A close relationship between microplastic contamination and coastal area use pattern
Graphical abstract
Introduction
Microplastics (MPs) are a form of marine debris measuring ≤ 5 mm in size (Arthur et al., 2009; GESAMP, 2019). MPs are classified as either primary or secondary according to their production method, such that primary MPs are intentionally manufactured and added to products such as cosmetic products and abrasive materials, and secondary MPs are formed through the breakdown of larger plastics during use or after disposal to the environment (Arthur et al., 2009). Contamination by MPs has become a global environmental concern due to their ubiquitous distribution in the ocean, from pole to pole, from the surface to the seafloor (Sul and Costa, 2014; Auta et al., 2017), and within marine species at every level of the food web (Gall and Thompson, 2015; Rochman, 2018). Ingested MPs can cause physical damage such as intestinal obstruction and stomach ulcers (Carpenter et al., 1972) and can transfer contaminants such as plastic additives and sorbed chemicals from seawater to marine organisms (Jang et al., 2016; Ziccardi et al., 2016), inducing adverse biological effects (von Moos et al., 2012; Browne et al., 2013; Rochman et al., 2013).
Like macro debris, MPs in the ocean can come from a variety of land- and marine-based sources. Roughly 80% of marine debris (of which 60–80% is plastic) has been estimated to originate from land-based sources, and the remainder from marine-based activity (Sheavly, 2005). Therefore, land-based input is considered a major source of microplastics in the ocean. Some studies have attempted to identify the sources of MPs on land (e.g., clothes washing and cosmetics; Fendall and Sewell, 2009; Browne et al., 2011) and input pathways into the ocean (e.g., sewage treatment plant effluents and riverine input; Leslie et al., 2017; Hurley et al., 2018). Previous studies have reported increasing MP levels in coastal sediments and seawater near populated areas (Frère et al., 2017; Vianello et al., 2013; Yonkos et al., 2014; Song et al., 2018), implying a close relationship between land-based human activities and MP pollution of marine environments. Not only land-based but also marine-based human activities (e.g. shipping, fisheries, and aquaculture) can be important sources of marine MPs. However, our understanding of these sources, their emission amounts, their pathway to the environment and the fragmentation of plastic debris after disposal remain minimal.
MP physicochemical properties such as shape, color, and polymer type can provide information about their sources (Shim et al., 2018). The original shape and color of plastics can be lost or changed by environmental weathering processes such as fragmentation and discoloration, but their main polymer type does not change. Therefore, polymer composition is a useful tool for identifying MP sources or origins in the environment. For example, alkyd particles on the ocean surface are derived from ship paint (Song et al., 2014). Polyester and acrylic fibers are commonly used for fabric (Browne et al., 2010), and synthetic rubber is a tire ingredient (Wagner et al., 2018). However, most studies performed polymer identification for a small portion of suspected particles in their samples to validate their optical microscopy particle count estimate (Li et al., 2016; Leslie et al., 2017; Rodrigues et al., 2018; Nel et al., 2018) because spectroscopic identification for all suspected particles on filter paper is a time-consuming job (Song et al., 2015). The Polymer composition of MP can provide additional information about chemical substances contained because additive chemicals differ among plastic products and polymer types (Lithner et al., 2011; Jang et al., 2017), and their leachates have a different toxicity to organisms (Bejgarn et al., 2015).
In this study, we hypothesize that the polymer composition of MPs in marine matrices would differ between regions according to coastal area use pattern, and that these compositions would be reflected in marine species inhabiting these regions. We analyzed MPs in abiotic matrices (seawater and sediment) and biotic matrices (mussels, oysters, and polychaetes) from three coastal sites representing urban, aquafarm, and rural areas. The polymer compositions of all plastic-like particles were identified. Road dust and creek water were also collected from the urban area to compare their polymer compositions with those of marine matrices collected nearby.
Section snippets
Sampling strategy
We collected samples of abiotic matrices, including seawater and sediment, and biotic matrices, including mussels (Mytilus edulis), oysters (Crassostrea gigas), and polychaetes (Perinereis aibuhitensis), from the southern part of South Korea between March and April 2016 (Fig. 1 and Fig. S1). We selected three sites (urban, aquafarm, and rural) differing in land (or sea) use and pollution load (Fig. 1). The urban site is located in Masan Bay, a semi-enclosed bay surrounded by the densely
Abundance, shape, color, and size of MPs
The mean MP abundances in seawater, sediment, oysters, mussels, and polychaetes were 0.77 ± 0.88 (median: 0.5) particles/L, 0.94 ± 0.69 (0.91) particles/g wet weight (w.w.), 1.13 ± 0.84 (0.84) particles/g w.w., 1.43 ± 1.45 (1.12) particles/g w.w., and 0.71 ± 1 (0.44) particles/g w.w., respectively. The MP levels in each matrix (except for sediment) were similar among the sites (p > 0.5, ANOVA or Kruskal–Wallis, Fig. 2). The mean MP levels in seawater and polychaetes from the aquafarm site were
Discussion
MPs collected from marine matrices in this study were mainly identified as PE and PP (Fig. 3), which are the most common polymer types in seawater, marine sediment, and marine organisms worldwide (Frère et al., 2017; Zhang et al., 2017; Phuong et al., 2018). PE and PP are produced in large quantities globally and are widely used (Andrady, 2015); their low specific density (PP, 0.95 g/cm3; PE, 0.91–0.97 g/cm3) allow them to float on water surfaces and travel long distances via ocean currents,
Conclusion
MPs are being introduced into the ocean at an unprecedented rate. Several studies have been conducted on the impact of human activities on the MP abundance in the surrounding marine environment. However, limited information is available on the impact of different types of human activity on the characteristics (e.g., shape and polymer type) of MPs in the marine environment. In this study, MP contamination was studied in abiotic and biotic marine matrices from three coastal regions with different
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was supported by a research project titled “Environmental Risk Assessment of Microplastics in the Marine Environment” from the Ministry of Oceans and Fisheries, South Korea.
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