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Microplastics in a Marine Environment: Review of Methods for Sampling, Processing, and Analyzing Microplastics in Water, Bottom Sediments, and Coastal Deposits

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Abstract

The basic approaches, methods, and procedures for collecting and analyzing samples of microplastics in a marine environment are briefly described.
137
ISSN 0001-4370, Oceanology, 2018, Vol. 58, No. 1, pp. 137–143. © Pleiades Publishing, Inc., 2018.
Original Russian Text © M.B. Zobkov, E.E. Esiukova, 2018, published in Okeanologiya, 2018, Vol. 58, No. 1, pp. 149–157.
Microplastics in a Marine Environment: Review of Methods
for Sampling, Processing, and Analyzing Microplastics in Water,
Bottom Sediments, and Coastal Deposits
M. B. Zobkov* and E. E. Esiukova
Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia
*e-mail: duet@onego.ru
Received December 15, 2015; accepted July 3, 2016
Abstract—The basic approaches, methods, and procedures for collecting and analyzing samples of micro-
plastics in a marine environment are briefly described.
DOI: 10.1134/S0001437017060169
Contamination of a marine environment by micro-
plastics is currently an urgent ecological problem
barely covered in the Russian scientific press. The
main difficulty when providing quantitative assess-
ment of microplastics in marine environment is the
absence of standard procedures for collecting and ana-
lyzing samples of water, bottom sediments, and coastal
deposits.
Today, plastics are one of the most demanded
materials used worldwide. The physicochemical prop-
erties of plastics, mainly endurance, light weight, and
durability combined with low manufacturing costs
make this material nearly irreplaceable in the produc-
tion of domestic goods, construction, and industry.
According to various estimates, the worldwide
annual production of plastics ranges from 275 to
299 mln t [13, 26, 29, 37], whereas the scales of utiliza-
tion and reprocessing are much lower.
Plastic products gradually break down under natu-
ral conditions. This results in huge amounts of macro-,
micro-, and nanoparticles, which are the most harm-
ful to the environment. The specific density of plastic
is clo se to that of water. Because of this, synthetic litter
is easily transported from a catchment area into lakes
and rivers and finally enters the seas and the World
Ocean [5, 37, 45]. Microplastics have various sizes and
low density. As a consequence, many living organisms
perceive them as food [2, 4, 19]. Since their enzymatic
system cannot break plastic down, ingestion of the lat-
ter is harmful by itself for organisms and may cause a
fatal outcome [9, 14, 16, 35]. However, the largest
concerns arise from the fact that microplastics are able
to adsorb contaminants on their surfaces [3, 12, 17, 27,
38] and thereby become a secondary source of con-
taminants. The latter travel up the food chain and
accumulate in higher predators and humans [25, 32].
In addition to the secondary microplastics, which
originate from breakdown of staff or large litter debris,
there are primary ones that penetrate the water bodies
in their initial state [18, 25]. These are plastic granules,
or pellets. They serve as a raw material for manufactur-
ing plastic sheets or ready-to-use items. The cosmetic
industry [15, 18, 44] uses micro granules (microspheres,
nanospheres, microcapsules, nanocapsules) [28, 44].
Currently, there is no final opinion on particle size that
corresponds to microplastics, but the majority of
researchers [20, 45] agree that these are particles from
0.5 to 5 mm in their larger dimension. Some authors
proposed a lower limit close to 0.3 mm [10] due to wide-
spread water sampling techniques using zooplankton
nets with a mesh size of 333 μm [18]; the maximum par-
ticle size corresponding to the definition of microplastic
continues to be a matter of discussion [32]. It is no acci-
dent that particles from 0.5 to 5 mm are considered as a
special group. This is due to the substantial technical
difficulties inherent to analyzing particles smaller than
0.5 mm [20]. In the present review, we adhere to exactly
this dimensional range when determining microplastic
particles. As yet, there is no clear answer to the question
which synthetic substances can be classified as micro-
plastics. This problem has been solved for the majority
of polymers, such as polyethylene, polypropylene,
polystyrene, etc. However, no solution has been found
for other anthropogenic substances such as alkyd resins
or viscose.
