Introduction
The problematic of plastic litter in aquatic environments is well-established and studied. Conventional petroleum-based plastics are associated with a high carbon footprint, environmental persistence and microplastic pollution. These microplastics can affect behavioural and neurological functions, metabolism, and intestinal permeability of fish (Jacob et al., 2020). Farmed fish species are of major concern, since they can be exposed to microplastics directly through seawater, from fragmentation of aquaculture infrastructures, daily maintenance materials, and aquafeeds. Additionally, microplastic presence in such species poses further risks for human health, due to the consumption of contaminated products (Mossotto et al., 2025).
In recent years, there has been an increasing concern to develop bio-based, sustainable and environmentally-friendly alternatives to conventional petroleum-based plastics. However, as any other disposable material, these bio-alternatives might accidently end up discarded into marine environments and fragment into microplastics. The current knowledge is very limitited in regard to the toxicological effects of bio-microplastics in fish species, especially concerning behavioural and neuronal alterations. Accordingly, it is essential to validate the eco-friendly claims of these emerging bio-based plastic alternatives.
The present study investigated the neurotoxicity and behavioural effects of chronic oral exposure to different bio-microplastics in the commercially and ecologically-relevant fish species gilthead seabream (Sparus aurata).
Materials and Methods
Farmed S. aurata juveniles (18.78 ± 0.51 cm total length, 103.46 ± 5.52 g weigth) were kept in recirculating aquaculture systems (RAS) under optimal rearing conditions. During the 28-day exposure trial, speciments were fed 1% body weight with a commercial-based diet (CTR) or with three contaminated diets, containing either i) polylactic acid microplastics (PLA); ii) polypropylene 2,5-furandicarboxylate microplastics (PPF), or iii) mixed polymer PLA/PPF microplastics. The three contaminated feeds contained ~60 particles g-1 feed, each ranging between 500 and 1000 µm.
During the trial, swimming activity was assessed twice a week (n = 8 fish per treatment) through direct observations to evaluate behavioural alterations elicited by bio-microplastics. After 28 days of trial, fish (n = 7 per treatment) were randomly collected and euthanized for dissection and collection of plasma and brain tissue. To evaluate the neurotoxic and stress effects of biobased microplastics, the following endpoints were assessed: brain condition index; plasmatic cortisol levels; neurotransmission (acetylcholinesterase activity, AChE); antioxidant defences (superoxide dismutase activity, SOD; catalase activity, CAT; glutathione S-transferase activity, GST; and glutathione peroxidase activity, GPX); and cell damage (ubiquitin content, UBI; lipid peroxidation, LPO; and caspase activity, CASP). Statistical differences between treatments were analysed through Generalized Linear Mixed Models (GLMMs) for swimming activity data, or via one-way ANOVA for all other endpoints.
Results and Discussion
No statistical differences were found for swimming activity, brain-somatic index, AChE activity and cortisol concentration. These findings indicate that the bio-microplastics investigated do not severaly alter neural transmission, affect the overall physiological condition of the brain, or elicit a generalized stress response in seabream. Concerning antioxidant defences, all three biopolymers increased the activity of CAT, GST and SOD. This activation of the antioxidant systems is most likely related to an increase in reactive oxygen species (ROS) in brain cells. However, severe lipid damage did not occur (i.e. no increase in LPO).
Although data analysis is still ongoing, preliminary results suggest that the exposure to PLA, PPF and the mixed polymer do not lead to severe toxic effects in brain health and function in S. aurata. These findings are optimistic for the bioplastic industry, which should strive to develop and produce plastics that are not only more environmentally sustainable, but also pose no harm to wildlife. Equally, these findings are useful to the aquaculture industry, since it should shift towards the use of bioplastics in tools and packaging that are non-toxic to farmed species. Nonetheless, these results need to be complemented with further research on other S. aurata tissues and other aquaculture-linked species.
Acknowledgment
This research was supported by the NextGenerationEU programme under the Recovery and Resilience Facility Plan for Portugal - Agenda VIIAFOOD - Platform for Valorization, Industrialization, and Commercial Innovation for the Agri-Food Sector (no. C644929456-00000040).
References
Jacob, H., Besson, M., Swarzenski, P. W., Lecchini, D., & Metian, M. (2020). Effects of virgin micro-and nanoplastics on fish: trends, meta-analysis, and perspectives. Environmental science & technology, 54(8), 4733-4745. https://doi.org/10.1021/acs.est.9b05995
Mossotto, C., Maganza, A., Gabetti, A., Esposito, G., Faggio, C., Renzi, M., Kazmi, S., Bozzetta, E., Prearo, M. & Pastorino, P. (2025). Tackling micro (nano) plastic pollution in aquaculture systems. Current Opinion in Chemical Engineering, 48, 101104. https://doi.org/10.1016/j.coche.2025.101104