A Biomarker Approach as Responses of Bioindicator Commercial Fish Species to Microplastic Ingestion: Assessing Tissue and Biochemical Relationships

SIMPLE SUMMARY: Microplastic (MP) ingestion was evaluated in the gastrointestinal tract of three fish species, Mullus surmuletus, Boops boops, and Engraulis encrasicolus, sampled around a marine protected area (MPA). Antioxidant and detoxifying enzymes in addition to malondialdehyde levels were measured in fish liver and brain homogenates. The ingestion of MPs differed among species, with M. surmuletus showing the lowest microplastic ingestion of MPs and B. boops the highest values. An increase in MDA levels was measured in the liver of E. encrasicolus, as well as in the brain related to MP ingestion. An increase in CAT activity was detected in the brains of M. surmuletus and B. boops. Furthermore, GST activity in the liver of M. surmuletus and in the brain of B. boops showed an increase as a consequence of MP ingestion. MP ingestion depends on fish species and can induce an activation of detoxifying and antioxidant mechanisms that is species specific. ABSTRACT: Plastic debris is a growing environmental problem on a global scale, as plastics and microplastics (MPs) can be ingested by marine organisms, inducing toxic effects. The aim of this study was to assess MP intake and antioxidant responses in three bioindicator species: red mullet, bogue, and anchovy (Mullus surmuletus, Boops boops, and Engraulis encrasicolus, respectively) for plastic contamination in the Mediterranean Sea. MP intake was assessed in the gastrointestinal tract of the fish. Further, several enzymes from both the liver and brain were analysed. The antioxidant defences, catalase (CAT) and superoxide dismutase (SOD), as well as the detoxifying enzyme glutathione-S-transferase (GST), were measured in both tissues. The acetylcholine esterase (AchE), as an indicator of neuronal damage, was measured in the brain. Malondialdehyde (MDA) was analysed as a marker of oxidative damage in the brain and liver samples. Total MP intake and MP typology differed between the three species, with M. surmuletus showing the lowest intake of MPs, while B. boops showed the highest intake of MPs. An increase in both antioxidant enzymes was evidenced in E. encrasicolus liver activity with respect to MP intake. In brain samples, an increase in CAT activity was found in M. surmuletus and B. boops as a consequence of MP ingestion. SOD activity in the brain increased in B. boops and E. encrasicolus that had ingested MPs. GST activity increased in the liver of M. surmuletus’ and in brains of B. boops that had ingested MPs. The intake of MPs is species related, as well as being inherently linked to the habitat they live in and being able to induce a light activation of species-specific detoxifying and antioxidant mechanisms.