Environmental Pollution 235 (2018) 899e906
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Sources and distribution of microplastics in China's largest inland lake e Qinghai Lake* Xiong Xiong a, Kai Zhang a, b, e, Xianchuan Chen a, e, Huahong Shi c, Ze Luo d, Chenxi Wu a, * a
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China State Key Laboratory in Marine Pollution, City University of Hong Kong, Hong Kong, China c State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, 200062, China d Computer Network Information Center, Chinese Academy of Sciences, Beijing, 100190, China e University of Chinese Academy of Sciences, Beijing, 100039, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 November 2017 Received in revised form 22 December 2017 Accepted 22 December 2017
Microplastic pollution was studied in China's largest inland lake e Qinghai Lake in this work. Microplastics were detected with abundance varies from 0.05 105 to 7.58 105 items km 2 in the lake surface water, 0.03 105 to 0.31 105 items km 2 in the inﬂowing rivers, 50 to 1292 items m 2 in the lakeshore sediment, and 2 to 15 items per individual in the ﬁsh samples, respectively. Small microplastics (0.1e0.5 mm) dominated in the lake surface water while large microplastics (1e5 mm) are more abundant in the river samples. Microplastics were predominantly in sheet and ﬁber shapes in the lake and river water samples but were more diverse in the lakeshore sediment samples. Polymer types of microplastics were mainly polyethylene (PE) and polypropylene (PP) as identiﬁed using Raman Spectroscopy. Spatially, microplastic abundance was the highest in the central part of the lake, likely due to the transport of lake current. Based on the higher abundance of microplastics near the tourist access points, plastic wastes from tourism are considered as an important source of microplastics in Qinghai Lake. As an important area for wildlife conservation, better waste management practice should be implemented, and waste disposal and recycling infrastructures should be improved for the protection of Qinghai Lake. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Remote lake Plastic debris Tourism Lake current Weathering
1. Introduction World annual production of plastics has increased by nearly 20 fold since the 1950s and reached 322 million metric tons in 2015 (PlasticsEurope, 2016). Although the use of plastic products brings great beneﬁt and convenience to people's lives, inappropriate disposal of plastic wastes has been causing serious environmental problems. Pollution of microplastics, which usually refer to plastic debris < 5 mm, is drawing closer attention in recent years (Cole et al., 2011; do Sul and Costa, 2014). Occurrence of microplastics in many marine environments has been extensively reported (Desforges et al., 2014; Lavers and Bond, 2017; Law et al., 2010). Presence of microplastics in the marine environment can adversely affect the health of marine organisms, and effects such as loss of
This paper has been recommended for acceptance by Maria Cristina Fossi. * Corresponding author. Donghu South Road #7, Wuhan, 430072, China. E-mail address: [email protected]
https://doi.org/10.1016/j.envpol.2017.12.081 0269-7491/© 2018 Elsevier Ltd. All rights reserved.
energy, intestinal blockage, alteration of hormone levels, growth inhibition, and delayed maturity have been observed (Chae and An, 2017; Galloway et al., 2017). Many previous studies have demonstrated that microplastics can be ingested by invertebrates, ﬁshes, seabirds, and even marine mammals (Devriese et al., 2015; Jabeen et al., 2017; Lusher et al., 2015; Zhao et al., 2016). Due to the potential risks of microplastics, legislation to ban the use microbeads in personal care products has been introduced in the United States, Canada, Australia, and some European Union countries (Rochman et al., 2016). Although major research efforts have been focused on microplastics related issues in the marine environment so far, inland water is facing similar problems. It was estimated that less than 5% of the total 275 million metric tons of plastic wastes generated in 192 coastal countries were discharged into the ocean in 2010 (Jambeck et al., 2015). The remaining 95% of the plastic wastes were either degraded or remained in the terrestrial environment. Therefore, inland water could also be very vulnerable to microplastic pollution. Microplastics have been detected with high