The first reports on the discovery of microplastics in
plankton samples go back to early 1970s [6, 7], but only
now is the problem of microplastics in the World Ocean
becoming a matter of discussion in foreign scientific lit-
erature [5, 11, 15, 25, 40]. Microplastics is an extremely
heterogeneous ensemble of particles that vary in size,
shape, color, density considerably and may incorporate
INSTRUMENTS
AND METHODS
138
OCEANOLOGY Vol. 58 No. 1 2018
ZOBKOV, ESIUKOVA
a wide variety of synthetic polymers. This is why reliable
methods of sample collecting, sample preparation, and
plastic detection remain one of the main difficulties in
quantitative assessment of the environment. Nearly all
researchers raise the question of developing standard
procedures. Despite the fact that the first steps in this
direction have already been taken [33], the problem as a
whole remains unsolved.
Nevertheless, many scientists devote efforts to
develop and test techniques for collecting and preparing
samples of water, bottom sediments, and coastal depos-
its, as well as to develop methods for detecting micro-
plastics in samples. Current laboratory procedures for
analyzing microplastics in a marine environment devel-
oped by NOAA [33] for studying marine litter have cer-
tain drawbacks and are voluntary in nature, while mon-
itoring programs require relying on specific solutions
depending on the problems to be solved.
To date, the occurrence and detection of micro-
plastics in a marine environment have not been raised
in Russian scientific publications. To expand the audi-
ence interested in contamination of a marine environ-
ment by microplastics and for convenience in search-
ing for relevant information, we have prepared transla-
tions of a number of foreign scientific papers on the
acquisition and analysis of samples of microplastics in
a marine environment, as well as descriptions of pro-
cedures and standards for testing the polymers. These
translations are available at site of the Shirshov Insti-
tute of Oceanology, Russian Academy of Sciences
(http://ioran.ocean.ru/index.php/news/anonsy/item/
337-anons-publikatsii) and involve complete transla-
tion of laboratory techniques for analyzing microplas-
tics in a marine environment [33] supplemented by
critical comments by authors, discussion of methods
for measuring the specific density of noncellular plas-
tic [22, 34], a method for determining plastic in water
samples with our improvements, and a complete bib-
liography of the sources found. Our intention is to
expand this list as new reviews appear. Among others,
we suggest adding author methods for obtaining and
processing samples of microplastics in water, bottom
sediments, and coastal deposits based on our own and
advanced foreign experiences.
Below is a brief description of the main approaches,
methods, and techniques for obtaining and analyzing
samples of microplastics in a marine environment.
Different types of equipment [42, 34] and analyti-
cal laboratory methods [20, 39] are needed for sam-
pling and determining plastic particles of different size
groups. Particle size determines the inf luence on the
life of oceanic communities and migration pathways in
the ocean.
Samples of microplastics in a marine environment
can be collected (1) from the surface layer, (2) from the
water column, and (3) by sampling bottom sediments or
(4) coastal deposits. Samples can be (1) selective,
(2) bulk, or (3) volume-reduced.
Selective sampling in situ means that plastic debris
usually is recognized by the naked eye and is picked up
from the sandy beach surface. This technique is useful
during assessment of plastic granules and is suitable
due to their spherical shape and relatively large sizes
(up to several millimeters), which facilitates their rec-
ognition on the sandy surface. However, chances of
missing plastic are high when it is mixed with other
rubbish or has an irregular shape.
No concentration of plastic takes place when bulk
samples are collected. Such a technique is the most
popular when studying bottom sediments, but it is
rarely used for water sampling due to low plastic con-
tent in water. Bulk sampling is preferable when visual
identification of plastic is impossible, i.e., if particles
are mixed with the bottom sediments or particles are
too small for filtration at the sampling site or for the
naked eye recognition.
