Trophic transfer of methyl siloxanes in the marine food web from coastal area of Northern China.

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Trophic transfer of methyl siloxanes in the marine food web from coastal area of Northern China Hongliang Jia, Zifeng Zhang, Chaoqun Wang, Wen-Jun Hong, Yeqing Sun, and Yi-Fan Li Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es505445e • Publication Date (Web): 27 Jan 2015 Downloaded from http://pubs.acs.org on February 7, 2015

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Environmental Science & Technology

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Trophic transfer of methyl siloxanes in the marine food web

2

from coastal area of Northern China

3

Hongliang Jia1, Zifeng Zhang2, Chaoqun Wang1, Wen-Jun Hong1, Yeqing Sun3,

4

Yi-Fan Li2,1*

5 6

1

7

College of Environmental Science and Engineering, Dalian Maritime University,

8

Dalian 116026, China

9

2

International Joint Research Centre for Persistent Toxic Substances (IJRC-PTS),

IJRC-PTS, State Key Laboratory of Urban Water Resource and Environment, Harbin

10

Institute of Technology, Harbin 150090, China

11

3

12

China

Institute of Environmental Systems Biology, Dalian Maritime University, Dalian,

13 14

*

15 16

Yi-Fan Li: tel: 86-411-8472-8489; [email protected]

Corresponding author phone: fax:

86-411-8472-8489;

E-mail:

1

ACS Paragon Plus Environment


17 18 19

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TOC figure

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2


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Abstract

22

Methyl siloxanes, which belong to organic silicon compounds and have linear and

23

cyclic structures, are of particular concern because of their potential characteristic of

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persistent, bioaccumulated, toxic, and ecological harm. This study investigated the

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trophic transfer of four cyclic methyl siloxanes (octamethylcyclotetrasiloxane (D4),

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decamethylcyclopentasiloxane (D5),

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tetradecamethylcycloheptasiloxane (D7)) in a marine food web from coastal area of

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Northern China. Trophic magnification of D4, D5, D6 and D7 were assessed as the

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slope of lipid equivalent concentrations regressed against trophic levels of marine

30

food web configurations. A significant positive correlation (R = 0.44, p < 0.0001) was

31

found between lipid normalized D5 concentrations and trophic levels in organisms,

32

showing the trophic magnification potential of this chemical in the marine food web.

33

The trophic magnification factor (TMF) of D5 was estimated to be 1.77 (95%

34

confidence interval (CI): 1.41 - 2.24, 99.8% probability of the observing TMF > 1).

35

Such a significant link, however, was not found for D4 (R = 0.14 and p = 0.16), D6 (R

36

= 0.01 and p = 0.92), and D7 (R = -0.15 and p = 0.12); and the estimated values of

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TMFs (95% CI, probability of the observing TMF > 1) were 1.16 (0.94 – 1.44,

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94.7%), 1.01 (0.84 - 1.22, 66.9%) and 0.85 (0.69 - 1.04, 48.6%) for D4, D6, and D7,

39

respectively. The TMF value for the legacy contaminant BDE-99 was also estimated

40

as a benchmark, and a significant positive correlation (R = 0.65, p < 0.0001) was

41

found between lipid normalized concentrations and trophic levels in organisms. The

42

TMF value of BDE-99 was 3.27 (95% CI: 2.49 – 4.30, 99.7% probability of the

43

observing TMF > 1), showing the strong magnification in marine food webs. To the

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best of our knowledge, this is the first report on the trophic magnification of methyl

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siloxanes in China, which provided important information for trophic transformation

46

of these compounds in marine food webs.

dodecamethylcyclohexasiloxane

(D6), and

3



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Introduction

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Methyl siloxanes, which consist of a backbone of alternating silicon-oxygen

49

(Si-O) units with methyl side attached to each silicon atom, belong to organic

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silicon compounds, including linear and cyclic structures. Linear methyl

51

siloxanes are also called polydimethylsiloxane (PDMS), usually expressed as Ln

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(L means linear structure and n is the number of silicon atom). Cyclic methyl

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siloxanes are usually expressed as Dn (D means cyclic structure and n is the

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numbers of silicon atom) (1-2). As the intermediates of silicone industrial products,

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methyl siloxanes were first produced by Dow Corning Corporation, USA, in the

56

1940’s (3-4), and have been widely used in our daily necessities, such as cosmetics,

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pharmaceuticals, health care products, cooking utensils, plastics, papers, building

58

materials, decoration materials, electronic products, and much more (5-6). It has been

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shown that there has been a rapid growth in the demand and production of some

60

cyclic methyl siloxanes in the Chinese market. For example, the Chinese market

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demand was 73 000 t in 2000, 141 000 t in 2003, then rose to 330 000 t in 2007 (7).

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Due to extensive production and usage of these chemicals, D4, D5, and D6 have been

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classified as high production volume (HPV) chemicals by the US Environmental

64

Production Agency (8) and the Organization for Economic Co-operation and

65

Development (9).

66

As a result of the widespread usage and physiochemical properties of methyl

67

siloxanes, these compounds have been detected in almost all kinds of environmental

68

media, such as air (10-12), fresh water (13-16), sea water (17), sediment (13,17-20),

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and biota (17,21-23). Studies showed that one of the most significant pollution

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sources of methyl siloxanes is the emission from cosmetics and household products

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used by the general public (24-27).

