This is probably one of the most prominent studies till date:
https://pubmed.ncbi.nlm.nih.gov/38446676Microplastics and nanoplastics in atheromas and cardiovascular events. N Engl J Med. 390(10):900-910, 2024.
Summary: People with artherial plaque that contains micro- and nano-plastics have a higher risk of death during the followup period. It's an observational study, sample size is not too big, but some findings look quite mechanistic suggesting causality, e.g. "electron microscopy revealed visible, jagged-edged foreign particles among plaque macrophages and scattered in the external debris". The effect size induced by microplastics on death risk also looks substantial.
Personally, I think microplastics are a very important pollutant, and evidence of this will unfold during the next years. Sadly, it is extraordinarily hard to remove them from our environment. They are everywhere. For example, car tires shed lots of microplastics that end up in eggs or inside vegetables and plants, which absorb them from soil. Most liquids are packaged inside plastic, which is continuously leaking into the content. We should at least be measuring their levels and setting up maximum concentration thresholds in our food chain. We should go back to glass bottles, whenever possible. Suspended microplastics in the air are also a major concern. Plastics are great for certain applications, but we use them in places where they don't belong.