The volume-reduced method is the most applicable
for water sampling and sometimes for bottom sedi-
ments. In this case, the volume of the initial sample is
decreased and only a small fraction of it containing
microplastics remains for subsequent analysis. Sam-
ples of bottom sediments and sand can be sieved
directly at the sampling site on the beach or aboard a
vessel, while water samples are usually concentrated
by filtration of large volumes of water through plank-
ton nets. The bulk and volume-reduced samples
require extra processing under laboratory conditions.
According to the NOAA recommendations [33],
the following procedures can be used for separating
microplastic particles from environmental samples
depending on their size: (1) flow Nanofiltering or
nanofractioning of particles smaller than 1 μm;
(2) a standard filter for particles sizing from 0.2 to
1 μm; (3) the use of phytoplankton neuston net 50–
80 μm (Phyto-P net); (4) zooplankton neuston net
(Zoo-P net) 330 μm; (5) a 5 mm sieve for sieving. It is
difficult to compare the results from sieving and
plankton nets. Therefore, it is recommended to use
sieves with a 500 μm mesh and separately process the
particles retaining and passing through the sieve as a
mandatory operation within each of the above proce-
dures [20]. This makes it possible to compare the results
from density separation and filtering to the data
obtained from analysis of larger fractions (0.5–5 mm)
with sieves.
Surface water samples. Neuston nets are mainly
used in this case. The main advantage is fast filtering of
large volumes of water and obtaining of a concentrated
sample. The nets make it possible to get a representa-
tive sampling from a large water surface, to collect
plastic particles of the millimeter range, and concur-
rently collect microplastics and zooplankton to com-
pare their amounts.
The mesh and opening sizes are the most import-
ant characteristics of sampling nets. However, the
parameters of sampling nets are rarely reported in full
OCEANOLOGY Vol. 58 No. 1 2018
MICROPLASTICS IN A MARINE ENVIRONMENT 139
and the mesh size is usually the only parameter men-
tioned in publications. The mesh size depends on the
research goals and varies from tens of microns to mil-
limeters, but it corresponds to the mesh size of zoo-
plankton nets on average. The opening size of neuston
nets is up to 2 m2. The length of these nets for surface
sampling varies substantially from one to several
meters, but nets 3–4 m long are the most common. The
surface layer sampled by such nets is about 15–25 cm
thick. The buoyancy of a net is supported by special
floats (manta trawl) or catamaran (neuston catama-
ran). The net towing speed varies from 1 to 5 knots.
The use of catamaran facilitates sampling in rough sea
conditions while the efficiency a manta trawl decreases
due to submersion of its inlet in waves. Therefore, the
latter net is applicable in calm waters. Duration of
towing varies from minutes to hours depending on the
SPM content in water.
The use of nets with different mesh sizes consider-
ably hampers comparison of the measurement results.
Samples from the water column. Zooplankton nets,
a continuous plankton recorder (CPR) [43], a near-
bottom trawl for catching benthic organisms (epiben-
thic sled) [31], and various submersible pumps are the
most commonly used tools in the water column. The
water intake system of a research vessel is used too, but
rarely. Niskin bottles are employed for full-volume
sampling of waters. Different studies used different
methods for water sampling at depth ranges from one
to hundreds of meters.
Samples of coastal deposits. The samples were
mainly collected at different parts of a beach and the
choice of the specific site can influence the analysis
results. The sample collection (or series of collections)
is performed (1) over the entire beach, (2) within a
number of separate zones, (3) along the alignment of
different zones of a beach, (4) along the line of maxi-
mum tide or uprush (on the upper beach), and (5) in
ditches or trenches beyond the beach.