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Three cyclic methyl siloxanes (D4, CAS No. 556-67-2; D5, CAS No. 541-02-6; D6,

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CAS No., 540-97-6) have been screened by Canada and Europe to determine whether

74

these chemicals present a risk to the environment or ecological harm (28-33). The

75

screening assessment results determined by government of Canada showed that D4 4


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and D5 were entering the environment where had the potential to cause ecological

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harm, while the quantities of D6 entering the environment are not large enough to

78

cause potential ecological harm (31-33). D4 was in accordance with the criteria of

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persistence, bioaccumulation, and toxicity (31). D5 conformed to persistence and

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toxicity criteria, but the bioaccumulation criterion was uncertain due to the

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contradictions of the modeling and experimental results (32). D6 was in according

82

with the criteria of persistence, but not with bioaccumulation and toxicity (33).

83

Compared to Canada, the risk assessment report published by Europe gained the same

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results for D4 and D6, but not for D5, they thought D5 was persistent and

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bioaccumulated, but not toxic to the ecological environment (28-30).

86

Due to the lack of relevant experiment data, the results from the above reports were

87

mainly obtained by using models, which led to greatly uncertainties, and controversies

88

exist over the bioaccumulation and biomagnification potential of methyl siloxanes

89

among scientific communities. The available BCFs for fish were 12 400 L/kg for D4

90

(34), ranging from 3 362 to 13 300 L/kg for D 5 (35-37), and 1 160 L/kg for D6 (38).

91

Published investigations evaluating TMF values for methyl siloxanes are limited to

92

five bodies of water in the USA, Norway and Canada (21-23, 39-40). The estimated

93

TMFs in a benthic freshwater food web of Lake Pepin, USA (39) and in the marine

94

food web of the Oslofjord, Norway (40) both indicated that D5 was not biomagnified

95

(TMF below 1). In the studies on Lakes Mjøsa and Randsfjorden, Norway, however,

96

the TMFs values for D5 and D6 were 2.9 and 2.3, respectively, indicating that trophic

97

magnification was occurring (21-22). In the study on Lake Erie, Canada, the TMF

98

values were highly dependent on food web configuration (23). Besides the BCFs and

99

TMFs, Kierkegaard et al. (19) reported that D4 and D5 presented relative high

100

bioaccumulation factors (BAFs) in ragworm and flounder. Previous studies have

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reported that biota sediment accumulation factor (BSAF) values were 0.7 ~ 2.2 for D4

102

(41) and 0.46 ~ 1.2 for D5 in midge (Chironomus riparius) (42), which were both

103

higher than the results conducted by Hong et al. (17), who estimated the values of

104

BSAF in fish were ranged 0.445~1.61 for D4, 0.0403 ~ 0.251 for D5, 0.632 ~ 2.06 for

105

D6, and 0.374 ~ 1.89 for D7 (17). 5



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In light of the limited and uncertain bioaccumulation data of methyl siloxanes in

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aquatic food webs, especially in marine food webs, the objective of present study is to

108

investigate the concentration and trophic magnification of methyl siloxanes in marine

109

food webs in coastal area of Northern China.

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Materials and Methods

111

Sample collection.

112

Dalian Bay is located in the north region of the Chinese Yellow Sea, with an area of

113

40 km2 and average depth of 15 m (maximum of 35 m). In the present study, all

114

marine organism samples were collected from Dalian Bay in September 2013, and the

115

sampling map was shown in Figure S1, Supporting Information (SI). Five fish species

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including pacific herring (Clupea pallasii) (n = 26), mackerel (Pneumatophorus

117

japonicus) (n = 15), greenling (Hexagrammos otakii) (n = 7), schlegel's black rockfish

118

(Sebastes schlegelii) (n = 6), sea catfish (Synechogobius hasta) (n = 7), and one

119

species of crustacean, mud crab (Scylla serrata) (n =15) were collected with a bottom

120

trawl at site S2, (the location of sampling sites can be also found in Figure S1, SI).

121

Four mollusk species including mactra quadrangularis (Mactra veneriformis) (n = 21),

122

short-necked

123

galloprovincialis) (n = 30), black fovea snail (Omphalus rustica) (n = 71) were

124

collected from culturing raft at site S2 and S3. In addition, clamworm (Perinereis

125

aibuhitensis) (n = 60) and another mollusk species, arthritic neptune (Neptunea

126

cumingi) (n = 9) was collected from sediment using a bucket at site S1 and S2, and

127

sea lettuce was collected at site S1, S2 and S3 from the surface of seawater. For fish

128

samples, an acetone rinsed bistoury was used to harvest the muscles. For mollusk and

129

crustacean samples, an acetone rinsed bistoury was used to collect the tissues.

130

Clamworm and sea lettuce samples were collected the whole body. All samples were

131

packed in solvent-rinsed glass bottles with Teflon-lined caps. After collection, all the

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biota samples were frozen immediately in the field and transported to the laboratory,

133

where were stored at -20oC. Detailed information for samples can be found in Table

clam

(Ruditapes philippinarum)

(n

=

30),

mussel

(Mytilus

6


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S1, SI, which including the species of biota, the Latin name of biota, the number of

135

individual, the moisture content, the fat content, stable isotope signatures of carbon

136

and nitrogen, estimated trophic level and the body length and weigh. The five fish

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species studied in the present study generally reside in Dalian Bay and coastal area

138

around over the entire year.

139

To reduce the risk of contamination during sampling, all sample preparation was

140

conducted outdoors, that is, the material was outdoors from the time of sampling until

141

it was sealed in bottles. All personal care products were prohibited 24 h prior to the

142

sample collection. In the whole process of sample collection, PE gloves were worn.

