[pcrh]

I've yet to see any evidence that microplastics are toxic. Plastics are generally inert, and by the time they have broken down into microscopic pieces, most plasticizers have already been leached from the particles.

Microplastics are an ugly witness to pollution, but are likely not themselves very harmful.

[Tagbert]

The base monomers and polymers of PET may not themselves be toxic, but there are plasticizer chemicals added to them to adjust the characteristics that can have biological impacts. Additionally, once the PET starts to break into microplastics, it can attract and accumulate other chemicals that are actually toxic.

Other plastics can be directly toxic, such as styrenes.