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Seasonal variation of micro- and meso-plastics in the seawater of Jiaozhou Bay, the Yellow Sea
Marine Pollution Bulletin 152 (2020) 110922
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Seasonal variation of micro- and meso-plastics in the seawater of Jiaozhou Bay, the Yellow Sea
T
Tao Liua,c, Yongfang Zhaoa,b, Mingliang Zhua,b, Junhua Lianga,b, Shan Zhenga,b, ⁎ Xiaoxia Suna,b,c,d, a
Jiaozhou Bay National Marine Ecosystem Research Station, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China c University of Chinese Academy of Sciences, Beijing 100049, China d Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China b
ARTICLE INFO
ABSTRACT
Keywords: Microplastics Mesoplastics Jiaozhou Bay Seasonal variation
The seasonal change in the concentrations and characteristics of micro- and meso-plastics in the surface seawater of Jiaozhou Bay were studied. The concentrations of micro- and meso-plastics were 0.063, 0.174, 0.094, and 0.050 pieces/m3 in February, May, August and November, respectively, with an annual average concentration of 0.095 pieces/m3. The size of the micro- and meso-plastics ranged from 346 to 155,200 μm, with an average of 5093 ± 43 μm. The overall percentages of fibers, fragments and plastic foams were 29%, 55% and 16%, respectively. The dominant chemical composition was polypropylene (PP), accounting for 51.04% of polymers, followed by polyethylene (PE), accounting for 26.04% of polymers. Strong rainfall resulted in an increase in the plastic concentration in May, and winds and eddies affected the spatial distribution of plastics in Jiaozhou Bay.
1. Introduction The presence and impact of plastic debris in the ocean have emerged rapidly in the last few years as an environmental situation in urgent need of attention (Avio et al., 2017). Micro- and meso-plastics are widely distributed in the marine environment (Barnes et al., 2009; Andrady, 2011) from the surface (Zhao et al., 2014; Song et al., 2015) and subsurface (Desforges et al., 2014) to the deep sea and the bottom of the ocean (Woodall et al., 2014). Micro- and meso-plastics can be ingested by marine organisms ranging from zooplankton to large cetaceans, and they can even be transferred through the food chain into seafood that may be consumed by humans, arousing widespread concern worldwide (Botterell et al., 2019). Higher levels of human impact lead to more plastic pollution and highlight the need to examine aquatic ecosystems under a range of conditions in order to adequately characterize the extent of plastic pollution in coastal systems (Hitchcock and Mitrovic, 2019). Understanding how plastics are distributed in the oceans is a prerequisite for assessing their potential impacts (GESAMP, 2015). To date, a series of studies have been conducted to reveal the concentration and spatial distribution of micro- and meso-plastics in various habitats. Most of this research has been conducted in the surface seawater, has provided very
useful information about the baseline of microplastics in marine environments and has improved our understanding of micro- and mesoplastics in coastal waters and the open ocean. The amount of microplastics detected in the coastal areas could vary significantly among seasons (Hitchcock and Mitrovic, 2019; Ramirez et al., 2019). However, most of the existing studies on microplastics are single-season surveys. Few studies have been performed on the seasonal variations (Cheung et al., 2016) in microplastics within the same region. The seasonal variations in micro- and meso-plastics in marine environments are largely unknown for most areas. To reveal seasonal variations of micro- and meso-plastics, we chose Jiaozhou Bay as a case study of a temperate coastal area to research the characteristics and variations of plastics in four seasons. Jiaozhou Bay is a semi-enclosed bay situated on the western side of the Yellow Sea. The bay is surrounded by Qingdao City, which has a population of over nine million people and experiences intensive human activities. Jiaozhou Bay is considered a typical bay in the northern part of China. The purpose of this work was to 1) reveal the characteristics of micro- and meso-plastics in the seawater of Jiaozhou Bay, 2) explore the seasonal variation of micro- and meso-plastics in Jiaozhou Bay and 3) analyze the factors affecting the seasonal changes of plastics in Jiaozhou Bay. We hope to provide more evidence for the seasonal changes of plastics in coastal areas.
⁎ Corresponding author at: Jiaozhou Bay National Marine Ecosystem Research Station, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China. E-mail address: [email protected] (X. Sun).
https://doi.org/10.1016/j.marpolbul.2020.110922 Received 31 October 2019; Received in revised form 19 January 2020; Accepted 19 January 2020 0025-326X/ © 2020 Published by Elsevier Ltd.
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Fig. 1. Sampling stations in Jiaozhou Bay.
2. Materials and methods
USA). In total, 100 particles were selected from four seasons for the chemical composition identification. The spectrum analysis followed the method of Woodall et al. (2014). Matches with a quality index ≥0.7 were accepted directly. Matches with a quality index < 0.7 and ≥0.6 were individually inspected and interpreted based on the proximity of their absorption frequencies to those of chemical bonds in known polymers. Matches with a quality index < 0.6 were rejected (Sun et al., 2018b). The 100 particles include 98 plastics, 1 cellulose and 1 silk.
2.1. Sampling stations Jiaozhou Bay has an area of 374 km2 and average water depth of approximately 7 m. The narrow bay mouth, which is only approximately 2.5 km wide, connects the bay with the South Yellow Sea. In total, 12 rivers flow into Jiaozhou Bay, including the Dagu River, Moshui River, Baisha River, Yang River and Licun River. They are all seasonal rivers. Dagu River is the largest of these rivers, and its flow accounts for 85% of the total runoff of the bay (Wang et al., 2006). There are four distinct seasons in Jiaozhou Bay, with the flood season in summer (July–September). The population in Qingdao City is over 9 million, and the tourist season starts from May to September. Micro- and meso-plastics in seawater were sampled at 14 stations in Jiaozhou Bay (Fig. 1) in four seasons. The sampling periods were Feb. 1–3 (winter), May 6, 9–10 (spring), Aug. 2–3 (summer), Nov. 14, 16–17 (autumn) in 2016. Samples were collected using a Bongo net with a 500 μm mesh size and 0.6 m mouth diameter (Hydro-Bios, Germany) via horizontal tows from the sea surface. The net was towed at 2 knots for periods of 10 min. The flowmeter installed in the center of the net recorded the seawater volume flowing through the net. After collection, the samples from the bucket of the net were transferred to glass bottles and preserved immediately in 5% formaldehyde solution. The collected samples usually contained plastics and zooplankton, and it has been reported that zooplankton ingest and retain a considerable amount of plastics (Desforges et al., 2014, Sun et al., 2017, 2018a,b). The formaldehyde solution was added to preserve the zooplankton, keeping them intact, which ensured that the seawater was not affected by the plastics in the zooplankton.
2.3. Meteorological observations The meteorological parameters of rainfall, wind direction and wind speed were from the automatic meteorological observation station (M520, Vaisala, Finland) of Jiaozhou Bay. Data from the three days before sampling and the sampling period were used to analyze the relationship between the distribution of plastics and precipitation and wind. 2.4. Data analysis The differences in the plastic concentration and size among the four seasons in Jiaozhou Bay were compared using the Kruskal-Wallis Test. The Pearson chi-square test was used to determine difference in shape and color composition among the four seasons. The unpaired t-test was used for the comparison between two seasons. The Pearson correlation analysis was applied to test the relationship between the meteorological factors and the plastic concentrations. Plots were created using Surfer 12.0, ArcGIS10.0 and Microsoft Excel 2013. 3. Results
2.2. Plastic sample analysis
3.1. The concentrations of micro- and meso-plastics in Jiaozhou Bay
The samples were processed by manual selection under a stereomicroscope (Stemi SV11, ZEISS, Shanghai, China) in a clean laboratory. Procedural blanks were set up to correct for the potential procedural contamination. No contamination occurred when the plastic items were picked out. Plastic items were selected and divided into three categories: fragments, fibers and plastic foams. The plastic numbers in the different categories were counted simultaneously. All plastic items were then photographed using a camera system connected with a stereomicroscope (Stemi SV11, ZEISS, Shanghai, China), and Carl Zeiss AxioVision 4.9.1 SP2 software was used to measure the size of plastics. The chemical composition was identified by a Nicolet iN 10 MX Fourier transform infrared (μFTIR) analyzer (Thermo Fisher Scientific,
The concentrations of micro- and meso-plastics in the surface water of Jiaozhou Bay ranged from 0 to 0.516 pieces/m3, with an average of 0.095 pieces/m3. In February, the concentration of micro- and mesoplastics was between 0 and 0.294 pieces/m3, with an average of 0.063 pieces/m3. The micro- and meso-plastic concentrations in May ranged from 0 to 0.516 pieces/m3, with an average of 0.174 pieces/m3. In August, the micro- and meso-plastic concentrations ranged from 0 to 0.395 pieces/m3, with an average of 0.094 pieces/m3. In November, the plastic concentration ranged from 0 to 0.126 pieces/m3, with an average of 0.050 pieces/m3 (Table 1). The highest concentration occurred in May, and the lowest concentration occurred in November. The overall seasonal variation in the concentration was not significant 2
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fibers, 58% for fragments and 6% for plastic foams. In November, the percentages were 24%, 62% and 14% for fibers, fragments and plastic foams, respectively. There was a significant difference in the percentages of different types of plastics among the four seasons (Pearson chisquare test, p < 0.001). The proportion of plastic foams in February was significantly higher than that in other seasons, and the proportion of fragments was significantly lower than that in other seasons (Pearson chi-square test, p < 0.001). There was no significant difference among the plastic-shape composition in May, August and November (Pearson chi-square test, p > 0.05).