143

Before sample collection, the surfaces of hands were rinsed by MilliQ water

144

thoroughly. All equipment and utensils were cleaned in acetone between samples. The

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samples were only in contact with acetone-cleaned utensils of stainless steel (tweezers,

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knife, bistoury). One field blank was collected for every 10 biota samples during

147

sampling process. Field blanks (10 mL n-hexane/ethyl acetate mixture (1:1 v/v)

148

contained in a glass dish with 5 cm diameter) were exposed to air and handled in the

149

same manner as the samples, and then sealed in glass jars with Teflon-lined caps.

150

Chemicals and Reagents.

151

For methyl siloxane analysis, standard samples of D4, D5 and D6 were obtained from

152

Tokyo Chemical Industry (Wellesley Hills, MA, USA). PDMS 200 fluid (Viscosity of

153

5 cSt) including D7 and linear siloxanes (L4~L17) was obtained from Sigma-Aldrich

154

(St.Louis,

155

(trimethylsiloxy)-silane (M4Q; PURITY 97%) was purchased from Aldrich. For

156

polybrominated

157

(2,2',4,4',5-pentabromodiphenyl ether) and BDE-71 (2,3’,4’,6-tetrabromadiphenyl

158

ether) were purchased from AccuStandard (New Haven, CT, USA). BDE-71 was used

159

as the surrogate standard during the PBDEs determinations. Organic solvents and

160

reagents used in this study were of pesticide grade purity (J.T. Baker, Phillipsburg,

161

NJ).

MO,

USA).

diphenyl

A

surrogate

ethers

standard

(PBDEs)

containing

analysis,

Tetrakis

BDE-99

7



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Chemical analysis of methyl siloxanes.

163

The procedures of methyl siloxanes dermination for biota samples were followed the

164

report previously (17), and a brief description is presented here. After homogenized, 1

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g biota samples (wet weight) was taken separately in a 10-mL glassware tube,

166

keep the glassware tube undisturbed for 30 min after 100 ng of surrogate standard

167

M4Q added. Then, samples were shaken with 5 ml of n-hexane/ethyl acetate mixture

168

(1:1 v/v) for 30 min and then centrifuged for 5 min at a centrifugal force of 1000g.

169

The solvent layer was then transferred into a flat-bottom flask. The process of

170

extraction was repeated three times, then combined the extractions and rotary

171

evaporated to 1 mL. The 1 mL extractions were passed through a 5.5 g silica

172

(activated at 130 oC for 7 hours and deactivated with 3.3% MilliQ water) gel column

173

after a 25 mL hexane pre-rinse and eluted with 50 mL of hexane/DCM mixture (1:1,

174

v/v). The extract was rotary evaporated to 1 ml, then solvent-exchanged into isooctane

175

and reduced to 1 mL under nitrogen (purity 99.999%) prior to GC-MS analysis.

176

All extracts were identified and quantified using a Thermo Trace gas chromatograph

177

(Thermo TRACE 2000) coupled with a Polaris Q mass spectrometer. Splitless

178

injection was used (2µL), along with a DB-5 column, (HP 30 m × 0.25 mm i.d.× 0.25

179

µm film thickness). The GC column oven temperature was programmed at a rate of

180

20oC /min from an initial temperature of 40oC to 220oC, then at a rate of 10 oC/min to

181

280 oC (held for 10min), then at a rate of 10 oC/min to 300 oC (held for 5 min). The

182

temperatures of injector, transfer line and ion source were held at 200, 280 and 250oC,

183

respectively. Electronic impact (EI) ionization with selective ion mode (SIM) was

184

used for quantification. Quantifications for all methyl siloxanes were based on the

185

responses of the external calibration standards.

186

Chemical analysis of PBDEs and lipid determination.

187

Samples for PBDEs analysis were extracted and analyzed according to the methods

188

established at the National Laboratory for Environmental Texting (NLET),

189

Environment Canada, and have been reported previously (43). Details for PBDEs 8


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analysis can be found in SI.

191

Two grams of biota samples were first oven dried at 105 °C for eight hours for

192

moisture determination. After that, the dried samples were Soxhlet extracted for 24 h

193

with 100 mL mixed solvent (hexane/acetone, 1:1 v/v). After extraction, water was

194

removed from the extract with anhydrous sodium and the sample was

195

rotary-evaporated to 1 mL. And then, lipid content was determined gravimetrically.

196

The details of the determination of lipid content can also be found elsewhere (43-44).

197

Trophic level descriptors.

198

Stable isotopic ratios of carbon (δ13C) and nitrogen (δ15N) were analyzed following

199

the method reported previously (23). Briefly, biota samples (~ 1.0 mg) were dried at

200

105 °C for 6 h and then ground to a fine power using a ball mill. Before instrument

201

analysis, samples were not lipid and carbonate removed or extracted. δ13C and δ15N

202

were determined by Thermo Delta V Advantage isotope mass spectrometer, coupled

203

with Thermo Flash EA 1112 HT elemental analyzer. Isotopic ratios are reported

204

relative to those determined for atmospheric air (N) and the Peedee Belemnite

205

formation (C). To reduce bias in δ13C affected by lipid content in samples, the δ13C

206

values were adjusted mathematically for the C:N ratio according to the previously

207

report (adjusted δ13C = δ13C – 3.32 + 0.99 × C:N) (45).

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Quality Assurance/Quality Control.