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abundance in lakes and rivers under intensive human impact (Baldwin et al., 2016; Klein et al., 2015; Su et al., 2016; Zhang et al., 2017). However, in remote areas such as Mongolia, subalpine area of Italy, and Qinghai-Tibet plateau, occurrence of microplastics has also been observed (Free et al., 2014; Imhof et al., 2013; Zhang et al., 2016). Qinghai Lake is the largest lake in China, which is a remote lake located on the northeast edge of Qinghai-Tibet Plateau. Qinghai Lake is a closed lake with a salinity of ~11‰ and an average depth of ~20 m. The surface area of the lake is about 4500 km2 and the watershed area is about 30,000 km2 (Ao et al., 2014). The population density around the Qinghai Lake area is about 9.3 person per km2. There are neither urban centers nor industry around the lake, and animal husbandry and tourism are the major human activities. The whole watershed is in the semi-arid region and the prevailing wind is westerly. More than forty rivers and creeks ﬂow into the lake, most of which are seasonal, and seven major rivers account for about 95% of the total discharge into the lake (Xu et al., 2010). The Qinghai Lake basin is a closed watershed with no river outﬂow and thus the lake can easily become a sink of pollutants from the watershed. Qinghai Lake area is also a very important habitat for many species of birds, ﬁsh and wild animals including several endangered ones. In recent years, tourism is blooming but infrastructure construction and management systems lag behind, which brings great pressure on the Qinghai Lake protection. No study on microplastic pollution has been performed previously in this area. Clear watershed boundaries and relatively simple human activities in the Qinghai Lake area make it an ideal place to study the source and distribution of microplastics. Therefore, microplastic pollution was investigated in Qinghai Lake in this work with the purpose of 1) revealing microplastic pollution characteristics and distribution patterns; 2) illustrating sources of microplastics; and 3) discussing the fate of microplastics. 2. Materials and methods 2.1. Sampling The Sampling campaign was carried out in July 2016. Geographic location and sampling sites are presented in Fig. 1 and Fig. S1. Microplastics in the lake surface water were collected following a previous method (Zhang et al., 2015, 2017). Brieﬂy, a trawl net (50 cm 100 cm 150 cm, 112 mm mesh size) was towed on the surface of the lake by the side of a vessel at a speed of 5 km h 1, approximately. The towing distance was 2 km as indicated using a Garmin Map62s Global Positioning System (GPS). After each sampling, the trawl net was rinsed with deionized water. The ﬂoating debris retained in the net was transferred into a 1 L glass bottle, and preserved with 5% methyl aldehyde before further treatment. The trawl was rinsed three times before the next sampling to reduce the cross contamination. Four major inﬂowing rivers were selected for the investigation (Table S1). One sample was collected for each river. Microplastics in the rivers were also collected using the trawl net but the net was held vertically to the ﬂow direction for 10e20 min according to the ﬂow velocity, which was measured using a starﬂow ultrasonic ﬂowmeter (Streamline Measurement Ltd., Derbyshire, UK). The cross-section area of water passed through the net was calculated by multiplying the ﬂow velocity and the sampling time. Sediment samples were collected from 7 sites around the lake. At each site, samples were taken above the lakeshore line (up) and at the lakeshore line (down). Top 0e2 cm sediment in a 20 cm 20 cm quadrat was collected using a stainless-steel shovel and transferred into a stainless-steel container. Three replicates
about 10 m away from each other were collected for each sample. Ten ﬁsh (Gymnocypris przewalskii) samples from the estuarine area of Buha River were obtained from the local ﬁshery administration department and were frozen before analysis. Gymnocypris przewalskii is an omnivorous and migratory ﬁsh belonging to cyprinid, which is endemic to the Qinghai Lake basin and is the dominant ﬁsh species in the Lake. It is listed as endangered on the China Species Red List due to over ﬁshing and habitat loss. 2.2. Sample analysis Water and sediment samples were pretreated following previously described methods with some slight modiﬁcations (Zhang et al., 2015, 2017). Water samples were passed through a 1 mm mesh size stainless steel sieve. Materials retained on the sieve were visually examined. Suspected microplastics were transferred to petri dishes for further examination. Water passed through the sieve was collected and transferred into a 1 L separating funnel. Potassium formate was added to a density of 1.54 g mL 1. Samples in