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Environmental Pollution 216 (2016) 711e719

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Environmental Pollution

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Microplastics in Taihu Lake, China*

Lei Su a, Yingang Xue b, Lingyun Li a, Dongqi Yang a, Prabhu Kolandhasamy a, Daoji Li a,Huahong Shi a, *

a State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, Chinab Key Laboratory of Environmental Protection of Water Environmental Biological Monitoring of Jiangsu Province, Changzhou Environmental MonitoringCentre, Jiangsu 213001, China

a r t i c l e i n f o

Article history:Received 5 March 2016Received in revised form9 June 2016Accepted 18 June 2016Available online 2 July 2016

Keywords:MicroplasticFreshwaterAsian clamBiomonitoring

* This paper has been recommended for acceptanc* Corresponding author.

E-mail address: hhshi@des.ecnu.edu.cn (H. Shi).

http://dx.doi.org/10.1016/j.envpol.2016.06.0360269-7491/© 2016 Elsevier Ltd. All rights reserved.

a b s t r a c t

In comparison with marine environments, the occurrence of microplastics in freshwater environments isless understood. In the present study, we investigated microplastic pollution levels during 2015 in TaihuLake, the third largest Chinese lake located in one of the most developed areas of China. The abundanceof microplastics reached 0.01 � 106e6.8 � 106 items/km2 in plankton net samples, 3.4e25.8 items/L insurface water, 11.0e234.6 items/kg dw in sediments and 0.2e12.5 items/g ww in Asian clams (Corbiculafluminea). The average abundance of microplastics was the highest in plankton net samples from thesoutheast area of the lake and in the sediments from the northwest area of the lake. The northwest areaof the lake was the most heavily contaminated area of the lake, as indicated by chlorophyll-a and totalphosphorus. The microplastics were dominated by fiber, 100e1000 mm in size and cellophane incomposition. To our best knowledge, the microplastic levels measured in plankton net samples collectedfrom Taihu Lake were the highest found in freshwater lakes worldwide. The ratio of the microplastics inclams to each sediment sample ranged from 38 to 3810 and was negatively correlated to the microplasticlevel in sediments. In brief, our results strongly suggest that high levels of microplastics occurred notonly in water but also in organisms in Taihu Lake.

© 2016 Elsevier Ltd. All rights reserved.

1. Introduction

Widespread use of synthetic polymers, so-called plastic, haschanged our ways of life. However, the huge production of plastichas resulted in serious environmental concerns (C�ozar et al., 2014;Rocha-Santos and Duarte, 2015). In particular, the small-sizedplastic particles that originate from manufacturing (primary sour-ces) and the degradation of large items (secondary sources) areprone to accumulate in the environment and may pose an unpre-dictable influence on the ecosystem (Cole et al., 2011; Wright et al.,2013). The small particles (<5 mm) are defined as microplastic(Thompson et al., 2004). Concerns about microplastic and itsassociated environmental issues have arisen worldwide (Barbozaand Gimenez, 2015).

Because of their ubiquitous presence and morphological fea-tures, microplastics are likely to threaten the life and development

e by Maria Cristina Fossi.

of biota via direct and indirect pathways, including contact, uptakeand digestion (Farrell and Nelson, 2013; Desforges et al., 2015; Longet al., 2015). Microplastics provide substratum sorption of variouspersistent organic pollutants (POPs). Microplastics may pose apotential risk to the ambient environment because of their ten-dency to release certain contaminants (Bakir et al., 2014; Napperet al., 2015). Microplastics also have potential risks for humanhealth because of their ability to persist through the food chain(Brennecke et al., 2015). Therefore, it is very important to under-stand the fate and behavior of microplastics in the environment.

