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Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution
Marine Pollution Bulletin xxx (2014) xxx–xxx
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Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution Shiye Zhao, Lixin Zhu, Teng Wang, Daoji Li ⇑ State Key Laboratory of Estuarine and Costal Research, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, China
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Suspended microplastic Yangtze Estuary East China Sea Marine debris
a b s t r a c t Levels of microplastics (MPs) in China are completely unknown. This study characterizes suspended MPs quantitatively and qualitatively for the Yangtze Estuary and East China Sea. MPs were extracted via a floatation method. MPs were counted and categorized according to shape and size under a stereomicroscope. The MP densities were 4137.3 ± 2461.5 and 0.167 ± 0.138 n/m3, respectively, in the estuarine and the sea samples. Plastic abundances varied significantly in the estuary. Higher densities in three sea trawls confirmed that rivers were the important sources of MP to the marine environment. Plastic particles (>5 mm) were observed with a maximum size of 12.46 mm, but MPs (0.5–5 mm) constituted more than 90% by number of items. The most frequent geometries were fibres, followed by granules and films. Plastic spherules occurred sparsely. Transparent and coloured plastics comprised the majority of the particles. This study provides clues in understanding the fate and potential sources of MPs. Ó 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Annual global production of plastic products has increased dramatically from 1.5 million tons in the 1950s to more than 250 million tons in 2011 (Wright et al., 2013). Mass production leads to plastic accumulation in terrestrial and aquatic habitats (Ryan et al., 2009; Thompson et al., 2004), and plastics make up the largest segment of marine litter worldwide (Cole et al., 2011). As a major contaminant, marine plastic not only threatens the safety of maritime activities but also the health of the ecosystem (Maximenko et al., 2012). In recent years, small-sized plastic debris termed microplastic (MP, fragments less than 5 mm) (Moore, 2008) has been reported as a ubiquitous marine litter. Occupying the size range of plankton, MP is available to a wide range of marine organisms (Lusher et al., 2012). Laboratory and field investigations showed that crustaceans, barnacles, lugworms, mussels, fishes and seals can ingest particles of MP (Boerger et al., 2010; Browne et al., 2008; Cole et al., 2013; Jantz et al., 2013; Murray and Cowie, 2011; Thompson et al., 2004). Ingested MP may result in physical harm within organisms, such as by internal abrasions and blockages. Besides the physical impact, toxicity could also arise from the leaching of plastic additives and POPs that are then absorbed from ambient seawater (Andrady, 2011; Wright et al., 2013).
⇑ Corresponding author. Tel.: +86 21 62237355; fax: +86 21 62546441. E-mail addresses: [email protected], [email protected] (D. Li).
MPs which enter the marine environment can be of primary (e.g., pellets and abrasive scrubbers used in cosmetics and granules used for air blasting) (Fendall and Sewell, 2009; Thompson et al., 2009) or secondary (breakdown of larger plastic items) origin (Wright et al., 2013). The occurrences of MP have been reported in different marine environments such as beaches, surface waters, water columns, benthic zones and shorelines (Hidalgo-Ruz et al., 2012). Plastics enter the marine environment mostly from landbased sources, often via estuaries (Ivar do Sul and Costa, 2013a). Industrial coastal marine environments and especially estuarine systems have been identified as MP hotspots (Browne et al., 2011; Wright et al., 2013); concentrations of MPs reached 100,000 particles m3 of seawater in a Swedish harbor area (Norén and Naustvoll, 2010). In terms of abundance, MPs accounted for 65% of debris recorded within the Tamar Estuary, UK (Browne et al., 2010). As the most important industrial and economic center for China, the region of the Yangtze Estuary is densely populated. Browne et al. (2011) demonstrated that there was a significant relationship between MP abundance and human population density. Due to dense population concentration, river discharge and various maritime activities, the Yangtze Estuary is vulnerable to plastic accumulation. Nevertheless, MPs in the Yangtze Estuary System are almost completely lacking. The objective of the present investigation was to examine the occurrence and distribution of MPs in surface water of the Yangtze Estuary and the adjacent East China Sea (ECS).
http://dx.doi.org/10.1016/j.marpolbul.2014.06.032 0025-326X/Ó 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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S. Zhao et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
The study was carried out in the Yangtze Estuary and the coastal water of the East China Sea (Fig. 1). The 7 samplings in the Yangtze Estuary were conducted from July 22 to 23, 2013 during the same low tide (Table 1). Fifteen neustonic trawls were collected from August 4 to 9, 2013 in the coastal water of the East China Sea. Depending on its distance from the shore, the designed sampling trawls were divided along five transects (B, C, D, E and F) and into 3 departments: trawls closest to the shore (TCS), trawls intermediate distance to the shore (TIS) and trawls farthest to shore (TFS) (Table 2). Surface water samples were collected from each location in the Yangtze Estuary using a 12 V DC Teflon pump at a depth of 1 m (Table 1). Two replicate samples were passed through a 32-lm steel sieve. The retained particulate material was washed into 50 mL glass bottles. The samples in the East China Sea were collected using a neuston net with a 30 40 cm2 opening and 333 lm mesh (Ryan et al., 2009) (Table 2). The net was towed along the surface layer at a nominal 2.0 knots (1.75–2.45 knots) for 25–30 min in each transect and towed off the port side of the vessel to avoid disturbance by the bow wave. Contents of the net were washed into a sample jar and fixed in 2.5% formalin (Lattin et al., 2004). In the laboratory, samples containing large quantities of organic matter were oxidatively cleaned using 30% H2O2 (Nuelle et al., 2014). Plastic particles were separated from organic matter by floating in a saturated zinc chloride solution (Liebezeit and Dubaish, 2012). The floating MP particles were filtered over gridded 1.2 lm cellulose nitrate filters. The MPs were enumerated under a dissecting microscope at up to 80 magnification. To avoid misidentification of MPs, we used the criteria applied to define a plastic particle in previous studies (Mohamed Nor and Obbard, 2014; Norén, 2007). Nevertheless, these selection criteria are considered applicable only for MP particles within the size range 0.5– 5 mm (Costa et al., 2010; Hidalgo-Ruz et al., 2012). Thus the MP particles with the same range size (>0.5 mm) were enumerated in this study. To avoid airborne contamination, the preventive measures used by Nuelle et al. (2014) were taken in the present study.
