CC BY
6Tomsk State University Journal of Chemistry, 2024, 34, 89-105
Original article
UDC 504.5:678.5-022.53:502.51(282.256.3) doi: 10.17223/24135542/34/8
Comparability of riverine microplastic sampling and processing techniques: intercalibration experiment for the Yenisei River
Yulia A. Frank1, Alexandra A. Ershova2, Egor D. Vorobiev3, Danil S. Vorobiev4
13'4 Tomsk State University, Tomsk, Russia 2 Russian State Hydrometeorological University, Saint-Petersburg, Russia
1 [email protected] 2 plasticlab. 2019@gmail. com
3 vorobievegor@gmail. com
4 danilvorobiev@yandex. ru
Abstract. Current methodologies for microplastic detection in the environment, including surface freshwaters, are imperfect; no standardized methods for sampling and sample preparation are available. The paper discusses the issues of comparability of microplastic surveys conducted by different methods. An intercalibration experiment carried out on the Yenisei River by two research labs - Research Center 'Microplastic Siberia', Tomsk State University, and PlasticLab, Russian State Hydrometeorological University - is described in detail, including the laboratory protocols and QA/QC issues. Two different sampling techniques - Manta trawl and filtration pump - showed that the total microplastic content in trawl samples was significantly lower (p < 0.01) than that in pump samples (on average 30-fold lower): 2.04-4.85 and 93.0-107 items/m3, correspondingly. The problem of incomparability of the quantitative estimates obtained by different sampling methods was confirmed, suggesting their complementarity. At the same time, differences in the morphology of the detected particles sampled by different instruments suggest that river surface and subsurface layers transport different microplastics. The study showed that sampling methods but not different laboratory protocols for sample processing are primarily important for the consistency of the results of quantitative analysis of riverine microplastics, which suggests relevance of harmonization of sampling methods.
Keywords: intercalibration, Manta trawl, riverine microplastics, water sampling, the Yenisei River
Acknowledgments: This research was funded by the Russian Science Foundation under the project No. 22-27-00720 'Abundance and accumulation of microplastics in Siberian Rivers'. We are grateful to Andrey Trifonov for help with the construction of the PP-3 Manta trawl in TSU, and Irina Makeeva for the excellent laboratory assistance during sample processing in PlasticLab, RSHU.
For citation: Frank, Y.A., Ershova, A.A., Vorobiev, E.D., Vorobiev, D.S. Comparability of riverine microplastic sampling and processing techniques: intercalibration experiment for the Yenisei River. Vestnik Tomskogo gosudarstvennogo universiteta.
© Y.A. Frank, A.A. Ershova, E.D. Vorobiev, D.S. Vorobiev, 2024
Chimia - Tomsk State University Journal of Chemistry, 2024, 34, 89-105. doi: 10.17223/24135542/34/8
Научная статья
doi: 10.17223/24135542/34/8
Сопоставимость методов отбора проб и обработки речного микропластика: эксперимент по взаимной калибровке для реки Енисей
Юлия Александровна Франк1, Александра Александровна Ершова2,
Егор Данилович Воробьев3, Данил Сергеевич Воробьев4
13 4 Томский государственный университет, Томск, Россия 2Российский государственный гидрометеорологический университет, Санкт-Петербург, Россия 1 yulia.a.frank@gmail. com 2 plasticlab. 2019@gmail. com
3 vorobievegor@gmail. com
4 danilvorobiev@yandex. ru
Аннотация. Современные методы обнаружения микропластика в окружающей среде, включая поверхностные пресные воды, несовершенны, отсутствуют стандартизированные методы отбора и подготовки проб. В статье рассматриваются вопросы сопоставимости результатов количественных оценок микропластика, проведенных различными методами. Подробно описан эксперимент по взаимной калибровке, проведенный на реке Енисей двумя исследовательскими лабораториями - Центром исследования микропластика в окружающей среде Томского государственного университета и лабораторией PlasticLab Российского государственного гидрометеорологического университета, включая лабораторные протоколы и вопросы контроля качества. Использование двух различных методов отбора проб - трала системы «Манта» и фильтрационной насосной установки - показали, что общее содержание микропластика в пробах, взятых тралом, было значимо ниже (р < 0,01), чем в пробах, взятых фильтрующим насосом (в среднем в 30 раз): 2,04-4,85 и 93,0-107 ед./м3 соответственно. Была подтверждена проблема несопоставимости количественных оценок, полученных различными методами отбора проб. В то же время различия в морфологии обнаруженных частиц, отобранных разными приборами, позволяют предположить, что поверхностные и подповерхностные слои реки переносят разный микропластик, что свидетельствует о взаимодополняемости двух методов пробоотбора.
