Marine Pollution Bulletin 150 (2020) 110776 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Microplastics composition and load from three wastewater treatment plants discharging into Mersin Bay, north eastern Mediterranean Sea T ⁎ Ceyhun Akarsua, , Halil Kumbura, Kerem Gökdağb, Ahmet E. Kıdeyşb, Anna Sanchez-Vidalc a Mersin University, Department of Environmental Engineering, 33343 Yenisehir, Mersin, Turkey b Middle East Technical University, Institute of Marine Science, 33731 Erdemli, Mersin, Turkey c CRG Marine Geosciences, Department of Earth and Ocean Dynamics, University of Barcelona, Barcelona, Spain ARTICLE INFO ABSTRACT Keywords: Copious quantities of microplastics enter the sewage system on a daily basis, and hence wastewater treatment Microplastics plants (WWTPs) could be an important source of microplastic pollution in coastal waters. Influent and effluent Mediterranean discharges from three WWTPs in Mersin Bay, Turkey were sampled at monthly intervals over a one-year period Wastewater treatment plants during 2017. When data from all WWTPs were combined, fibers constituted the dominant particle form, ac- Fibers counting for 69.7% of total microplastics. Although notable oscillations in microplastic particle concentrations Mersin Bay were observed throughout the year influent waters on average contained about 2.5-fold greater concentrations of microplastics compared to the effluent waters. An average of 0.9 microplastic particles were found per liter of effluent from the three WWTPs amounting to around 180 × 106 particles per day to Mersin Bay. This shows that despite their ability to remove 55–97% of microplastics, WWTPs are one of the main sources of microplastics to the northeast Mediterranean Sea. 1. Introduction through the consumption of edible fish and shellfish. Accumulation of microplastics in surface waters (of lakes, ponds, Annual global plastic production exceeds 336 million metric tons in estuaries and seas) is reported to originate from a variety of sources year and is expected to increase at an annual rate of 4% (Plastic Europe, such as domestic and urban activities, industrial sources and roads 2018). With growing plastic production, plastic litter in the environ- (mainly through tyre degradation) which could often end up in was- ment is increasing and accumulating in various environments, in- tewater treatment plants (WWTPs) in many densely populated coastal cluding marine habitats (Andrady, 2011). Similar to other regions, cities (Faure et al., 2012; Sadri and Thompson, 2014; Lechner et al., coastal marine litter in the northeastern Mediterranean consists of 2014; Estahbanati and Fahrenfeld, 2016). Processed municipal waste- 60–80% of plastics (Aydın et al., 2016). Over the past decade, there has waters contain, for example, synthetic textile fibers from household been increased awareness of micro-size plastic litter found in the laundry and abrasive plastic particles from cleaning agents (Browne marine environment. Particles which are very small (< 5 mm) termed et al., 2011). In addition, almost all microplastics break down into even as microplastics (Thompson et al., 2004; Barnes et al., 2009). smaller pieces further contributing to the microplastic pool that may Experimental studies have shown that many marine invertebrates reach the WWTPs through city liquid-waste collection systems. such as bivalves, echinoderms, amphipods and zooplankton ingest mi- Microplastics concentrations in the influent of wastewater treatment croplastics (Browne et al., 2008; Cole et al., 2013) which can be plants could vary substantially ranging from 103 to as high as transferred through the food chain from prey to predator (Setälä et al., 108 microplastic particles/m3 (Carr et al., 2016; Murphy et al., 2016; 2013). In different regions of the world, microplastics (MPs) have also Hidayaturrahman and Lee, 2019). It has been reported that the mi- been found in the digestive systems of many species of fish (Foekema croplastic removal efficiencies of wastewater treatment plants are ra- et al., 2013; Zhu et al., 2019; Garnier et al., 2019). In Mersin Bay, ther high with values of 80–95% (Magnusson and Wahlberg, 2014; Carr Turkey, of 1337 fish specimens (belonging to 28 species), 58% had et al., 2016; Leslie et al., 2017). However, overall, the number of dis- microplastics in their digestive system (Güven et al., 2017). Besides charged microplastics in effluent could still be very significant despite direct harm to many marine organisms, one other main concern is that such high removal efficiencies. the plastics entering the food chain can ultimately pass to humans The Mediterranean Sea which is the largest sea in the world and ⁎ Corresponding author. E-mail address: [email