Microplastics have always fascinated me, because I keep seeing article after article about how much microplastic exists around us, but far less strong evidence about its actual effects. That is not to say there are no effects, of course. Maybe we just have not found them yet.

A friend of mine worked on her bachelor’s thesis about the effects of microplastics on the immune system, specifically T cells. Her result was that the microplastic particles she studied were too large to interact with T cells.

She probably will not publish this result because she thinks it is not interesting enough. Classic file-drawer problem in academic science.

While I encourage her to do it anyways as a negative results is also interesting but she wanted results that are worthing of headlines in magazines.

> She probably will not publish this result because she thinks it is not interesting enough. Classic file-drawer problem in academic science.

It's truly insane that everyone in the academic class understands the fundamental problems of herding and sampling bias and yet every incentive is in place to do this.

> but far less strong evidence about its actual effects.

Yeah, but we shouldn't take absence of evidence as evidence of absence. The fact is that it's just really really hard to establish a causal relationship, even if it's there, because of all the cofounders. Heck even if you constructed a study with a known poison, like lead, and you might not see the results in a single study. You could give 50 participants water with flint levels of lead in it for a month, and you might not get scientifically significant result just due to the wide variance in a population.

Or another example is just thinking how hard it would be construct a study with a control, when every single construction material has plastics in it and they are floating in the air around us all the time (as mentioned in the article). Could it affect mental or reproductive wellbeing? Certainly. Can we construct a study to establish either way? Not easily.

And one of the plasticizers they talk about, pthalates, are known to be endocrine disruptors (i.e. mess with hormones).

I participated in research from 2017-2022 that found similar results regarding bio-interactions, generally.

Learned a lot about making microfludic flow cells at least

> ... too large to interact with T cells.

Also, unfortunately, a result that industry and the anti-regulation crowd will use to say microplastics are harmless.

Can microplastics never get small enough to interact with T cells?

One thing I learned from this article is that even though the plastic particles themselves are poorly studied the chemical additives, such as phthalates and bisphenols, are very well studied and are known toxins. So even if the tiniest plastic particles (smaller than the ones your friend studied, that can cross from your gut into your bloodstream), don't affect your health at all, you still don't want to ingest these things because of the other chemicals in them.

She should at least put it on https://www.biorxiv.org/ !

I expect many researchers are using fresh lab-made microplastics, which are indeed mostly harmless. However part of the problem is that real-world plastics are chemical sponges that absorb toxins (heavy metals, PCBs, etc) from the environment and deliver them in a concentrated dose into the body.

https://www.eurekalert.org/news-releases/923529

> Her result was that the microplastic particles she studied were too large to interact with T cells.

Her "result" of what? Was there an actual experiment and what was its scope or was this by surveying literature?

Microplastics are of a pretty large range of size, and then there are nanoplastics below that.

I'm also not an expert, but a quick search shows a number of results of microplastics affecting T cells, some directly and some in terms of immune signaling, so this negative result doesn't seem that definitive.

(as usual, the difficulty is in teasing out in vivo effects)