Dr. Anne Marie Mahon:

There are two aspects to this. There is the polymer itself which has inherent chemicals. Some are plasticisers and some are additives to give that plastic whatever function it should have. These plastics can leach and the smaller the particle, the more readily these processes will happen.

Additionally, microplastics can absorb pollutants in the environment and these have been used in various situations to mop up. Some studies have been done to show that if a small invertebrate ate some microplastics, the level of persistent organic chemicals in the animal will have reduced once the plastics have gone through. The problem is that they are a vector of pollution. They can attract, for example, polyaromatic hydrocarbons and transport them. Whether these chemicals absorb or desorb - or let go - of the pollutants is affected greatly by pH. It is a concern that in the gut where the pH is lower, this could promote the release of the toxins.

Further up the course, the particles going through a wastewater treatment plant interact with many pathogens. One study has shown that microplastics downstream from a wastewater treatment plant have more pathogens on them, which would be associated with that pathway.