Simple tools are frequently used for collecting sam-
ples of plastic granules and fragments (tweezers, metal
spoons, or scoops) or particles are simply collected by
hand using a special container or bag. The collecting
strategy varies: movement in the same direction along
the shoreline and picking up material with a spoon or
scoop or sometimes from a certain area within a spe-
cial frame. In a number of cases, stratified sampling
with special tubes is used.
Sampling units directly depend on the tools used.
In the case of frames or pipes, the concentrations were
calculated per area (from several cm2 to 5 m2). In other
cases, the concentration is calculated per sample
weight, which can range from hundreds of grams to
10 kg, or per sample volume, which varies from tens of
milliliters to several liters.
As a rule, the sampling comprises the upper 5 cm
of sediment, but it may be limited to the surface of a
beach or as deep as tens of centimeters. Microplastics
are able to accumulate in sand in the same way as
organic particles and can be buried in deeper layers.
In this case, it is desirable to use a stratified sampling
procedure with a tube.
Bottom sediments samples. Procedures for bottom
deposits sampling for microplastics content are similar
to those to determine their chemical composition or for
biological assessment. The samples are collected by
grabs (Ekman-Birdge, Van- Veen, Peter son), a bottom
trawl, or core sampler. The distribution of microplastics
as particulate matter in bottom sediments may be sub-
stantially heterogeneous. Therefore, it is necessary to
perform several sediment samplings to obtain a single
representative sample when using point-by-point
devices such as a grab or a corer. This is particularly
important in the case of compact samplers.
Conservation, storage, and quality control. Incorrect
storage of samples can cause a change in their particle
size distribution due to partial destruction of plastic
particles and, as a consequence, the impossibility of
their detection by available methods. Therefore, when
storing or transporting samples, it is desirable to use
procedures that can maintain the plastic in its initial
state at the moment of sampling from the environment.
The principles of storage and conservation of sam-
ples before laboratory analysis: (1) in darkness (if pos-
sible, at 4°С regardless of sample matrix), (2) freezing
(down to –20°С) the samples of bottom sediments
and filters, (3) the use of various fixing solutions (eth-
anol, DESS, 4–5% formalin solution, 5–10% HCl
solution), (4) combined use of fixing solution and
storage at 4°С, (5) drying at room temperature and
storage in the dark (shipborne analysis).
It is proper to avoid and replace when possible the
potential sources of plastic contamination (plastic lab-
oratory ware, plastic sieves and devices) for metal or
glassware. However, it is impossible in the case of nets
and a number of other instruments. A control with
empty samples is obligatory when plasticware is used
for storing the samples. The contamination of samples
may be due to insufficient air quality in the laboratory,
particles of synthetic working cloths, poor cleaning of
tools, loosely closed containers with samples, paint
particles broken off from the side of the vessel by sam-
plers, or particles of synthetic nets used for water sam-
pling. Blank samples must be used in routine for con-
tamination monitoring.
Sample preparation. There are four main stages:
(1) density separation, (2) filtering, (3) sieving, and
(4) organic matter digestion. All are aimed at separat-
ing microplastic particles from the main sample mate-
rial (water, bottom sediments, and sand) and remov-
ing of organic material.