Table 1 List of the seven sampling sites in the Yangtze Estuary. Station Y1 Y2 Y3 Y4 Y5 D1 D2
Longitude (N) 0
31°41.724 31°47.0040 31°30.8460 31°20.8980 31°08.7780 31°000 31°000
Latitude (E) 0
121°10.56 120°56.760 121°26.460 121°39.480 121°55.080 122°150 122°300
Volume of water filtered (L) 20 20 20 20 12 12 12
Plastic items were widely distributed in the study areas. The average density of MP in the Yangtze Estuary was 4137.3 ± 2461.5 n/m3 with a range from 500 to 10,200 n/m3 (Table 3). Compared to the 32 lm mesh in the Yangtze Estuary, 80 lm meshes were used in the Jade system which may underestimate the plastic particle concentration (Dubaish and Liebezeit, 2013). However, the densities reported here are considerably lower than that in the Jade system (6.4 104 ± 1.94 104 n/m3 for granular particles and 8.8 104 ± 8.2 104 n/m3 for fibres). This may be due to two main factors. First, higher river flows in the rainy season from May to October might result in decreases in these pelagic MP items (Ivar do Sul and Costa, 2013a; Williams and Simmons, 1999). The estuarine sampling was after a three-day rain event. Consequently, a significant amount of plastic debris retained in the estuary might have been washed out to the sea. Secondly, the limited water volume filtered may contribute to the low particle density. The MP distributed heterogeneously in the water body (Dubaish and Liebezeit, 2013). Small sampling volumes may miss debris present in the estuary. Variability in the density of particles were apparent in the estuarine samples (Kruskal–Wallis test, p = 0.013 < 0.05). The maximum density value (8550 ± 1788 n/m3) was obtained at the Y1 site (Xuliujing) where the discharge could be considered the total discharge into the estuary (Chen et al., 2013). Y3, Y4 and Y5 had intermediate densities that were added by plastic particles from the Yangtze tributaries (Fig. 2). The results agreed that
Fig. 1. Research area in the Yangtze estuarine system with the sampling sites and trawl stations for microplastic.
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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S. Zhao et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx Table 2 Sampling trawls in the East China Sea (TCS: trawls closest to the shore, TIS: trawls intermediate distance to the shore, TFS: trawls farthest to shore). Transect
Department
Trawl
Starting point 0
Water filtered (m3)
Ending point 0
0
0
B
TCS TIS TFS
B1 B2 B3
122°14.980 W 32°00.373 N 122°45.3180 W 31°59.9450 N 123°06.8530 W 31°59.0060 N
122°16.757 W 32°00.698 N 122°48.4580 W 31°59.5140 N 123°08.3480 W 31°59.1680 N
130.57 111.12 108.34
C
TCS TIS TFS
C1 C2 C3
122°18.7450 W 31°29.3110 N 122°51.9620 W 31° 30.7050 N 123°15.7710 W 31° 30.5860 N
122°17.5300 W 31° 29.0570 N 122°50.2070 W 31° 30.4980 N 123°14.0120 W 31° 30.4600 N
144.46 136.12 181.50
D
TCS TIS TFS
D1 D2 D3
122°16.5040 W 30° 59.1380 N 122°43.9060 W 30° 59.6690 N 123°10.4490 W 30° 59.0580 N
122°19.1670 W 30° 59.0890 N 122°46.5750 W 30° 59.4220 N 123°12.4730 W 30° 59.0510 N
129.64 194.46 200.02
E
TCS TIS TFS
E1 E2 E3
122°18.5690 W 30° 30.4750 N 122°51.7430 W 30° 30.3720 N 123°14.4720 W 30° 30.2650 N
122°17.7360 W 30° 30.5250 N 122°50.1370 W 30° 30.4590 N 123°13.4770 W 30° 30.6510 N
66.67 200.02 211.13
F
TCS TIS TFS
F1 F2 F3
122°29.9020 W 29° 59.6890 N 122°44.9080 W 29° 59.8570 N 123°14.4670 W 30° 00.5850 N
122°29.1200 W 29° 59.8410 N 122°44.3060 W 29° 59.7040 N 123°14.2010 W 30° 00.8760 N
175.94 185.20 194.46
Table 3 Composition of suspended microplastics in Yangtze estuarine and coastal waters (ECS: the East China Sea). Categories
Fibres Films Granules Spherules Total Density Calibrated density Minimum Maximum
Yangtze Estuary
Coastal waters of ECS
No. item
%
No. item
%
1178 135 173 3 1489 4137.3 ± 2461.5 n/m3 2984.7 ± 2219.3 n/m3 500 n/m3 10,200 n/m3
79.1 9.1 11.6 0.2 375
312 8 55 0
83.2 2.1 14.7 0
0.167 ± 0.138 n/m3 0.030 n/m3 0.455 n/m3
the presence of rivers with catchments draining populated areas increased quantities of MPs (Claessens et al., 2011; Santos et al., 2005). Overall, our results indicated a mass of plastic items flowed through those sampling sites and entered the coastal waters. The mean MP density (0.167 ± 0.138 n/m3) in the ECS had the same order of magnitude as the density found for the Northwestern Mediterranean (0.116 n/m3, Collignon et al., 2012). Nevertheless, the density was lower than those reported in the North Pacific Central Gyre (2.23 n/m3, Moore et al., 2001), the Southern California coastal waters (7.25 n/m3, Moore et al., 2002) and the Santa Monica Bay of Southern California (3.92 n/m3, Lattin et al., 2004). The probable reasons are complicated. Plastic particle load seems to be low in those productive coastal ecosystems which involve more organisms than in the less productive ocean ecosystems (Doyle et al., 2011; Gilfillan et al., 2009). Different criteria for size classes also had