Dr. Anne Marie Mahon:

Yes, sewage sludge is used as a fertiliser for tillage, not for crops for human consumption. There are regulations or guidelines regarding the application of sewage sludge. For example, there are regulations regarding the distance from a watercourse and what kind of weather one should or should not spread in. Some sewage sludge is applied untreated. Most is applied treated. These treatments, which we looked at in one study, have an impact on the microplastics. They can exacerbate the problem by breaking the particles down further. One of the main threats or reasons we are concerned about microplastics is the size. The smaller they get the more environmental compartments they can penetrate. They can go into the lower bottom of the food chain and can be transported up readily. Once they go into the nanometer range, they can cross a cell membrane. The smaller they get, the more concerned we are about it.