Microplastics pollution in inland freshwaters of China: A case study in urban surface waters of Wuhan, China

Highlights

• Microplastics were studied in urban waters of the largest city in central China.

• Anthropogenic factors greatly affected the abundance of microplastics in water.

• Fibrous, colored and small-sized were main features of the detected microplastics.

Abstract

Microplastics have been considered as an emerging pollutant in the aquatic environment. However, research about microplastic pollution in inland freshwaters of China is insufficient. The present study investigated the levels of microplastics in surface water of 20 urban lakes and urban reaches of the Hanjiang River and Yangtze River of Wuhan, the largest city in central China. Microplastic concentrations ranged from 1660.0 ± 639.1 to 8925 ± 1591 n/m³ for the studied waters, with the highest concentration found in Bei Lake. Microplastic abundance in lakes varied markedly in space, and negatively correlated with the distance from the city center (p < 0.001), which confirmed the important role of anthropogenic factors in microplastic distribution. Urban reaches of the Hanjiang River and Yangtze River were found to have relatively lower levels of microplastics than most of the studied lakes. The major type of microplastics among the studied waters was colored plastic, with fiber being the most frequent shape. More than 80% of microplastics in number had a size of < 2 mm. Polyethylene terephthalate and polypropylene were the dominant polymer-types of microplastics analyzed. This study provided important reference for better understanding microplastic levels in inland freshwaters.

Introduction

Due to its lightweight, durable nature and impressive ratio of cost to performance, plastic has become an impartible role in sustaining and delivering the quality, comfort and safety of modern life-styles (Phuong et al., 2016). The global production of plastics increased rapidly since the realization of mass production in 1950s, and the annual yield reached 311 million tons in 2014 (PlasticsEurope, 2015). However, difficulty in degradation also makes the heavily generated plastic waste a serious environmental issue (Barnes et al., 2009). Although a large proportion of the waste has been recycled or landfilled, still a considerable amount of plastic waste entered into the aquatic system (Cole et al., 2011, Eerkes-Medrano et al., 2015). For instance, approximately 4.8–12.7 million tons of plastic waste was estimated to get into the ocean from land per year (Jambeck et al., 2015). Microplastics are defined as small plastic particles with a size of < 5 mm (Arthur et al., 2009). They can originate primarily from plastics that are manufactured to be of a microscopic size, or secondarily from the fragmentation of larger plastic debris (Cole et al., 2011). These tiny plastic items, as reported by a large number of researchers, are ubiquitously present in the marine ecosystems worldwide (Derraik, 2002, do Sul and Costa, 2014, Wang et al., 2016). Concerns about potential threats of microplastics to aquatic organisms, birds, mammals and even human beings via mistaken ingestion or food web are rising (Graham and Thompson, 2009, Miranda and de Carvalho-Souza, 2016, Wright et al., 2013). Nevertheless, little information is available about microplastics in freshwater systems (Eerkes-Medrano et al., 2015, Wagner et al., 2014), especially in China, the largest producer of plastics around the world (PlasticsEurope, 2015).

Wuhan is the largest city and center of economy, culture and education in central China, with a population of > 10 million in the urban area. Because of richness of water resources, including 166 lakes and the Yangtze River (and its largest tributary – the Hanjiang River) flowing through the city, Wuhan is also known as the “city of hundreds of lakes” and “river city”. However, along with the fast growing economy, population and urbanization since 1970s, the ecological health of aquatic environments in this city is threatened by various kinds of pollutants. Lakes and rivers were successively reported with toxic organic or/and inorganic pollutants, some of which were proved to pose risks to the aquatic organisms and even human (Cui et al., 2015, Yang et al., 1997, Yang et al., 2009). Nevertheless, pollution status of the new pollutant - microplastics in aquatic ecosystems within Wuhan and even China, is still unclear at present. Hence, in this study, we investigated the abundance, distribution, and morphological characteristics of microplastics in surface water of 20 urban lakes and also the urban sections of the Yangtze River and Hanjiang River in Wuhan. This study could provide useful reference for monitoring microplastic pollution in inland freshwater systems.