209

In order to reduce the contamination, special care was taken in sampling and

210

treatment. All personal care products were prohibited and PE gloves were worn during

211

sample collection, packaging and treatment. Instrument contamination test was

212

performed with isooctane injection. Besides, we checked all the appliance, equipment,

213

solvent in order to reduce contamination. The sample treatment process was

214

performed in a clean air cabinet. All samples were spiked with labeled recovery

215

standard (M4Q) prior to extraction. In addition to field blanks, procedure blanks were

216

also analyzed in sequence to check for contaminations. Method recoveries and

217

repeatabilities of methyl siloxanes were assessed by spiking anhydrous sodium sulfate 9



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(spike sample) with the calibration solution. During treatment, procedure blank and

219

spike sample were analyzed with each batch of 10 samples. In addition to spike

220

samples, a batch of 7 internal matrix controls (homogenate of fish muscle) was also

221

analyzed prior to sample treatment.

222

The limits of detection (LODs) and the limit of quantification (LOQ) were defined as

223

the average blank concentrations plus 3 and 10 times the standard deviation (SD)

224

respectively for compounds which were detectable in blanks (D4 – D7), and were

225

determined by assessing the injection amount that corresponded to a signal-to-noise

226

ratio (S/N) of 3 and 10 for compounds which were not detectable in blanks (L4 – L17

227

and BDE-99). The values of methyl siloxanes were not blank corrected.

228

Data analysis.

229

The relative trophic level (TL) of each sample (consumer) was calculated from δ15N

230

using an enrichment factor ∆N of 3.4‰ (21, 46-48). In the present study, short necked

231

clams (Ruditapes philippinarum) were used to estimate the δ15N baseline and were

232

assumed to represent the trophic level 2 as used in previous studies (49-51) (eq 1).

TLconsumer = ((δ 15 N consumer − δ 15 N Ruditapes philippinarum ) / ∆N ) + 2

(1)

233

Trophic magnification factors (TMFs) can be estimated as the slope (b) of the lipid

234

normalized contaminant concentrations ([chemical concentration]lw) regressed onto

235

the TL (21,49-51) (eq2 and eq 3). log[chemical concentration] lw = a + bTL

(2)

TMF = 10 b

(3)

236

Statistical analysis of the data was performed using Microsoft Excel 2003 and SPSS

237

10.0, and Monte-Carlo simulations were performed by the R Programming Language.

238

For values below LOQ, the concentrations were set to 2/3 of LOQ during statistical

239

analysis.

10


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Results and discussion

241

QA/QC results.

242

In order to minimize background levels of methyl siloxanes, particular cautions were

243

performed during sample preparation and analysis following the procedures given by

244

Hong et al. (17) Before GC-MS analysis, isooctane was injected twice as a purge of

245

the GC system after every 5 injections of samples. Blank examination of organic

246

solvents and reagents used in this study were all far below LOQs for methyl siloxanes.

247

During sample treatment, all storage tanks and containers that were used were made

248

of glass, metal and Teflon.

249

The content of methyl siloxanes in blanks were listed in Table S2, SI, showing that,

250

D4, D5, D6, and D7 were all detectable in field and procedure blanks, with mean

251

contents (ng) of 1.54 ± 0.35, 1.37 ± 0.25, 0.95 ± 0.24 and 0.70 ± 0.12, respectively.

252

Methods LODs and LOQs for methyl siloxanes and BDE-99 were listed in Table S3,

253

SI, which indicates that the LOQs ranged from 0.36 to 5.07 ng/g wet weight (ww) for

254

methyl siloxanes, and was 0.07 ng/g ww for BDE-99. The recoveries of spike samples

255

were averaged from 71 ± 11% (L17) to 103 ± 11 % (D6) for methyl siloxanes and 89 ±

256

10 % for BDE-99. The recoveries of surrogate standard were from 76% to 109% for

257

M4Q and 73% to 110% for BDE-71 in all samples. The repeatability of the method

258

was assessed using the spike samples and internal matrix controls. For methyl

259

siloxanes and BDE-99, the relative standard deviation (RSD) was from 7% to 16% in

260

the spike samples, and from 8% to 17% in internal matrix controls.

261

Methyl siloxanes concentrations.

262

The concentrations of methyl siloxanes detectable in biota samples were listed in

263

Table S4, SI. D4, D5, D6 and D7 were quantified above the LOQ in 77%, 93%, 94%

264

and 79% of the total samples, respectively, while L9, L10 and L11 were detectable in

265

less than 30% of the total samples; and other methyl siloxanes (L4 – L8 and L12 – L17)

266

were not detectable in any sample. Thus linear methyl siloxanes were not included in

267

further discussions in the present study. Table 1 lists the mean concentrations of 4 11



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cyclic methyl siloxanes depending on biota species. The mean concentrations (ng/g

269

ww) of D4, D5, D6 and D7 were 10.6 ± 7.81, 21.0 ± 24.9, 16.5 ± 11.1 and 3.23 ± 2.11

270

from all samples, respectively. The concentrations of D5 and D6 were significantly

271

higher than D4 and D7 (p < 0.01). The average concentrations of D4 were 14.0 ± 8.98

272

ng/g ww in fish samples (ranged from 10.0 ± 5.80 ng/g ww in mackere to 19.3 ± 12.4

273

ng/g ww in greenling), which was significantly higher (p < 0.01) than that in

274

invertebrate samples (averaged 6.51 ± 2.90 ng/g ww with a range from 4.39 ± 1.74

275

ng/g ww in arthritic neptune to 9.64 ± 5.04 ng/g ww in mud crab), and in plant

276

samples (sea lettuce, averaged 6.33 ± 2.31 ng/g ww). Observed concentrations of D5

277

in biota were similar to those of D4, which averaged 31.7 ± 29.6 ng/g ww in fish,

