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Supplementary information for Archives of Environmental Contamination and Toxicology
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Authors: D.-H. Chae, I.-S. Kim, S.-K. Kim, Y.K. Song, W.J. Shim
Manuscript title: Abundance and Distribution Characteristics of microplastics in Surface
Seawaters of Incheon/Kyeonggi Coastal Region.
Number of Page: 7 (including this cover page)
Number of Figures: 4
Number of Tables: 1
Section-S1. Methods for microplastic identification and quantification (Chae et al., 2014)
In our previous study (Chae et al., 2014) entitled “Development of analytical method for
microplastics in seawater”, we performed quality control for quantification. Because the
reference (Chae et al., 2014) was published in Korean journal written in Korean, we present
the abstract of the methodology and result here.
(1) Correction of collection surface area for in-situ SML sample
The SML seawater samples were collected by gently touching a stainless steel sieve (2
mm mesh size; 20 cm diameter) to the seawater surface in order to obtain SML seawater based
on surface tension. At each station, sieve collection on board was repeated 120-times. SML
samples can be lost during sampling on board, amount of which depends on field condition.
Thus, collection surface area (sample-by-sample) is serious when reporting data as particles
per m2 and must be corrected by the volume collected (or lost).
We transported 10 L seawater samples to the laboratory and stored in stainless tank.
Thereafter, the SML samples were collected in the same way as the field-collection method
under the laboratory condition with no wind and wave. The sieve collection was repeated 10times for one sample (n=10). The cumulative volume of 10-times sampling was 313.5±12.5
ml (RSD=3.9%), which corresponds to 3.76±0.15 L when is converted to 120-times sampling
volume. In-situ 120-times cumulative volume collected in this study was 2.57±0.29 L
(RSD=11.9%). Thus, the surface area collected in filed can be estimated by the equation-1
below.
𝑉
𝐴𝑆𝑀𝐿_𝐹 = (120 × 𝐴𝑆𝐶 ) × (𝑉𝑆𝑀𝐿_𝐹 ) (Eq. 1)
𝑆𝑀𝐿_𝐿
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Where, ASML_L, ASC, VSML_F, VSML_L indicate field-collected surface area by 120-times
sampling, theoretical collection surface area (i.e., sieve area) by one-time sampling, 120-times
collected volume in field, and 120-times collected volume in laboratory, respectively.
(2) Quantification of microplastics (50-300 m) on GF/F filter paper
We filtered seawater samples passing through 300 m sieve using 0.75 m×47mm Ø
GF/F (n=3). The sampled area on each filter paper was divided to four quadrants (i.e., 1/4, 2/4,
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3/4, and 4/4 quadrants) and plastic-like particles within the whole area of each quadrant were
counted using FT-IR. The number of microplastic present in each quadrant showed a similar
range values (RSD=8.4%, 12.7%, and 6.7%; n=3).
Identifying and counting all of plastic-like particles in the whole filter paper is time- and
cost-consuming work. As next step, thus we selected three squares (5×5 mm for each square)
randomly from each of the center, middle, and outer zone of sampled area on the same filter
paper (see Figure 4S). All of microplastic particles present in each zone were identified and
counted using FT-IR. Four filtered samples was analyzed. The relative standard deviations
(RSD) among the microplastic numbers in center, middle, and outer zone on the same GF/F
ranged from 12.3 to 43.3%. Afterward, total number of microplastic in three squares on the
same filter paper was converted to the number of microplastic in 1/4 quadrat of each filter paper,
which was compared with that counted in the whole area of 1/4 quadrat selected randomly on
each paper (equation-2). The difference between converted and measured values for 1/4
quadrat was 3.1-11.2% (n=4).
𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 (%) =
|𝑋−𝑌|
𝑌
× 100 (Eq. 2)
X = the number of microplastics converted from that in three squares to that in 1/4 quadrat.
