Googling epidemiological study of the effects of plastics on human health is a decent place to start.
Asking about it here on hn is very definitely not.
The question was about plastic pollution, and specifically the effect of micro plastic particulates on humans. I couldn't find anything after a cursory search, although to be honest I don't really know what terms I should be searching for.
Personally I have only so much emotional energy to spend, and I spend it on real issues. Not made-up ones.
As for "the environment is full of tons of stuff", microplastics are pretty new to the biosphere, so who knows what we should suspect? Personally I think microplastics are bad at all scales, and it'll just get worse. They weaken individuals, species, and whole ecosystems right as we're delivering them a big punch in the gut with habitat destruction, overfishing, and climate change. Are they what's going to kill the world? Nah, maybe only #4 on the list. Only!
Structurally, we concentrate exotic materials and then disperse them. Nothing like that has ever happened at global scale to life before. The economic changes to achieve a system that doesn't make this its default trend are almost unthinkable. That's what I see as the real #4 (or whatever) on the list.
I've used this information to try to eke out my single use plastic use. (Use of single use plastic? single plastic use?)
The cause for concern?
"Adverse effects of microplastics ingestion have only been observed in aquatic organisms under laboratory conditions, usually at very high exposure concentrations that exceed present environmental concentrations by several orders of magnitude"
No.
Note that this does not mean they're safe. It means we don't know if they're safe, or the extent to which they're harmful if they're dangerous. It goes from "we got lucky, it's all going to be fine" to "literally everyone will die from the plastics equivalent of asbestosis in the near future". If that doesn't scare the living shit out of you then you've misunderstood the scale of the problem.