Density separation. The specific density of most
plastics ranges from 0.8 to 1.70 g/cm3.The range
extends down from <0.05 g/cm3 for expanded polysty-
rene and up to 2.1–2.3 g/cm3 for polytetrafluoro-
ethylene/Teflon [8]. Generally, the density of sand
140
OCEANOLOGY Vol. 58 No. 1 2018
ZOBKOV, ESIUKOVA
and other deposits is 2.65 g/cm3. This difference is
used widely to separate comparatively light plastics
from heavier soil particles by placing the sample in a
saturated saline solution and mixing it for a certain
period of time. After mixing, sand and bottom sedi-
ments settle out, while lighter particles (including
plastic ones) remain suspended or float on the solu-
tion surface. The floating particles are collected for
further processing. As a separating solution, fresh or
tap water, sea water, a concentrated NaCl solution
(with a density of 1.2 g/cm3), sodium polytungstate,
lithium metatungstate, zinc chloride, sodium iodide,
and other salts are used. Lightweight and foamed plas-
tics, whose density is less than 1 g/cm3, can also be
separated using fresh water. Plastics that float in sea-
water include expanded polystyrene and high- and
low- density polyethylene and polypropylene. Poly-
styrene in solid form emerges only in a saturated saline
NaCl solution. Elastic and rigid polyvinyl chloride
(PVC), polyethylene terephthalate (PET), and nylon
float up in a sodium metatungstate solution. Since the
density of some plastics reaches 1.7 g/cm3, the use of a
saturated solution of sodium chloride and especially
fresh water can lead to underestimation of the total
microplastic content. Various instruments (shakers,
mixers, centrifuges, flotators, and separators) are
employed to mix the solution. In the simplest case, the
sample is placed in a beaker and mixed with a glass stir
rod. The time of mixing is one of the main parameters
of the extraction. It can vary considerably depending
on the volume of the sample and can range from tens
of seconds to several hours. The settling time also var-
ies greatly and ranges from a few minutes to a day. It is
also expedient to carry out sequential extractions from
the sediment, which leads to increase in the efficiency
of microplastics extraction significantly, but at the
expense of increasing the analysis time also. The most
effective extraction method at this time involves the
Munich Plastic Sediment Separator (MPSS) [21].
Filtration. Vacuum filtration is usually employed
for a solution obtained at the density separation stage
that contains afloat plastic particles. For this, fiber-
glass, polycarbonate membrane, paper, nitrocellulose,
and silicon filters specially designed for FT-IR spec-
troscopy are used. The pore size varies from 1 to
1.6 μm. Filters with a pore size of 2 μm are rarely used.
Sometimes, the working solution with afloat particles
is passed through a fine mesh.
Filtration is also used to isolate microplastics from
bulk water samples. In this case, filters up to 15 cm in
diameter and with a pore size of up to 47 μm are used.
It is possible to collect microplastic particles from
the surface of the solution with tweezers. For separa-
tion of large particles, samples before filtration can be
passed through a sieve with a mesh size of 500 μm [20].
An important point is the process of moving the f loat-
ing particles from the surface of the solution to the fil-
ters and sieves. To prevent any loss of analyte associ-
ated with the adherence of particles to the walls of the
laboratory ware, it is recommended to sequentially
wash the walls of glassware directly on the filter.
Sieving. Microplastics can be isolated from samples
by sieving the latter through sieves with different mesh
sizes. The material on the sieves is further sorted, and
the remainder that has passed through the sieve is dis-
carded. The use of sieves with meshes of various sizes
makes it possible to separate microplastic particles into
several size groups. A cascade of several sieves (one to
six) with sizes of 0.038 to 4.75 mm is usually used. The
sieve material is usually stainless steel or copper.
Filters and sieved material is dried at room tem-
perature or in desiccators. The temperature in the des-
iccators varies greatly in different methods (from 60 to
90°C), but the standard [24] sets the conditions for
preparing plastic samples before testing and recom-
mends not to exceed the temperature of 50 ± 2°C, with
a drying time of 24 h with subsequent bringing the
temperature to normal conditions in a desiccator. This
is established to prevent changes in the composition
and physicochemical properties of the plastics.
Organic matter digestion. The amount of natural
organic matter (algae, zooplankton, and phytoplank-
ton and remnants of tests and shells of marine organ-
isms) in samples can significantly exceed the volume
of the analyte. Plastic particles are susceptible to foul-
ing by some forms of brown algae and bacterial film.
This can introduce an error in determining certain
physical characteristics, e.g., specific density. To elim-
inate the effect of biomaterial dissolution in alkalis,
acids, and oxidizers or decomposition by enzymes are
applied. Sometimes ultrasonic washing of plastic par-
ticles in distilled or deionized water is used to remove
possible surface contamination by sand or silt.