278

significantly higher (p < 0.01) than that in invertebrate (averaged 8.92 ± 6.03 ng/g ww)

279

and in sea lettuce (averaged 5.83 ± 3.38 ng/g ww). A similar trend was not observed

280

for D6 and D7. As for D6 and D7, the observed concentrations averaged respectively

281

19.1 ± 12.2 ng/g ww and 3.36 ± 2.29 ng/g ww in fish, 14.0 ± 8.48 ng/g ww and 3.14 ±

282

1.98 ng/g ww in invertebrate, and 10.5 ± 11.7 ng/g ww and 2.73 ± 1.52 ng/g ww in

283

sea lettuce. Depending on species, the highest concentrations for D4, D5 and D6 were

284

observed in greenling (19.3 ± 12.4 ng/g ww, 54.9 ± 44.4 ng/g ww, and 26.9 ± 24.8

285

ng/g ww, respectively), and for D7 were observed in arthritic neptune (4.68 ± 3.02

286

ng/g ww).

287

The lipid contents of organisms varied greatly, from 1.98 ± 0.79 to 9.23 ± 2.77% in

288

fish species, from 1.46 ± 0.04 to 2.83 ± 0.24% in invertebrate species, and 1.91 ±

289

0.06% in sea lettuce (Table 1). Lipid weight (lw) normalized concentrations for

290

methyl siloxanes and BDE-99 are also presented in Table 1 and Table S4, SI, showing

291

that the normalized concentrations of D4 and D5 in fish were not significantly higher

292

(p = 0.06) than that in invertebrate and sea lettuce, which is different from the

293

concentrations observed in wet weight.

294

The results are compared with those reported in other places worldwide (see Table S5,

295

SI). As shown in Table S5, SI, concentrations of D4, D5 and D6, not D7, were reported

296

in aquatic biota by other groups. Apart from our study, there is only one report on

297

methyl siloxanes in the marine food web in Inner Oslofjord, Norway (40). In 12


Page 13 of 25


298

comparison, the results of D4 and D6 in the marine food web measured in Dalian Bay

299

were similar to those in Inner Oslofjord, but the range of concentration of D5 in the

300

former (ND-120 ng/g ww) was one order of magnitude lower than that in the latter

301

(6.7-1435 ng/g ww), which may indicate the different methyl siloxane composition of

302

the local sources in the two places. Our results are also comparable to those observed

303

in the fresh water food web measured in Lake Mjøsa and Lake Randsfjorden, Norway

304

(21-22), Lake Erie, Canada (23), and Lake Pepin, USA (39), with an exception of D5

305

in Lake Mjøsa and Lake Randsfjorden, Norway. Again, very high concentrations of

306

D5 in these two Norwegian lakes were found, which, along with the high

307

concentration of D5 in Inner Oslofjord, Norway, possibly indicate high local sources

308

of D5 in this country.

309

Besides the aquatic food web samples, the concentrations of D4, D5 and D6 were also

310

reported in fish from some European countries, such as Atlantic cod and sculpin from

311

Svalbard, Norway (52), ragworm and flounder from Humber Estuary, England (19),

312

perch from Swedish Lakes (53), herring from Baltic Sea (54), marine fish and

313

freshwater fish from the Nordic countries (15) (Table S5, SI). In general, our results

314

were in line with these reports and close to the upper levels of those studies. It was

315

also determined that D5 had the higher concentrations than the other congeners in our

316

study and all other studies worldwide.

317

Food web structure.

318

The stable carbon (adjusted mathematically for the C:N ratio according to Post et

319

al.(45)) and nitrogen isotope values for organisms collected from Dalian Bay are

320

shown in Figure 1 and Table S1, SI. The stable nitrogen isotope ratios (‰) were 10.3

321

± 0.3 to 15.6 ± 0.7 for fish species, 7.7 ± 0.1 to 12.4 ± 0.8 for invertebrate species, and

322

9.2 ± 0.2 for plant (sea lettuce). The adjusted stable carbon isotope ratios (‰) were

323

from -22.7 ± 0.5 to -25.7 ± 0.5 for fish species, from -23.3 ± 0.5 to -26.2 ± 0.2 for

324

invertebrate species (except for arthritic neptune (-19.4 ± 0.4) and clamworm (-20.1 ±

325

0.5)), and -22.7 ± 0.8 for sea lettuce. As shown in Figure 1, the mean value (as all

326

biota included) of stable carbon isotope ratio was -24.1‰ (vertical line in Figure 1), 13



Page 14 of 25

327

and all biota species were distributed in the vicinity of vertical line (mean value of

328

stable carbon isotope ratio) except for arthritic neptune and clamworm. It seemed that

329

the stable carbon isotope ratios for arthritic neptune and clamworm were not related

330

with other species in the food web, which reflects their different food sources. This

331

may be supported by the fact that the arthritic neptune and clamworm were collected

332

from sediments, while all the other organisms were collected from seawater. Besides,

333

the relatively high δ13C values of benthic organisms were also observed previously

334

(51, 55). Thus, the two species were not included in the TMF calculation in the

335

present study.

336

Trophic transfer of methyl siloxanes.

337

Trophic magnification of methyl siloxanes was assessed as the slope of lipid

338

equivalent concentrations of D4, D5, D6 and D7 regressed against trophic level for

339

marine food web configurations (except arthritic neptune and clamworm) (Figure 2).