the funnel were settled overnight, then the settled materials were discarded through a valve at the bottom of the funnel. Floating particles were digested using 30% hydrogen peroxide at 60 C overnight, then ﬁltrated onto GF/C ﬁlters (1.2 mm pore size), and dried in desiccators. Sediment samples were sieved with 2 mm mesh size sieves. Materials retained on the mesh were visually examined. Suspected microplastics were transferred to petri dishes for further examination. Samples passed through the sieve were transferred to a 2.5 L ﬂask and separated with the potassium formate solution (1.54 g mL 1). Samples were settled overnight. The ﬂoating debris in the ﬂask was overﬂowed into a stainless-steel tray by adding potassium formate solution from a tube at the neck. Then materials on the tray were transferred into a 500 mL beaker and ﬁltrated onto GF/C ﬁlters. The process was repeated for three times. The retained particles were digested using 30% hydrogen peroxide at 60 C overnight, then ﬁltrated onto GF/C ﬁlters, and dried in desiccators. The gastrointestinal tract of each ﬁsh was dissected and digested using a 10% potassium hydroxide solution (Foekema et al., 2013). The digested solutions were ﬁltrated onto GF/C ﬁlters. All prepared samples on the ﬁlters were stored in covered petri dishes for further examination. All ﬁlters were visually examined under a stereomicroscope up to 40 magniﬁcation. Suspected microplastics were identiﬁed based on their morphology. The quantity, shape, color, and size of microplastics were recorded. Microplastics were divided into three categories according to their sizes (0.112e0.5 mm; 0.5e1 mm; 51 mm) and four categories according to their shapes (sheet, ﬁber, fragment, and foam). The suspected microplastics were randomly picked out with tweezers for the further conﬁrmation using a Renishaw inVia Raman microscope (Wotton-under-Edge, Gloucester-shire, UK). For those sites with a high microplastic abundance (>100 items), 10e15% of the suspected microplastics were identiﬁed. For those sites with a low microplastic abundance (<100 items), all suspected microplastics were identiﬁed. During the identiﬁcation, suspected microplastics in different size and shape categories were approximately equally represented. Microplastics <200 mm were not identiﬁed due to the difﬁculty in handling. To prevent contamination during sample analysis, nitrile gloves, cotton laboratory coat, and shower cap were worn during the whole process. All containers were covered with aluminum foil if not in use. Sample pretreatment was performed in a fume hood, and a sticky dust drum was used to clean the desktop, hands, and clothes. Blank controls were also carried out following the same procedures to assess the contamination.
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Fig. 1. Occurrence of microplastics detected in Qinghai Lake (a) and contour map of microplastic distribution and lake current direction (b).
2.3. Data analysis The abundance of microplastics in the water from each site was calculated by dividing the number of microplastics (Table S2) by the towing area or the cross-section area and was expressed as items km 2. The abundance of microplastics in the lakeshore sediment was calculated by dividing the number of microplastics by the sampling area (0.04 m2) and was expressed as items m 2. The abundance of microplastics in ﬁsh was expressed as items per individual. Distribution of microplastics in the Qinghai Lake surface water was analyzed using spatial interpolation analysis. Inverse distance weighted (IDW) method of interpolation analysis was performed using ArcGIS 9.2 (ESRI, Redlands, CA). Watershed data of Qinghai Lake were downloaded from inland water dataset of China from www.gscloud.cn. 3. Results 3.1. Microplastic pollution in lake surface water and rivers The abundance of microplastics varied from 0.05 105 to 7.58 105 items km 2 in the Qinghai Lake surface water (Table 1). The abundance of microplastics varied from 0.03 105 to 0.31 105 items km 2 in the four inﬂowing rivers, and was the
