Occurrence and characteristics of microplastic pollution in Xiangxi Bay

Subscriber access provided by University of Newcastle, Australia

Article

Occurrence and characteristics of microplastic pollution in Xiangxi Bay of Three Gorges Reservoir, China Kai Zhang, Xiong Xiong, Hongjuan Hu, Chenxi Wu, Yonghong Bi, Yonghong Wu, Bingsheng Zhou, Paul Kwan-Sing Lam, and Jiantong Liu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b00369 • Publication Date (Web): 16 Mar 2017 Downloaded from http://pubs.acs.org on March 16, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

Environmental Science & Technology

TOC Art 270x151mm (300 x 300 DPI)

ACS Paragon Plus Environment


1

Occurrence and characteristics of microplastic pollution in Xiangxi Bay of Three

2

Gorges Reservoir, China

3

Kai Zhang1,2,4, Xiong Xiong1, Hongjuan Hu1, Chenxi Wu1*, Yonghong Bi1, Yonghong

4

Wu3, Bingsheng Zhou1, Paul K. S. Lam2, Jiantong Liu1

5

1

6

Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China

7

2

8

Kong SAR, China

9

3

State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of

State Key Laboratory in Marine Pollution, City University of Hong Kong, Hong

State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Sciences,

10

Chinese Academy of Sciences, Nanjing 21008, China

11

4

University of Chinese Academy of Sciences, Beijing 100039, China

12 13

* Corresponding author

14

Chenxi Wu

15

Address: Donghu South Road No.7, Wuhan, P.R.China, 430072

16

Tel: +86-27-68780712

17

Fax: +86-27-68780123

18

E-mail: [email protected]

19 20 21 22 1


Page 2 of 36

Page 3 of 36


23

ABSTRACT: Microplastic pollution in inland waters is receiving growing attentions.

24

Reservoirs are suspected to be particularly vulnerable to microplastic pollution.

25

However, very limited information is currently available on pollution characteristics

26

of microplastics in reservoir ecosystems. This work studied the distribution and

27

characteristics of microplastics in the backwater area of Xiangxi River, a typical

28

tributary of the Three Gorges Reservoir. Microplastics were detected in both surface

29

water and sediment with concentrations ranging from 0.55×105 to 342×105 items km-2

30

and 80 to 864 items m-2, respectively. Polyethylene, polypropylene, and polystyrene

31

were identified in surface water, while polyethylene, polypropylene, and polyethylene

32

terephthalate, and pigments were observed in sediment. In addition, microplastics

33

were also detected in the digestion tracts of 25.7% of fish samples, and polyethylene

34

and nylon were identified. Redundancy analysis indicates a weak correlation between

35

microplastics and water quality variables but a negative correlation with water level of

36

the reservoir and Secchi depth. Results from this study confirm the presence of high

37

abundance microplastics in reservoir impacted tributaries, and suggest that water level

38

regulated hydrodynamic condition and input of nonpoint sources are important

39

regulators for microplastic accumulation and distribution in the backwater area of

40

reservoir tributaries.

41 42 43 44 2



45

INTRODUCTION

46

Plastic products are extensively used in the modern world. The annual global

47

production of plastics increased 40% in the past decade and reached 322 million

48

tonnes in 2015.1 However, improper use and disposal of plastics are causing severe

49

environmental problems.2, 3 Most plastics are resistant to degradation and are able to

50

persist in the environment for tens to hundreds of years.4 Worse still, smaller plastic

51

debris can be generated during the breakdown of large plastic products and plastics

52

measuring less than 5 mm are commonly referred to as microplastics.2, 5 In the past

53

decade, detection of microplastics in marine and terrestrial environments has been

54

increasingly reported, and microplastics are considered as contaminants of emerging

55

concern.6-8

56

Microplastics in aquatic ecosystems can be mistakenly ingested by aquatic

57

animals and water birds,9-11 and food chain transfer has also been found to be

58

possible.12, 13 Therefore, microplastic pollution in aquatic environments has raised

59

growing concerns regarding their potential threats to aquatic animals and even

60

seafood safety.14-16 Recently, microplastics were found to be able to inhibit hatching,