To date, microplastics have been well documented in marineenvironments worldwide (Thompson et al., 2004; C�ozar et al.,2014; Law and Tompson, 2014). Microplastics have even beenfound in abiotic sea products such as sea salts (Yang et al., 2015).However, the occurrence of microplastics in freshwater environ-ments is less understood (Driedger et al., 2015; Eerkes-Medranoet al., 2015). Freshwater systems have several important func-tions, such as the use as providing sources of drinking water andfisheries. Some freshwater systems are surrounded by a highpopulation density, and such intensive anthropogenic activity canintroduce various contaminants, including microplastics, into the

L. Su et al. / Environmental Pollution 216 (2016) 711e719712

body of water (Floehr et al., 2013; Ismail et al., 2014; Driedger et al.,2015). In recent years, the occurrence of microplastics has beendocumented in several lakes and rivers (Eriksen et al., 2013;Castaneda et al., 2014; Yonkos et al., 2014). To date, however, fieldstudies have only reported microplastic burden in limited fresh-water organisms (Faure et al., 2015; Peters and Bratton, 2016).

Taihu Lake is the third largest fresh water lake in China. It islocated in one of the most developed areas of China, the YangtzeRiver Delta. Taihu Lake is also well known for its fisheries andtourism. However, with the development of the local economy andindustry, Taihu Lake has become one of the most severely pollutedlakes in China (Liu et al., 2009; Yan et al., 2014). In the present study,we investigated microplastic pollution levels in water, sedimentsand an organism of Taihu Lake. Our purpose is to determine theextent of microplastic pollution in a lake located in an area withintensive anthropogenic activities. We found high levels of micro-plastic pollution in Taihu Lake and propose that the Asian clam(Corbicula fluminea) could be used in the biomonitoring of micro-plastic pollution in this freshwater system.

2. Material and method

2.1. Research area and sampling sites

Taihu Lake has a surface area of approximately 2000 km2 and amean depth of 1.9 m (Hu et al., 2006). Three rivers (YincungangRiver, Wujingang River and Zhihugang River) are connected to thenorthern bay of Taihu Lake and account for 1/3 of the total inflow toTaihu Lake (Fig. 1). The Taipu River is connected to the southern

Fig. 1. Geographic position of sample sites and t

region of Taihu Lake and accounts for 2/3 of the total outflow fromTaihu Lake. There are three waste water treatment plants that havea treatment capacity of larger than 5 � 104 m3/day. Taihu Lakerepresents a critical drinking water source for local population ofapproximately 20 million people. The industry and agriculture inthe Taihu Basin provide 14% of China’s gross domestic product(Wang et al., 2015). Therefore, Taihu Lake plays an important role inthe regional economy and social development.

In August 2015, samples were collected from 11 locations, whichwere chosen for prospective pollution level and geographic region(Fig. 1). These sites represent three different areas of Taihu Lake.Sites 1e4were located at the northwest area of the lake and close tocities and rural areas. These sites were believed to be affected byintense levels of anthropogenic activity. Sites 5e8 were located inthe central area of the lake. Sites 9e11were located in the southeastarea of the lake, where there is less anthropogenic pollution comingfrom the surrounding land. Two other farmed sites (F1-2) wereadded to the sample collection in November 2015.

2.2. Sample collection

In August 2015, water, sediment and organism samples werecollected. The dissolved oxygen (DO), pH, chlorophyll-a (Chl-a) andammonia nitrogen (NH4

þ) were also measured in situ using a multi-parameter probe system. One liter of surface water was sampled ateach site and sealed in glass bottles for further analysis of totalphosphorus (TP) and total nitrogen (TN). The wind condition wasmeasured using a Kestrel 4500 shooter’s weather meter.

Prior to sampling, all sampling containers and tools were

he distribution of cities around Taihu Lake.

L. Su et al. / Environmental Pollution 216 (2016) 711e719 713

washed using filtered tap water (0.45 mm) and sealed. A cotton coatand nitrile gloves were worn at all time during sampling. A total of11 floating microplastic samples were collected using a nylonplankton net with a circular opening (0.65 m in diameter, 1.55 m inlength and 333 mm in mesh size). Three individual tows were fixedat the opening of the net and towed by the side of boat at a speed of2 km/h for 1e30 min. Half of the net was deliberately kept underwater during towing, and the floating microplastics from the sur-face water layer (less than 0.3 m deep) were collected. The towingdistances used for each sample varied with the degree of algaeblooming at each site. With the exception of S7 (towing distance of1700 m) and S8 (towing distance of 2500 m), the towing distancesranged from 25 to 125 m due to the large algae blooms present.Approximately 250 mL of sample was collected and immediatelypreserved with 5% methylaldehyde in a l-L glass bottle. The bulksurface water was collected three times using a steel sampler ateach site. The water was then pooled, and 5 L of bulk water waskept as one sample for each site. Similarly, the sediments werecollected three times using a Peterson sampler and pooled.Approximately 2 kg of the pooled sediments were kept in analuminum foil bag as one sample from each site.