It is important to use proper identification tech-
niques for analysis of different size groups of plastics.
Today, visual detection methods, pyrolysis gas chro-
matography with mass spectrometry, etc. are widely
used, but the spectrometric techniques yield the most
qualitative identification results.
Identification of microplastics. Visual examination
(with the naked eye or a microscope) and sorting of
concentrated samples are often the first step in sepa-
rating plastic from organic residues and other non-
plastic waste, such as glass or resin. In the case of
visual examination without a microscope, attribution
of a particle to the plastics is usually determined by
such subjective characteristics as gloss, brightness,
unusual color, shape, structure or elasticity or hard-
ness determined by tweezers.
Microplastic particles larger than 1 mm can be
visually detected under a microscope in accordance
with the following rules [36]:
(1) Cell structure and other organic forms of parti-
cles are absent.
(2) Fibers should have uniform color and thickness
along the entire length.
OCEANOLOGY Vol. 58 No. 1 2018
MICROPLASTICS IN A MARINE ENVIRONMENT 141
(3) Particles must have a clean and uniform color.
(4) If they are transparent or a white, then they
should be examined by a fluorescence microscope at
large magnification.
In some cases, it is proposed that white, transpar-
ent, and black particles should not be accounted as
plastics, because they interfere with biological mate-
rial and other substances. This approach deliberately
underestimates the microplastic content and should
be applied with caution.
It is expedient to use pyrolysis gas chromatogra-
phy with mass spectrometry (pyrolysis GC-MS,
PyrGC-MS) and FT-IR spectrometry.
Visual methods should not be used separately from
chemical or spectroscopic ones (the latter should be
used to confirm the results of visual determination). To
identify microplastics of lower size groups, only the
spectrometric method should be used (although this
method is very time-consuming) [41]. The choice of a
representative detection method is of paramount
importance in evaluating microplastics contamination.
Microplastic particles found in a marine environ-
ment can be characterized by several criteria, such as
size, shape, specific density, color, chemical composi-
tion, and concentration in water. Therefore, micro-
plastics analysis can be divided into two main compo-
nents: morphological description with determination
of the physical and chemical characteristics of parti-
cles and quantitative analysis with determination of
the chemical composition of the polymers.
Physicochemical characteristics. Particle size is the
main characteristic, with the exception of chemical
composition. The size of a particle is usually under-
stood as its length according to the largest dimension.
The size can be determined directly, using measuring
instruments, e.g., a microscope with a graduated scale,
a digital microscope, or a caliper in visual analysis; indi-
rectly using a set of sieves with separation of a sample of
microplastics into size groups; or with combined use of
sieves and measuring instruments. The size groups of
particles assigned during the analysis depend directly on
the sampling and separation techniques used and are
related to the nominal sizes of the filters or sieves
involved.
Microplastics particles differ in shape: they can be
spherical, irregular, or long fibers. The shape of parti-
cles depends on the degree of destruction and the res-
idence time in the environment. For morphological
characterization of the surface of plastics, scanning
electron microscopy (SEM) and some of its variants
are used, but no method has yet been developed to
determine how long the particle had been in the
marine environment.
The number of categories used to classify microplas-
tic particles depends on the aim of the study and varies
greatly. The morphological description of microplastics
is based on the origin, type, shape, color, and/or degree
of degradation. The reference collections describing the
characteristics of the particles found in the sea have high
significance.
Color is one of the main characteristics of plastics
when using visual identification. The most common
color is white or close to it (faded yellow, cream-col-
ored). The color of particles can introduce uncertainty
into the extraction process in cases where plastic is hid-
den by a large number of biological residues. Particles
with bright colors are highly likely to be selected as plas-
tic, while those with faded colors can easily be missed,
thus contributing a fraction of bias to the analysis pro-
cess . Color i s used to as ses s the d egree of ph otodegrada -
tion, the residence time of a particle on the water sur-
face, and the degree of fouling and weathering.