impacts on the density. Comparing the size ranges used in other studies (Table 5), the MP size range (>0.5 mm) utilized in this study resulted in a loss of plastic particles enumerated. Another reason may be the wind. Based on a one-dimension model, surface trawl cannot elucidate the total amount of plastic content in the surface water column when the wind speed l10 (wind velocity at height 10 m above the sea surface) is larger than 5 m/s. The wind-driven mixing distributes the plastic items throughout the upper water column (Kukulka et al., 2012). The mean l10 was 5.2 m/s during the sea surface sampling with a range of 1.5–9.7 m/s (unpublished data), and as a consequence the abundance of plastic debris in the ECS surface waters may be underestimated by the surface trawl sampling method. Another potential cause is that the Southern California coastal area may have plastic debris inputted by the southerly flowing California current which is the eastern current of the North Pacific Central
Fig. 2. Means and standard errors of density of microplastics in the (A) Yangtze Estuary (n/m3), (B) trawls in the East China Sea (ESC, n/m3) and (C) transects in the ESC (n/m3). The letters (a, b and c) indicate the results of the nonparametric Kruskal–Wallis test and Mann–Whitney U test. Bars with the same letter indicate no significant difference. (TCS: trawls closest to the shore, TIS: trawls intermediate distance to the shore, TFS: trawls farthest to shore).
Gyre known for its high levels of plastic debris (Doyle et al., 2011; Pichel et al., 2007). No significant difference was found between the three sectors (TCS, TIS and TFS) (Kruskal–Wallis test, p = 0.454 > 0.05). This widespread pattern of MPs is consistent with the tendency for the size distribution of MPs to be skewed towards abundant small particles (Browne et al., 2011; Goldstein et al., 2013). Smaller particles with a longer residence time would be dispersed greatly by ocean circulation (Doyle et al., 2011). Surprisingly, the density of
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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Table 4 Distribution of total plastic abundance (items) per sampling site for each size class (mm). Study area
Site/trawl >0.5–1 mm >1–2.5 mm
>2.5–5 mm >5 mm
Y1 Y2 Y3 Y4 Y5 D1 D2
Yangtze Estuary
Percentage (%)
100 34 46 42 63 14 13
144 49 99 46 48 17 20
22 10 6 4 10 8 6
1 0 0 0 0 0 1
67.0
28.4
4.4
0.2
16 7 8 16 10 17 3 3 5 8 3 5 10 8 14
5 5 1 23 21 23 7 2 4 2 0 4 10 2 3
0 0 1 18 11 14 36 1 5 0 3 3 2 2 1
1 0 2 4 9 8 1 2 3 0 0 3 0 0 0
35.4
29.9
25.9
8.8
Coastal waters B1 B2 B3 C1 C2 C3 D1 D2 D3 E1 E2 E3 F1 F2 F3 Percentage (%)
the C transect was significantly higher than any of the other transects (Kruskal–Wallis test, p = 0.029 < 0.05; Mann–Whitney U test, all p < 0.05) (Fig. 2). Directly facing the south branch of the Yangtze Estuary, the C transect was subject to more influences of riverine discharge. This finding confirmed that rivers have a huge effect on MP abundance in the marine environment (Barnes et al., 2009; Claessens et al., 2011). Due to the non-standard sampling mesh sizes used in the two study areas, we calibrated the density of fibrous MPs in the Yangtze Estuary with 333 lm mesh-sieves (Supplementary Information, SI). Compared with the calibrated density value in the Yangtze Estuary, the lower abundance of the ECS was mainly attributed to the oceanic dilution (Mann–Whitney U test, all p < 0.05). Simultaneously, the disparity between the original (4137.3 ± 2461.5 n/m3) and calibrated (2984.7 ± 2219.3 n/m3) MP densities in the Yangtze Estuary suggests that the employment of smaller mesh sizes is more beneficial to the monitoring the MPs in the water bodies. MPs were classified into four size categories: >0.5–1 mm, >1–2.5 mm, >2.5–5 mm and >5 mm. In both two research areas, plastics (<5 mm) comprised more than 90% of total abundance (Table 4). The average MP size in the Yangtze Estuary and East China Sea were 0.90 ± 0.74 mm (range: 0.51–6.29 mm) and 2.01 ± 2.01 mm (range: 0.5–12.46 mm), respectively. Smaller plastic fragments have been classified either as large MP (L-MPP, 1–5 mm) or small MP particles (S-MPP, 61 mm) (Imhof et al., 2012). S-MMP in the Yangtze Estuary and East China Sea accounted for 67.0% and 35.4%, respectively. Our findings implied that the
