Single and combined effects of microplastics and pyrene on juveniles (0+ group) of the common goby Pomatoschistus microps (Teleostei, Gobiidae)

Microplastic particles have increasingly been detected in aquatic biota, from zooplankton to fish, raising concern for potential effects on aquatic organisms. In addition, they may potentially influence the toxicity of other contaminants in the marine environment. The aim of this study was to clarify whether polyethylene microspheres (1-5 μm) modulate short-term toxicity of the polycyclic aromatic hydrocarbon pyrene to juveniles (0+ group) of the common goby (Pomatoschistus microps). Fish were exposed for 96 h to pyrene (20 and 200 μg L−1) in the absence and presence of microplastics (0, 18.4 and 184 μg L−1). Mortality, bile pyrene metabolites, and biomarkers involved in neurotransmission, aerobic energy production, biotransformation and oxidative stress were quantified. Microplastics delayed pyrene-induced fish mortality and increased the concentration of bile pyrene metabolites. Microplastics, alone or in combination with pyrene, significantly reduced acetylcholinesterase (AChE) activity, an effect also observed for pyrene alone. The mixture also decreased isocitrate dehydrogenase (IDH) activity. No significant effects were found for glutathione S-transferase activity or lipid peroxidation. Overall, results show that: (i) microplastics modulate either the bioavailability or biotransformation of pyrene; (ii) simultaneous exposure to microplastics and pyrene decrease the energy available through the aerobic pathway of energy production; and (iii) microplastics inhibit AChE activity. The mechanism for AChE inhibition appeared to be different for pyrene and microplastics, since simultaneous exposure to both did not increase significantly the inhibitory effect. The observed neurotoxic effects of microplastics per se and the effects on IDH activity of the two stressors combined are of concern because they may increase mortality in natural fish populations. More studies need to be carried out on possible combined effects of microplastics and polycyclic aromatic hydrocarbons on fish, particularly juveniles.