A bottom fauna trawl was used to collect clams. All of the sed-iments were pooled into a steel mesh with pore size of 1 mm andwashed in situ using lake water. The clams were picked up and keptin an aluminum foil bag. Clams were collected from sites S3-11,with 3e20 individual specimens collected from each site inAugust. An additional survey for microplastics in clams was con-ducted in November. Clams were collected from all 11 sites as wellas two farmed sites (F1 and F2), with 5e50 individual specimenscollected from each site. The water and sediment samples werekept at 4 �C, and the clams were kept at�20 �C in the laboratory forfurther analysis.

2.3. Isolation of microplastics

A series of efforts weremade to avoid airborne contamination inthe laboratory. The liquid used in all of the experiments was filteredwith a 0.45-mm filter prior to use, and all of the equipment wasrinsed three times with filtered tap water. The samples wereimmediately covered by aluminum foil if they were not in use.Blank groups were analyzed simultaneously to estimate the back-ground contamination. Samples from the plankton net and surfacewater were filtered through a 47-mm-diameter filter (MilliporeTMTP polycarbonate filter). The filter pore size was 100 mm forplankton net samples and 5 mm for surface water samples. Thesubstances collected on the filters were immediately washed intoglass bottles using hydrogen peroxide to digest any organic matter(30%, V/V). The glass bottles were covered and placed in an oscil-lating incubator at 65 �C and 80 rpm for approximately 72 h. Theliquid in the bottles was filtered again, and these filters were storeddry for further observation. It was necessary to filter the samplestwice to remove the organic matter in these biota-rich samples dueto the eutrophication.

The microplastics were isolated from sediments was done usingthe method of Klein et al. (2015) with modification. Briefly, 1 kg ofwet sediment was mixed with a saturated sodium chloride solution(360 g/L) using a ratio of 1:2 (V/V) in a 10-L glass container with adepth of 40 cm. The mixture was stirred for 30 min and allowed tosettle overnight. The supernatant, including any floating particle,was transferred onto a 47-mm-diameter filter with a 5-mm poresize. The hydrogen peroxide treatment and the isolation of micro-plastics was then performed as with the plankton sample pro-cessing method above.

The isolation of microplastics from organisms was carried outaccording to the method of Li et al. (2015a). Briefly, the shell length

andweight of each individual clamwere recorded. The soft tissue ofthe clam was separated and weighted (Supplementary materialsTable 1). For the samples collected in August, the soft tissue ofthe clams from a sampling site was pooled into a single sample. Forthe samples collected in November, the soft tissues from 1 to 5clams was used as a replicate. Approximately 200 mL of hydrogenperoxide was added to each bottle, and the isolation of micro-plastics was performed as with the plankton sample processingmethod above.

2.4. Observation of microplastic

The filters were observed under a Carl Zeiss Discovery V8 Stereomicroscope (MicroImaging GmbH, Goottingen, Germany), and allimages were taken with an AxioCam digital camera. Visual as-sessments were applied first to quantify the suspected micro-plastics according to the physical characteristics of the particles. Inall, 1805 particles were visually identified. A subset of 113 particleswere then selected and verified using micro-fourier transformedinfrared spectroscopy (m-FT-IR) or scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The selected particlesrepresented the most common types of visually identified particlesand were selected from all of the filters. The final number ofmicroplastics was recalculated by removing the verified non-plastics. The microplastics were classified into four morphotypes:fiber, pellet, film and fragment (Li et al., 2016). A fiber was definedas a microplastic with a slender and greatly elongated appearance;pellets were roundmicroplastic with a spherical shape; a filmwas asmall and very thin layer or a piece of large plastic debris; a frag-ment was an isolated or incomplete part of large plastic debris. Theclassification of fragment was used, when a microplastic could notbe classified as a fiber, pellet or film.