61

decrease growth rate, and alter the feeding preferences and innate behavior of

62

European perch (Perca fluviatilis) larvae at environmentally relevant concentrations.17

63

Leachates from plastics are reported to affect larval development in brown mussels

64

and inhibit barnacle settlement.18, 19

65

Information on microplastic pollution from freshwater environments is limited

66

compared to that from marine environments.7, 20 However, the majority of plastic 3


Page 4 of 36

Page 5 of 36


67

debris in oceans is derived from the use of plastics on land although discharges from

68

ocean vessels and general shipping activities can also contribute a minor portion.21 It

69

was estimated that 275 million tonnes of plastic wastes were generated in 2010 in 192

70

coastal countries, and about 2.5 to 6.6% of the total plastic wastes ended up in the

71

ocean.21 The remainder of plastic wastes could be either recycled, disposed of in

72

landfills, incinerated (with or without energy recovery), or stay in terrestrial

73

environment.3 Recent works show the ubiquitous presence of microplastics in many

74

inland waters, and their abundances in some inland waters are found to be much

75

higher than those reported in marine environments.22-25 Therefore, microplastic

76

pollution from inland waters deserves more attention.

77

The Three Gorges Dam (TGD) is the largest hydropower project in the world. It

78

is of great importance to electric power generation, river transportation, and water

79

conservancy and control. But controversy has never stopped since the project was first

80

proposed in the early 20th century due to its unprecedented magnitude and broad

81

impacts especially on environmental and ecological aspects.26 Many environmental

82

problems have emerged in the Three Gorges Reservoir (TGR) area since the

83

impoundment of the TGD, such as algal blooms, water quality deterioration, and

84

reduction of domestic fish species.27 Floating garbage, including many plastic wastes,

85

is another issue in the TGR especially during rainy season.28 In our previous work,

86

surface water from the TGR was found to be seriously polluted by microplastics, and

87

tributaries are believed to be contributors of microplastic pollutants in the Yangtze

88

River mainstream in the TGR.23 4



89

Since the impoundment of the TGD, intense algal blooms have been observed in

90

many tributary backwater areas due to a drastic decrease in flow rate.29 Many villages

91

and towns are located near the banks of tributaries. But anthropogenic wastes in these

92

underdeveloped areas are poorly managed and can be discharged into the tributaries

93

intentionally, or following surface runoff, causing pollution of the tributaries. In this

94

work, microplastic pollution was studied in Xiangxi River, a typical tributary within

95

the TGR area which has attracted great research interest previously.29-31 Planktonic

96

samples were collected seasonally from upstream to downstream sites in the

97

backwater area of Xiangxi River to reveal the spatial and temporal distribution

98

patterns of microplastics in surface water and to investigate their relation with

99

phytoplankton, zooplankton, and environmental variables. Sediment and fish samples

100

were also collected and analyzed for microplastics to illustrate their fate. This

101

comprehensive study contributes to a better understanding of the occurrence,

102

distribution, and potential impacts of microplastics in reservoir ecosystems.

103 104

MATERIALS AND METHODS

105

Study Area. Xiangxi River is the largest Yangtze River tributary in the TGR area

106

in Hubei Province. It originates from Shennongjia mountain area and flows through

107

Xingshan and Zigui Counties with a watershed area of 3099 km2.30 The main human

108

activities in this area include mining, chemical industry, agriculture, and tourism. The

109

water level of Xiangxi River has risen about 40 m since 2003, and varies seasonally as

110

regulated by the TGD. The TGR is usually operated at a high water level in winter for 5


Page 6 of 36

Page 7 of 36


111

electric power generation and at a low water level in summer for flood control. Seven

112

sampling sites were selected from upstream to downstream of the Xiangxi River

113

backwater area (Fig. 1). The most upstream site ZJ was located near Zhaojun Town

114

within the uppermost area that backwater can reach in summer. The most downstream

115

site XX was located near Xiangxi Town within the estuary area entering the Yangtze

116

River mainstream. Site GL was at the mouth of Gaolan River - a major tributary of

117

Xiangxi River. Another four sites were roughly evenly distributed along the Xiangxi

118

River main channel.