Table 1 Concentrations of micro- and meso-plastics in four seasons in Jiaozhou Bay (Unit: pieces/m3). Month
Mean ± SD
Range
n
February May August November Mean
0.063 0.174 0.094 0.050 0.095
0–0.294 0–0.516 0–0.395 0–0.126 0–0.516
14 14 14 14 56
± ± ± ± ±
0.074 0.161 0.104 0.042 0.113
in Jiaozhou Bay (Kruskal-Wallis Test, p > 0.05), whereas the difference was significant between May and February and between May and November (t-test, p < 0.05). The spatial distribution of micro- and meso-plastics in the surface water of Jiaozhou Bay in four seasons is shown in Fig. 2. Overall, the concentrations in February and August were highest in the western part of the bay, especially in areas with a high number of islands in the west of the bay mouth. The distribution of plastics in May and November was relatively uniform. The highest plastic concentration (0.516 pieces/m3) in the four seasons occurred at St. 12 in May, and the lowest value (0 pieces/m3) occurred at St. 7 in February; St. 1, 11 and 14 in May; St. 7 and 14 in August and St. 12 and 14 in November.
3.3. The size of micro- and meso-plastics in Jiaozhou Bay The size of micro- and meso-plastics in the surface seawater of Jiaozhou Bay in four seasons is shown in Fig. 5. Overall, the size ranged from 346 to 155,200 μm, with an average of 5093 ± 43 μm. Most plastics fell in the range of 500–1100 μm and 1700–3000 μm. The composition of plastics in the range of 500–1100 μm was mainly fragments and fibers, whereas the plastics in the range of 1700–3000 μm were mainly fragments and foams. The size composition was similar among the four seasons. In February, 74.1% of the plastics were < 3 mm, 16.3% were between 3 and 5 mm, and only 9.6% were mesoplastics. Similarly, in May, 79.3% of the plastics were < 3 mm, 12.4% of plastics ranged from 3 to 5 mm, and 8.3% of the plastics were mesoplastics. In August, 72.9% of the plastics were < 3 mm, 12.5% of the plastics fell in the range of 3–5 mm and 14.6% of the plastics were meso-plastics. In November, 77.5% of the plastics were < 3 mm, 18.3% of the plastics fell in the range of 3–5 mm and 4.2% of the plastics were meso-plastics (Fig. 5). The detailed size information of micro- and meso-plastics is shown in Table 2. No significant differences were detected in the sizes among the four seasons (Kruskal-Wallis, p > 0.05).
3.2. The shape of micro- and meso-plastics in Jiaozhou Bay Fragments, fibers and plastic foams were identified in Jiaozhou Bay (Fig. 3). The proportions of the three types of plastics are shown in Fig. 4. The overall percentages of fibers, fragments and plastic foams were 29%, 52% and 19%, respectively. Fragments were the most dominant shape in the four seasons. Specifically, the fibers, fragments and plastic foams accounted for 30%, 35% and 35% in February and 27%, 62% and 11% in May. In August, the percentages were 36% for
Fig. 2. The spatial distribution of micro- and meso-plastic concentrations in four seasons in Jiaozhou Bay. 3
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Fig. 3. Micro- and meso-plastics from Jiaozhou Bay (a, b. fragments, c. foam, d. fiber).
fibers, accounting for 68% of the fibers. Fragments were mostly white and transparent, each color representing 47% of the fragments. There was a significant difference in the color percentages of plastics among the four seasons (Pearson chi-square test, p < 0.001). 3.5. The chemical composition of micro- and meso-plastics in Jiaozhou Bay Nine plastic polymers were detected in the surface water of Jiaozhou Bay. As shown in Table 3, the dominant chemical composition was polypropylene (PP), accounting for 51.04% of the polymers, followed by polyethylene (PE), with a percentage of 26.04%. The remaining components had percentages < 10%.The percentage of PP decreased from February to November, whereas the percentage of PE increased. The composition was more diverse in August than in the other seasons (Fig. 6b). 4. Discussion
Fig. 4. Plastic-shape compositions of four seasons in Jiaozhou Bay.
4.1. Overall concentration and characteristics of micro- and meso-plastics in the seawater of Jiaozhou Bay
3.4. The color of micro- and meso-plastics in Jiaozhou Bay Seven colors of plastics were observed in the surface water of Jiaozhou Bay (Fig. 6a). The main colors were white, transparent and green, accounting for 40%, 37% and 20% of the plastics, respectively. All plastic foams were white. Green was the predominant color of
4.1.1. Concentration of micro- and meso-plastics in Jiaozhou Bay The average annual concentration of micro- and meso-plastics in Jiaozhou Bay is 0.095 pieces/m3. Compared with the coastal areas of China, the concentration of plastics in Jiaozhou Bay is lower than that 4
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Fig. 5. Size composition of micro- and meso-plastics in Jiaozhou Bay.
in the Yellow Sea (0.13 pieces/m3) (Sun et al., 2018a) and the East China Sea (0.31 pieces/m3) (Liu et al., 2018) using the same sampling method. It is also lower than that in the Bohai Sea (0.33 pieces/m3) (Zhang et al., 2017), the Chabahar Bay, Gulf of Oman (0.49 pieces/m3) (Aliabada et al., 2019), and the Bay of Brest (0.24 pieces/m3) (Frere et al., 2017) and significantly lower than that in Tampa Bay, Florida, USA (4.5 pieces/m3) (McEachern et al., 2019), and the Guanabara Bay of Brazil (7.1 pieces/m3) (Olivatto et al., 2019) using the different sampling methods. For the isolation of plastics from seawater, the direct isolation method was used in this research, which was usually lower than the digestion methods used in some studies because the results obtained by the digestion method include the plastics in both seawater and organisms. Jiaozhou Bay has a low concentration of plastics because most of the rivers in the Jiaozhou Bay area are seasonal. Studies have shown that terrestrial input is the main way for plastics to enter the ocean (Ribic et al., 2010). As mentioned above, the Dagu River is the largest river flowing into Jiaozhou Bay, and its flow accounts for 85% of the total runoff of the bay (Wang et al., 2006). The Dagu River has a large runoff during the flood season and a relatively small runoff during the flat water period. The river often appears dry in the downstream section during the dry season. This prevents plastics on the land from entering Jiaozhou Bay through rivers during the dry season, which is a reason for the low concentration of plastics in Jiaozhou Bay. Moreover, to
improve the water quality in Jiaozhou Bay, the Qingdao City government issued the “2013–2015 Jiaozhou Bay Pollution Comprehensive Improvement Plan”. By the end of 2015, all of the Haibo River, Licun River, Loushan River, and Moshui River completed sewage interception and river dredging projects. All of the straight drains along the river were cleaned and sealed. There is no obvious sewage runoff in the river, and the ecological status of rivers and river banks is significantly improved. This also helps to reduce the amount of plastic entering Jiaozhou Bay through the river. In addition, the water exchange in Jiaozhou Bay is good. The tidal current in the bay mouth channel is very strong. The observed peak current speed during the spring tide period was 2.01 m/s. A few tidal residual eddies are found on both sides of the headland of Tuandao. Residual eddies converge near Tuandao, forming an offshore jet current of 57 cm/s (Lu et al., 2010). The fast exchange of seawater makes the transport of plastics from Jiaozhou Bay to the Yellow Sea feasible. 4.1.2. Characteristics of micro- and meso-plastics in Jiaozhou Bay Among the three types of plastics in Jiaozhou Bay, plastic fragments were dominant. This may be because the 500 μm mesh size did not collect fibers efficiently, causing the proportion of fibers in Jiaozhou Bay to be underestimated. Compared with the plastic-shape compositions of the Yellow Sea and the East China Sea, the proportions of fragments, fibers and foams in Jiaozhou Bay are similar to those of the 5
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Table 2 Size of micro- and meso-plastics in Jiaozhou Bay in four seasons.