A number of indirect characteristics, such as specific
density or color, make it possible to roughly identify the
polymer of which the particle consists. However, to
make a final decision, chemical analysis is needed
For a rough identification of the polymer type, sub-
jective characteristics such as the color of the f lame or
smell of smoke released during its burning can be used.
Although plastics belong to amorphous materials,
many of them (HDPE, PVD, PP, PET, etc.) have a
partial crystal structure and can be characterized by a
certain melting point, which can be used for an
approximate evaluation of the type of polymer. The
melting point of plastic granules can be evaluated by
differential scanning calorimetry.
To determine the specific density, it is expedient to
use the method proposed by Kolb and Kolb [30], the
method for measuring the density of noncellular plas-
tics by the titrimetric method [22], or a similar flota-
tion method [1]. However, it is worth considering that
these methods are designed to determine the density
of noncellular plastics only.
The use of such indirect characteristics as density,
color, or melting point can be useful for rapid and
inexpensive determination of the polymer type of plas-
tic granules, since the granules manufacturer describes
these characteristics. However, this approach cannot
be used for plastic fragments, since their shape and
color vary within a wider range, in particular, due to
fragmentation and erosion, and cannot be unambigu-
ously associated with a particular type of plastic.
Determination of the chemical composition of
microplastics and the type of polymer. To identify
microplastics, analytical techniques such as pyrolysis
GC-MS, Raman spectroscopy, SEM, and some of its
varieties are used, as well as IR Fourier spectrometry.
Pyrolysis GC-MS is used to assess the chemical
composition of microplastic particles by analyzing the
gaseous products of their thermal decomposition. A
polymer is identified by characteristic pyrograms, via
their comparison with reference pyrograms of known
pure polymer samples. Pyrolysis GC-MS makes it
possible to determine the types of polymers with suff i-
cient accuracy. However, in the case of analysis of
microplastics, this approach has a significant disad-
142
OCEANOLOGY Vol. 58 No. 1 2018
ZOBKOV, ESIUKOVA
vantage: particles must be manually placed in a pyrol-
ysis tube. Since manual manipulation is applicable
exclusively to relatively large particles, this imposes a
limit on the minimum size of microplastics to be ana-
lyzed. In addition, the method allows one to analyze
only one particle per cycle, and is therefore poorly
suited for processing a large number of samples.
Raman spectroscopy is an efficient chemical anal-
ysis method. In contrast to IR-spectrometry, Raman
scattering results from inelastic scattering of light by
molecules of a substance, and scattered light differs
from the exciting one in terms of wavelength. Advan-
tages of this technology are no need for sample prepa-
ration, the ability to conduct measurements directly in
water, and the use of glass or quartz cells for measur-
ing. By combining this method with microscopic anal-
ysis, it is possible to obtain a more powerful tool for the
study of microplastics – Raman microspectroscopy,
which also provides information on the crystal struc-
ture of a polymer. Raman microspectroscopy makes it
possible to determine the type of a polymer for ultras-
mall plastic particles up to a few microns in size.
At present, IR spectrometry is most commonly
used to identify microplastics. This method compares
the IR absorption spectrum or transmission of a sam-
ple with the spectra of known synthetic substances.
For this, various spectrometric instruments are used:
an infrared spectrometer, an IR Fourier spectrometer,
and an infrared spectrometer for near-IR operation.
