The NIH has begun doing studies on the effects of nanoplastics, and it appears there is evidence for buildup in the liver [1]. If asprin had a long half-life in your body, you'd have a maximum lifetime dose. The reason it makes a good medicine is due to the fact that it has a positive effect and leaves your body in a timely manner.
A good example in this instance is Lead. Its bad to have lead in your water even in relatively small amounts, because the half-life of lead in your soft tissues is months, and in your bone is 20-30 years. If nanoplastics end up being similar, you could end up with liver damage, or other medical complications if your exposure is high.