2.5. Verification of microplastics using m-FT-IR and SEM/EDS

The verification of microplastics using a m-FT-IR microscopyfollowed themethod describe by Yang et al. (2015). All spectrawerecompared with a data base (Hummel Polymer and Additives,Polymer Laminate Films, Cross Sections Wizard, HR Specta IRDemo, Aldrich Vapor Phase Sample Library) to verify the individualplastic item. For SEM observation, samples were spread on double-sided adhesive tape and coated with a thin film of evaporated gold.Themorphology of the samples was examined using a SEM (HitachiS-4800, Japan). The images were taken with an optimized accel-eration voltage of 3 kV and detector working distance of approxi-mately 2 mm. Subsequently, qualitative elemental composition ofparticles was confirmed using an EDS (EMAX).

2.6. Analysis of total phosphorus/nitrogen in water and grain size ofthe sediments

The concentrations of total phosphorus and total nitrogen inwater samples were analyzed using spectrophotometric analysisafter digestion according to the national standard for surface waterquality. Sub-samples of sediments in each sampling site (10 g wetweight) were treated with 30% hydrogen peroxide solution for24e48 h to digest organic materials, and then the analysis ofsediment grain size was conducted in the laboratory using an LS-100 particle size analyzer. The sediment components were classi-fied into clay (8e12 F), silt (4e8 F) and sand (�1 to 4 F) based onthe Udden-Wentworth grain size classification.

2.7. Data analysis

The difference between the quantities of microplastic for more

L. Su et al. / Environmental Pollution 216 (2016) 711e719714

than two groups was determined by one-way analysis of variance(ANOVA) followed by Tukey’s HSD test (homogeneous variances) orthe Tamhane-Dunnett test (heterogeneous variances), along withmultiple comparisons. A significance level of 0.05 was chosen, andthe difference between two groups was analyzed using Student’s-TTest. The concentrated factor, a dimensionless value, defined as therelative ratio of the abundance of microplastics in organism tosediment, was used to depict the degree of bioaccumulation in theclams living in sediment.

Fig. 2. Abundance and spatial distribution of microplastics detected in plankton net (A), surcentral area (CA) and the southeast area (SEA) of Taihu Lake in August 2015. * means p < 0

3. Results

3.1. Water quality and grain size of sediments in Taihu Lake

The concentration of total phosphorus was highest in thenorthwest area of Taihu Lake, followed by the central area. Theconcentration of Chl-a in the northwest area was also significantlyhigher than that in the southeast area (Supplementary materialsTable 2). Silt dominated the sediments of Taihu Lake, accounting

face water (B) and sediment (C) samples collected from the northwest area (NWA), the.05.

L. Su et al. / Environmental Pollution 216 (2016) 711e719 715

for 65e80% of total sediment particles. The distribution of grain sizeshowed little variance among different sites.

3.2. Abundances of microplastics in Taihu Lake

The background contamination represented 6.8% of the averageabundance of microplastic detected in field samples. The distribu-tion of microplastic pollution showed significant spatial variationsamong different types of samples in Taihu Lake. The abundance ofmicroplastic was 0.01 � 106e6.8 � 106 items/km2 in plankton netsamples (Fig. 2A1). For plankton net samples, the average abun-dance of microplastics in the southeast area was approximately sixtimes higher than that in central area (p < 0.05). The abundance ofmicroplastic was 3.4e25.8 items/L in surface water samples andshowed less spatial variance than the plankton net samples(Fig. 2B1). The abundance of microplastics was 11.0e234.6 items/kgdw in sediments (Fig. 2C1). The average abundance of microplasticsin sediments from the northwest area was approximately six timeshigher than that of the northwest area (p < 0.05).

