What are some of the major research gaps in this area that are hindering the development of robust risk assessments of MNP pollution?
There are several grey areas, but I would like to highlight the following:
Trophic transfer of MNPs can occur for the small MP/NP section (<10 µM). The extent to which this occurs remains largely unquantified. Some effects (altered brain structure) of trophic transfer were shown on fish but much remains unknown.
Human MNP ingestion via food and beverage consumption is an important exposure factor, next to inhalation. Cross contamination through food handling and packaging may be a more major contributor to MP pollution of food as trophic transfer.
MNPs ingestion in livestock is understudied. Studies on larger grazers are scarce or non-existent. Such studies are needed since it is well known these animals ingest MNPs.
Plastisphere communities are insufficiently characterised. We need to understand if these communities are transient or specific and quantify the risk of pathogen/gene transport by MNPs into the food system. Studies on the effects of plastisphere communities on open ocean ecosystems and soil ecosystems are particularly needed.
Plastic additives are understudied. Studies quantifying leaching profiles of plastic additives from any plastic (be it pristine or weathered) in animal tissue/digestive systems or complex soils are scares or non-existent. Nonetheless, matrix related physicochemical factors govern leaching profiles and this must be understood to quantify the potential food safety risk of plastic additives.
