Microplastics in the surface sediments from the Beijiang River littoral zone: Composition, abundance, surface textures and interaction with heavy metals
Introduction
Microplastics that are less than 5 mm in size (Arthur et al., 2009, Hidalgo-Ruz et al., 2012) have been almost ubiquitous in the global marine environment, including surface waters (Collignon et al., 2012, Frias et al., 2014), beaches (Browne et al., 2011, Claessens et al., 2011, Thompson et al., 2004) and deep sea (Van Cauwenberghe et al., 2013, Woodall et al., 2014). More importantly, plastic debris would continuously degrade into microplastics or nanoplastics (Andrady, 2011, da Costa et al., 2016, Ivar do Sul and Costa, 2014, Wang et al., 2016) as a result of physical, chemical and microbial effects. The majority of marine plastics are considered to originate from land-based source (Allsopp et al., 2006, Andrady, 2011, Wagner et al., 2014), including transport from rivers that may be important pathways (Cheung et al., 2016, Morritt et al., 2014, Rech et al., 2014). Furthermore, one of the few studies focusing on the floating microplastics in the estuary found that the Tamar River could not be identified as a net source or sink, with as many microplastic particles entering the estuary as leaving it (Sadri and Thompson, 2014). Nevertheless, there are very few studies on microplastics in freshwater environment (see reviews by Dris et al., 2015, Duis and Coors, 2016, Eerkes-Medrano et al., 2015, Wagner et al., 2014). Some studies not only reported the occurrence of microplastics in freshwater environment (Eriksen et al., 2013, Faure et al., 2012, McCormick et al., 2014, Moore et al., 2011, Morritt et al., 2014), but show that contamination level is as severe as in the marine environment. And fishes in rivers (Sanchez et al., 2014) and birds in terrestrial environment (Zhao et al., 2016) have also been shown to ingest microplastics.
The great concerns about microplastics in the environment are the association with toxic chemicals and subsequent exposure of these chemicals to the multiple kinds of organisms that ingest the debris (Bakir et al., 2014, Bejgarn et al., 2015, Browne et al., 2008, Browne et al., 2013, Rochman et al., 2013b, Van Cauwenberghe and Janssen, 2014). Plastic debris is capable of concentrating hydrophobic organic pollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and DDTs (Endo et al., 2005, Gauquie et al., 2015, Hirai et al., 2011, Rochman et al., 2013a, Van et al., 2012), increasing their concentration even up to the order of 106 (Mato et al., 2001). Plastic debris could also accumulate metals from the surrounding environment and the accumulation has been demonstrated by laboratory experiments (Holmes et al., 2012, Holmes et al., 2014, Turner and Holmes, 2015) and environmental monitoring (Rochman et al., 2014). Metal pollution is common in the environment and is derived from multiple sources such as the industrial and domestic sewage discharges, mining, smelting and e-wastes (Pan and Wang, 2012, Deheyn and Latz, 2006, Wang et al., 2013). However, data on the content of metals accumulation by microplastics in the actual environment is very limited. One of the few studies on the effects of metals interaction with microplastics found a significant decrease of the predatory performance (referred to Artemia franciscana nauplii used as preys) and a significant inhibition of AChE activity under simultaneous exposure to Cr(VI) and microplastics, while fewer inhibition caused by microplastics alone and no observed inhibition caused by Cr(VI) alone (Luís et al., 2015).
Accordingly, more research efforts should be contributed to investigate the occurrence and characteristics, especially the interaction with heavy metals, of microplastics in the freshwater environment so as to further assess the potential environmental risks. Additionally, shore surface sediment samples could reflect the result of long-term interfacial interaction between waters and land surface (Yu et al., 2016), and thus provide vital information on the transportation and fate of pollutants. And similar types of plastics in the water column as in sedimentary habitats have been previously shown (Thompson et al., 2004), suggesting that density was not a dominant factor influencing distribution of microplastics and sediment samples are good representations for long-term accumulating result of microplastics. In this study, thus, microplastics were retrieved in the surface sediment samples from the Beijiang River littoral zone, and the main objective is to provide data on their characteristics including composition, abundance, surface textures acting as an indicator of degradation and interaction with heavy metals.
Section snippets
Sampling sites
Sediment samples were collected from 8 sites chosen in the surface layer of Beijiang River littoral zone (shown in Fig. 1). In each site, three sediments were randomly sampled to a depth of 2 cm using a stainless-steel shovel and a 20 × 20 cm wooden frame with a 2-cm height, and then these sediments were transferred into an aluminum foil bag, in which they were mixed together as one single sample. Sample collection was conducted in March 2015. Beijiang River is one of the three main streams of
Abundance
Microplastics were found in triplicate sediment samples from all sites, indicating that the sediments are vulnerable to microplastics pollution and could be good representations for the long-term accumulation of microplastics. Microplastics might be washed ashore from the water surface (Lumpkin et al., 2012) and derived from fragmentation of larger plastics littered on shore sediments as a result of physical, chemical and microbial effects (Cooper and Corcoran, 2010, Zbyszewski and Corcoran,
Conclusion
In the present study, a preliminary assessment of microplastics pollution in the surface sediments from Beijiang River littoral zone was presented. However, concentrations of microplastics were underestimated, because saturated NaCl solution that was commonly used in previous studies could float up the materials with a density <1.2 g/cm3 but fail to float up some types of plastics, e.g. PVC. ZnCl2 (Liebezeit and Dubaish, 2012) and NaI (Van Cauwenberghe et al., 2013, Nuelle et al., 2014)
Acknowledgement
This study was financially supported from National Natural Science Foundation of China (No. 41676104) and program of Science and Technology development of Dongguan City (No. 201650710100435).
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