Table 3 The chemical composition of micro- and meso-plastics in Jiaozhou Bay.
Month
Mean ± SE (μm)
Range (μm)
n
Fragment February May August November Mean
2512 4504 9513 2897 4370
564–12,500 596–155,200 694–124,700 586–15,400 564–155,200
48 75 28 44 195
Fiber February May August November Mean
12,650 ± 817 6223 ± 359 8588 ± 1052 2115 ± 64 8349 ± 209
346–147,500 433–62,800 568–71,500 487–3698 346–147,500
40 33 17 17 107
Plastic-foams February May August November Mean
2474 1917 1121 1980 2252
± ± ± ± ±
20 35 22 46 12
1533–6500 1086–2887 1053–1183 1233–2864 1053–6500
Total February May August November Mean
5503 4695 8661 2581 5093
± ± ± ± ±
136 128 449 36 43
346–147,500 433–155,200 568–124,700 487–15,400 346–155,200
± ± ± ± ±
45 240 883 72 76
Chemical composition
Proportion
Polypropylene Polyethylene Polymerized oxidized organic material Polystyrene Poly (1-chloro-2-phenylacetylene) Polyisoprene Polyoctadecyl acrylate Alkyd resin Polyamide
51.04% 26.04% 7.29% 5.21% 4.17% 2.08% 2.08% 1.04% 1.04%
Table 4 Comparison of the characteristics of plastics between Jiaozhou Bay and other areas (based on the same sampling method).
47 13 3 10 73 135 121 48 71 375
Yellow Sea but different from those of the East China Sea (Table 4). This is because the East China Sea is the largest fishery ground in China, and foam is the most commonly used material in the transportation of fish. The chemical composition of plastics in Jiaozhou Bay is dominated by PP and PE, similar to the situation of other coastal waters, such as the Yellow Sea, the East China Sea (Table 4), the Chabahar Bay (Aliabada et al., 2019), the Bay of Brest (Frere et al., 2017), the Persian Gulf (Kor and Mehdinia, 2020) and the Guanabara Bay (Olivatto et al., 2019). PP and PE are widely used for plastic bags, storage containers, rope, bottle caps, gear, strapping, etc. The bulk of common thermoplastics manufactured (PE, PP) are used in packaging products that have a relatively short useful lifetime and rapidly end up in the waste and litter streams (GESAMP, 2015). Jiaozhou Bay is surrounded by the densely populated city of Qingdao. PP and PE are widely used in the daily lives of people. Ports, urban construction, tourism, and marine recreational activities are all closely related to plastics. We also found plastic foam in the sample. They are usually used in vessel insulation
Jiaozhou Bay (August)
The Yellow Sea
East China Sea
Concentration Range (pieces/m3) Average (pieces/m3)
0–0.395 0.094
0–0.81 0.13
0.011–2.198 0.31
Shape composition Fragment Fiber Plastic foam
59.8% 32.0% 8.2%
64.3% 16.6% 19.1%
41.6% 3.6% 54.8%
Chemical composition Polypropylene 40.9% Polyethylene 36.4% Polystyrene 0.0%
32.2% 55.9% 6.8%
34.6% 45.5% 5.5%
Color composition Transparent White Black Colorful
– – – –
6.90% 71.90% 2.70% 18.50%
47.92% 20.83% 0 31.25%
and floats and are employed extensively in the marine environment. This should be relevant to the commercial vessels in the port of Jiaozhou Bay. 4.2. Seasonal variation of micro- and meso-plastics in the seawater of Jiaozhou Bay 4.2.1. Seasonal change in the plastic concentration The distributions of micro- and meso-plastics in May and August are approximately twice as high as those in February and November. The
Fig. 6. The color and chemical composition of micro- and meso-plastic in Jiaozhou Bay. 6
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distribution of plastics in the ocean is mainly influenced by input of land sources, and the river affects the distribution of plastics in the seawater indirectly by affecting the flow of the seawater (Galgani et al., 2000). As mentioned above, the rivers around Jiaozhou Bay are mainly seasonal rivers, and the runoff is highly dependent on rainfall. The main reason for the higher plastic concentration in May and August is the larger runoff of rivers, resulting in the increased input of micro- and meso-plastics to Jiaozhou Bay. August is usually the flood season in Jiaozhou Bay; however, there was strong rainfall in May in the sampling year. According to the precipitation data of Jiaozhou Bay, before and during the plastic collection, there was precipitation in May and August but no precipitation in February and November. The plastic concentration was positively correlated with the cumulative rainfall amount during and before the sampling period (Pearson, p < 0.05). The highest daily precipitation was 13.6 mm in May, and the associated runoff from the land to the sea resulted in the increased amount of plastic. Similar changes were also found in other areas. The amount of microplastics detected in the sediments of the coast and the Ria of Campeche, Mexico, varied significantly among sites (p = 0.001) and seasons (p = 0.001), with the greatest amount of microplastics detected during the rainy season (Ramirez et al., 2019). Hitchcock and Mitrovic (2019) reported a year-long study on the abundance of microplastics in the water column of three estuaries on the east coast of Australia. Microplastic abundance was positively related to the maximum antecedent rainfall in the Bega estuary. Microplastics were generally highest in summer and following freshwater inflow events. Based on a study on the seasonal dynamics of marine litter along the Bulgarian Black Sea coast, the seasonal dynamics showed higher quantities in summer than in the other seasons (Simeonova et al., 2017). Cheung et al. (2016) sampled plastic debris at 25 beaches during the wet and dry seasons and found significant seasonal variations in both large debris and microplastics, suggesting that the marine debris in estuaries is largely controlled by fluvial inputs. In addition to rainfall, the peak tourist season in Qingdao occurs during spring and summer, resulting in an increase in the usage of plastic items, which may further increase the amount of plastic transported into the ocean.
