Investigation of Microplastic Contamination in Vietnamese Sea Salts Based on Raman and Fourier-Transform Infrared Spectroscopies
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EnvironmentAsia 14(2) 2021 1-13
DOI 10.14456/ea.2021.11
ISSN 1906-1714; ONLINE ISSN: 2586-8861
Investigation of Microplastic Contamination in Vietnamese
Sea Salts Based on Raman and Fourier-Transform Infrared
Spectroscopies
Vo Thi Kim Khuyen1*, Dinh Vu Le2*, Le Hung Anh3, Axel René Fischer1
and Christina Dornack1
1
Institut für Abfall- und Kreislaufwirtschaft, Technische Universität Dresden, Pirna, Germany
2
Faculty of Chemical Engineering, Industrial University of Ho-Chi-Minh City,
Ho-Chi-Minh City, Vietnam
3
Institute for Environmental Science, Engineering and Management,
Industrial University of Ho-Chi-Minh City, Ho-Chi-Minh City, Vietnam
*Corresponding author: kimkhuyenvo@gmail.com, ledinhvu@iuh.edu.vn
Received: January 14, 2021; Revised: February 26, 2021; Accepted: March 28, 2021
Abstract
Microplastics (MPs) are plastic items smaller than 5 mm as a result of the degradation of
plastic products and wastes in the environment. They have been encountered in a variety of
sea products, including sea salts. The aim of this research is to investigate the microplastic
contamination in Vietnamese sea salts based on Raman and Fourier-Transform infrared
(FT-IR) spectroscopies. A total of 14 salt brands and no-name salt bags collected randomly at
six urban and suburban groceries in Ho-Chi-Minh city were analyzed. The results showed the
presence of polymers in the decreasing percentages - PET, PE, PP, PVC, PS, PA-6, and PMMA.
there was a higher fluctuation in MPs amount in non-branded salts compared with branded
salts. However, the average of MPs was fairly similar – 133.62 items/kg, corresponding to
487.71 items entering the human body per year via salt consumption. All these obtained results
revealed MPs pollution in Vietnam sea salts may come from seawater. This study supplied more
information about MPs pollution in the sea and for environmental research and food safety.
Keywords: Anthropogenic microfibers; Sea salt contamination; Raman and Fourier-Transform
infrared spectroscopies; Can Gio Vietnam
1. Introduction
Plastic pollution has been one of the a result of physical, chemical and biological
major global environmental concerns due to fragmentation of larger plastics (Urbanek
the triple increase in amount of the global et al., 2018). The later form can be seen in
plastic waste (Lebreton and Andrady, 2019). a heterogeneous mixture of diverse shaped
Vietnam is in world-top 5 countries with the plastic materials such as pellets, fragments,
estimated amount of plastic waste discharged fibers and other shapes in the range of
into the sea from 0.28 to 0.73 million tons/year 0.1 – 5000 µm (Hidalgo-Ruz et al., 2012).
(Le, 2019). Plastic waste experienced They have a variety of colors and shapes
degradation in silent ways in the environment commonly particles and fibers depending
by breaking into tiny pieces called micro on their sources and relevant degradations
plastics (MPs). They are classified into (Rezania et al., 2018). Light micro debris
primary meso plastics (
V. T. K. Khuyen et al / EnvironmentAsia 14(2) (2021) 1-13
away from pollution sources (Urbanek et al., Sever studies have reported the presence of
2018). Hence, an exact identification of micro MPs in 94% of salts tested worldwide (Lee
plastic pollution sources and their behaviors et al., 2019). The MPs abundance in table salts
is still an extreme challenge. varied with countries, from 9.7 MPs/kg (PP,
Although MPs have been found in PE, PET) in Taiwan salts (Lee et al., 2019),
various types of samples, it is difficult to 56 – 103 MPs/kg (polyesters, PET, PP, PA, PE
compare their abundance exactly owing to and PS) in Indian salts (Seth and Shriwastav,
no standardized MPs analysis procedures at 2018) to 50 – 280 MPs/kg (mostly PE and PP)
this moment. A typical workflow comprises in Spain (Iñiguez et al., 2017).