340

Besides, bootstrapped estimates of TMF based on 10000 Monte-Carlo simulations

341

(input variables are listed in Table S6, SI) for each of the food web configurations

342

were performed and the frequency distributions of D4, D5, D6, D7 and BDE-99 are

343

provided in Figure 3. Significant positive relationships (R = 0.44, p < 0.0001) were

344

found between lipid normalized D5 concentrations and trophic levels in organisms

345

(Figure 2), showing the trophic magnification potential of the chemical in the marine

346

food web from Dalian Bay. The TMFs values of D5 estimated by the slope of

347

concentration-trophic level relationship was 1.77 (95% confidence interval (CI): 1.41

348

- 2.24, 99.8% probability of the observing TMF > 1). The TMF values for D5 were

349

estimated to be below 1 in the benthic freshwater food web of Lake Pepin, USA (39)

350

and in the marine food web of the Oslofjord, Norway (40), but exceeded 1 in Lake

351

Mjøsa and Lake Randsfjorden, Norway (21-22). In the study on Lake Erie, Canada,

352

the TMF values were highly dependent on food web configuration, being >1 in only 1

353

of the 5 food web configurations investigated (23).

354

In this study, no significant correlations between lipid normalized concentrations and

355

trophic levels were found for D4, D6 and D7 (Figure 2, R = 0.14 and p = 0.16 for D4, R 14


Page 15 of 25


356

= 0.01 and p = 0.92 for D6, R = -0.15 and p = 0.12 for D7). The estimated values of

357

TMFs were 1.16 (95% CI: 0.94 – 1.44, 94.7% probability of the observing TMF > 1),

358

1.01 (95% CI: 0.84 - 1.22, 66.9% probability of the observing TMF > 1) and 0.85

359

(95% CI: 0.69 - 1.04, 48.6% probability of the observing TMF > 1) for D4, D6 and D7,

360

respectively. For the results of D6, our findings were in contrast to another available

361

food web study (22), which reported significant D6 food web biomagnification with

362

TMF > 1. For both D4 and D6, our results consisted with the reports in the benthic

363

freshwater food web from Lake Pepin, Mississippi, USA (39), in the marine food web

364

of Oslofjorden, Norway (40), and in freshwater food web of Lake Erie, Canada (23).

365

For the TMF value of D7, no available data can be used for the comparison.

366

The TMF value for the legacy contaminant BDE-99 was also estimated in this study

367

as a benchmark chemical. Significant positive relationship (R = 0.65, p < 0.0001) was

368

found between lipid normalized concentrations and trophic levels in organisms. The

369

TMFs values of BDE-99 estimated by the slope of concentration-trophic level

370

relationship was 3.27 (95% CI: 2.49 – 4.30, 99.7% probability of the observing

371

TMF > 1), showing the strong magnification in marine food webs. Generally, both D5

372

and BDE-99 have strong biomagnifications potentials in marine food webs, although

373

the value of TMF was lower for D5 than that of BDE-99. However, for those of D4, D6

374

and D7, the TMF regression model was weaker (the ability of trophic level to predict

375

the contaminant concentration) compared to both D5 and BDE-99, as indicated by the

376

lower R and higher p values (Figure 2) and the lower probability of the observing

377

TMF > 1 (Figure 3). For congeneric compounds, logarithm of octanol-water partition

378

coefficients (log KOW) values can be used to explain the ability of biomagnification

379

(51).

380

biomagnification potential than those with lower ones. However, the estimated TMF

381

values in the present study for D4, D5, D6 and D7 has formed an inverted “V” against

382

the values of log KOW (Figure S2, SI). This can be explained by the fact that

383

compounds with low KOW do not biomagnify because they are rapidly excreted (like

384

D4 in this study) (21-22), which was suggested by biotransformation rates in fish

385

derived from inverse modeling of bioconcentration studies (56). However, as for

Generally,

compounds

with

higher

log

Kow

values

have

greater

15



Page 16 of 25

386

“superhydrophobie” chemicals (with very high KOW values), association with

387

suspended organic matter in the water column become important, the “bioavailability”

388

is reduced (like D6 and D7) (57).

389

Uncertainties analysis.

390

There are two sources of uncertainties in evaluation of TMF values in the present

391

study. Firstly, the TMF values evaluation was based on lipid normalized

392

concentrations for chemicals in biota samples, including sea lettuce. However, the

393

literature on land plants has suggested that the sorption capacity of vegetation is

394

determined by cuticle polymers in additional to extractable lipids. In this case it would

395

be appropriate to acknowledge the uncertainty associated with the assumption that

396

lipid normalization will put sea lettuce on the same chemical fugacity scale as the

397

other organisms. Secondly, during chemical analysis, muscle from fish was analyzed

398

whereas whole body from invertebrates, which produced uncertainties when TMF

399

values were calculated for methyl siloxanes. Although these uncertainties existed

400

when TMF values were calculated for methyl siloxanes, the benchmark chemical

401

BDE-99 analysis gave the confidence to our results in general.

402

The published work on TMF investigations of methyl siloxanes in aquatic food webs

403

gave mixed information. The possible reasons for these contradicted observations are

404

complex and not fully understood due to their high dependence on the composition of

405

the food web configuration. More investigation should be carried out to assess the

406

ability of trophic magnification for methyl siloxanes.

407

Acknowledgments

408

This work was supported by the National Natural Science Foundation of China

409

(21207011 and 21207026) and the Fundamental Research Funds for the Central

410

Universities (3132014306).