Bay. The seasonal variation of plastics in Jiaozhou Bay indicated that meteorological and physical processes such as rainfall, wind and eddies have an important influence on the concentration and distribution pattern of marine surface plastics. CRediT authorship contribution statement Tao Liu: Writing - original draft, Investigation. Yongfang Zhao: Data curation, Formal analysis, Visualization. Mingliang Zhu: Investigation. Junhua Liang: Investigation. Shan Zheng: Investigation. Xiaoxia Sun: Writing - review & editing, Supervision, Funding acquisition, Project administration. 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 work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA23050303, No. XDA19060204) and the Project from Shandong Academy for Environmental Planning: Research on the Prevention and Control of Marine Microplastic Pollution in Key Industries in Shandong Province. References Aliabada, M.K., Nassiria, M., Korb, K., 2019. Microplastics in the surface seawaters of Chabahar Bay, Gulf of Oman(Makran Coasts). Mar. Pollut. Bull. 143, 125–133. https://doi.org/10.1016/j.marpolbul.2019.04.037. Andrady, A.L., 2011. Microplastics in the marine environment. Mar. Pollut. Bull. 62 (8), 1596–1605. https://doi.org/10.1016/j.marpolbul.2011.05.030. Avio, C.G., Gorbi, S., Regoli, F., 2017. Plastics and microplastics in the oceans: from emerging pollutants to emerged threat. Mar. Environ. Res. 128, 2–11. https://doi. org/10.1016/j.marenvres.2016.05.012. Barnes, D.K.A., Galgani, F., Thompson, R.C., Barlaz, M., 2009. Accumulation and fragmentation of plastic debris in global environments. Philos. Trans. R. Soc. B 364, 1985–1998. https://doi.org/10.1098/rstb.2008.0205. Botterell, Z.L.R., Beaumont, N., Dorrington, T., Steinke, M., Thompson, R.C., Lindeque, P.K., 2019. Bioavailability and effects of microplastics on marine zooplankton: a review. Environ. Pollut. 245, 98–110. https://doi.org/10.1016/j.envpol.2018.10. 065. Browne, M.A., Galloway, T.S., Thompson, R.C., 2010. Spatial patterns of plastic debris along estuarine shorelines. Environ. Sci. Technol. 44, 3404–3409. https://doi.org/10. 1021/es903784e. Cheung, P.K., Cheung, L.T.O., Fok, L., 2016. Seasonal variation in the abundance of marine plastic debris in the estuary of a subtropical macro-scale drainage basin in South China. Sci. Total Environ. 562, 658–665. https://doi.org/10.1016/j.scitotenv. 2016.04.048. Desforges, J.P.W., Galbraith, M., Dangerfield, N., Ross, P.S., 2014. Widespread distribution of microplastics in subsurface seawater in the NE Pacific Ocean. Mar. Pollut. Bull. 79, 94–99. https://doi.org/10.1016/j.marpolbul.2013.12.035. Frere, L., Paul-Pont, I., Rinnert, E., et al., 2017. Influence of environmental and anthropogenic factors on the composition, concentration and spatial distribution of microplastics: a case study of the Bay of Brest (Brittany, France). Environ. Pollut. 225, 211–222. https://doi.org/10.1016/j.envpol.2017.03.023. Galgani, F., Leaute, J.P., Moguedet, P., Souplet, A., Verin, Y., Carpentier, A., Goraguer, H., Latrouite, D., Andral, B., Cadiou, Y., Mahe, J.C., Poulard, J.C., Nerisson, P., 2000. Litter on the sea floor along European coasts. Mar. Pollut. Bull. 40 (6), 516–527. https://doi.org/10.1016/S0025-326X(99)00234-9. GESAMP, 2015. Sources, fate and effects of microplastics in the marine environment: a global assessment. In: GESAMP Rep. Stud. No. 90, (96 pp.). Hitchcock, J.N., Mitrovic, S.M., 2019. Microplastic pollution in estuaries across a gradient of human impact. Environ. Pollut. 247, 457–466. https://doi.org/10.1016/j.envpol. 2019.01.069. Kor, K., Mehdinia, A., 2020. Neustonic microplastic pollution in the Persian Gulf. Mar. Pollut. Bull. 150, 110665. https://doi.org/10.1016/j.marpolbul.2019.110665. Liu, T., Sun, X.X., Zhu, M.L., Liang, J.H., Zhao, Y.Y., 2018. Distribution and composition of microplastics in the surface water of the East China Sea. Oceanol. Limnol. Sin. 49 (1), 62–69. https://doi.org/10.11693/hyhz20170100021. Lu, X.G., Zhao, C., Xia, C.S., Qiao, F.L., 2010. Numerical study of water exchange in the Jiaozhou Bay and the tidal residual currents near the bay mouth. Acta Oceanol. Sin. 32 (2), 20–30. https://doi.org/10.3788/HPLPB20102209.2186. McEachern, K., Alegria, H., Kalagherb, A.L., et al., 2019. Microplastics in Tampa Bay, Florida: abundance and variability in estuarinewaters and sediments. Mar. Pollut.
4.2.2. Seasonal change in the spatial distribution of plastics According to Fig. 2, the distribution of plastics in spring and autumn is relatively uniform, but the plastics in winter and summer are mainly concentrated in the bay mouth. The distribution of plastics in the ocean is influenced by the nature and location of the source of entry, as well as the subsequent complex interactions of physical, chemical and biological processes (GESAMP, 2015). Plastics are susceptible to physical processes such as eddies and wind. Due to the influence of the complex terrain of the bay mouth and region north of the mouth, there are vortices around the mouth of Jiaozhou Bay. Microplastics tend to stay inside eddies, so the presence of eddies forms regions of high microplastic concentrations (Zheng et al., 2019). This should be the main reason for the presence of plastic high-value areas in the western part of the bay near the bay mouth in February and August. The distribution of plastics in May and November was relatively uniform, mainly due to the presence of high-speed winds before sampling. In this study, the plastics collected were larger than microplastics. Larger floating objects will be more prone to transport by winds than microplastics (Browne et al., 2010; GESAMP, 2017). According to the wind speed and wind direction data three days before plastic sampling, the maximum wind speed was higher than 12 m/s in the first three days of sampling in May, and the daily average wind speed was above 7 m/s. Regarding wind direction, there were northwest winds during this period. The wind speed was higher than 11 m/s in November, and the daily average wind speed was close to 5 m/s. There were south-southwest winds, which blew the plastics from the eddy convergence zone to the eastern and northern regions, respectively, resulting in a relatively even distribution of plastics in Jiaozhou 7
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T. Liu, et al. Bull. 148, 97–106. https://doi.org/10.1016/j.marpolbul.2019.07.068. Olivatto, G.P., Martins, M.C.T., Montagner, C.C., Henry, T.B., Carreira, R.S., 2019. Microplastic contamination in surface waters in Guanabara Bay, Rio de Janeiro, Brazil. Mar. Pollut. Bull. 139, 157–162. https://doi.org/10.1016/j.marpolbul.2018. 12.042. Ramirez, M.M.B., Caamal, R.D., von Osten, J.R., 2019. Occurrence and seasonal distribution of microplastics and phthalates in sediments from the urban channel of the Ria and coast of Campeche, Mexico. Sci. Total Environ. 672, 97–105. https://doi.org/ 10.1016/j.scitotenv.2019.03.472. Ribic, C.A., Sheavly, S.B., Rugg, D.J., Erdmann, E.S., 2010. Trends and drivers of marine debris on the Atlantic coast of the United States 1997–2007. Mar. Pollut. Bull. 60, 1231–1242. https://doi.org/10.1016/j.marpolbul.2010.03.021. Simeonova, A., Chuturkova, R., Yaneva, V., 2017. Seasonal dynamics of marine litter along the Bulgarian Black Sea coast. Mar. Pollut. Bull. 119 (1), 110–118. https://doi. org/10.1016/j.marpolbul.2017.03.035. Song, Y.K., Hong, S.H., Jang, M., Han, G.M., Shim, W.J., 2015. Occurrence and distribution of microplastics in the sea surface microlayer in Jinhae Bay, South Korea. Arch. Environ. Contam. Toxicol. 69 (3), 279–287. https://doi.org/10.1007/s00244015-0209-9. Sun, X.X., Li, Q.J., Zhu, M.L., Liang, J.H., Zheng, S., Zhao, Y.F., 2017. Ingestion of microplastics by natural zooplankton groups in the northern South China Sea. Mar. Pollut. Bull. 115 (1–2), 217–224. https://doi.org/10.1016/j.marpolbul.2016.12.004. Sun, X.X., Liang, J.H., Zhu, M.L., Zhao, Y.F., Zhang, B., 2018a. Microplastics in seawater
and zooplankton from the Yellow Sea. Environ. Pollut. 242, 585–595. https://doi. org/10.1016/j.envpol.2018.07.014. Sun, X.X., Liu, T., Zhu, M.L., Liang, J.H., Zhao, Y.F., Zhang, B., 2018b. Retention and characteristics of microplastics in natural zooplankton taxa from the East China Sea. Sci. Total Environ. 640, 232–242. https://doi.org/10.1016/j.scitotenv.2018.05.308. Wang, X.L., Li, K.Q., Shi, X.Y., 2006. Marine Environmental Capacity of Main Chemical Pollutant in Jiaozhou Bay. Beijing Science Press. Woodall, L.C., Sanchez-Vidal, A., Canals, M., Paterson, G.L.J., Coppock, R., Sleight, V., Calafat, A., Rogers, A.D., Narayanaswamy, B.E., Thompson, R.C., 2014. The deep sea is a major sink for microplastic debris. R. Soc. Open Sci. 1 (4), 140317. https://doi. org/10.1098/rsos.140317. Zhang, W.W., Zhang, S.F., Wang, J.Y., Wang, Y., Mu, J.L., Wang, P., Lin, X.Z., Ma, D.Y., 2017. Microplastic pollution in the surface waters of the Bohai Sea, China. Environ. Pollut. 231, 541–548. https://doi.org/10.1016/j.envpol.2017.08.058. Zhao, S.Y., Zhu, L.X., Wang, T., Li, D.J., 2014. Suspended microplastics in the surface water of the Yangtze Estuary System, China: first observations on occurrence, distribution. Mar. Pollut. Bull. 86, 562–568. https://doi.org/10.1016/j.marpolbul.2014. 06.032. Zheng, Y.F., Li, J.X., Cao, W., Liu, X.H., Jiang, F.H., Ding, J.F., Yin, X.F., Sun, C.J., 2019. Distribution characteristics of microplastics in the seawater and sediment: a case study in Jiaozhou Bay, China. Sci. Total Environ. 674, 27–35. https://doi.org/10. 1016/j.scitotenv.2019.04.008.