119

Sample Collection. Microplastics in surface water were collected by surface

120

trawling in April, July, and October 2015 and in January 2016. Surface trawling was

121

performed following a previous method.23 Briefly, a trawl net (50 × 100 × 150 cm,

122

with a mesh size of 112 µm) was towed vertically to the flow direction by the side of a

123

boat at a speed of ~5 km h-1 from one side to the other side of the river and back. The

124

towing distance varied from 190 to 480 m depending on the river width at the

125

sampling site. After each towing, the net was rinsed with river water from outside and

126

floating debris retained in the net was transferred into a 1-L glass bottle and preserved

127

with 5% methyl aldehyde before analysis. The net was turned over and rinsed three

128

times with distilled water before next sampling to reduce cross contamination. At the

129

same site, phytoplankton, zooplankton, and water samples were collected according to

130

the standard methods for plankton survey,32 and analyzed after being transported back

131

to the laboratory in a cooler. Dissolved oxygen (DO), pH, water temperature (T), and

132

conductivity (EC) were measured in situ using a HQ40d meter (Hach, Loveland, CO, 6



133

USA). Secchi depth (SD) was measured using a Secchi disk. Water level (WL) data

134

were obtained from China Three Gorges Corporation. Sediment samples were

135

collected from the midstream channel in January 2016 with a Petersen grab sampler

136

with an opening area of 0.0625 m2. Collected sediment samples were passed through

137

a 0.3-mm mesh sieve, and debris retained on the sieve was rinsed into a 500-mL glass

138

bottle with distilled water. Sediment samples were preserved with 5% methyl

139

aldehyde before analysis. Fish samples were acquired from local fishermen in June

140

2016. Thirty five fish belonging to 13 species were obtained and were dissected after

141

weight and length measurements. Digestive tracts were stored in glass vials and

142

transported back to the laboratory in a cooler for further treatment.

143

Sample Analysis. Surface water and sediment samples were processed following

144

previous methods.23, 33 Detailed procedure is provided in Supplementary Information.

145

The digestion tract of each fish was weighed and digested using a 10% KOH solution

146

following Foekema et al.34 The digested solution was filtrated onto Whatman GF/C

147

glass fiber filters (1.2-µm pore size). Samples on filters were examined under a

148

stereomicroscope up to 40× magnification, suspected microplastics were identified

149

primarily based on their shape, surface texture, color and luster, and picked out with

150

tweezers for further confirmation. During sample analysis, nitrile gloves and cotton

151

laboratory coat were worn, all containers were washed with distilled water and

152

covered with aluminum foil if not in use, and sample pretreatment were performed in

153

hood with laminar flow to reduce contamination.

154

All suspected microplastics were examined using a Renishaw inVia Raman 7


Page 8 of 36

Page 9 of 36


155

microscope (Wotton-under-Edge, Gloucestershire, UK). Raman spectra were recorded

156

from 300-3200 cm-1 with a laser excitation wavelength of 785 nm. The spectra of the

157

samples were searched in the Renishaw Polymeric Materials Database and types of

158

microplastics were identified based on the similarity to the spectra of standards.

159

Presence of pigments was observed in sediment samples, which interfered with the

160

identification. To distinguish between pure pigments and pigment containing

161

microplastics, we followed the protocol of Imhof et al,35 and particles showing C-H

162

stretching peaks around 2800-3100 cm-1 were considered as microplastics and were

163

identified based on the match of characteristic peaks with references. The Raman

164

spectra of typical samples are presented in Fig. S1.

165

Phytoplankton and zooplankton identification and quantification were performed

166

by reference to Zhang and Huang.36 Total phosphorus (TP), total nitrogen (TN),

167

ammonia nitrogen (NH4+-N), and nitrate nitrogen (NO3--N) in surface water samples

168

were analyzed following standard methods.37

169

Data Analysis. The abundance of microplastics in surface water and sediment

170

from each sampling site was calculated by dividing the number of identified

171

microplastics by the towing area (found by multiplying the towing distance by the

172

width of the trawl net) and the opening area of the Peterson grab sampler expressed as

173

items km-2 and items m-2, respectively.

