Micro- and nanoplastics (MNPs; < 5 mm and < 1 mu m, respectively), are contaminants of emerging concern representing a major part of global plastic pollution, due to their ubiquity both in natural and urbanised environments. Although environmental concentrations of these pollutants have been measured in a variety of matrices, information on the occurrence of MNPs in recirculated aquaculture system (RAS) farms, is scarce. The present study aimed to investigate the presence of MNPs in a commercial European RAS farm, by identifying the occurring polymers in both the system water and in a variety of fish tissues and quantifying their concentration. To this end, adult Oreochromis niloticus (Nile tilapia) were sampled for brain, liver, gut, stomach, muscle and gonads, and water was collected from both the influent and the effluent of the system. Size exclusion chromatography coupled to high resolution mass spectrometry equipped with an atmospheric photoionization source was employed to identify five distinct polymers, namely polyethylene (PE), polyisoprene (PI), polysiloxane, perhydropolysilazane (PHPS), and poly-dimethylsiloxane (PDMS). Two polymers were present in the system water, with PI being found at considerably greater concentrations in the effluent than in the influent. By order, the tissues that retained the greater number of polymers were: muscle > gut = brain > stomach > liver = gonads. The analyses indicated that liver and gonads did not contain any MNPs particles, whereas muscular tissue contained up to 3 distinct compounds. The results may reflect different uptake pathways of MPNs depending on the polymer type and its respective properties. The presence of these emergent contaminants in the muscle represents an additional exposure pathway for humans, through the ingestion of contaminated RAS-farmed fish, adding to the long list of confirmed exposure routes. Investigating the input of MNPs in RAS facilities through the weathering of its plastic components and assessing non-plastic alternatives to these components (e.g. natural biofilters), as well as MNPs removal techniques from the system, is of utmost importance to minimise the presence of these contaminants in RAS, and their impact on global food security.
