Spatiotemporal microplastic occurrence study of Setiu Wetland, South China Sea

https://doi.org/10.1016/j.scitotenv.2021.147809Get rights and content

Highlights

  • Microplastics were detected in both water surface and sediment of a pristine area.

  • Filaments and transparent microplastics were the most abundant in both matrices.

  • Seasonality was the most important variable explaining the distribution of microplastics.

  • The presence of microplastics could be related to environmental physical parameters and water intrusion.

Abstract

This study reports the distribution of microplastics (MPs) in surface water and estuarine sediments in South and North Setiu Wetland in the South China Sea. Sampling was conducted bimonthly for one year from November 2016 to November 2017, including the northeast and southwest monsoons. Water surface and sediment samples were collected from six different sampling stations (STs). Samples were sorted based on physical analysis (optical observation) and selected particles were further analyzed by chemical characterizations. The findings of this study indicate that a total of 0.36 items/L and 5.97 items/g particles of MPs were found from characterizations surface water and dry sediment, respectively. Among the selected stations included in this research, ST3 (1.375 ± 0.347 items/L) and ST2 (14.250 ± 4.343 items/g) were individually identified as high potential MP sinking areas, exacerbated during the northeast and southwest monsoons. Transparent, film, and filament MP types were consistently found across all stations. Microplastic filaments revealed a functional group of polypropylenes based on the main peak spectrum at 2893–2955 cm−1 (Csingle bondH alkyl stretching), 1458 cm−1 (Csingle bondH2 bending), and 1381 cm−1 (CH3 bending). Microplastic materials were thermally decomposed by pyrolysis-gas chromatography–mass spectrometry (Pyr–GC/MS) and identified as cyclohexane and cyclohexene derivatives, as well as precursors of polymer blends. The distribution of MPs in both matrices varied according to different seasons. These findings provide useful baseline information on the distribution of MPs from the estuarine area in Malaysia and South China Sea waters.

Introduction

Microplastics (MPs) are small synthetic polymer particles less than 5 mm in size (Arthur et al., 2009). In the aquatic environment, MPs can be classified into primary and secondary types, representing the originally manufactured sizes of polymer products and the plastic fragmented into smaller sizes, respectively (Cole et al., 2011). Microplastics have been found in freshwater (Alam et al., 2019) and marine environments (Maes et al., 2017; Khalik et al., 2018), as well as in mangrove ecosystems (Mohamed Nor and Obbard, 2014; Peng et al., 2017). Previous studies indicated that filaments/fibers, films, and fragments were the most frequently isolated MP types, among which filaments were the most abundant based on a variety of environmental matrices (Xu et al., 2018; Maes et al., 2017; Peng et al., 2017). For example, filaments originated from different anthropogenic activities such as sewage and aquaculture activities. Once MPs enter the aquatic environment, a wide variety of organisms become susceptible to their presence, sometimes in high abundance. Previously, Rochman et al. (2016) revealed that if plastic debris were to ecologically impact an ecosystem, and sublethal (suborganismal changes) or lethal effects could result. Ingested MPs have been proven to cause weight loss and low energy in marine organisms, a slow egestion process, and their transfer within the trophic level (Besseling et al., 2013; Farrell and Nelson, 2013; Ory et al., 2018).

International statistics in 2017 showed that 50.1% of global plastic production has originated in Asia, with 29.4% from China (which has the most significant global plastic industry globally), 3.9% from Japan, and 16.8% from the rest of Asia, including Malaysia (PlasticsEurope, 2018). The increase in plastic manufacturing has been accompanied by an increase in plastic waste because of the lack of public awareness and plastic dumping into the marine environment, both directly and indirectly. This has become an emerging topic among researchers, and MP distribution has been studied globally, and more specifically in Asian countries such as Indonesia (Alam et al., 2019), Korea (Eo et al., 2018), China (Li et al., 2018), and the Philippines (Kalnasa et al., 2019). Malaysia ranked as the eighth country in terms of the mismanaged plastic waste problem in 2010, contributing up to 0.37 million metric tons per year (Jambeck et al., 2015). To deal with this problem, the Ministry of Environment and Water in Malaysia created a strategy roadmap for achieving zero single-use plastic production between 2018 and 2030 (Ministry of Energy, Science, Technology, Environment and Climate Change, 2018; Ma et al., 2020).