physical and spectroscopic qualification. The There are three salt types on Vietnamese
anthropogenic debris could be directly seen market: crystalized salt coarse, fine salt refined
under a stereomicroscope, or a dissection by companies, and iodized salt. An average of
microscope after stained with Rose Bengal 5 g per day for a healthy adult is recommended
(Kosuth et al., 2018), or a fluorescence by The World Health Organization (Peixoto
microscope after incubated with fluorescent et al., 2019), and MPs entered in the human
dye Nile Red. Although Nile Red method body with a large amount, (0 – 7.3) x 104 items
is highly sensitive, biogenic materials such annually via salt consumption (Zhang et al.,
as lipids and chitin creating fluorescent 2020). The trend in salty food consumption
signals will interfere the plastic detection is increasing in several nations including
(Erni-Cassola et al., 2017). Thus, this Vietnam with up to 10 g/day (Jensen
method is preferable for environmental et al., 2018) because salts are the main
than biota samples. In the meanwhile, component in almost Vietnamese kinds
the Fourier Transform infrared (FT-IR) of spices. Though, the research of MPs in
spectroscopies have become a conventional Vietnamese marine salts is still very rare.
tool to determine MPs in bivalves, honey Up to now, only study of Kim et al. (2018)
and sugar, tap water and beer (Kosuth et used FT-IR to detect MPs in two salt brands
al., 2018), drinking water, table salt and air of Vietnam. Focus on these points, this
(Zhang et al., 2020). Recently, Raman has study aims to quantify the MPs in all salt
attracted more attention in the literature due types of branded and non-branded salts in
to more advantages than FT-IR. Raman is Ho-Chi-Minh city by Raman microscope
considered to replace for FT-IR thanks to and FT-IR for further prediction of MPs
better resolution, wider spectral coverage accumulation in the human body via salt
and lower water interference (Ribeiro - Claro digestion.
et al., 2017), and was employed to identify
16 – 84 items/kg MPs in table salt of Turkey 2. Materials and Methods
(Gündoğdu, 2018) and other countries
(Karami et al., 2017). 2.1 Sampling
There are no salt mines in Vietnam
and the salt manufacture relies on water A total of 14 brands were purchased
evaporation and salt crystallization from from urban and suburban markets of Ho-Chi
seawater under the prolonged exposure to Minh city. The commercial names are kept
strong sunlight, favorable wind and moisture confidential and marked by alphabetically
on thousands of hectares of open ponds letters. Branded products are labeled with
along with coastal provinces from Northern, ingredients, production place and expiration
Central Coast to Southern (Bac Lieu, Ben date. The salts were categorized into two
Tre, Vung Tau and Can Gio). Thus, table types: coarse (P), refined (R) including
salt is one of the main transport pathways non-iodized and iodized (Table S1).
of substances including MPs from aquatic In addition, refined salts are manually
environment to human. In addition, airborne, packaged in 1 - kg plastic bag without
refinery, packaging and transportation are any descriptions and sold in local
highly feasible contamination sources since markets (Figure 1). They are regarded as
sea-salt manufacturing processes are open. non-branded salts.
2
V. T. K. Khuyen et al / EnvironmentAsia 14(2) (2021) 1-13
Figure 1. Vietnamese commercial sea salts branded (a) and non-branded (b)
2.2 Sample preparation procedure polystyrene (PS) and acrylonitrile butadiene
styrene (ABS) pellets from Vietnam plastic
A weight of 200 g of salts was transferred production companies.
into a glass bottle. The sample in one bottle The MPs analysis is subject to
was a replicate, and three replicates were determine individual particles by using
processed to receive representative results of a Raman microscope (XploRA Horiba
each brand. A particular volume of filtered Scientific). The microscopic mode was used
water was added and stirred until obtaining to observe shape and color and their sizes
the homogenized brine solution. Then 30% were manually calculated. The number of
hydrogen peroxide was added and stirred at pieces was noted down and classified into
70 - 80°C until the solution was discolored, shape, color categories (Hidalgo-Ruz et al.,
and stored in dark at room temperature 2012). The Raman spectrometer included
(30 ± 5°C, 60 ± 10% moisture) overnight. a single beam laser operating at 532 nm of
The extraction was carried out on the wavelength coupled with a charge-coupled
funnel so that micro-particles could be device (CCD) detector. Every individual
captured in the center of filter papers. The particle was analyzed in a wavelength range
matter in the solution was captured on of 50 to 3600 cm-1 with an acquisition time
1.6-μm pore size, 47-mm diameter glass fiber of 15 seconds and a grating of 900 lines
(GF) membrane (GE Healthcare Whatman). per mm.
