Microplastics are now present in everything we eat, whether it be plant-based, animal based, or fish. And so we have microplastics in human tissue as well.
The reason is that plastic gets eroded and degraded into microplastic particles. These particles are small enough to be absorbed by plants, and are ingested by fish. This, in turn, finds its way into land animals who eat them.
There is a widespread belief that these microplastics have harmful effects on human health. However, we do not precisely know how it harms us and what harm it causes.