Cellular impact of polypropylene nanofibers and their leachate on the soft coral Pinnigorgia flava: an additional threat to Maldivian coral reefs?

After the spreading of COVID-19, the amount of plastics in the ocean was severely enhanced, especially due to the increased production of Personal Protective Equipment (PPE), in particular surgical masks. This happened also in the Maldives, where plastic and microplastic pollution and the increased spreading of disposable items have been already documented and represent a massive threat for their coral reefs. Although the effects of microplastics on corals are widely documented, those generated by nanoplastics have to date been very little analysed. In particular, the toxicity at the coral cellular level of nanoplastics and nanoplastics leachate from fibers degradation of synthetic fabrics have been totally neglected until now. Nanoplastics leachate refers to chemicals added during the manufacturing process of plastic that, are lost in the environment since not chemically bound to plastic polymer. In this study, the possible effect and impact of nanofibers and nanofibers leachate exposition on the cell of the Maldivian soft coral species Pinnigorgia flava was analyzed, focusing in particular on the coral antioxidant cellular response. The alcyonacean was exposed for 72 h to different concentrations of polypropylene nanofibers (0.1 and 1 mg/L) and nanofibers leachate (0.1 and 1 mg/L) under controlled aquaria conditions. The cellular response was assessed through antioxidant enzymatic assays, namely Superoxide Dismutase (SOD), Catalase (CAT), Glutathione Reductase (GR), and Glutathione-S-Transferase (GST). Results showed that for all treatments, oxidative stress was experienced in all samples. However, different patterns of enzymatic activity were observed between nanofibers and leachates, with a general higher toxicity generated by leachates exposition that produced an inhibition and/or impairment of the antioxidant defense mechanisms at cellular level. This study represents a new area of investigation and is one of the first to focus on such stressors in a Maldivian coral species. In addition, the results highlight that nanofibers and leachates are indeed a major threat to Maldivian coral reefs, which are already exposed to multiple climate change stressors and relentless anthropogenic pressures.