Microalgal-based biopolymer for nano- and microplastic removal: a possible biosolution for wastewater treatment ਮ C  esar Cunha a , Laura Silva a , Jorge Paulo a , Marisa Faria a, b , Natacha Nogueira c, d , Nereida Cordeiro a, d, * a LB3 - Faculty of Science and Engineering, University of Madeira, 9000-390, Funchal, Portugal b Oceanic Observatory of Madeira (OOM), ARDITI, Madeira Tecnopolo, 9020-105, Funchal, Portugal c Mariculture Center of Calheta, Fisheries Directoriate, 9370-134, Calheta, Portugal d CIIMAR - Interdisciplinary Centre of Marine and Environmental Research, University of Porto, 4450-208, Matosinhos, Portugal article info Article history: Received 11 November 2019 Received in revised form 18 February 2020 Accepted 14 March 2020 Available online 16 March 2020 Keywords: Cyanothece sp. Microplastics Nanoplastics Extracellular polymeric substances (EPS) Bioflocculant abstract The increasing water pollution caused by the presence of nano- and microplastics has shown a need to pursue solutions to remediate this problem. In this work, an extracellular polymeric substance (EPS) producing freshwater Cyanothece sp. strain was exposed to nano- and microplastics. The bioflocculant capacity of the biopolymer produced was evaluated. The influence of different concentrations (1 and 10 mg L 1 ) of polystyrene nano- and microplastics in the extracellular carbohydrates and in the EPS production was studied. The presence of nano- and microplastics induced a negative effect on the microalgal growth (of up to 47%). The results show that the EPS produced by Cyanothece sp. exhibits high bioflocculant activity in low concentrations. Also, the EPS displayed very favourable characteristics for aggregation, as the aggregates were confirmed to consist of microalga, EPS and both the nano- and microplastics. These results highlight the potential of the microalgal-based biopolymers to replace hazardous synthetic flocculants used in wastewater treatment, while aggregating and flocculating nano- and microplastics, demonstrating to be a multi-purposed, compelling, biocompatible solution to nano- and microplastic pollution. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Plastic pollution has become a concern due to the increased plastic production every year, which tends to accumulate in the environment (Geyer et al., 2017). Plastic particles can come in a variety of sizes and types, one being microplastics commonly defined as plastic particles with sizes below 5 mm (Andrady, 2011). There is still no general consensus regarding the size of nano- plastics, but it is generally defined as particles below 0.1 mm in diameter (Mattsson et al., 2018). Microplastics can be divided by origin into two main categories: primary and secondary micro- plastics. Primary microplastics originate from the intentional pro- duction of commercialized products such as microbeads, which are used in personal care products. Secondary microplastics enter the environment via ‘leakage’ during manufacture, transportation or use (Andrady, 2017), as a result of the fragmentation of macro- plastics, mainly caused by UV-induced degradation or physical abrasion (GESAMP, 2016). Thus, the process results in the release of increasingly smaller sized low-molecular-weight polymer frag- ments. It is therefore crucial to understand the interaction of nano- and microplastics with the aquatic microbiota. Given the nature and small dimensions, the ingestion of such products by marine organisms has had a subsequent impact on marine life, including the transfer of biological or chemical contaminants (Wright et al., 2013). This is especially true when considering transfer along the trophic chain and possible translocation, for which the hazards are less well understood (Chae and An, 2017; Paul-Pont et al., 2018). While large plastics can be easily removed during water pro- cessing, the currently used technologies are unable to retain neither nano- nor microplastics (Mintenig et al., 2016), since these are too small and cannot be detected and eliminated cost- effectively (Andrady, 2017). Regarding microplastic pollution in wastewater treatment plants (WWTPs), a recent overview by Sun ਮ This paper has been recommended for acceptance by Maria Cristina Fossi. * Corresponding author. LB3 - Faculty of Science and Engineering, University of Madeira, 9000-390, Funchal, Portugal. E-mail address: ncordeiro@staff.uma.pt (N. Cordeiro). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol https://doi.org/10.1016/j.envpol.2020.114385 0269-7491/© 2020 Elsevier Ltd. All rights reserved. Environmental Pollution 263 (2020) 114385