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Seasonal variation of micro- and meso-plastics in the seawater of Jiaozhou Bay, the Yellow Sea
T
Tao Liua,c, Yongfang Zhaoa,b, Mingliang Zhua,b, Junhua Lianga,b, Shan Zhenga,b, ⁎ Xiaoxia Suna,b,c,d, a
Jiaozhou Bay National Marine Ecosystem Research Station, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China c University of Chinese Academy of Sciences, Beijing 100049, China d Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China b
ARTICLE INFO
ABSTRACT
Keywords: Microplastics Mesoplastics Jiaozhou Bay Seasonal variation
The seasonal change in the concentrations and characteristics of micro- and meso-plastics in the surface seawater of Jiaozhou Bay were studied. The concentrations of micro- and meso-plastics were 0.063, 0.174, 0.094, and 0.050 pieces/m3 in February, May, August and November, respectively, with an annual average concentration of 0.095 pieces/m3. The size of the micro- and meso-plastics ranged from 346 to 155,200 μm, with an average of 5093 ± 43 μm. The overall percentages of fibers, fragments and plastic foams were 29%, 55% and 16%, respectively. The dominant chemical composition was polypropylene (PP), accounting for 51.04% of polymers, followed by polyethylene (PE), accounting for 26.04% of polymers. Strong rainfall resulted in an increase in the plastic concentration in May, and winds and eddies affected the spatial distribution of plastics in Jiaozhou Bay.
1. Introduction The presence and impact of plastic debris in the ocean have emerged rapidly in the last few years as an environmental situation in urgent need of attention (Avio et al., 2017). Micro- and meso-plastics are widely distributed in the marine environment (Barnes et al., 2009; Andrady, 2011) from the surface (Zhao et al., 2014; Song et al., 2015) and subsurface (Desforges et al., 2014) to the deep sea and the bottom of the ocean (Woodall et al., 2014). Micro- and meso-plastics can be ingested by marine organisms ranging from zooplankton to large cetaceans, and they can even be transferred through the food chain into seafood that may be consumed by humans, arousing widespread concern worldwide (Botterell et al., 2019). Higher levels of human impact lead to more plastic pollution and highlight the need to examine aquatic ecosystems under a range of conditions in order to adequately characterize the extent of plastic pollution in coastal systems (Hitchcock and Mitrovic, 2019). Understanding how plastics are distributed in the oceans is a prerequisite for assessing their potential impacts (GESAMP, 2015). To date, a series of studies have been conducted to reveal the concentration and spatial distribution of micro- and meso-plastics in various habitats. Most of this research has been conducted in the surface seawater, has provided very
useful information about the baseline of microplastics in marine environments and has improved our understanding of micro- and mesoplastics in coastal waters and the open ocean. The amount of microplastics detected in the coastal areas could vary significantly among seasons (Hitchcock and Mitrovic, 2019; Ramirez et al., 2019). However, most of the existing studies on microplastics are single-season surveys. Few studies have been performed on the seasonal variations (Cheung et al., 2016) in microplastics within the same region. The seasonal variations in micro- and meso-plastics in marine environments are largely unknown for most areas. To reveal seasonal variations of micro- and meso-plastics, we chose Jiaozhou Bay as a case study of a temperate coastal area to research the characteristics and variations of plastics in four seasons. Jiaozhou Bay is a semi-enclosed bay situated on the western side of the Yellow Sea. The bay is surrounded by Qingdao City, which has a population of over nine million people and experiences intensive human activities. Jiaozhou Bay is considered a typical bay in the northern part of China. The purpose of this work was to 1) reveal the characteristics of micro- and meso-plastics in the seawater of Jiaozhou Bay, 2) explore the seasonal variation of micro- and meso-plastics in Jiaozhou Bay and 3) analyze the factors affecting the seasonal changes of plastics in Jiaozhou Bay. We hope to provide more evidence for the seasonal changes of plastics in coastal areas.
⁎ Corresponding author at: Jiaozhou Bay National Marine Ecosystem Research Station, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China. E-mail address: [email protected] (X. Sun).
https://doi.org/10.1016/j.marpolbul.2020.110922 Received 31 October 2019; Received in revised form 19 January 2020; Accepted 19 January 2020 0025-326X/ © 2020 Published by Elsevier Ltd.
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Fig. 1. Sampling stations in Jiaozhou Bay.
2. Materials and methods
USA). In total, 100 particles were selected from four seasons for the chemical composition identification. The spectrum analysis followed the method of Woodall et al. (2014). Matches with a quality index ≥0.7 were accepted directly. Matches with a quality index < 0.7 and ≥0.6 were individually inspected and interpreted based on the proximity of their absorption frequencies to those of chemical bonds in known polymers. Matches with a quality index < 0.6 were rejected (Sun et al., 2018b). The 100 particles include 98 plastics, 1 cellulose and 1 silk.
2.1. Sampling stations Jiaozhou Bay has an area of 374 km2 and average water depth of approximately 7 m. The narrow bay mouth, which is only approximately 2.5 km wide, connects the bay with the South Yellow Sea. In total, 12 rivers flow into Jiaozhou Bay, including the Dagu River, Moshui River, Baisha River, Yang River and Licun River. They are all seasonal rivers. Dagu River is the largest of these rivers, and its flow accounts for 85% of the total runoff of the bay (Wang et al., 2006). There are four distinct seasons in Jiaozhou Bay, with the flood season in summer (July–September). The population in Qingdao City is over 9 million, and the tourist season starts from May to September. Micro- and meso-plastics in seawater were sampled at 14 stations in Jiaozhou Bay (Fig. 1) in four seasons. The sampling periods were Feb. 1–3 (winter), May 6, 9–10 (spring), Aug. 2–3 (summer), Nov. 14, 16–17 (autumn) in 2016. Samples were collected using a Bongo net with a 500 μm mesh size and 0.6 m mouth diameter (Hydro-Bios, Germany) via horizontal tows from the sea surface. The net was towed at 2 knots for periods of 10 min. The flowmeter installed in the center of the net recorded the seawater volume flowing through the net. After collection, the samples from the bucket of the net were transferred to glass bottles and preserved immediately in 5% formaldehyde solution. The collected samples usually contained plastics and zooplankton, and it has been reported that zooplankton ingest and retain a considerable amount of plastics (Desforges et al., 2014, Sun et al., 2017, 2018a,b). The formaldehyde solution was added to preserve the zooplankton, keeping them intact, which ensured that the seawater was not affected by the plastics in the zooplankton.