abundance of plastic items increased with the decreasing size of such items (Barnes et al., 2009; Doyle et al., 2011). These plastic fragments constitute a frequently reported size inventory in many ingestion studies (Eriksson and Burton, 2003; Foekema et al., 2013; Graham and Thompson, 2009). The size range of MP determines the potential impact of these contaminants on ecosystem biota (Mohamed Nor and Obbard, 2014). Dominance of smaller particles increases the risks related to encounter frequency. SMPPs were easily found in filter feeders in contrast to L-MPPs which were found frequently in carnivorous taxa (Foekema et al., 2013). The two research areas shared a similar composition of MP types. According to their shape, MP particles were categorized into four types: fibres, granules, plastic films and spherules. The fibres were the most common type, followed by granules and films. Spherules were the least common type (Table 3). The similar share of MP types in the Yangtze Estuary and East China Sea indicated a possible MP flux from the river to the adjacent sea. Fibrous MPs seems to be most abundant in the marine environment (Wright et al., 2013). Being adjacent to the most highly populated region, the study areas are bound to accept large amounts of land-based debris. This is in accordance with Browne et al. (2011) who suggested that the majority of MP fibres found in the marine environment may be derived from sewage as a consequence of laundering clothes. On the other hand, the fibres may derive from rope material. Heavy marine traffic and fishery activities in the study areas brought more discarded rope material (Andrady, 2011; Thompson et al., 2004). Lacking identification of the polymer types, further speculation on the origins of plastic particles cannot be made. The potential negative impacts of plastic particles ingested were proved to be associated with various particle shapes (Wright et al., 2013). If ingested, organisms inhabiting the study areas are vulnerable to the shape-related toxicity of fibrous MPs. Strikingly, spherules were rarely found in our study while commonly existing in water column samples (Moore et al., 2001; Law et al., 2010). A decrease in spherules may suggest that industry initiatives have been useful in reducing the loss of pellets into the environment during transportation. Similar results have been reported in two other studies (Ivar do Sul et al., 2013b; Ryan, 2008). Transparent and coloured MPs were the majority of plastic items, with small fractions of white and black plastic items (Fig. 3). Prominence of transparent and coloured MP corresponds to the prevalence of clear plastics used in the plastic products, such as packaging, clothing and fishing line (Cole et al., 2014). The colours may potentially contribute to the likelihood of MP ingestion due to food resemblance, the prevalence of plastics with these colours in the environment and an actual colour preference by the biota (Costa et al., 2010; Shaw and Day, 1994; Verlis et al., 2013; Wright et al., 2013). Typical examples of MP material encountered in this study are given in Fig. 4. China has been considered as one of the three biggest producers of plastic waste (Rochman et al., 2013). Understanding the properties and distribution of plastics is useful in considering how MP impacts the social economy, what influence the items have on the marine ecosystem and how to target management. Our study
Table 5 Comparison between this study and other studies that used the 333 lm mesh size for sampling suspended microplastics. Study area
Size class (mm)
Mean plastic items (n/m3)
References
North Pacific Central Gyre Southern California coastal waters Santa Monica Bay Northwestern Mediterranean East China Sea
>0.35 >0.35 >0.35 0.333–5 >0.5
2.23 7.25 3.92 0.116 0.167
Moore et al. (2001) Moore et al. (2002) Lattin et al. (2004) Collignon et al. (2012) This study
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
S. Zhao et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
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Fig. 3. Composition of coloured microplastic sampled in the (a) Yangtze Estuary and (b) East China Sea.
Fig. 4. (a) Fibres of different colors (c) coloured granule and (f) transparent film from the Yangtze Estuary, sampling site Y1; (b) blue fibre, (d) green and (e) yellow fragments from the East China Sea, B transect, TCS (trawls closest to the shore). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
provides a baseline of MP contamination in the Yangtze Estuarine system, as well as the first quantitative description of MP debris in China. The size, abundance and characters of floating MPs
(0.5–5 mm) were established in the Yangtze Estuarine System. The unique design of spatial scales provides good insights into MP source and fate. Further research is planned to assess
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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distribution of MP transported via estuaries in differing marine environments and the probable transfer of MP in the food chain. Acknowledgements We thank the editor and the anonymous reviewers for their useful comments on the manuscript. This paper was funded by the Ministry of Science and Technology of China (2010CB951203), the Natural Science Foundation of Shanghai Municipality (11ZR1438800) and the State Key Laboratory of Estuarine and Coastal Research of China (200KYYW03). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.marpolbul.2014. 06.032.