protected] (C. Akarsu). https://doi.org/10.1016/j.marpolbul.2019.110776 Received 15 September 2019; Received in revised form 21 November 2019; Accepted 23 November 2019 Available online 27 November 2019 0025-326X/ © 2019 Elsevier Ltd. All rights reserved. C. Akarsu, et al. Marine Pollution Bulletin 150 (2020) 110776 surrounded by 22 countries is susceptible to high levels of pollution due December. Samples (each 10 L volume) were collected in triplicate to its huge coastal population. Marine debris, including microplastics, is (with the exception of Karaduvar sampling in January, which was only a particularly important problem for the unique biodiversity of the one replicate of 10 L). Mediterranean (Deudero and Alomar, 2015; Pedrotti et al., 2016) which is further aggravated by a low level of environmental awareness in 2.3. Particle filtration and analyses particular among populations living in the eastern and southern coasts. Although other kinds of pollution studies have been investigated for At the laboratory, collected samples were filtered with a standard decades in the Mediterranean (e.g. at least 50 years for the metal pol- zooplankton sampling net (mesh diameter 26 μm). In general, the lution) (Fernex and Migon, 1994; Kütting, 1994; Marmer and standard EC guideline for processing of microplastic samples was con- Langmann, 2005; Ochoa-Hueso et al., 2017), microplastic pollution sidered (Euoropean Commission, 2013). Hydrogen peroxide (35%) was studies are relatively new (Pedrotti et al., 2016; Abidli et al., 2018; used to remove organics on the filter prior to microscopic observation Giani et al., 2019; De Haan et al., 2019), particularly in the eastern and counting. Mediterranean (relevant references cited in the next paragraph). The detected particles under microscope were categorized as one of Therefore, any studies on microplastics from wastewater treatment fa- the following 4 major forms: fiber, soft plastic, hard plastic and others cilities should be very important for the determination of sources of (styrofoam or polystyrene, rubber, etc.). A small force is applied with microplastics in the Mediterranean Sea. the help of forceps to separate the soft plastics from the hard ones and Despite several published studies reporting microplastic levels at the the classification is made according to the reaction of the particle. It is sea surface, in sediment and the digestive systems of fish from Turkish thought that it will be easier to identify the source of the plastic by coasts (Gündoğdu et al., 2017; Gündoğdu et al., 2018; Güven et al., classifying in this way. For example, while hard plastics are often part 2017), so far there is only one published study on wastewater con- of a bottle cap or similar hard macroplastic product, soft plastic often tribution to the microplastic load in the eastern Mediterranean Sea comes out of shopping bags or local greenhouse material. Microplastic based on only one-week sampling at two WWTPs in Adana, Turkey particles in each form were further sub-divided into categories based on (Gündoğdu et al., 2018). The amount of unretained microplastics from colour. All filters were visually examined under a digital optical mi- WWTPs is expected to differ depending on many conditions, such as croscope (Olympus SZX16 Stereomicroscope) with maximum magnifi- their level, capacity, location, region as well as season, rainfall, urban cation of 30×. All microplastics and non-plastic particles (including waste etc. (Conley et al., 2019). For example, due to large increases in pieces of wood, paper and metal) were collected and transferred to a seasonal populations, WWTPs must operate at their highest capacities clean grid filter in a petri dish. Photos were taken using a DP26 - in the summer which may decrease their efficiency to retain the mi- Olympus 5.0 MP High Color Fidelity Microscope Digital Camera and all croplastic load. Moreover, calculation of total load from WWTPs to a particles were further examined for secondary visual classification. specific marine region requires sampling from different areas and sea- After discarding non-plastic natural particles, microplastic particles sons. Therefore, it is also important to analyze the spatial-temporal were processed using Olympus cellSens (Image Analysis software) in changes in microplastic composition. order to determine the diameter/length of each individual particle. The aim of this study is to evaluate abundances and forms/types of Only pieces of plastic litter with a diameter < 5 mm were considered as microplastics in influent and effluent waters from three main WWTPs of microplastic while pieces with a diameter > 5 mm were excluded from Mersin, in Turkey, in order to understand their role in microplastic any further analysis.