2.3. Meteorological observations The meteorological parameters of rainfall, wind direction and wind speed were from the automatic meteorological observation station (M520, Vaisala, Finland) of Jiaozhou Bay. Data from the three days before sampling and the sampling period were used to analyze the relationship between the distribution of plastics and precipitation and wind. 2.4. Data analysis The differences in the plastic concentration and size among the four seasons in Jiaozhou Bay were compared using the Kruskal-Wallis Test. The Pearson chi-square test was used to determine difference in shape and color composition among the four seasons. The unpaired t-test was used for the comparison between two seasons. The Pearson correlation analysis was applied to test the relationship between the meteorological factors and the plastic concentrations. Plots were created using Surfer 12.0, ArcGIS10.0 and Microsoft Excel 2013. 3. Results
2.2. Plastic sample analysis
3.1. The concentrations of micro- and meso-plastics in Jiaozhou Bay
The samples were processed by manual selection under a stereomicroscope (Stemi SV11, ZEISS, Shanghai, China) in a clean laboratory. Procedural blanks were set up to correct for the potential procedural contamination. No contamination occurred when the plastic items were picked out. Plastic items were selected and divided into three categories: fragments, fibers and plastic foams. The plastic numbers in the different categories were counted simultaneously. All plastic items were then photographed using a camera system connected with a stereomicroscope (Stemi SV11, ZEISS, Shanghai, China), and Carl Zeiss AxioVision 4.9.1 SP2 software was used to measure the size of plastics. The chemical composition was identified by a Nicolet iN 10 MX Fourier transform infrared (μFTIR) analyzer (Thermo Fisher Scientific,
The concentrations of micro- and meso-plastics in the surface water of Jiaozhou Bay ranged from 0 to 0.516 pieces/m3, with an average of 0.095 pieces/m3. In February, the concentration of micro- and mesoplastics was between 0 and 0.294 pieces/m3, with an average of 0.063 pieces/m3. The micro- and meso-plastic concentrations in May ranged from 0 to 0.516 pieces/m3, with an average of 0.174 pieces/m3. In August, the micro- and meso-plastic concentrations ranged from 0 to 0.395 pieces/m3, with an average of 0.094 pieces/m3. In November, the plastic concentration ranged from 0 to 0.126 pieces/m3, with an average of 0.050 pieces/m3 (Table 1). The highest concentration occurred in May, and the lowest concentration occurred in November. The overall seasonal variation in the concentration was not significant 2
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fibers, 58% for fragments and 6% for plastic foams. In November, the percentages were 24%, 62% and 14% for fibers, fragments and plastic foams, respectively. There was a significant difference in the percentages of different types of plastics among the four seasons (Pearson chisquare test, p < 0.001). The proportion of plastic foams in February was significantly higher than that in other seasons, and the proportion of fragments was significantly lower than that in other seasons (Pearson chi-square test, p < 0.001). There was no significant difference among the plastic-shape composition in May, August and November (Pearson chi-square test, p > 0.05).
Table 1 Concentrations of micro- and meso-plastics in four seasons in Jiaozhou Bay (Unit: pieces/m3). Month
Mean ± SD
Range
n
February May August November Mean
0.063 0.174 0.094 0.050 0.095
0–0.294 0–0.516 0–0.395 0–0.126 0–0.516
14 14 14 14 56
± ± ± ± ±
0.074 0.161 0.104 0.042 0.113
in Jiaozhou Bay (Kruskal-Wallis Test, p > 0.05), whereas the difference was significant between May and February and between May and November (t-test, p < 0.05). The spatial distribution of micro- and meso-plastics in the surface water of Jiaozhou Bay in four seasons is shown in Fig. 2. Overall, the concentrations in February and August were highest in the western part of the bay, especially in areas with a high number of islands in the west of the bay mouth. The distribution of plastics in May and November was relatively uniform. The highest plastic concentration (0.516 pieces/m3) in the four seasons occurred at St. 12 in May, and the lowest value (0 pieces/m3) occurred at St. 7 in February; St. 1, 11 and 14 in May; St. 7 and 14 in August and St. 12 and 14 in November.
3.3. The size of micro- and meso-plastics in Jiaozhou Bay The size of micro- and meso-plastics in the surface seawater of Jiaozhou Bay in four seasons is shown in Fig. 5. Overall, the size ranged from 346 to 155,200 μm, with an average of 5093 ± 43 μm. Most plastics fell in the range of 500–1100 μm and 1700–3000 μm. The composition of plastics in the range of 500–1100 μm was mainly fragments and fibers, whereas the plastics in the range of 1700–3000 μm were mainly fragments and foams. The size composition was similar among the four seasons. In February, 74.1% of the plastics were < 3 mm, 16.3% were between 3 and 5 mm, and only 9.6% were mesoplastics. Similarly, in May, 79.3% of the plastics were < 3 mm, 12.4% of plastics ranged from 3 to 5 mm, and 8.3% of the plastics were mesoplastics. In August, 72.9% of the plastics were < 3 mm, 12.5% of the plastics fell in the range of 3–5 mm and 14.6% of the plastics were meso-plastics. In November, 77.5% of the plastics were < 3 mm, 18.3% of the plastics fell in the range of 3–5 mm and 4.2% of the plastics were meso-plastics (Fig. 5). The detailed size information of micro- and meso-plastics is shown in Table 2. No significant differences were detected in the sizes among the four seasons (Kruskal-Wallis, p > 0.05).
3.2. The shape of micro- and meso-plastics in Jiaozhou Bay Fragments, fibers and plastic foams were identified in Jiaozhou Bay (Fig. 3). The proportions of the three types of plastics are shown in Fig. 4. The overall percentages of fibers, fragments and plastic foams were 29%, 52% and 19%, respectively. Fragments were the most dominant shape in the four seasons. Specifically, the fibers, fragments and plastic foams accounted for 30%, 35% and 35% in February and 27%, 62% and 11% in May. In August, the percentages were 36% for
Fig. 2. The spatial distribution of micro- and meso-plastic concentrations in four seasons in Jiaozhou Bay. 3
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Fig. 3. Micro- and meso-plastics from Jiaozhou Bay (a, b. fragments, c. foam, d. fiber).
fibers, accounting for 68% of the fibers. Fragments were mostly white and transparent, each color representing 47% of the fragments. There was a significant difference in the color percentages of plastics among the four seasons (Pearson chi-square test, p < 0.001). 3.5. The chemical composition of micro- and meso-plastics in Jiaozhou Bay Nine plastic polymers were detected in the surface water of Jiaozhou Bay. As shown in Table 3, the dominant chemical composition was polypropylene (PP), accounting for 51.04% of the polymers, followed by polyethylene (PE), with a percentage of 26.04%. The remaining components had percentages < 10%.The percentage of PP decreased from February to November, whereas the percentage of PE increased. The composition was more diverse in August than in the other seasons (Fig. 6b). 4. Discussion
Fig. 4. Plastic-shape compositions of four seasons in Jiaozhou Bay.
4.1. Overall concentration and characteristics of micro- and meso-plastics in the seawater of Jiaozhou Bay
3.4. The color of micro- and meso-plastics in Jiaozhou Bay Seven colors of plastics were observed in the surface water of Jiaozhou Bay (Fig. 6a). The main colors were white, transparent and green, accounting for 40%, 37% and 20% of the plastics, respectively. All plastic foams were white. Green was the predominant color of
4.1.1. Concentration of micro- and meso-plastics in Jiaozhou Bay The average annual concentration of micro- and meso-plastics in Jiaozhou Bay is 0.095 pieces/m3. Compared with the coastal areas of China, the concentration of plastics in Jiaozhou Bay is lower than that 4
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Fig. 5. Size composition of micro- and meso-plastics in Jiaozhou Bay.
