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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
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TOC figure
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Abstract
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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
24
persistent, bioaccumulated, toxic, and ecological harm. This study investigated the
25
trophic transfer of four cyclic methyl siloxanes (octamethylcyclotetrasiloxane (D4),
26
decamethylcyclopentasiloxane (D5),
27
tetradecamethylcycloheptasiloxane (D7)) in a marine food web from coastal area of
28
Northern China. Trophic magnification of D4, D5, D6 and D7 were assessed as the
29
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
37
TMFs (95% CI, probability of the observing TMF > 1) were 1.16 (0.94 – 1.44,
38
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
44
best of our knowledge, this is the first report on the trophic magnification of methyl
45
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
48
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
50
silicon compounds, including linear and cyclic structures. Linear methyl
51
siloxanes are also called polydimethylsiloxane (PDMS), usually expressed as Ln
52
(L means linear structure and n is the number of silicon atom). Cyclic methyl
53
siloxanes are usually expressed as Dn (D means cyclic structure and n is the
54
numbers of silicon atom) (1-2). As the intermediates of silicone industrial products,
55
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,
57
pharmaceuticals, health care products, cooking utensils, plastics, papers, building
58
materials, decoration materials, electronic products, and much more (5-6). It has been
59
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
61
demand was 73 000 t in 2000, 141 000 t in 2003, then rose to 330 000 t in 2007 (7).
62
Due to extensive production and usage of these chemicals, D4, D5, and D6 have been
63
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),
69
and biota (17,21-23). Studies showed that one of the most significant pollution
70
sources of methyl siloxanes is the emission from cosmetics and household products
71
used by the general public (24-27).
72
Three cyclic methyl siloxanes (D4, CAS No. 556-67-2; D5, CAS No. 541-02-6; D6,
73
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
79
persistence, bioaccumulation, and toxicity (31). D5 conformed to persistence and
80
toxicity criteria, but the bioaccumulation criterion was uncertain due to the
81
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
84
results for D4 and D6, but not for D5, they thought D5 was persistent and
85
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
101
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
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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
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investigate the concentration and trophic magnification of methyl siloxanes in marine
109
food webs in coastal area of Northern China.
110
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
116
including pacific herring (Clupea pallasii) (n = 26), mackerel (Pneumatophorus
117
japonicus) (n = 15), greenling (Hexagrammos otakii) (n = 7), schlegel's black rockfish
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(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.
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Clamworm and sea lettuce samples were collected the whole body. All samples were
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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
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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
137
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
145
samples were only in contact with acetone-cleaned utensils of stainless steel (tweezers,
146
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.
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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.
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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
165
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.
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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).
208
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.
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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
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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
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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
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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
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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
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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
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418
References
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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.
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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.
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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
2.0 2.5 3.0 3.5 Trophic levels
4.0
2.5 2.0 1.5 1.0 1.5
4.5
3.0
1.5 1.0 1.0
1.5
Log-concentrations (ng/g lw)
2.0 1.5 1.0 0.5 0.0 1.5
2.0 2.5 3.0 3.5 Trophic levels
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
2.0 2.5 3.0 3.5 Trophic levels
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
Log-concentrations (ng/g lw)
Log-concentrations (ng/g lw)
3.5
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4.5
2.0 2.5 3.0 3.5 Trophic levels
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
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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
Probability > 1 of TMF is 66.9%
D6
2000 Frequency
2500
3000 D4
BDE-99
0 0.6
0.8
1.0
1.2
1.4
1.6
1.8
TMF
Probability > 1 of TMF is 99.7%
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.
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