, could act as a “Trojan horse,” introducing harmful drug-resistant bacteria and their genes, as some researchers put it.

It’s a deeply unsettling thought. As research plows on, hopefully we’ll learn not only what microplastics are doing to us, but how we might tackle the problem.

It is too simplistic to say we should ban all plastic. But we could do with revolutionizing the way we recycle it, as my colleague Casey Crownhart pointed out in an article published last year. 

We can use sewage to track the rise of antimicrobial-resistant bacteria, as I wrote in a previous edition of the Checkup. At this point, we need all the help we can get …

… which is partly why scientists are also exploring the possibility of using tiny viruses to treat drug-resistant bacterial infections. Phages were discovered around 100 years ago and are due a comeback!

Our immune systems are incredibly complicated. And sex matters: there are important differences between the immune systems of men and women, as Sandeep Ravindran wrote in this feature, which ran in our magazine issue on gender.

It is difficult to work out how the pollutants in our environments might be affecting us. But exposomics is on the case. 

An eating disorder helpline sacked its staff and used a chatbot to support people instead. Within weeks, the National Eating Disorder Association had to take the chatbot offline—it had been found to give information that was “harmful and unrelated to the program,” a spokesperson said. (Motherboard)

Members of the billionaire Sackler family will be protected from future legal claims surrounding the involvement of their company in opioid prescriptions. The family, which owns Purdue Pharma, is receiving immunity in exchange for a $6 billion payment, which will go toward victim compensation and overdose rescue medication. (New York Times)

The people making lab-grown meat may argue that it’s better for animal welfare and the environment, but what about the religious perspectives of the people who might buy and eat it? According to surveys, 68% of Hindus would eat cultivated chicken, and 81% of Buddhist people surveyed said they’d eat cultivated beef. (Nature Food)

What happens if you inject a psychedelic into the veins of healthy volunteers? Everything from mystical experiences and the transcendence of time and space to nausea, high blood pressure, and uneasiness. (Translational Psychiatry)

Coral reefs are among the most diverse ecosystems on Earth. Now it appears that the microbiome of the Pacific coral reef is as diverse as that of the rest of the planet combined. Scientists found 2.87 billion genetic sequences in samples taken from 99 reefs. (Nature Communications)