They can determine a wide range of polymers, e.g.,
PP, PE, and polyester. However, for microplastic par-
ticles studied on a conventional IR spectrometer,
technical difficulties arise due to the small particle
size. This problem can be solved by using micro-IR
Fourier spectrometry, as well as measurement of spec-
tra under conditions of attenuated total ref lectance
(ATR). In some cases, these approaches can be
achieved by purchasing additional equipment: a spe-
cial microscope or ATR-FTIR cells available for many
modern FTIR spectrometers. The combination of
these two approaches (micro-ATR and FT-IR analy-
ses), in addition to measuring the particle spectra,
makes it possible to add visualization and mapping of
samples and to automate the determination of the
polymer type. However, this procedure is very expen-
sive, time-consuming, and requires highly qualified
specialists; however, it is most suitable for identifying
microplastic particles and exhibits high reliability and
reproducibility. In connection with the laboriousness
of spectrometric analyzers, they are often used to
determine not all the material obtained from the sam-
ple, but only some fraction of the latter.
To increase the effectiveness of monitoring pro-
grams, it should be remembered that the choice of an
appropriate method for selecting and identifying
microplastics is crucial for assessing this type of con-
tamination [41]. When planning monitoring studies, it
is important, if possible, to adhere to the most strin-
gent requirements for sampling, preparation, and
analysis of samples while retaining the maximum
amount of information for comparison of the results
obtained by different research groups in order to esti-
mate the magnitude of the problem on a global scale.
When developing new methodological approaches, it
should be remembered that plastics are industrial
materials whose testing methods are already widely
known. These methods, with some modifications, can
be improved and implemented for analysis of micro-
plastics. Some standards [23] describe sample prepa-
ration techniques that can also be adapted for use in
this field.
We hope that this material will help other research-
ers in solving problems of estimating the amount and
dynamics of microplastics in a marine environment
and determining its role in the world pollution.
ACKNOWLEDGMENTS
This work was supported by the Russian Science
Foundation, project no. 15-17-10020.
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Translated by G. Karabashev
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... These properties make plastics a unique material for the production of goods in the household, construction, and industrial sectors. According to various estimates, the worldwide annual production of plastics ranges from 275 to 299 million metric tons (Mt), whereas much lower scales of utilization and reprocessing have been reported [4]. ...
... MPs in environment make them deceptively perceived as food by many living organisms. Since MPs cannot be broken down by an enzymatic system, MPs ingestion by organisms is harmful and potentially fatal by itself [4]. However, the primary concerns arise from the fact that MPs are prone to adsorb contaminants on their surfaces, thereby becoming a secondary source of contaminants. ...
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Determining the exact abundance of microplastics on the sea surface can be susceptible to the sampling method used. The sea surface microlayer (SML) can accumulate light plastic particles, but this has not yet been sampled. The abundance of microplastics in the SML was evaluated off the southern coast of Korea. The SML sampling method was then compared with bulk surface water filtering, a hand-net (50 μm mesh), and a Manta trawl net (330 μm). The mean abundances were in the order of SML water > hand-net > bulk water > Manta trawl net. Fourier transform infrared spectroscopy (FT-IR) identified that alkyds and poly(acrylate:styrene) accounted for 81% and 11%, respectively, of the total polymer content of the SML samples. These polymers originated from paints and the fiber-reinforced plastic (FRP) matrix used on ships. Synthetic polymers from ship coatings should be considered to be a source of microplastics. Selecting a suitable sampling method is crucial for evaluating microplastic pollution.
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Microplastic litter is a pervasive pollutant present in aquatic systems across the globe. A range of marine organisms have the capacity to ingest microplastics, resulting in adverse health effects. Developing methods to accurately quantify microplastics in productive marine waters, and those internalized by marine organisms, is of growing importance. Here we investigate the efficacy of using acid, alkaline and enzymatic digestion techniques in mineralizing biological material from marine surface trawls to reveal any microplastics present. Our optimized enzymatic protocol can digest >97% (by weight) of the material present in plankton-rich seawater samples without destroying any microplastic debris present. In applying the method to replicate marine samples from the western English Channel, we identified 0.27 microplastics m(-3). The protocol was further used to extract microplastics ingested by marine zooplankton under laboratory conditions. Our findings illustrate that enzymatic digestion can aid the detection of microplastic debris within seawater samples and marine biota.