A close relationship between microplastic contamination and coastal area use pattern

Highlights

• Microplastic (MP) contamination was compared in urban, aquafarm, and rural areas.

• MP shape, size, and polymer type were examined in various marine matrices.

• Coastal area use pattern and MP contamination were found to be closely related.

• Diverse polymers were found in marine matrices, creek, and road dust from urban.

• Marine-based activities are important contributors to MP contamination.

Abstract

Human activity is thought to affect the abundance and contamination characteristics of microplastics (MPs) in the environment, which may in turn affect aquatic species. However, few studies have examined the impact of coastal area use pattern on characteristics of MPs in coastal regions. In this study, we investigated MP contamination of abiotic matrices (seawater and sediment) and biotic matrices (bivalves and polychaetes) in three coastal regions characterized by different types of human activity, covering urban, aquafarm, and rural areas. MP abundance was higher in sediment from the urban site than in that from the rural site, but similar to that from the aquafarm site. In the abiotic matrices, different MP polymer compositions were observed among the three sites. Diverse polymers were found in marine matrices from the urban site, implying diverse MP sources in highly populated and industrialized areas. Polystyrene was more abundant in the aquafarm site, reflecting the wide use of expanded polystyrene aquaculture buoys. Polypropylene was more abundant at the rural site, probably due to the use of polypropylene ropes and nets in fishing activity. MP accumulation profiles in marine invertebrates showed trends similar to those exhibited by abiotic matrices, reflecting coastal area use patterns. These results indicate that marine MPs are generated from both land- and marine-based sources, and that the abiotic and biotic marine matrices reflect the MP characteristics.

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.