411

Supporting Information Available

412

Figures addressing sampling location and relationship between Log KOW and TMF 16


Page 17 of 25


413

values for D4, D5, D6 and D7; tables describing sample information, individual

414

chemical results, QA/QC results, comparison of methyl siloxane concentrations at

415

different locations, input variables for Monte-Carlo simulations; text describing

416

analysis method for PBDEs. This information is available free of charge via the

417

Internet at http://pubs.acs.org/

17



Page 18 of 25

418

References

419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460

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Page 22 of 25

602

Table 1. Estimated trophic level (TL), Lipid content (%) and concentrations and their standard deviations in ng/g ww (ng/g lw) of selected methyl

603

siloxanes and PBDEs depending species collected from Dalian Bay, China.

604

Species

na

TL

Lipid content

D4

D5

D6

D7

BDE-99

Pacific Herring

26

3.15 ± 0.11

9.23 ± 2.77

Mackerel

15

2.22 ± 0.10

5.45 ± 1.65

Greenling

7

3.58 ± 0.20

3.60 ± 1.25

Schlegel's black rockfish

6

3.40 ± 0.18

1.98 ± 0.79

Sea catfish

7

3.79 ± 0.22

3.18 ± 0.81

Mactra quadrangularis

21

1.46 ± 0.04

2.44 ± 0.30

short-necked clam

30

2.00 ± 0.07

3.73 ± 0.36

Mussel

30

1.58 ± 0.11

3.44 ± 0.90

Arthritic Neptune

9

2.69 ± 0.08

2.12 ± 0.52

Black Fovea Snail

71

2.06 ± 0.02

3.84 ± 0.53

Mud crab

15

2.83 ± 0.24

4.15 ± 0.72

Clamworm

60

1.61 ± 0.07

2.79 ± 0.92

Sea lettuce

8

1.91 ± 0.06

1.48 ± 0.39

All samples

305

-

-

15.3 ± 9.18 (104 ± 109) 10.0 ± 5.80 (107 ± 78.0) 19.3 ± 12.4 (376 ± 112) 15.3 ± 10.1 (519 ± 586) 11.7 ± 6.23 (185 ± 86.8) 5.62 ± 1.66 (118 ± 40.0) 6.71 ± 3.21 (93.0 ± 53.6) 5.76 ± 1.69 (89.3 ± 44.9) 4.39 ± 1.74 (108 ± 47.2) 8.63 ± 1.62 (83.1 ± 32.4) 9.64 ± 5.04 (126 ± 83.9) 6.01 ± 2.10 (113 ± 58.1) 6.34 ± 2.31 (239 ± 127) 10.6 ± 7.81 (152 ± 179)

28.0 ± 24.6 (168 ± 147) 20.8 ± 15.5 (238 ± 245) 54.9 ± 44.4 (856 ± 834) 31.0 ± 34.5 (845 ± 883) 46.5 ± 39.0 (686 ± 466) 8.02 ± 3.94 (164 ± 82) 5.44 ± 1.04 (74.1± 19.2) 6.18 ± 3.70 (102 ± 66.3) 11.2 ± 3.21 (289 ± 143) 16.4 ± 4.43 (155 ± 76.6) 20.7 ± 5.29 (253 ± 72.0) 5.30 ± 1.93 (96.0 ± 50.4) 5.83 ± 3.39 (226 ± 175) 21.0 ± 24.9 (283 ± 401)

20.2 ± 9.29 (124 ± 84.2) 15.6 ± 6.96 (153 ± 73.4) 26.9 ± 24.8 (314 ± 295) 8.90 ± 5.67 (255 ± 213) 22.8 ± 12.1 (365 ± 156) 20.6 ± 10.8 (415 ± 178) 13.0 ± 3.64 (175 ± 46.3) 8.33 ± 6.62 (127 ± 107) 23.5 ± 13.7 (534 ± 191) 14.7 ± 3.24 (187 ± 39.4) 18.4 ± 6.06 (224 ± 66.7) 9.29 ± 5.77 (160 ± 87.3) 10.5 ± 11.7 (320 ± 286) 16.5 ± 11.1 (220 ± 178)

3.42 ± 2.85 (21.1 ± 20.9) 3.18 ± 1.53 (32.8 ± 21.9) 3.49 ± 1.82 (66.1 ± 40.7) 2.63 ± 1.07 (77.3 ± 37.0) 4.05 ± 2.75 (67.7 ± 44.2) 2.32 ± 0.740 (48.9 ± 18.1) 2.65 ± 1.70 (35.3 ± 21.8) 3.13 ± 1.86 (54.6 ± 48.8) 4.68 ± 3.02 (105.4 ± 44.6) 3.39 ± 1.24 (34.4 ± 19.4) 4.53 ± 3.54 (53.7 ± 35.9) 2.54 ± 1.44 (39.8 ± 11.7) 2.73 ± 1.52 (104 ± 70.6) 3.23 ± 2.11 (47.8 ± 40.9)

15.4 ± 9.08 (88.7 ± 57.2) 5.26 ± 1.84 (51.0 ± 20.1) 8.07 ± 4.36 (166 ± 62.7) 8.59 ± 6.42 (222 ± 167) 5.19 ± 3.91 (78.0 ± 45.1) 0.646 ± 0.385 (13.1 ± 7.07) 0.446 ± 0.395 (6.02 ± 5.31) 0.542 ± 0.224 (7.67 ± 4.03) 2.14 ± 1.00 (54.0 ± 34.3) 2.71 ± 1.56 (35.4 ± 20.5) 1.78 ± 1.02 (20.5 ± 9.05) 1.03 ± 0.72 (18.7 ± 12.4) 0.254 ± 0.199 (8.58 ± 6.26) 5.93 ± 7.51 (58.0 ± 72.4)

a

For sea lettuce, n is the numbers of sample treated, for other species, n is the numbers of individual collected.

