Microplastics - a Trojan horse for hydrophobic pollutants?

I just went through my book Introduction to Aquatic Toxicology, which was written in 2012-2013 and published in 2014. When reading it, one noticed that it did not have anything on microplastics, although today it is a major topic in aquatic toxicology. How on earth could one have missed such an important topic? To understand why it was not included, I checked the Web of Science, searching for articles including the word microplastics, and found that although in the past five years close to 17600 articles were published, there were only 81 published before the end of 2013, approximately half of them in 2013. Thus, the topic was virtually unknown for aquatic toxicologists, when I wrote the book. Since, further, I was not involved in studies in that area, not picking it up as a possibly popular future topic is understandable.

In contrast, nanotoxicology, which started as a study area in early 2000’s, was quite fashionable with the largest number of publications in 2014. I was then worried about the lack of environmental relevance of the studies, because without a link between the environmental exposure and toxic effects, the studies of nanomaterial toxicity lack real importance. I suppose the ecological importance of nanotoxicology has not been established, as the number of articles on nanotoxicology keeps decreasing, being about 60 % of the highest article number last year.

It remains to be seen if microplastics are shown to be an ecologically relevant issue. So far most of the studies have demonstrated that microplastic particles are found everywhere. Thus, they are taken up by organisms, and can also penetrate cells. However, as long as the microplastic is inert material, little toxicity is expected, since small inert particles  such as cellulose has always entered organisms. The situation may change radically, if microplastics are in contact with hydrophobic pollutants. They will preferably attach to the plastics, and when the microplastic particle enters organism, exert toxicity. In this case, the microplastic particle is the Trojan horse in which toxic materials can enter the cells and induce damage. I am expecting to see these kinds of studies: clean microplastic particles showing little toxicity, and particles associated with hydrophobic pollutants being toxic. If and when this prediction is right, we should aim at decreasing microplastic contamination, but especially releasing hydrophobic pollutants to the environment.