lowest in Quanji River and the highest in Heima River. As presented in Fig. 1a, the highest abundance of microplastics in the lake surface water was observed at site W07, which is near the Haixin Island in the center of the lake. While the lowest abundance of microplastics was observed at site W01, which is near the Buha River estuary. Sites on the northern part of the lake showed relatively lower microplastic abundances than sites on the southern part of the lake. Pictures of typical microplastic samples detected in this study are presented in Fig. S2. As shown in Fig. 1a, <0.5 mm microplastics dominated in the lake surface water samples except W01, while the 1e5 mm microplastics were more abundant in the river water samples. As showed in Fig. 2a, sheets dominated in most lake sites and fragments and foams were only observed in a few samples. However, ﬁbers dominated in most river sites. Microplastics were found in transparent, blue, green, white, and red colors, and transparent microplastics were more abundant except in samples from Heima River (Fig. S3). The polymer types of microplastics in water samples were identiﬁed as polypropylene (PP), polyethylene (PE), polystyrene (PS), and polyethylene terephthalate (PET) using the Raman Microscope (Fig. 2b). PP and PE were predominant in all samples. 3.2. Microplastic pollution in lakeshore sediment The abundances of microplastics at the lakeshore line ranged
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Table 1 Abundance (mean ± standard deviation, range in parentheses) of microplastics detected in water, sediment, and ﬁsh samples collected from the Qinghai Lake area. Sample Water (items km
Lakeshore sediment (items m
Qinghai Lake Heima River Buha River Quanji River Shaliu River
180900 ± 229533 (5000e757500) 31292 7363 3090 8708 Above the lakeshore line 575 ± 205 (400e800) 308 ± 238 (75e550) 508 ± 118 (375e600) 933 ± 1295 (100e2425) 50 ± 50 (0e100) 167 ± 38 (125e200) 83 ± 76 (0e150) 5.4 ± 3.6 (2e15)
West North East
S01 S02 S03 S04 S05 S06 S07
Fish (items per individual)
At the lakeshore line 1292 ± 582 (625e1700) 325 ± 189 (125e500) 317 ± 80 (225e375) 217 ± 293 (0e550) 67 ± 63 (0e125) 117 ± 95 (50e225) 133 ± 138 (0e275)
Fig. 2. Shape distribution and composition of microplastics detected in water (a, b) and lakeshore sediment samples (c, d).
from 67 to 1292 items m 2 with the highest abundance detected in south followed by west, east, and north. The abundances of microplastics above the lakeshore line ranged from 83 to 933 items m 2 with the highest abundance detected in west followed by south, east, and north (Table 1). Site S04 had the highest ratio between the up and down lakeshore sites. Different from water samples, lakeshore sediment samples were dominated by ﬁbers and sheets (Fig. 2c). PE and PP also dominated in all lakeshore sites, but Ethylene Vinyl Acetate copolymer (EVA) and some high-density (>1 g cm 3) microplastics such as polyvinyl chloride (PVC), nylon, and polycarbonate (PC) were detected in the lakeshore sediment (Fig. 2d). 3.3. Microplastic pollution in ﬁsh Information on body weight, digestive tract weight, and body length of the ﬁsh samples is provided in Table S3. Microplastics were found in the digestive tracts of all ﬁsh samples with the abundance varied from 2 to 15 items per individuals (Table 1). Fibers were found in all ﬁsh samples, while sheets were observed in half of the samples. Microplastics in ﬁsh samples were identiﬁed as PE, PS, nylon, and PP.
4. Discussion 4.1. Microplastic pollution level in Qinghai Lake Compared with data reported from the marine environment and other inland waters (Table S4), the abundance of microplastics in Qinghai Lake is comparable to those detected in North Atlantic Subtropical Gyre (Law et al., 2010), South Paciﬁc Subtropical Gyre (Eriksen et al., 2013b), North-Western Mediterranean (Collignon et al., 2012), Laurentian Great Lakes (Eriksen et al., 2013a), and Lake Winnipeg (Anderson et al., 2017). However, the abundances of microplastics in Qinghai Lake are in a much lower range compared with inland waters in developed area, such as Taihu Lake (Su et al., 2016), Three Gorges Reservoir (Zhang et al., 2015), Rhine River (Mani et al., 2015) and the North Shore Channel in Chicago (McCormick et al., 2014). The abundance of microplastics in Qinghai Lake is higher than in Lake Hovsgol, which is also a remote lake in Mongolia (Free et al., 2014). In Qinghai Lake lakeshore sediment, the abundance of microplastics is higher than that detected in Lake Huron (Zbyszewski and Corcoran, 2011) and Siling Co basin (Zhang et al., 2016), and is similar to that detected in Guanabara Bay, Brazil (de Carvalho and
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Baptista Neto, 2016). The highest abundance observed in Qinghai Lake is within the same orders of magnitudes compared with the average microplastic abundance detected in Lake Garda (Imhof et al., 2013), Lake Bolsena, and Lake Chiusi (Fischer et al., 2016), but much lower than that observed in beaches in South Korea (Lee et al., 2013). Microplastic pollution in Qinghai Lake is generally at moderate levels, higher than pristine region but lower than areas under intensive human impact.