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Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution Shiye Zhao, Lixin Zhu, Teng Wang, Daoji Li ⇑ State Key Laboratory of Estuarine and Costal Research, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, China
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Suspended microplastic Yangtze Estuary East China Sea Marine debris
a b s t r a c t Levels of microplastics (MPs) in China are completely unknown. This study characterizes suspended MPs quantitatively and qualitatively for the Yangtze Estuary and East China Sea. MPs were extracted via a floatation method. MPs were counted and categorized according to shape and size under a stereomicroscope. The MP densities were 4137.3 ± 2461.5 and 0.167 ± 0.138 n/m3, respectively, in the estuarine and the sea samples. Plastic abundances varied significantly in the estuary. Higher densities in three sea trawls confirmed that rivers were the important sources of MP to the marine environment. Plastic particles (>5 mm) were observed with a maximum size of 12.46 mm, but MPs (0.5–5 mm) constituted more than 90% by number of items. The most frequent geometries were fibres, followed by granules and films. Plastic spherules occurred sparsely. Transparent and coloured plastics comprised the majority of the particles. This study provides clues in understanding the fate and potential sources of MPs. Ó 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Annual global production of plastic products has increased dramatically from 1.5 million tons in the 1950s to more than 250 million tons in 2011 (Wright et al., 2013). Mass production leads to plastic accumulation in terrestrial and aquatic habitats (Ryan et al., 2009; Thompson et al., 2004), and plastics make up the largest segment of marine litter worldwide (Cole et al., 2011). As a major contaminant, marine plastic not only threatens the safety of maritime activities but also the health of the ecosystem (Maximenko et al., 2012). In recent years, small-sized plastic debris termed microplastic (MP, fragments less than 5 mm) (Moore, 2008) has been reported as a ubiquitous marine litter. Occupying the size range of plankton, MP is available to a wide range of marine organisms (Lusher et al., 2012). Laboratory and field investigations showed that crustaceans, barnacles, lugworms, mussels, fishes and seals can ingest particles of MP (Boerger et al., 2010; Browne et al., 2008; Cole et al., 2013; Jantz et al., 2013; Murray and Cowie, 2011; Thompson et al., 2004). Ingested MP may result in physical harm within organisms, such as by internal abrasions and blockages. Besides the physical impact, toxicity could also arise from the leaching of plastic additives and POPs that are then absorbed from ambient seawater (Andrady, 2011; Wright et al., 2013).
⇑ Corresponding author. Tel.: +86 21 62237355; fax: +86 21 62546441. E-mail addresses: [email protected], [email protected] (D. Li).
MPs which enter the marine environment can be of primary (e.g., pellets and abrasive scrubbers used in cosmetics and granules used for air blasting) (Fendall and Sewell, 2009; Thompson et al., 2009) or secondary (breakdown of larger plastic items) origin (Wright et al., 2013). The occurrences of MP have been reported in different marine environments such as beaches, surface waters, water columns, benthic zones and shorelines (Hidalgo-Ruz et al., 2012). Plastics enter the marine environment mostly from landbased sources, often via estuaries (Ivar do Sul and Costa, 2013a). Industrial coastal marine environments and especially estuarine systems have been identified as MP hotspots (Browne et al., 2011; Wright et al., 2013); concentrations of MPs reached 100,000 particles m3 of seawater in a Swedish harbor area (Norén and Naustvoll, 2010). In terms of abundance, MPs accounted for 65% of debris recorded within the Tamar Estuary, UK (Browne et al., 2010). As the most important industrial and economic center for China, the region of the Yangtze Estuary is densely populated. Browne et al. (2011) demonstrated that there was a significant relationship between MP abundance and human population density. Due to dense population concentration, river discharge and various maritime activities, the Yangtze Estuary is vulnerable to plastic accumulation. Nevertheless, MPs in the Yangtze Estuary System are almost completely lacking. The objective of the present investigation was to examine the occurrence and distribution of MPs in surface water of the Yangtze Estuary and the adjacent East China Sea (ECS).
http://dx.doi.org/10.1016/j.marpolbul.2014.06.032 0025-326X/Ó 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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S. Zhao et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
The study was carried out in the Yangtze Estuary and the coastal water of the East China Sea (Fig. 1). The 7 samplings in the Yangtze Estuary were conducted from July 22 to 23, 2013 during the same low tide (Table 1). Fifteen neustonic trawls were collected from August 4 to 9, 2013 in the coastal water of the East China Sea. Depending on its distance from the shore, the designed sampling trawls were divided along five transects (B, C, D, E and F) and into 3 departments: trawls closest to the shore (TCS), trawls intermediate distance to the shore (TIS) and trawls farthest to shore (TFS) (Table 2). Surface water samples were collected from each location in the Yangtze Estuary using a 12 V DC Teflon pump at a depth of 1 m (Table 1). Two replicate samples were passed through a 32-lm steel sieve. The retained particulate material was washed into 50 mL glass bottles. The samples in the East China Sea were collected using a neuston net with a 30 40 cm2 opening and 333 lm mesh (Ryan et al., 2009) (Table 2). The net was towed along the surface layer at a nominal 2.0 knots (1.75–2.45 knots) for 25–30 min in each transect and towed off the port side of the vessel to avoid disturbance by the bow wave. Contents of the net were washed into a sample jar and fixed in 2.5% formalin (Lattin et al., 2004). In the laboratory, samples containing large quantities of organic matter were oxidatively cleaned using 30% H2O2 (Nuelle et al., 2014). Plastic particles were separated from organic matter by floating in a saturated zinc chloride solution (Liebezeit and Dubaish, 2012). The floating MP particles were filtered over gridded 1.2 lm cellulose nitrate filters. The MPs were enumerated under a dissecting microscope at up to 80 magnification. To avoid misidentification of MPs, we used the criteria applied to define a plastic particle in previous studies (Mohamed Nor and Obbard, 2014; Norén, 2007). Nevertheless, these selection criteria are considered applicable only for MP particles within the size range 0.5– 5 mm (Costa et al., 2010; Hidalgo-Ruz et al., 2012). Thus the MP particles with the same range size (>0.5 mm) were enumerated in this study. To avoid airborne contamination, the preventive measures used by Nuelle et al. (2014) were taken in the present study.