It depends on the capacity of filter paper, for For larger pieces with complex Raman
each sample, the filtration was divided into spectra, the FT-IR spectroscopy (PerkinElmer
stages: (i) light and floated MPs; (ii) heavy Frontier, USA) was used to reaffirm the
MPs mixed with undissolved impurities. All polymer type. The visible item was transferred
filter membranes were kept in Petri dishes, onto KBr membrane and its IR spectrum
carefully wrapped and let for drying at room was recorded in the range of mid-infrared
temperature for further analysis. wavelength (450 – 4000 cm -1 ) in both
transmission and absorbance modes.
2.3 Microplastic analysis
2.4 Quality control
The library included GF membrane,
polyethylene terephthalate (PET) 300 µm, Two types of blank samples were tested
low–density polyethylene (LDPE) 300 µm, simultaneously to correct the potential
un-plasticized polyvinyl chloride (uPVC) procedural contamination. The air controls
250 µm, poly(methyl methacrylate) (PMMA) were clean filter membranes on glass Petri
85 µm, and nylon-6 (PA-6) 15 – 20 µm dishes around the working area. The water
purchased from Goodfellow (UK); and, controls were processed by the same sample
high – density PE (HDPE), polypropylene (PP), procedure with filtered water.
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2.5. Statistical analysis so time - consuming and, in some cases,
relatively complicated. In fact, the steps were
One-way analysis of variance (ANOVA) based on properties of each particular sample.
was chosen to establish differences in MPs Depending on the cleanness of salt samples,
abundance (items/kg) between products. hydrogen peroxide is necessary to oxidase
A Turkey’s multiple comparison test was used dissolved organic compounds and discolored
analyze the mean differences. All statistical the solution mixture to a large extent, which
analyses were performed at 95% confidence is beneficial for the following MPs floatation
interval on SPSS v22 software. and filtration. The solution discoloration
and matter distribution was clearly observed
3. Results and Discussion after overnight static incubation (Figure 2c of
G - branded salt), compared with the status
3.1 Evaluation of sample handling process once peroxide was added (Figure 2b). The
results show that the oxidation and amount of
There are different sample treatment oxidants varied by samples, particularly large
procedures to extract MPs from sea salts. amount of hydrogen peroxide was required for
The whole handling process is generally non-branded and some of branded products.
Figure 2. The oxidation steps in the samples preparation: (a) before oxidation, (b) once
adding H2O2, (c) after oxidation – brand G
Figure 3. Microplastics found in the supernatant of brand G (a, b),
and in the sediment of brand N (c, d). Pink circles are visible stone grains, black circles are
visible undissolved salt particles, blue circle is invisible fiber which was observed at the
magnification x10 under Raman microscope
4
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The insoluble impurities are the main and in some cases, the real colors were slightly
interference. The remaining products such as different from visible colors (Figure 4d).
algae fibers floating on the surface could be A very hot needle pointed directly at particle
removed easily after oxidation, while others tend bundles and plastic debris will produce melting
to experience temporal accumulation, commonly odor or get curl especially fibers. If bundles were
sedimentation in the water column (Wang et al., broken, they were not plastics. If they changed
2016). The MPs distribution in the mixture has the cellular structure, twisted and stuck around
changed over time and their movements are easily the needle, they would be microalgae filaments.
affected by physical forces during the incubation Microplastics were classified into two
with hydrogen peroxide and filtration process. In shape groups: (i) fibers and (ii) non-fibers. In the
addition, smaller MPs preferentially aggregate former group, pieces are fibrous or thin uniform
with other matter due to strong Brownian motion plastic strands, but not segmented (Zhang
to form larger and heavier precipitated particles et al., 2019). The fibers should be equally thick
(Sun et al., 2020). Thus, long time oxidation is throughout their entire length so that Raman
not recommended to minimize the aggregation spectra could be exactly produced (Figure 4e).
of MPs with impurities. To avoid missing If the fibers were too thin and segmented, they
MPs, the extraction were carried out by stages would be organic fibers (Figure 4f). In later
depending on the capacity of filter membranes. group, MPs were observed in pellets (rounds
The first stage called supernatant, and the last with solid structure, cylindrical, flat, sphere,
stage so-called sediment should be paid attention ovoid), fragments (round, sub - round), or
to. Filter membranes of supernatant filtrate had other shapes (rectangle, triangle, angular,
brighter (Figure 3a) with clearer micro plastic sub-angular). The last care is overlapping
observation at x10 magnification (Figure b) between particles. Invisible MPs, especially
than the sediment’s membranes (Figure 3c, d). microfibers were encountered on the surface of
As many particles were on the membranes, larger MPs (Figure 4g).
