[quirkot]

it took me a minute to parse that sentence also. They are saying that health tissue makes up < 100% of the body, but that microplastics can be found in a full 100% of the body (healthy and non-healthy). Therefore microplastic prevalence > healthy tissue. It's saying that there is no part of the body that isn't impacted

[equinoxnemesis]

I think it's saying there's more microplastics in unhealthy than healthy tissue is all, your interpretation is technically possible but phrasing it that way would be so misleading as to basically be lying.

The reason more microplastics in unhealthy tissue doesn't necessarily mean microplastics cause unhealthy tissue is that unhealthy tissue would be worse at removing substances irrespective of whether the substances cause the harm.