4.2. Source of microplastic pollution in the Qinghai Lake area Previous studies indicated that the urbanization level and population density are related to the level of microplastic pollution (Biginagwa et al., 2016; Sruthy and Ramasamy, 2017; Vaughan et al., 2017). However, there is no industry and a very low resident population within the Qinghai Lake watershed. But as a famous place of interest, there were over 1 million tourist arrivals in the Qinghai Lake area in 2012 (Wu et al., 2014), which were over 10 times higher than the resident population in the whole basin. The number of tourists is still increasing rapidly in recent years. Additionally, main tourist areas are close to the lake while local resident area are usually more far away from the lake. Many scenic spots located on the south and west shore of the Lake. The road around Qinghai Lake is much closer to the lakeshore in south and west than in north and east. Tourists not only bring income to the Qinghai Lake area but also leave their garbage behind. Insufﬁcient garbage collection and disposal facilities and poor waste management allow the disposed garbage to enter the environment. As reported by the local media, more than 270 tons of garbage had been cleaned up from 6 scenic spots one week after the peak tourist season in 2015. Plastic wastes account for a great proportion of the garbage. These plastic wastes could be an important source of microplastics. A high of tourist density in the southern part of the lake are in accordance with the high abundances of microplastics observed in the lake water near the area. Therefore, tourism is an important source of microplastics in Qinghai Lake. Previous studies of remote lakes in Mongolia and Italy also considered tourism as an important source of microplastics (Free et al., 2014; Imhof et al., 2013). Research in coastal areas has also revealed that the beaches with more tourist arrivals had a high microplastic abundance (Costa et al., 2010; Yu et al., 2016). The materials, shapes, and colors of the microplastics also
indicate tourism as an important source of microplastics. PP and PE dominated in all microplastic samples, which are mainly used as packages for food and supplies and are frequently carried out and carelessly disposed by tourists (Siracusa et al., 2008). Fiber was found to be more abundant in the lakeshore sediment but rare in lake surface water. Fiber can originate from ﬁshery, shipping, and textile (Claessens et al., 2011; Napper and Thompson, 2016). In Qinghai Lake, ﬁshery and shipping are strictly prohibited. Therefore, ﬁbers in the lake shore sediment can only originate from the clothes of the tourists or prayer ﬂags which are broadly deployed around the lake. Low abundance of ﬁber in water might be related to a higher than water density of most ﬁber materials which can sink to the bottom of the lakes. High proportion of transparent microplastics also indicates the use of plastic bags, food boxes, plastic bowls, and/or disposable raincoats. Riverine input is another important source for microplastic pollution (Klein et al., 2015; Lebreton et al., 2017). Estuary areas were recognized as hot spots of microplastics in the marine environment (Fok and Cheung, 2015). The Sampling campaign was carried out in July, corresponding to the beginning of the wet season in the study area. Therefore, plastic wastes from land can be transported to rivers via rainfall induced surface runoff and the abundance of microplastics should be at a higher level compared with the dry season. Nevertheless, the abundance of microplastics in four major inﬂowing rivers and their estuaries is much lower than that observed from other sites (Fig. 1a). This result suggests that riverine input might be a less important source than nonpoint sources from tourism. Moreover, there is no outﬂow from Qinghai Lake and thus microplastics are concentrated in Qinghai Lake as the degradation of most plastics is a very slow process. Therefore, Qinghai Lake can be a sink of plastic waste from the whole lake watershed.
4.3. Distribution of microplastics in Qinghai Lake Ocean currents are believed to be responsible for transport of microplastics to subtropical convergence zones (van Sebille et al., 2015). As a case of large inland water, distribution of plastic debris in Laurentian Great Lakes has also been found to be affected by the lake current (Hoffman and Hittinger, 2017). On the other hand, the source input and wind direction are found to be responsible for the distribution of microplastics in some small lakes
Fig. 3. Raman spectrum of PE and PP virgin pellets (a, b) and PP and PE samples (c, d).
