Uh oh. They found microplastics in humans: https://www.theguardian.com/environment/2018/oct/22/microplastics-found-in-human-stools-for-the-first-time
8 people from Europe, Japan and Russia participated in a study of stool samples, and microplastics were found in all 8 samples.
More studies are needed, but I think this means that every living human and animal on Earth is full of microplastics...