Table 1 List of the seven sampling sites in the Yangtze Estuary. Station Y1 Y2 Y3 Y4 Y5 D1 D2
Longitude (N) 0
31°41.724 31°47.0040 31°30.8460 31°20.8980 31°08.7780 31°000 31°000
Latitude (E) 0
121°10.56 120°56.760 121°26.460 121°39.480 121°55.080 122°150 122°300
Volume of water filtered (L) 20 20 20 20 12 12 12
Plastic items were widely distributed in the study areas. The average density of MP in the Yangtze Estuary was 4137.3 ± 2461.5 n/m3 with a range from 500 to 10,200 n/m3 (Table 3). Compared to the 32 lm mesh in the Yangtze Estuary, 80 lm meshes were used in the Jade system which may underestimate the plastic particle concentration (Dubaish and Liebezeit, 2013). However, the densities reported here are considerably lower than that in the Jade system (6.4 104 ± 1.94 104 n/m3 for granular particles and 8.8 104 ± 8.2 104 n/m3 for fibres). This may be due to two main factors. First, higher river flows in the rainy season from May to October might result in decreases in these pelagic MP items (Ivar do Sul and Costa, 2013a; Williams and Simmons, 1999). The estuarine sampling was after a three-day rain event. Consequently, a significant amount of plastic debris retained in the estuary might have been washed out to the sea. Secondly, the limited water volume filtered may contribute to the low particle density. The MP distributed heterogeneously in the water body (Dubaish and Liebezeit, 2013). Small sampling volumes may miss debris present in the estuary. Variability in the density of particles were apparent in the estuarine samples (Kruskal–Wallis test, p = 0.013 < 0.05). The maximum density value (8550 ± 1788 n/m3) was obtained at the Y1 site (Xuliujing) where the discharge could be considered the total discharge into the estuary (Chen et al., 2013). Y3, Y4 and Y5 had intermediate densities that were added by plastic particles from the Yangtze tributaries (Fig. 2). The results agreed that
Fig. 1. Research area in the Yangtze estuarine system with the sampling sites and trawl stations for microplastic.
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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S. Zhao et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx Table 2 Sampling trawls in the East China Sea (TCS: trawls closest to the shore, TIS: trawls intermediate distance to the shore, TFS: trawls farthest to shore). Transect
Department
Trawl
Starting point 0
Water filtered (m3)
Ending point 0
0
0
B
TCS TIS TFS
B1 B2 B3
122°14.980 W 32°00.373 N 122°45.3180 W 31°59.9450 N 123°06.8530 W 31°59.0060 N
122°16.757 W 32°00.698 N 122°48.4580 W 31°59.5140 N 123°08.3480 W 31°59.1680 N
130.57 111.12 108.34
C
TCS TIS TFS
C1 C2 C3
122°18.7450 W 31°29.3110 N 122°51.9620 W 31° 30.7050 N 123°15.7710 W 31° 30.5860 N
122°17.5300 W 31° 29.0570 N 122°50.2070 W 31° 30.4980 N 123°14.0120 W 31° 30.4600 N
144.46 136.12 181.50
D
TCS TIS TFS
D1 D2 D3
122°16.5040 W 30° 59.1380 N 122°43.9060 W 30° 59.6690 N 123°10.4490 W 30° 59.0580 N
122°19.1670 W 30° 59.0890 N 122°46.5750 W 30° 59.4220 N 123°12.4730 W 30° 59.0510 N
129.64 194.46 200.02
E
TCS TIS TFS
E1 E2 E3
122°18.5690 W 30° 30.4750 N 122°51.7430 W 30° 30.3720 N 123°14.4720 W 30° 30.2650 N
122°17.7360 W 30° 30.5250 N 122°50.1370 W 30° 30.4590 N 123°13.4770 W 30° 30.6510 N
66.67 200.02 211.13
F
TCS TIS TFS
F1 F2 F3
122°29.9020 W 29° 59.6890 N 122°44.9080 W 29° 59.8570 N 123°14.4670 W 30° 00.5850 N
122°29.1200 W 29° 59.8410 N 122°44.3060 W 29° 59.7040 N 123°14.2010 W 30° 00.8760 N
175.94 185.20 194.46
Table 3 Composition of suspended microplastics in Yangtze estuarine and coastal waters (ECS: the East China Sea). Categories
Fibres Films Granules Spherules Total Density Calibrated density Minimum Maximum
Yangtze Estuary
Coastal waters of ECS
No. item
%
No. item
%
1178 135 173 3 1489 4137.3 ± 2461.5 n/m3 2984.7 ± 2219.3 n/m3 500 n/m3 10,200 n/m3
79.1 9.1 11.6 0.2 375
312 8 55 0
83.2 2.1 14.7 0
0.167 ± 0.138 n/m3 0.030 n/m3 0.455 n/m3
the presence of rivers with catchments draining populated areas increased quantities of MPs (Claessens et al., 2011; Santos et al., 2005). Overall, our results indicated a mass of plastic items flowed through those sampling sites and entered the coastal waters. The mean MP density (0.167 ± 0.138 n/m3) in the ECS had the same order of magnitude as the density found for the Northwestern Mediterranean (0.116 n/m3, Collignon et al., 2012). Nevertheless, the density was lower than those reported in the North Pacific Central Gyre (2.23 n/m3, Moore et al., 2001), the Southern California coastal waters (7.25 n/m3, Moore et al., 2002) and the Santa Monica Bay of Southern California (3.92 n/m3, Lattin et al., 2004). The probable reasons are complicated. Plastic particle load seems to be low in those productive coastal ecosystems which involve more organisms than in the less productive ocean ecosystems (Doyle et al., 2011; Gilfillan et al., 2009). Different criteria for size classes also had impacts on the density. Comparing the size ranges used in other studies (Table 5), the MP size range (>0.5 mm) utilized in this study resulted in a loss of plastic particles enumerated. Another reason may be the wind. Based on a one-dimension model, surface trawl cannot elucidate the total amount of plastic content in the surface water column when the wind speed l10 (wind velocity at height 10 m above the sea surface) is larger than 5 m/s. The wind-driven mixing distributes the plastic items throughout the upper water column (Kukulka et al., 2012). The mean l10 was 5.2 m/s during the sea surface sampling with a range of 1.5–9.7 m/s (unpublished data), and as a consequence the abundance of plastic debris in the ECS surface waters may be underestimated by the surface trawl sampling method. Another potential cause is that the Southern California coastal area may have plastic debris inputted by the southerly flowing California current which is the eastern current of the North Pacific Central
Fig. 2. Means and standard errors of density of microplastics in the (A) Yangtze Estuary (n/m3), (B) trawls in the East China Sea (ESC, n/m3) and (C) transects in the ESC (n/m3). The letters (a, b and c) indicate the results of the nonparametric Kruskal–Wallis test and Mann–Whitney U test. Bars with the same letter indicate no significant difference. (TCS: trawls closest to the shore, TIS: trawls intermediate distance to the shore, TFS: trawls farthest to shore).
Gyre known for its high levels of plastic debris (Doyle et al., 2011; Pichel et al., 2007). No significant difference was found between the three sectors (TCS, TIS and TFS) (Kruskal–Wallis test, p = 0.454 > 0.05). This widespread pattern of MPs is consistent with the tendency for the size distribution of MPs to be skewed towards abundant small particles (Browne et al., 2011; Goldstein et al., 2013). Smaller particles with a longer residence time would be dispersed greatly by ocean circulation (Doyle et al., 2011). Surprisingly, the density of
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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Table 4 Distribution of total plastic abundance (items) per sampling site for each size class (mm). Study area
Site/trawl >0.5–1 mm >1–2.5 mm
>2.5–5 mm >5 mm
Y1 Y2 Y3 Y4 Y5 D1 D2
Yangtze Estuary
Percentage (%)
100 34 46 42 63 14 13
144 49 99 46 48 17 20
22 10 6 4 10 8 6
1 0 0 0 0 0 1
67.0
28.4
4.4
0.2
16 7 8 16 10 17 3 3 5 8 3 5 10 8 14
5 5 1 23 21 23 7 2 4 2 0 4 10 2 3
0 0 1 18 11 14 36 1 5 0 3 3 2 2 1
1 0 2 4 9 8 1 2 3 0 0 3 0 0 0
35.4
29.9
25.9
8.8
Coastal waters B1 B2 B3 C1 C2 C3 D1 D2 D3 E1 E2 E3 F1 F2 F3 Percentage (%)
the C transect was significantly higher than any of the other transects (Kruskal–Wallis test, p = 0.029 < 0.05; Mann–Whitney U test, all p < 0.05) (Fig. 2). Directly facing the south branch of the Yangtze Estuary, the C transect was subject to more influences of riverine discharge. This finding confirmed that rivers have a huge effect on MP abundance in the marine environment (Barnes et al., 2009; Claessens et al., 2011). Due to the non-standard sampling mesh sizes used in the two study areas, we calibrated the density of fibrous MPs in the Yangtze Estuary with 333 lm mesh-sieves (Supplementary Information, SI). Compared with the calibrated density value in the Yangtze Estuary, the lower abundance of the ECS was mainly attributed to the oceanic dilution (Mann–Whitney U test, all p < 0.05). Simultaneously, the disparity between the original (4137.3 ± 2461.5 n/m3) and calibrated (2984.7 ± 2219.3 n/m3) MP densities in the Yangtze Estuary suggests that the employment of smaller mesh sizes is more beneficial to the monitoring the MPs in the water bodies. MPs were classified into four size categories: >0.5–1 mm, >1–2.5 mm, >2.5–5 mm and >5 mm. In both two research areas, plastics (<5 mm) comprised more than 90% of total abundance (Table 4). The average MP size in the Yangtze Estuary and East China Sea were 0.90 ± 0.74 mm (range: 0.51–6.29 mm) and 2.01 ± 2.01 mm (range: 0.5–12.46 mm), respectively. Smaller plastic fragments have been classified either as large MP (L-MPP, 1–5 mm) or small MP particles (S-MPP, 61 mm) (Imhof et al., 2012). S-MMP in the Yangtze Estuary and East China Sea accounted for 67.0% and 35.4%, respectively. Our findings implied that the
abundance of plastic items increased with the decreasing size of such items (Barnes et al., 2009; Doyle et al., 2011). These plastic fragments constitute a frequently reported size inventory in many ingestion studies (Eriksson and Burton, 2003; Foekema et al., 2013; Graham and Thompson, 2009). The size range of MP determines the potential impact of these contaminants on ecosystem biota (Mohamed Nor and Obbard, 2014). Dominance of smaller particles increases the risks related to encounter frequency. SMPPs were easily found in filter feeders in contrast to L-MPPs which were found frequently in carnivorous taxa (Foekema et al., 2013). The two research areas shared a similar composition of MP types. According to their shape, MP particles were categorized into four types: fibres, granules, plastic