22


Page 23 of 25


18

15

Mean value of δ13C Schlegel's Black Rockfish Greenling Sea Catfish Pacific Herring Arthritic Neptune

δ15N

12 Mackerel

Mud Crab Short-necked Clam

9 Black Fovea Snail Mussel Sea Lettuce Clamworm Mactra Quadrangularis 6 -27 -26 -25 -24 -23 -22 -21 -20 -19 δ13C 605 606

Figure 1. Relationship between the dietary descriptors δ15N and C:N adjusted δ13C

607

values in biota from Dalian Bay.

23



3.5

y = 0.07x + 1.85 3.0 R = 0.14, p = 0.16 2.5 2.0 1.5 1.0 1.0

1.5

2.0 2.5 3.0 3.5 Trophic levels

4.0

3.5 Log-concentrations (ng/g lw)

Log-concentrations (ng/g lw)

D4

3.0 2.5 2.0 1.5 1.0 1.0

1.5


4.0

2.5 2.0 1.5 1.0 1.5

4.5

3.0

1.5 1.0 1.0

1.5


2.0 1.5 1.0 0.5 0.0 1.5


4.0

D7

2.0

2.5

-0.5 1.0

4.5

2.5

BDE-99

y = 0.51x + 0.11 R = 0.65, p < 0.0001

4.0

y = -0.07x +1.71 R = -0.15, p = 0.12

3.5 3.0


3.5

D6

y = 0.004x + 2.20 R = 0.01, p = 0.92

D5

y = 0.25x + 1.58 3.0 R = 0.44, p < 0.0001

1.0

4.5



3.5

Page 24 of 25

4.5


4.0

4.5

Pacific Herring Mackerel Mactra Quadrangularis Mussel Short-necked Clam Black Fovea Snail Mud Crab Greenling Schlegel's Black Rockfish Sea Catfish Sea Lettuce

608

Figure 2. Relationships between log transformed concentrations of compounds (ng/g lw) and tropic levels

609

in marine food webs from Dalian Bay. Regression analysis based on the 95% confidence interval for each

610

compounds. 24


Page 25 of 25


611 3000 Probability > 1 of TMF is 94.7% 2500

1500 1000 500 0

Probability > 1 of TMF is 99.8% 2500

2000 Frequency

Frequency

2000

3000 D5

1500 1000 500 1.0

1.5

2.0

TMF

D7

3000

Probability > 1 of TMF is 48.6%

2500

2500

2000

2000

1500 1000 500 0

2.5

3.0

3.5

TMF

Frequency

Frequency

3000

1500 1000 500

0

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4


D6

2000 Frequency

2500

3000 D4

BDE-99

0 0.6

0.8

1.0

1.2

1.4

1.6

1.8

TMF


1500 1000 500

0.6

0.8

1.0

1.2 TMF

1.4

1.6

1.8

0

1

2

3

4

5

6

7

8

9

TMF

612

Figure 3. Frequency distribution of trophic magnification factors determined for lipid normalized methyl siloxanes and BDE-99 in marine food web from

613

Monte-Carlo simulation (n = 10000). TMF = 1.0 (equilibrium) denoted by red vertical line.

25


Bioaccumulation and trophic transfer of short chain chlorinated paraffins in a marine food web from Liaodong Bay, North China.

Future climate scenarios for a coastal productive planktonic food web resulting in microplankton phenology changes and decreased trophic transfer efficiency.

Unifying ecological stoichiometry and metabolic theory to predict production and trophic transfer in a marine planktonic food web.

Consistency in trophic magnification factors of cyclic methyl siloxanes in pelagic freshwater food webs leading to brown trout.

Trophic coherence determines food-web stability.

Global change in the trophic functioning of marine food webs.

Distribution, source, fate and bioaccumulation of methyl siloxanes in marine environment.

Determination of methylmercury in marine fish from coastal areas of Zhejiang, China.

Marine metaproteomics: deciphering the microbial metabolic food web.

sardine food web: a case study from the Gulf of Lion (NW Mediterranean Sea).

Monitoring and analysis of coastal reclamation from 1995-2015 in Tianjin Binhai New Area, China.

Low mercury levels in marine fish from estuarine and coastal environments in southern China.

fat from both general industries and residential areas in China.

Winter and spring controls on the summer food web of the coastal West Antarctic Peninsula.

Trophic transfer and accumulation of mercury in ray species in coastal waters affected by historic mercury mining (Gulf of Trieste, northern Adriatic Sea).

Trophic magnification of chlorinated flame retardants and their dechlorinated analogs in a fresh water food web.

Concentrations and trophic magnification of cyclic siloxanes in aquatic biota from the Western Basin of Lake Erie, Canada.

Eating up the world's food web and the human trophic level.

Risk and benefit assessment of potential neurodevelopmental effect resulting from consumption of marine fish from a coastal archipelago in China.

Trace elements in major marketed marine bivalves from six northern coastal cities of China: concentrations and risk assessment for human health.

Transfer of cadmium from soil to vegetable in the Pearl River Delta area, South China.

Bioconcentration and trophic transfer of polychlorinated biphenyls and polychlorinated dibenzo-p-dioxins and dibenzofurans in aquatic animals from an e-waste dismantling area in East China.

Consistent multi-level trophic effects of marine reserve protection across northern New Zealand.

Effects and implications of trophic transfer and accumulation of CeO2 nanoparticles in a marine mussel.