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(Free et al., 2014; Imhof et al., 2013; Vaughan et al., 2017; Zhang et al., 2016). In Qinghai Lake, tourism on the southern and western shore may have contributed to a higher microplastic abundance observed in the southern part of lake. While, the highest microplastic abundance observed in the lake center should be attributed to the transport of lake current as illustrated in Fig. 1b. Previous research showed that circulation exists in the central part of Qinghai Lake (Han et al., 2016; Xu et al., 2006). In general, lake current is driven by wind and riverine discharge. Lake current can bring the ﬂoating plastic debris from the near shore and the estuarine areas into the circulation zone and accumulate there. Therefore, lake current can be an important factor affects the distribution
of microplastics in Qinghai Lake. 4.4. Fate of microplastics in Qinghai Lake Microplastics can originate from both primary and secondary sources. Resin pellets and microbeads used in personal care products or polishing materials are usually considered as primary microplastics while plastic debris derived from the breakdown of large plastic products are referred to as secondary microplastics (Cole et al., 2011). Primary microplastics usually observed in samples from many developed areas were not detected in this study. Plastic wastes are subject to weathering once enter into the
Fig. 4. Pictures of PE (a) and PP (b) microplastics in the Qinghai Lake surface water under the light microscope (400 magniﬁcation).
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environment. Weather conditions within the Qinghai Lake area are characterized by strong ultraviolet (UV) irradiation, windy, and dry (Hu et al., 2007). Extensive UV exposure can cause the photooxidation of plastics (ter Halle et al., 2016). Compared with virgin pellet, characteristic peaks (corresponding to C]O) showed up in the Raman spectrum of microplastics (Fig. 3), reﬂecting oxidative weathering of the microplastics. Meanwhile, solution pits were observed on the surface of PE microplastics while cracks were observed on the surface of PP microplastics (Fig. 4), which might suggest that PP can be broken down into smaller particles more easily than PE. It was previously found that after UV irradiation, PP became more fragile than PE and PVC and generates more microplastics particles following mechanical abrasion (Song et al., 2017). Size distribution of microplastics shows that in four inﬂowing rivers 1e5 mm microplastics were more abundant while in the lake surface water 0.1e0.5 mm microplastics dominated, suggesting that large particles are breaking down into small particles in the lake, which could also contribute to an increase in microplastic abundance in the lake. Microplastics in water can be mistakenly ingested by aquatic animals (Jabeen et al., 2017; Lusher et al., 2015). Fish (Gymnocypris przewalskii) samples from Qinghai Lake were also found with the presence of microplastics in their digestive tract, suggesting that microplastics in the lake are ingested by the ﬁsh. Qinghai Lake is also an important habitat for birds in Northeast Asia. Many species of birds feed on the ﬁsh in Qinghai Lake. Microplastics in ﬁsh can be transferred to those ﬁsh-eating birds inhabit around the Qinghai Lake via food chain. The impact of microplastics on ﬁsh and birds following their ingestion should be further assessed. 5. Conclusions Microplastics were detected in water, lakeshore sediment, and ﬁsh samples in the Qinghai Lake area. Distribution pattern and characteristics of the microplastics indicate that tourism is an important source of microplastics in the study area. The distribution of microplastics in the lake surface water is related to the tourism sites and the transport of lake current. As no water outﬂow from the lake, Qinghai Lake can be a sink for the accumulation of microplastics from the lake basin. In the lake, microplastics can break down into smaller particles due to weathering and can be ingested by ﬁsh, which might cause potential adverse effects. More work should be carried out to assess the risks of microplastic pollution in the Qinghai Lake area for the protection purpose. Acknowledgements This work is funded by the State Key Laboratory of Freshwater Ecology and Biotechnology (2016FBZ11). We would like to thank the support from Joint Research Center of Chinese Academy of Sciences and Qinghai Lake National Natural Reserve, and Min Huang from the analysis and test center of the Institute of Hydrobiology for her assistance in Raman Microscopic analysis. Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.envpol.2017.12.081. References Anderson, P.J., Warrack, S., Langen, V., Challis, J.K., Hanson, M.L., Rennie, M.D., 2017. Microplastic contamination in lake Winnipeg, Canada. Environ. Pollut. 225, 223e231. Ao, H.Y., Wu, C.X., Xiong, X., Jing, L.D., Huang, X.L., Zhang, K., Liu, J.T., 2014. Water and sediment quality in Qinghai Lake, China: a revisit after half a century.
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