physical methods were firstly applied for fast The polymer identification is based on
characterization. The suspected particles were specific bands caused by vibrations of the
analyzed with Raman spectroscopy. functional groups (Table 2). An example is
taken in Figure 5. In the initial observation,
3.2 Microplastic characterizations it is a pink non-fiber fragment. As the piece
was seen by the naked eyes (1 mm in length),
MPs could be recognized by the physical it could be analyzed by both FT-IR and Raman
appearance. Many impurities with certain microscope. In Raman spectrum (Figure 5a),
shapes similar to MPs might be distinguished a medium band at 1440.82 cm-1 is subjected to
by the color. The impurities usually appeared -CH2- bending. The last signal is a strong band
in dim black color and unclear shapes (Figure at 2852.09 cm-1, which assigns to stretching
4a) while the color of MPs should be clear and vibrations of C - H bonds. The second
homogenous (Figure 4b) (Hidalgo-Ruz et al., intensive band at 830.103 cm-1 is in the border
2012). Since plastic products were produced of 550 - 800 cm-1 range of vibrations of C - Cl
with various colors, colored particles such as bonds. However, a different study assigned
yellow or pink would be highly potential MPs. stretching vibrations of C - Cl bonds to
The color was categorized in 4 groups – (i) bands at 635 and 695 cm-1 (Solodovnichenko
light color, (ii) mid color, (iii) dark color et al., 2016). The comparison with the library
(Hidalgo - Ruz et al., 2012). If the filter shows its spectrum looks like the spectrum
membrane was seen through homogenous of PVC and PS. Hence, it is necessary to use
pieces, the pieces were called colorless (group iv). an additional method to confirm the polymer
Brown debris was investigated carefully to avoid type. Three regions should be taken into
the false identification with sand or mud particles account in FT - IR spectrum (Figure 5b).
which tended to gather and overlap plastic Firstly, 1200-1400 cm-1 is assigned to
particles (Figure 4c). A melting test was applied C - H bonds, particularly medium peak
to separate sand, salt particles from visible at 1426.57 cm -1 in bending structure of
whitish and brown MPs (De Witte et al., 2014) CH2-, 1254.87 cm-1 (Ul-Hamid et al., 2015)
5
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and 1322.96 cm -1 of C-H bending (Jung to C - C stretching. The most important
et al., 2017). This medium band of CH2- band is 614.30 cm-1 corresponding to C - Cl
was also observed in Raman spectra at stretching (Ul - Hamid et al., 2015; Jung
1440.82 cm-1. The CH2- rocking is present et al., 2017). This fragment is now believed to
at 961.65 cm -1 (Ul-Hamid et al., 2015). be PVC as only PVC has C - Cl bonds amongst
A relative small band at 1094 cm-1 is assigned the plastic types within this study scope.
Figure 4. The recognition of micro plastics by naked eyes and stereomicroscope:
(a) Blurred items were discarded, and b) Shaped items were highly potential MPs; (c)
Distiguish mud and sand particles with microplastics under microscope; (d) Distinguish
white salt particles and non-plastic items with visible MPs by smelting test and observe
color of MPs under the stereomicroscope; (e) Anthropogenic microfibers and f) Organic
bundle of fibers; (g) The overlap between micro plastics.
6
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Table 1. IR and Raman band assignments of seven investigated polymers
(a) Ung et al (2017); (b) Daniel and Hélio (2019); (c) Gopanna et al (2018);
(d) Solodovnichenko et al., 2016; (e) Anwar Ul-Hamid et al. (2015);
(f) Gündoğdu (2018); (g) Käppler et al. (2015); (h) Alexiou et al. (2020);
(i) Bruckmoser et al. (2015); (j) Milani (2015)
7V. T. K. Khuyen et al / EnvironmentAsia 14(2) (2021) 1-13
Figure 5. Polymer identification of a visible potential microplastic: Raman spectrum (a)
and FT-IR spectrum (b).