Y = the number of microplastics counted directly in 1/4 quadrat
(3) Comparison between counting by stereomicroscopy and FT-IR (<300 m)
Frequently, seawater samples include a number of interfering materials which make the
identification of microplastics (MPs) obscure when counting by stereomicroscopy only. We
compared the numbers of microplastics counted by two methods (i.e., visual counting v.s. FTIR counting) as for particles with <300 m in SML and SSW-hand net samples. MPs numbers
counted using two methods showed a good correlation (r2=0.67) in SML that was relatively
clean while exhibited a poor correlation (r2=0.44) for SSW-hand net that contained more
plentiful other particles. Both SML and SSW-hand net sample underestimated MP number
when counted by microscopy only, indicating a necessity of FT-IR counting.
Section-S2. FT-IR analysis for identification of polymer-types
All spectra of samples were recorded as 20 scans in the spectral range of 8000-650 cm-1
at a resolution of 4 cm-1. Synthetic polymers found in this study were polypropylene (PP),
polyethylene (PE), polyvinylchloride (PVC), polyvinyl alcohol (PVA), polyvinyl sulfate (PVS),
polyethylene terphthalate (PET), expanded polystyrene (EPS), and paint particles (alkyd and
poly(acrylate/styrene)). The wave numbers and vibration modes for identification of each
polymer are provided in Table S1.
An alkyd on the FT-IR spectrum showed a C-H stretch peak at 2920 and 2850 cm-1, C=O
stretch at 1725 cm-1, C-O stretch at 1450 and 1500 cm-1, and ester linkage at 1300-1000 cm-1
(Figure S1(a)). On the other hand, the FT-IR spectrum of poly(acrylate/styrene) exhibited
vibrations of the aromatic ring =C-H stretch at 3030 cm-1, C-H stretch at 2920 cm-1, C=O
stretch at 1724 cm-1, the stretch of carbons in the aromatic ring at 1600-1480 cm-1, the out-ofplane C-H band at 740 cm-1, and the ring band at 700 cm-1 (Figure S1(b)).
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Table S1. Wave numbers and vibration modes on FT-IR spectrum of individual synthetic
polymers.
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Figure S1. FT-IR spectra assigned to (a) alkyd and (b) poly(styrene/acrylate). The spectra on
the each upper, middle and bottom panels indicate those on FT-IR instrument library, of paint
chips collected around the shipyard, and of SML samples, respectively. See Table S1 and
Section-2 in the text for the vibration modes of each peak that each arrow in the panels indicate.
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(a)
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(b)
Figure S2. Relative composition of synthetic polymers by sampling methods when including
(a) and excluding (b) paint particles.
(b)
(a)
(c)
N
I1
O1
O2
M1
O3
M2
O4
M3
O5
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120
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I2
I3
I4
10km
10km
I1
O1
particle/m3
N
N
10km
O2
M1
O3
M2
O4
M3
particle/m3
I2
I3
O5
I1
O1
I4
O2
M1
O3
M2
O4
M3
particle/m3
I2
I3
I4
O5
Figure S3. Contour map of total microplastic abundance in (a) SML, (b) SSW-trawl (b), and
(c) SSW-hand net. The dashed lines indicate the legal voyage route of large vessels.
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(a)
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(b)
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Figure S4. Three blank samples were analyzed in the same way as SML sample. Pictures of
FT-IR microscope for SML sample (a) and three blank samples (b). All of plastic-like particles
with size of >50 m within three squares (5×5mm) on each filter paper, randomly assigned
from a center (B), middle (A), and outer zone (C), were analyzed by FT-IR to confirm the
identification of plastic polymer type. The lower case letters (a, b, c) indicate the magnified
picture (×40) of individual cells on each zone. Contrary to plastic particles observed on GF/F
paper of SML sample (Figure S4(a)), neither synthetic plastic particles nor even particles bigger
than 50 m which was the smallest cut-off size in the present study were found on all of filter
papers of blank samples (Figure S4(b)).
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