174

Microplastics were treated as a taxon of plankton. Together with other taxa of

175

planktons, their relationship with environmental variables was determined using

176

ordination analysis. Linear ordination method was applied according to the Detrended 8



177

Correspondence Analysis (DCA) of the taxa and environmental variables, and

178

Redundancy Analysis (RDA) was performed to obtain appropriate ordination. Taxa

179

data and environmental variables (except pH) were logarithmically transformed

180

before RDA to eliminate the influence of extreme values on ordination scores.

181

Environmental variables with high correlation coefficients (r > 0.6) were excluded in

182

the final RDA analysis, and 6 out of 10 environmental variables were selected using a

183

forward selection of environmental variables. The analysis of RDA was performed

184

using Canoco Version 4.5.

185 186

RESULTS AND DISCUSSION

187

Occurrence of Microplastics in Surface Water. Microplastics were detected in

188

all sampling sites and their abundances varied from 0.55×105 to 342×105 items km-2

189

(Table 1). A typical microplastic sample from surface water is presented in Fig. 2a.

190

Microplastic abundances observed in this study were similar to our previous

191

observation in the Yangtze River mainstream and the tributary estuaries

192

(1.92×105-136×105 items km-2) of the TGR.23 Relatively high abundance of

193

microplastics has also been reported in Taihu Lake (0.1×105-68×105 items km-2),24

194

North Shore Channel in Chicago (7.3×105-67×105 items km-2),38 and Rhine River

195

(1.45×105-30.7×105 items km-2).39 Whereas, relatively lower abundance of

196

microplastics was detected in the Laurentian Great Lakes (0-4.66×105 items km-2),

197

estuarine rivers in the Cheaspeake Bay (0.055×105-2.6×105 items km-2),22 and Swiss

198

lakes (0.11×105-2.2×105 items km-2).40 9


Page 10 of 36

Page 11 of 36


199

Spatially, relatively higher microplastic abundances were observed at XKD

200

downstream from Xiakou Town except in January 2016 (Fig. 3a), which could be

201

related to the input of plastic wastes from Xiakou - the largest town along the

202

riverside of the backwater area with a population of 24,582 in 2010 according to the

203

data from Xingshan County Bureau of Statistics. Sewer systems are not installed in

204

this town, and municipal wastewater is treated primarily using onsite septic systems

205

or is discharged directly. Wastes are poorly managed, and many untended trash dump

206

sites were observed in the town. Therefore, wastewater discharge and surface runoff

207

may carry plastic wastes and other pollutants into the river. Additionally, input from

208

Gaolan River could also increase microplastic abundance in the main channel. All

209

these sources together might have led to the higher microplastic abundances at XKD.

210

Seasonally, the highest and lowest average abundances of microplastics were

211

observed in July 2015 (65.6×105 item km-2) and in January 2016 (4.5×105 item km-2),

212

respectively. Microplastics collected in July 2016 at GL had the highest abundance

213

among all samples, which was one or two orders of magnitude higher than those

214

observed at other sampling sites. According to the records from a local experimental

215

station, the study area experienced heavy precipitation in July 2015 (Fig. S2).

216

Therefore, higher microplastic abundances observed in July may be related to an

217

increase in surface runoff during heavy rainfall evens, which could carry plastic

218

wastes within the watershed into the river. Relatively steep slopes along both sides of

219

the river also exacerbate the transport of plastic wastes from the river bank to the

220

water. 10



221

The distinctive hydrodynamic characteristics of tributaries in the TGR can also

222

influence the spatial and seasonal distribution of microplastics. Based on water flow

223

velocity and direction, Xiangxi River can be divided into riverine, transitional,

224

lacustrine, and mainstream influenced zones.41 The site XKD is within the lacustrine

225

zone (Fig. S3), which is characterized by a very low surface flow velocity (

Occurrence and characteristics of microplastic pollution in Xiangxi Bay

Recommend Documents