in the Yellow Sea (0.13 pieces/m3) (Sun et al., 2018a) and the East China Sea (0.31 pieces/m3) (Liu et al., 2018) using the same sampling method. It is also lower than that in the Bohai Sea (0.33 pieces/m3) (Zhang et al., 2017), the Chabahar Bay, Gulf of Oman (0.49 pieces/m3) (Aliabada et al., 2019), and the Bay of Brest (0.24 pieces/m3) (Frere et al., 2017) and significantly lower than that in Tampa Bay, Florida, USA (4.5 pieces/m3) (McEachern et al., 2019), and the Guanabara Bay of Brazil (7.1 pieces/m3) (Olivatto et al., 2019) using the different sampling methods. For the isolation of plastics from seawater, the direct isolation method was used in this research, which was usually lower than the digestion methods used in some studies because the results obtained by the digestion method include the plastics in both seawater and organisms. Jiaozhou Bay has a low concentration of plastics because most of the rivers in the Jiaozhou Bay area are seasonal. Studies have shown that terrestrial input is the main way for plastics to enter the ocean (Ribic et al., 2010). As mentioned above, the Dagu River is the largest river flowing into Jiaozhou Bay, and its flow accounts for 85% of the total runoff of the bay (Wang et al., 2006). The Dagu River has a large runoff during the flood season and a relatively small runoff during the flat water period. The river often appears dry in the downstream section during the dry season. This prevents plastics on the land from entering Jiaozhou Bay through rivers during the dry season, which is a reason for the low concentration of plastics in Jiaozhou Bay. Moreover, to
improve the water quality in Jiaozhou Bay, the Qingdao City government issued the “2013–2015 Jiaozhou Bay Pollution Comprehensive Improvement Plan”. By the end of 2015, all of the Haibo River, Licun River, Loushan River, and Moshui River completed sewage interception and river dredging projects. All of the straight drains along the river were cleaned and sealed. There is no obvious sewage runoff in the river, and the ecological status of rivers and river banks is significantly improved. This also helps to reduce the amount of plastic entering Jiaozhou Bay through the river. In addition, the water exchange in Jiaozhou Bay is good. The tidal current in the bay mouth channel is very strong. The observed peak current speed during the spring tide period was 2.01 m/s. A few tidal residual eddies are found on both sides of the headland of Tuandao. Residual eddies converge near Tuandao, forming an offshore jet current of 57 cm/s (Lu et al., 2010). The fast exchange of seawater makes the transport of plastics from Jiaozhou Bay to the Yellow Sea feasible. 4.1.2. Characteristics of micro- and meso-plastics in Jiaozhou Bay Among the three types of plastics in Jiaozhou Bay, plastic fragments were dominant. This may be because the 500 μm mesh size did not collect fibers efficiently, causing the proportion of fibers in Jiaozhou Bay to be underestimated. Compared with the plastic-shape compositions of the Yellow Sea and the East China Sea, the proportions of fragments, fibers and foams in Jiaozhou Bay are similar to those of the 5
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Table 2 Size of micro- and meso-plastics in Jiaozhou Bay in four seasons.
Table 3 The chemical composition of micro- and meso-plastics in Jiaozhou Bay.
Month
Mean ± SE (μm)
Range (μm)
n
Fragment February May August November Mean
2512 4504 9513 2897 4370
564–12,500 596–155,200 694–124,700 586–15,400 564–155,200
48 75 28 44 195
Fiber February May August November Mean
12,650 ± 817 6223 ± 359 8588 ± 1052 2115 ± 64 8349 ± 209
346–147,500 433–62,800 568–71,500 487–3698 346–147,500
40 33 17 17 107
Plastic-foams February May August November Mean
2474 1917 1121 1980 2252
± ± ± ± ±
20 35 22 46 12
1533–6500 1086–2887 1053–1183 1233–2864 1053–6500
Total February May August November Mean
5503 4695 8661 2581 5093
± ± ± ± ±
136 128 449 36 43
346–147,500 433–155,200 568–124,700 487–15,400 346–155,200
± ± ± ± ±
45 240 883 72 76
Chemical composition
Proportion
Polypropylene Polyethylene Polymerized oxidized organic material Polystyrene Poly (1-chloro-2-phenylacetylene) Polyisoprene Polyoctadecyl acrylate Alkyd resin Polyamide
51.04% 26.04% 7.29% 5.21% 4.17% 2.08% 2.08% 1.04% 1.04%
Table 4 Comparison of the characteristics of plastics between Jiaozhou Bay and other areas (based on the same sampling method).
47 13 3 10 73 135 121 48 71 375
Yellow Sea but different from those of the East China Sea (Table 4). This is because the East China Sea is the largest fishery ground in China, and foam is the most commonly used material in the transportation of fish. The chemical composition of plastics in Jiaozhou Bay is dominated by PP and PE, similar to the situation of other coastal waters, such as the Yellow Sea, the East China Sea (Table 4), the Chabahar Bay (Aliabada et al., 2019), the Bay of Brest (Frere et al., 2017), the Persian Gulf (Kor and Mehdinia, 2020) and the Guanabara Bay (Olivatto et al., 2019). PP and PE are widely used for plastic bags, storage containers, rope, bottle caps, gear, strapping, etc. The bulk of common thermoplastics manufactured (PE, PP) are used in packaging products that have a relatively short useful lifetime and rapidly end up in the waste and litter streams (GESAMP, 2015). Jiaozhou Bay is surrounded by the densely populated city of Qingdao. PP and PE are widely used in the daily lives of people. Ports, urban construction, tourism, and marine recreational activities are all closely related to plastics. We also found plastic foam in the sample. They are usually used in vessel insulation
Jiaozhou Bay (August)
The Yellow Sea
East China Sea
Concentration Range (pieces/m3) Average (pieces/m3)
0–0.395 0.094
0–0.81 0.13
0.011–2.198 0.31
Shape composition Fragment Fiber Plastic foam
59.8% 32.0% 8.2%
64.3% 16.6% 19.1%
41.6% 3.6% 54.8%
Chemical composition Polypropylene 40.9% Polyethylene 36.4% Polystyrene 0.0%
32.2% 55.9% 6.8%
34.6% 45.5% 5.5%
Color composition Transparent White Black Colorful
– – – –
6.90% 71.90% 2.70% 18.50%
47.92% 20.83% 0 31.25%
and floats and are employed extensively in the marine environment. This should be relevant to the commercial vessels in the port of Jiaozhou Bay. 4.2. Seasonal variation of micro- and meso-plastics in the seawater of Jiaozhou Bay 4.2.1. Seasonal change in the plastic concentration The distributions of micro- and meso-plastics in May and August are approximately twice as high as those in February and November. The
Fig. 6. The color and chemical composition of micro- and meso-plastic in Jiaozhou Bay. 6
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distribution of plastics in the ocean is mainly influenced by input of land sources, and the river affects the distribution of plastics in the seawater indirectly by affecting the flow of the seawater (Galgani et al., 2000). As mentioned above, the rivers around Jiaozhou Bay are mainly seasonal rivers, and the runoff is highly dependent on rainfall. The main reason for the higher plastic concentration in May and August is the larger runoff of rivers, resulting in the increased input of micro- and meso-plastics to Jiaozhou Bay. August is usually the flood season in Jiaozhou Bay; however, there was strong rainfall in May in the sampling year. According to the precipitation data of Jiaozhou Bay, before and during the plastic collection, there was precipitation in May and August but no precipitation in February and November. The plastic concentration was positively correlated with the cumulative rainfall amount during and before the sampling period (Pearson, p < 0.05). The highest daily precipitation was 13.6 mm in May, and the associated runoff from the land to the sea resulted in the increased amount of plastic. Similar changes were also found in other areas. The amount of microplastics detected in the sediments of the coast and the Ria of Campeche, Mexico, varied significantly among sites (p = 0.001) and seasons (p = 0.001), with the greatest amount of microplastics detected during the rainy season (Ramirez et al., 2019). Hitchcock and Mitrovic (2019) reported a year-long study on the abundance of microplastics in the water column of three estuaries on the east coast of Australia. Microplastic abundance was positively related to the maximum antecedent rainfall in the Bega estuary. Microplastics were generally highest in summer and following freshwater inflow events. Based on a study on the seasonal dynamics of marine litter along the Bulgarian Black Sea coast, the seasonal dynamics showed higher quantities in summer than in the other seasons (Simeonova et al., 2017). Cheung et al. (2016) sampled plastic debris at 25 beaches during the wet and dry seasons and found significant seasonal variations in both large debris and microplastics, suggesting that the marine debris in estuaries is largely controlled by fluvial inputs. In addition to rainfall, the peak tourist season in Qingdao occurs during spring and summer, resulting in an increase in the usage of plastic items, which may further increase the amount of plastic transported into the ocean.