Previous research documented the presence and analysis of MPs in Malaysian coastal areas, beaches, marine water, and rivers (Barasarathi et al., 2014; Fauziah et al., 2015; Khalik et al., 2018; Sarijan et al., 2018). Microplastics from personal care and cosmetic products were discharged as part of treated and untreated waste into the environment (Praveena et al., 2018). Recently, the presence of MPs was detected in marine species of commercial fish from a local market in Malaysia (Karbalaei et al., 2019; Jaafar et al., 2020) and in zooplankton in the South China Sea (Amin et al., 2020). Studies presented the characterization of MPs found in marine organisms collected from Setiu Wetland, e.g., filter feeder bivalve (Scapharca cornea) and estuarine fish (Lates calcarifer) (Ibrahim et al., 2016, Ibrahim et al., 2017). However, there remain a limited number of related publications on the distribution and occurrence of MPs in surface water and sediments, hampering a true perspective of the current situation of this emergent issue in Malaysia.

The Setiu Wetland is officially recognized as a protected area that has become an important region for ecotourism activities. Furthermore, it is considered a representative of a natural officially recognized area in Malaysia for investigating a baseline level of MP abundance. Therefore, this research focuses on documenting the spatiotemporal variation of MP abundance along the Setiu Wetland, located in the South China Sea, particularly in sediment and surface water matrices. Physical and chemical characterizations were defined to identify the surface morphology and composition of polymers.

Section snippets

Study area and sample collection

Prior to sample collection, physicochemical data of water (temperature, dissolved oxygen (DO)), salinity, and pH were taken in situ using a hand-held multiparameter hydro-lab (Quanta, Hydrolab Corp., USA) instrument. Triplicates of all parameter readings at both water and sediment were taken at various sampling stations (STs). The sample collections were completed during high tide to ensure boat accessibility. Sample collections were conducted bimonthly at six different stations (STs) and

Distribution of microplastics

The results of the MP analysis in the sediment and seawater during a specific sampling time started from November 2016 until November 2017 for the six stations are shown in Fig. 2(a)–(d). Microplastics in surface water ranged from 0.251 ± 0.139 items/L (ST1) to 0.540 ± 0.139 items/L (ST3). Individually, ST4 was found to have the lowest level of MPs with 0.042 items/L, and the highest level of MPs was found in ST3 with 1.375 items/L. Both results were sampled in November 2016. The total mean

Microplastics spatial variability

It is difficult to compare MP abundance with other studies because of the different methodologies in sample collection and sample processing (Table 3). Different tools can also lead to different results, making it difficult to discover the actual concentration of MPs because of underestimation or overestimation. In the present study, the abundance of MPs in estuarine water was lower than in a study conducted in the estuarine area of Shanghai (27.84 ± 11.81 items/L; Zhang et al., 2019). However,

Conclusions

This study presented evidence of the widespread nature of MPs and their spatiotemporal distribution in Setiu Wetland Malaysian estuarine area for the first time. A high distribution of MPs in this area may be the result of floating MPs derived from marine water, water stagnation and in situ fragmentation from fisheries and aquaculture sites. In addition, cyclohexane and its derivatives, the pyrolytic products found associated to the thermal degradation of polypropylene, may leach out into the

CRediT authorship contribution statement

S.R.H. carried out the sampling and laboratory works, including physical and chemical analysis, drafted the manuscript; S.T.A. performed the chemical analysis and interpretation; W.M.A.W.M.K and K.M.K.K·Y analyzed the data and performed the statistical analysis; Y.S.I. designed the study, carried out the sampling, drafted the manuscript and completed the manuscript.

Funding

This research was funded by a grant (FRGS 59457) under the Ministry of Higher Education (MOHE), Malaysia.

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.

Acknowledgments

The authors are very grateful to the Ministry of Higher Education (MOHE) for awarding research grant FRGS 59457 to Y.S. Ibrahim and financially support the research. The authors also thank UNESCO IOC-WESTPAC and other MRIG team members, Prof. Dr. Norhayati Tahir, Dr. Siti Aishah Abdullah, Che Mohd Zan Husin, Yuzwan Mohamad and Siti Syazwani Azmi for their guidelines and technical supports throughout the study. The authors are thankful to the Faculty of Science and Marine Environment, Institute

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