The maximum and minimum microplastic levels across thethree sites were 1.3e12.5 items/g ww in clams in August (Fig. 3A1)and 0.2e9.6 items/g ww in November (Fig. 3B1). There was nosignificant difference in the abundance of microplastics betweenAugust and November (Paired T-Test, p > 0.05). For the spatialdistribution, the average microplastic pollution burden was thehighest in clams from the northwest area in August and November.

Fig. 3. Abundance and spatial distribution of microplastics detected in Asian clams (Corbicularea (CA) and the southeast area (SEA) Taihu Lake in 2015. Three replicates were set for cla

There was no significant difference between farmed clams (F1 andF2) and field clams (S3 and S4) in the northwest area (p > 0.05)(Fig. 3B2).

3.3. Shape, color and size of microplastics in Taihu Lake

Fiber was the most dominant component across all sampletypes with a proportion of 48e84% (p < 0.01) (Fig. 4A). Blue itemswere prevalent in plankton net samples and surface water samples,accounting for 50e63% of microplastics (p < 0.01) (Fig. 4B). Whiteand transparent items were more common in sediments and or-ganisms, accounting for 29e44% of microplastics. Within the largersize range from 5 to 5000 mm, microplastics with a size of100e1000 mm were more frequently observed than other sizefractions in surface water, sediments and organisms (p < 0.01)(Fig. 4C). Within the range from 333 to 5000 mm,microplastics witha size of 333e1000 mm were dominant in plankton net samples(p < 0.01).

3.4. Validation of microplastics

The identification of microplastics was validated using spec-troscopic methods (Fig. 5). Of all 113 randomly selected items, 81items were identified as microplastics using m-FT-IR(Supplementary materials Table 3). For all samples, the mostcommon type of plastic was cellophane, followed by polyethylene

a fluminea) in August (A) and November (B) from the northwest area (NWA), the centralms at each site (n ¼ 3), and 1e5 individuals were pooled as one replicate.

Fig. 4. Composition of microplastics by the categories of shape (A), color (B) and size(C) in different samples from Taihu Lake in 2015.

L. Su et al. / Environmental Pollution 216 (2016) 711e719716

terephthalate, polyester, terephthalic acid and polypropylene. Inaddition, some white pellets, approximately 100 mm in diameter,were identified as non-microplastics in sediment samples usingSEM/EDS.

4. Discussion

4.1. Microplastic pollution levels and characteristic in Taihu Lake

Our results suggested that thewater, sediment and organisms ofTaihu Lake have all been polluted by microplastics. In comparisonwith worldwide investigations of microplastic pollution in fresh-water systems, the abundance of microplastics in plankton netsamples was almost two orders of magnitude higher than those inLaurentian Great Lakes of the United States and Lake Hovsgol ofMongolia (Eriksen et al., 2013; Free et al., 2014). To our bestknowledge, the levels reported in this study are the highest forfreshwater lakes worldwide (Supplementary materials Table 4).The levels of microplastic pollution in the clams from Taihu Lake

(0.2e12.5 items/g ww) were similar to those in bivalves from China(0.9e10.5 items/g) (Li et al., 2015a, 2016). In a worldwide compar-ison, these bivalves have been classified as highly polluted organ-isms by microplastics (Li et al., 2015a, 2016). The average level ofmicroplastics in Taihu Lake clams was much higher than that inbivalves (0.36 items/g) cultured for human consumption (VanCauwenberghe and Janssen, 2014). Therefore, the results of ourpresent strongly suggest that high levels of microplastics occur notonly in the water of Taihu Lake but also in organisms present in thelake.

It is reasonable to findmuch higher levels of microplastics in thelakes in areas with intensive anthropogenic activities (Eriksen et al.,2013). However, high levels of microplastics have even been foundin a remote mountain lake of Mongolia (Free et al., 2014). There are22 main influent rivers connecting the lower Yangtze River area toTaihu Lake (Wang et al., 2015), and three of these rivers connectedto the northern bay contribute 1/3 of the total inflow to Taihu Lake(Fig. 1). These rivers are spread across the most developed regionsin the Taihu Basin and carry contaminants from drainage and in-dustry. These rivers are therefore identified as the major contrib-utors of contamination to the lake (Li et al., 2013). In the vicinity ofTaihu Lake, cities with a high population density (e.g., Suzhou,Wuxi and Changzhou) are also suspected sources of the micro-plastic pollution because of the huge amounts of effluent andwaste, that may enter the lake through rivers and non-pointsources (Li et al., 2015b). In particular, the high relative abun-dance of fibers in this study indicates domestic microplastic sour-ces, such as washing machines (Browne et al., 2011). Even if wastewater treatment plants are able to remove microplastics from theireffluent (Carr et al., 2016), waste water originating from rural non-point sources has no treatment and will still constitute a significantsource of water pollution to Taihu Lake (Wang et al., 2010).