films and spherules. The fibres were the most common type, followed by granules and films. Spherules were the least common type (Table 3). The similar share of MP types in the Yangtze Estuary and East China Sea indicated a possible MP flux from the river to the adjacent sea. Fibrous MPs seems to be most abundant in the marine environment (Wright et al., 2013). Being adjacent to the most highly populated region, the study areas are bound to accept large amounts of land-based debris. This is in accordance with Browne et al. (2011) who suggested that the majority of MP fibres found in the marine environment may be derived from sewage as a consequence of laundering clothes. On the other hand, the fibres may derive from rope material. Heavy marine traffic and fishery activities in the study areas brought more discarded rope material (Andrady, 2011; Thompson et al., 2004). Lacking identification of the polymer types, further speculation on the origins of plastic particles cannot be made. The potential negative impacts of plastic particles ingested were proved to be associated with various particle shapes (Wright et al., 2013). If ingested, organisms inhabiting the study areas are vulnerable to the shape-related toxicity of fibrous MPs. Strikingly, spherules were rarely found in our study while commonly existing in water column samples (Moore et al., 2001; Law et al., 2010). A decrease in spherules may suggest that industry initiatives have been useful in reducing the loss of pellets into the environment during transportation. Similar results have been reported in two other studies (Ivar do Sul et al., 2013b; Ryan, 2008). Transparent and coloured MPs were the majority of plastic items, with small fractions of white and black plastic items (Fig. 3). Prominence of transparent and coloured MP corresponds to the prevalence of clear plastics used in the plastic products, such as packaging, clothing and fishing line (Cole et al., 2014). The colours may potentially contribute to the likelihood of MP ingestion due to food resemblance, the prevalence of plastics with these colours in the environment and an actual colour preference by the biota (Costa et al., 2010; Shaw and Day, 1994; Verlis et al., 2013; Wright et al., 2013). Typical examples of MP material encountered in this study are given in Fig. 4. China has been considered as one of the three biggest producers of plastic waste (Rochman et al., 2013). Understanding the properties and distribution of plastics is useful in considering how MP impacts the social economy, what influence the items have on the marine ecosystem and how to target management. Our study
Table 5 Comparison between this study and other studies that used the 333 lm mesh size for sampling suspended microplastics. Study area
Size class (mm)
Mean plastic items (n/m3)
References
North Pacific Central Gyre Southern California coastal waters Santa Monica Bay Northwestern Mediterranean East China Sea
>0.35 >0.35 >0.35 0.333–5 >0.5
2.23 7.25 3.92 0.116 0.167
Moore et al. (2001) Moore et al. (2002) Lattin et al. (2004) Collignon et al. (2012) This study
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
S. Zhao et al. / Marine Pollution Bulletin xxx (2014) xxx–xxx
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Fig. 3. Composition of coloured microplastic sampled in the (a) Yangtze Estuary and (b) East China Sea.
Fig. 4. (a) Fibres of different colors (c) coloured granule and (f) transparent film from the Yangtze Estuary, sampling site Y1; (b) blue fibre, (d) green and (e) yellow fragments from the East China Sea, B transect, TCS (trawls closest to the shore). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
provides a baseline of MP contamination in the Yangtze Estuarine system, as well as the first quantitative description of MP debris in China. The size, abundance and characters of floating MPs
(0.5–5 mm) were established in the Yangtze Estuarine System. The unique design of spatial scales provides good insights into MP source and fate. Further research is planned to assess
Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032
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distribution of MP transported via estuaries in differing marine environments and the probable transfer of MP in the food chain. Acknowledgements We thank the editor and the anonymous reviewers for their useful comments on the manuscript. This paper was funded by the Ministry of Science and Technology of China (2010CB951203), the Natural Science Foundation of Shanghai Municipality (11ZR1438800) and the State Key Laboratory of Estuarine and Coastal Research of China (200KYYW03). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.marpolbul.2014. 06.032.
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Please cite this article in press as: Zhao, S., et al. Suspended microplastics in the surface water of the Yangtze Estuary System, China: First observations on occurrence, distribution. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.06.032