Bay. The seasonal variation of plastics in Jiaozhou Bay indicated that meteorological and physical processes such as rainfall, wind and eddies have an important influence on the concentration and distribution pattern of marine surface plastics. CRediT authorship contribution statement Tao Liu: Writing - original draft, Investigation. Yongfang Zhao: Data curation, Formal analysis, Visualization. Mingliang Zhu: Investigation. Junhua Liang: Investigation. Shan Zheng: Investigation. Xiaoxia Sun: Writing - review & editing, Supervision, Funding acquisition, Project administration. 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 work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA23050303, No. XDA19060204) and the Project from Shandong Academy for Environmental Planning: Research on the Prevention and Control of Marine Microplastic Pollution in Key Industries in Shandong Province. References Aliabada, M.K., Nassiria, M., Korb, K., 2019. Microplastics in the surface seawaters of Chabahar Bay, Gulf of Oman(Makran Coasts). Mar. Pollut. Bull. 143, 125–133. https://doi.org/10.1016/j.marpolbul.2019.04.037. Andrady, A.L., 2011. Microplastics in the marine environment. Mar. Pollut. Bull. 62 (8), 1596–1605. https://doi.org/10.1016/j.marpolbul.2011.05.030. Avio, C.G., Gorbi, S., Regoli, F., 2017. Plastics and microplastics in the oceans: from emerging pollutants to emerged threat. Mar. Environ. Res. 128, 2–11. https://doi. org/10.1016/j.marenvres.2016.05.012. Barnes, D.K.A., Galgani, F., Thompson, R.C., Barlaz, M., 2009. Accumulation and fragmentation of plastic debris in global environments. Philos. Trans. R. Soc. B 364, 1985–1998. https://doi.org/10.1098/rstb.2008.0205. Botterell, Z.L.R., Beaumont, N., Dorrington, T., Steinke, M., Thompson, R.C., Lindeque, P.K., 2019. Bioavailability and effects of microplastics on marine zooplankton: a review. Environ. Pollut. 245, 98–110. https://doi.org/10.1016/j.envpol.2018.10. 065. Browne, M.A., Galloway, T.S., Thompson, R.C., 2010. Spatial patterns of plastic debris along estuarine shorelines. Environ. Sci. Technol. 44, 3404–3409. https://doi.org/10. 1021/es903784e. Cheung, P.K., Cheung, L.T.O., Fok, L., 2016. Seasonal variation in the abundance of marine plastic debris in the estuary of a subtropical macro-scale drainage basin in South China. Sci. Total Environ. 562, 658–665. https://doi.org/10.1016/j.scitotenv. 2016.04.048. Desforges, J.P.W., Galbraith, M., Dangerfield, N., Ross, P.S., 2014. Widespread distribution of microplastics in subsurface seawater in the NE Pacific Ocean. Mar. Pollut. Bull. 79, 94–99. https://doi.org/10.1016/j.marpolbul.2013.12.035. Frere, L., Paul-Pont, I., Rinnert, E., et al., 2017. Influence of environmental and anthropogenic factors on the composition, concentration and spatial distribution of microplastics: a case study of the Bay of Brest (Brittany, France). Environ. Pollut. 225, 211–222. https://doi.org/10.1016/j.envpol.2017.03.023. Galgani, F., Leaute, J.P., Moguedet, P., Souplet, A., Verin, Y., Carpentier, A., Goraguer, H., Latrouite, D., Andral, B., Cadiou, Y., Mahe, J.C., Poulard, J.C., Nerisson, P., 2000. Litter on the sea floor along European coasts. Mar. Pollut. Bull. 40 (6), 516–527. https://doi.org/10.1016/S0025-326X(99)00234-9. GESAMP, 2015. Sources, fate and effects of microplastics in the marine environment: a global assessment. In: GESAMP Rep. Stud. No. 90, (96 pp.). Hitchcock, J.N., Mitrovic, S.M., 2019. Microplastic pollution in estuaries across a gradient of human impact. Environ. Pollut. 247, 457–466. https://doi.org/10.1016/j.envpol. 2019.01.069. Kor, K., Mehdinia, A., 2020. Neustonic microplastic pollution in the Persian Gulf. Mar. Pollut. Bull. 150, 110665. https://doi.org/10.1016/j.marpolbul.2019.110665. Liu, T., Sun, X.X., Zhu, M.L., Liang, J.H., Zhao, Y.Y., 2018. Distribution and composition of microplastics in the surface water of the East China Sea. Oceanol. Limnol. Sin. 49 (1), 62–69. https://doi.org/10.11693/hyhz20170100021. Lu, X.G., Zhao, C., Xia, C.S., Qiao, F.L., 2010. Numerical study of water exchange in the Jiaozhou Bay and the tidal residual currents near the bay mouth. Acta Oceanol. Sin. 32 (2), 20–30. https://doi.org/10.3788/HPLPB20102209.2186. McEachern, K., Alegria, H., Kalagherb, A.L., et al., 2019. Microplastics in Tampa Bay, Florida: abundance and variability in estuarinewaters and sediments. Mar. Pollut.
4.2.2. Seasonal change in the spatial distribution of plastics According to Fig. 2, the distribution of plastics in spring and autumn is relatively uniform, but the plastics in winter and summer are mainly concentrated in the bay mouth. The distribution of plastics in the ocean is influenced by the nature and location of the source of entry, as well as the subsequent complex interactions of physical, chemical and biological processes (GESAMP, 2015). Plastics are susceptible to physical processes such as eddies and wind. Due to the influence of the complex terrain of the bay mouth and region north of the mouth, there are vortices around the mouth of Jiaozhou Bay. Microplastics tend to stay inside eddies, so the presence of eddies forms regions of high microplastic concentrations (Zheng et al., 2019). This should be the main reason for the presence of plastic high-value areas in the western part of the bay near the bay mouth in February and August. The distribution of plastics in May and November was relatively uniform, mainly due to the presence of high-speed winds before sampling. In this study, the plastics collected were larger than microplastics. Larger floating objects will be more prone to transport by winds than microplastics (Browne et al., 2010; GESAMP, 2017). According to the wind speed and wind direction data three days before plastic sampling, the maximum wind speed was higher than 12 m/s in the first three days of sampling in May, and the daily average wind speed was above 7 m/s. Regarding wind direction, there were northwest winds during this period. The wind speed was higher than 11 m/s in November, and the daily average wind speed was close to 5 m/s. There were south-southwest winds, which blew the plastics from the eddy convergence zone to the eastern and northern regions, respectively, resulting in a relatively even distribution of plastics in Jiaozhou 7
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and zooplankton from the Yellow Sea. Environ. Pollut. 242, 585–595. https://doi. org/10.1016/j.envpol.2018.07.014. Sun, X.X., Liu, T., Zhu, M.L., Liang, J.H., Zhao, Y.F., Zhang, B., 2018b. Retention and characteristics of microplastics in natural zooplankton taxa from the East China Sea. Sci. Total Environ. 640, 232–242. https://doi.org/10.1016/j.scitotenv.2018.05.308. Wang, X.L., Li, K.Q., Shi, X.Y., 2006. Marine Environmental Capacity of Main Chemical Pollutant in Jiaozhou Bay. Beijing Science Press. Woodall, L.C., Sanchez-Vidal, A., Canals, M., Paterson, G.L.J., Coppock, R., Sleight, V., Calafat, A., Rogers, A.D., Narayanaswamy, B.E., Thompson, R.C., 2014. The deep sea is a major sink for microplastic debris. R. Soc. Open Sci. 1 (4), 140317. https://doi. org/10.1098/rsos.140317. Zhang, W.W., Zhang, S.F., Wang, J.Y., Wang, Y., Mu, J.L., Wang, P., Lin, X.Z., Ma, D.Y., 2017. Microplastic pollution in the surface waters of the Bohai Sea, China. Environ. Pollut. 231, 541–548. https://doi.org/10.1016/j.envpol.2017.08.058. Zhao, S.Y., Zhu, L.X., Wang, T., Li, D.J., 2014. Suspended microplastics in the surface water of the Yangtze Estuary System, China: first observations on occurrence, distribution. Mar. Pollut. Bull. 86, 562–568. https://doi.org/10.1016/j.marpolbul.2014. 06.032. Zheng, Y.F., Li, J.X., Cao, W., Liu, X.H., Jiang, F.H., Ding, J.F., Yin, X.F., Sun, C.J., 2019. Distribution characteristics of microplastics in the seawater and sediment: a case study in Jiaozhou Bay, China. Sci. Total Environ. 674, 27–35. https://doi.org/10. 1016/j.scitotenv.2019.04.008.
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