The fishing industry plays an important economical role in theTaihu Lake area, with the total aquatic products reaching 30,000tons per year (Chen and Zhu, 2008). The Asian clam is one of themost popular freshwater shellfish and one of the most commonlycultured species in the middle and lower reaches of the YangtzeRiver as well as in Taihu Lake. Accumulating evidence has suggestedthat microplastics can bring adverse effects on energy metabolism,immunity and even reproduction of organisms (Wright et al., 2013;Sussarellu et al., 2016; Galloway and Lewis, 2016). Microplastics canalso be retained through the food chain and enter human bodiesthrough diverse pathways (Farrell and Nelson, 2013; Seltenrich,2015; Yang et al., 2015). Therefore, we need to pay close attentionto the high levels of microplastic contamination in Taihu Lake andany possible human health risk from consumption of fisheryproducts.

In the present study, cellophane was the dominant particle.Cellophane is a typical semi-synthetic material because a lot ofadditives have been added to the products. It shows low biode-gradability though it is biomass derived. It was even not destroyedby hydrogen peroxide in this study. Synthetic polymer frombiomass derived is also regarded as microplastic in a recent reportof UNEP (2016). Cellophane has been defined as microplastic inprevious studies (Denuncio et al., 2011; Yang et al., 2015). Manyplastics labelled as biodegradable will breakdown completely onlywhen subjected to prolonged temperatures above 50 �C, andbiodegradable plastic seems to be a “false solution” for oceanwasteproblem (UNEP, 2016). Therefore, cellophane was defined asmicroplastic in the present study.

4.2. Spatial features of microplastic pollution in Taihu Lake

The abundance of microplastics showed great spatial variabilitywithin the same type of sample (e.g., plankton net samples). There

Fig. 5. Photographs of plastic (A1) and non-plastic (B1) items identified using m-FTIR (A2) and SEM/EDS (B2 and B3). A1 and B1 were taken under microscopes, and B2 was taken underSEM for the white box areas in B1. A2 is the spectrum for the particle in A1, and B3 is the spectrum for the particle in B2.

L. Su et al. / Environmental Pollution 216 (2016) 711e719 717

was also considerable variation between different samplescollected within the same area. Microplastic levels are known to becorrelated with anthropogenic activities (Cole et al., 2011; Barbozaand Gimenez, 2015). In Taihu Lake, the index of eutrophication has aclose relationship with the level of pollutant inflow, which alsogreatly depends on anthropogenic activities (Zhang et al., 2008).According to the index of eutrophication in this study, the north-west area of the lake was heavily polluted, and the southeast areawas relatively clean. These area-specific contamination patternsmatch well with previous studies on other chemical pollutants inTaihu Lake, such as heavy metals (Liu et al., 2012; Yu et al., 2012). Inthis study, more microplastic could come from the northwest areaof Taihu Lake than from the southeast area due to the inflows ofdifferent pollutants. Eutrophication can also decrease the lightpenetration depth and result in less plastic degradation in lakes(Andrady et al., 2011; Free et al., 2014). Therefore, further studiesare needed to illuminate the effects of accumulation of microplasticin the water of eutrophic lakes.