3.3. The microplastics abundance in For this reason, the quality of non - branded
commercial sea salts salts was affected by not only the seawater
where their pellets were crystalized but
As seen in Figure 6, the proportions also the quality of local water sources,
of MPs were generally below 50% of the production environment where the salt
total number of potential plastics identified coarse were ground and minced salts were
by microscopic observation in individual packaged. As a result, the MPs quantities
sediment and supernatant parts. More varied in the markets. Can Gio non-
importantly, the majority of MPs were branded salts contained a low level of MPs,
partitioned in the supernatant. For instance, only 56.98 ± 23.81 items/kg. The MPs
the percentage of MPs was only 3 - 5% abundance in salts bought at the urban
sediment in G - brand salts, and no micro markets of Ho-Chi-Minh city varies in
plastics were found in the sediment of other a small range (48.93 ± 25.14 to 119.07
brands (E, F, J, K L, M). However, MPs ± 71.80 items/kg). Nevertheless, there
accounted for high proportions in the sediment was a considerably high number of MPs
of several brands (A, B, I and N). Although in salts purchased at a suburban district,
the number of particles depositing in the up to 402.52 ± 168.43 items/kg (MM4).
sediment of non-branded products was higher Indeed, the Turkey’s test shows that
than those of branded salts, the most of them only MM4 was statistically different
were grain stones. These stone particles had from other non-branded samples (Sig.
similar appearances to plastic particles, for values < 0.014, Table S2c). Figure 7a
example, homogenous black, pink and yellow shows that PET accounted for highest
particles (Figure 3). Brand B is a special case. percentage (33.63%), followed by
The vast sum of MPs was encountered in the PE (24.78%), PS (20.35%) and PVC
sediment of salt coarse particle (B.P), while (8.85%). In contrast, PP and acrylic
they tended to distribute in the supernatant of glass were not dominant. Almost non-
refined type (B.R sample). fibrous items were fragments smaller
The ANOVA analysis shows statistically than 50 µm, and their minimal size
significant differences in MPs amount was 20 µm. Nevertheless, for fibrous
between non-branded salts (n = 6, Sig. structures, long fibers ( >100 µm) were
= 0.00185, Table S2b), possibly because predominant, and only there were few
contaminations came from different of fibers longer than 500 µm.
sources. The refined salt is more widely used The plastic composition in brands was
in daily cooking and meals. Therefore, non- different from non-labeled salts. The period
branded fine salts were manually produced of use of branded salts is one to two years
on the household scales or local factories. from the production date. The samples
8V. T. K. Khuyen et al / EnvironmentAsia 14(2) (2021) 1-13
were analyzed within 5 months from the differences between brands (n = 14,
production date. Hence, the possibility Sig. = 0.473 - ANOVA in Table S3b. In
of transferring PP micro plastics from addition, the Turkey’s test shows that
polypropylene packages to the salts inside there were no differences among branded
was fairly low. PET was again dominant products with the minimum Sig. value of
(51.74%), followed by PE (23.7%) (Figure 0.483 (Table S3c – Supplementary data).
7b). The findings are similar to Spanish The salts had similar quality because the
(Iñiguez et al., 2017) and Chinese salts process and quality were controlled to
(Yang et al., 2015). It is suggested heavy meet Vietnam’s food safety regulations.
PET debris tended to move to the bottom Nevertheless, in this group, the presence
and remain with the salt during the salt of MPs varies from pellet to refined salts,
crystallization because of high density (1.3 which reveals the effects of salt processing
g/cm3) compared with PE (0.94 g/cm3) and on MPs accumulation in salts to some
PP (0.90 g/cm3) (Yang et al., 2015). extent. In refined salts, the amount of
On the other hands, MPs amounts did insoluble impurities was lower, thereby
not demonstrate statistically significant requiring simpler sample treatment.
Figure 6. The partition of micro debris in the saline mixture
Figure 7. Anthropogenic pieces in non-branded (a) and branded salts (b).
9V. T. K. Khuyen et al / EnvironmentAsia 14(2) (2021) 1-13
MPs might be removed along with the 3.4. The enhanced toxicity of MPs-contaminated
impurities. This is why refined type salt consumption
contained 140 plastic items slightly lower
than the pellet type (178 items/kg) in brand The daily salt intake has increased by
A. In contrast, salts could be contaminated 50 times in the civilized societies, average
with MPs from the environment during from 9 to 12 g/day today. WHO recommends
the grinding and refinery, leading to the a healthy level of 5.1 g salt because an
higher number of MPs in the refined inappropriate salt/sodium intake has resulted
salts (201 items) compared with 144 in kidney diseases, hypertension, and mortality
items/kg in salt pelelts of brand B. PVC (Partearroyo et al., 2019). The daily salt intake
fibers was most predominant in fine salts varies from genders, ages to countries, and is
though PVC is not a common plastic in not fully conscious during cooking or at the
the sea water. Hence, PVC from water table (Partearroyo et al., 2019). Therefore, the
pine could probably intrude into the salt exact amount of daily digested plastic items
during the refinery. In Figure 8, PMMA via salts cannot well established.