The highest abundance of microplastics in plankton net sampleswas observed in the southeast area of Taihu Lake. This distributionof microplastic is odds with the hypothesized of microplastics fromthe different areas of Taihu Lake. Previous studies have suggestedthat floating plastics are likely affected by meteorological condi-tions (Browne et al., 2011; Free et al., 2014; Fischer et al., 2016);Specifically, strong wind can increase the dissipation of floatingmicroplastic (Collignon et al., 2012). Generally, the hydrodynamicsprocesses are the poorest in the southeast area of Taihu Lake basedon the characteristics of wind and wave of the whole lake regions,and the wind speed was less than 2 m/s in southeast area duringthe sampling period in Taihu Lake. Therefore, a minor disturbancein meteorological and hydrological conditions could result in anincrease in the accumulation of floating microplastics and beresponsible for the high abundance observed in the southeast area.

Unlike in plankton net samples, the abundance of microplasticsin sediments was the lowest in all three sites located in thesoutheast area, and there was a clear trend, increasing from thesoutheast to the northwest area of the lake. This trend matchedwell with the chemical contaminants (Supplementary materialsTable 2). The microplastics can be carried from the rivers, float in

the surface water, stay in the water column or sink into sedimentsof the lake. The sediments were more stable than water, andmicroplastics in the sediments will be transported more slowlythan those floating in surface water. Therefore, the microplasticpollution levels in sediments from the lake were more closelyrelated to the distance from the contamination source asmentioned above.

4.3. Bioaccumulation of microplastics in clams and biomonitoringof microplastics in freshwater

In the present study, Asian clams were available at most of thesampling sites in Taihu Lake. No significant differences were foundin the presence of microplastics in clams among the different areasof the lake (Fig. 6). The concentrated factor ranged from 38 to 3810and was negatively correlated with the abundance of microplasticsin sediments (p < 0.05). In laboratory studies, the bioaccumulationof microplastics has been proved to occur in coastal invertebrateseven when the background concentration of microplastics is rela-tively low (Set€al€a et al., 2016). Our results suggest that clamsshowed a higher concentrated factor when the abundance ofmicroplastics was lower in lake sediments. This phenomenonmight be one of the reasons why the abundances of microplastics inclams showed no significant differences in different areas of thelake.

Bivalves are of particular interest in microplastic studies andmonitoring because their extensive filter-feeding activity exposesthem directly to microplastics present in aquatic environments(Farrell and Nelson, 2013; Li et al., 2015a; Sussarellu et al., 2016).Clams are representative benthic filter feeders and a diet item ofmany other benthic species. The Asian clam originates in Asia andcan now be found worldwide (Sousa et al., 2008). It has a widerange of habitats from freshwater (e.g., river and lake) to estuarineenvironments. It has been successfully used in the biomoniotoringof emerging contaminants (e.g., nanoparticles) owing to the ad-vantages stated above (Pereira et al., 1999; dos Santos andMartinez,2014; Cid et al., 2015). Our findings suggest that microplastics arenot only ingested by benthonic organisms but are also likely toaccumulate in clams to a great extent. The large concentrated factor

0 100 200101

102

103

104

R=0.69

Microplastics in sediments (items/kg dw)

The

conc

entra

ted

fact

or

Fig. 6. The relationship of the concentrated factor (the microplastics in clams/themicroplastics in sediments) and the abundance of microplastics in sediments from 9sites of Taihu Lake in August 2015.

L. Su et al. / Environmental Pollution 216 (2016) 711e719718

indicated that Asian clams could also be an ideal indicator ofmicroplastic pollution in freshwater and estuarine environments.Nevertheless, larger-scale investigations on microplastics are stillrequired to validate this proposal of clams in the future.

In conclusion, we found that high levels of microplasticsoccurred not only in the water but also in the organisms of TaihuLake. To our best knowledge, the microplastic levels found in TaihuLake was the highest in plankton net samples in freshwater lakesworldwide. We need to pay close attention to the microplasticcontamination in Taihu Lake and the possible link to human healthrisks resulting from the consumption of fishery products. We pro-pose that the widespread Asian clam could serve as a useful bio-indicator for microplastics pollution in freshwater and estuarineenvironments.

Notes

The authors declare no competing financial interest.

Acknowledgments

This work was supported by grants from the Natural ScienceFoundation of China (21507031, 41571467) and the Natural ScienceFoundation of Jiangsu (BK2012152).

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.envpol.2016.06.036.

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