did not appear in salt pellets, whilst small The annual MPs intake was calculated
particles were present in refined salts. PE on daily salt consumption of 10 g/day (Table
fibers dominated while PA-6 fibers were 3). Though MPs in Turkish sea salts were
not found in the coarse salts. In contrast relatively low, the salt consumption was
long fibers were found in fine salts that very high, up to 18.5 g per day, leading to
could come from the clothing of workers a high number of 554.95 MPs consumed per
at the factory. PE, PVC and PMMA pieces year. In almost European countries, the daily
were commonly in transparent and light to salt consumption is 7 to 13 g/day in adults
mid colors (white, blue), while PET and (Partearroyo et al., 2019), and an estimated
PS pieces were in mid to dark colors (blue, of over 1000 plastic pieces could be digested
orange, purple). There was no presence via Spanish salts (Iñiguez et al., 2017).
of green and white-striped black items The MPs contents in Vietnamese, Indonesian
in all salts. and Korean commercial salts were similar
No MPs or impurities were seen in (Kim et al., 2018), much higher than
water control. Several black particles Taiwanese (9.77 particles/kg) (Lee et al.,
were on air controls, however, they were 2019). The amount of MPs in Chinese
dust. MPs frequently appeared when the sea salts was highest, up to 718 particles/
laboratory was so crowded, but in a small kg (Yang et al., 2015) relevant to 2620
amount, only 5 ± 2 particles/filter. It is MPs ingested annually as effects of heavy
strongly believed contamination from the plastic pollution in 81% of coastal regions
laboratory coat did not occur because of no according to the Chinese State Oceanic
cotton fibers found Administration (SOA) (Wang et al., 2019).
Figure 8. Composition and size of microplastics in branded coarse salts (a) and refined salts (b)
10V. T. K. Khuyen et al / EnvironmentAsia 14(2) (2021) 1-13
Table 3. Summarized information of in commercial sea salts and their annual
intake via salt consumption route in the world
Humans are ingesting hundreds of MPs combination harmful effects of inappropriate
from salt alone. Nonetheless, the particular salt consumption and hundreds of plastic
harmful effects of MPs on human health are particles via salt digestion every year.
still being investigated. MPs of 0.2 to 150 µm The success of salt reduction depends
were believed to translocate across living cells on eating habits of consumers and objective
to intestinal lymphatic and circulatory systems factors such as availability, food accessibility
of human body (Hussain et al., 2001), but their and salt costs on the market. On Vietnamese
mechanisms has not fully understood yet. A salt market, in no-name bags varied
study reported the human’s excretory system noticeably, up to 402.67 items/kg, compared
could itself eliminate over 90% of micro with maximum of 276.25 items/kg in
to nano - plastic debris via feces (Peixoto branded salts. Hence, it is so necessary to
et al., 2019) while the 10% were absorbed add MPs parameter in food safety standards,
into the blood steam and actually their control more strictly the quality and price of
behaviours in our body are well unknown. non - labeled salts as well.
Bioaccumulation of non-degradable plastics
is dangerous because they can be a home Supplementary data
for microorganisms, hydrophobic organic
substances and heavy metals. Supplementary data are available at
EnvironmentAsia Journal website.
4. Conclusions
Acknowledgment
Although there were differences in the
number of MPs in brands and no - name This research was funded by German
salts, the average of MPs was finally similar Academic Exchange Service (DAAD) under
(133.62 items/kg), which shows MPs the doctoral program Sustainable Water
contamination in seawater of coastal salt Management 2018. The authors gratefully
production locations was similar in Vietnam. thank the support of MSc. Nguyen Vu Duy
PET was dominant followed by PE and Khang at Vietnam Academy of Science
PP, whilst PMMA was the least common. and Technology for facilities and scientific
Vietnamese people are suffering from equipment.
11V. T. K. Khuyen et al / EnvironmentAsia 14(2) (2021) 1-13
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