Ключевые слова: речной микропластик, отбор проб воды, интеркалибровка, трал Манта, фильтрационная установка, река Енисей
Благодарности: Исследование поддержано Российским научным фондом в рамках проекта № 22-27-00720. Авторы благодарны Андрею Трифонову за помощь в изготовлении трала Манта ПП-3 в ТГУ и Ирине Макеевой за отличную лабораторную помощь при обработке образцов в PlasticLab, РГГМУ.
Для цитирования: Франк Ю.А., Ершова А.А., Воробьев Е.Д., Воробьев Д.С. Сопоставимость методов отбора проб и обработки речного микропластика: эксперимент по взаимной калибровке для реки Енисей // Вестник Томского государственного университета. Химия. 2024. №> 34. С. 89-105. doi: 10.17223/24135542/34/8
1. Introduction
Pollution of the world's oceans with microplastics is a complex and cross-cutting global issue with implications for ecosystems and human health we have yet to face [1-4]. A significant portion of marine microplastics is assumed to come from rivers [5-6]. Microplastics enter continental waters from various sources [78], including diffuse (for example, plastic waste from catchment area watercourses, microparticles from groundwater) and point sources (agricultural, atmospheric, domestic and industrial wastewaters). Accurate quantification of stream fluxes of terrestrial plastics litter and microplastics is crucial for effective management of aquatic plastic pollution [9]. However, the study of riverine microplastics is still in its infancy, and one of the causes is numerous and unhar-monized sampling methods, which hinders accumulation of survey data for more accurate assessment of global riverine microplastic fluxes [10].
Numerous authors report imperfection of the methodology to study microplastics in the environment, including surface freshwaters [11-15]. Currently, no standardized methods for sampling and sample preparation are available. The authors use a variety of methods for microplastic sampling, sample preparation, and qualitative analysis of particles from river water; the variety of methods and units used to express microplastic concentrations affect data interpretation and impede their comparative analysis [13, 16-18].
The choice of the method and instruments to sample surface waters for quantitative assessment of microplastics largely depends on study objectives. Fine mesh nets and pump filtration systems are among the instruments most frequently used for sampling freshwater [18]. Neuston nets and Manta trawls are often used to collect microparticles from the surface and from the upper layers. It is assumed that many polymers are found in the surface layer due to their small size and density lower than that of freshwater (<1.00 g/cm3) [14]. However, some types of microplastics such as polyamide (PA), polyethylene terephthalate (PET) and poly-vinyl chloride (PVC) particles can sink due to their higher density and, therefore, can be partially ignored [19]. Manta nets are used to collect particles >300 ^m, which are typically ingested by birds and larger marine animals; particles <300 ^m are underrepresented [20]. Yet, net sampling is the most common type of river water sampling despite its drawbacks. A recent review by Bai et al. [10] showed that neuston nets were used in 50 of 63 surveys conducted on rivers worldwide, which is almost 80%. In surveys of reservoirs and watercourses in Russia, the proportion of neuston net sampling was only 50%; in 44% of cases, pump filtration systems were used [15].
Pump filtration systems capture particles less than 100 ^m (down to nanoplas-tics <1 ^m) that are more likely to be transferred through the animal and human cell membranes. Various modifications of such instruments are used by different research groups [21-22], always including the pump (autonomous or built in a vessel flow-through system), the flowmeter, and the filtration unit with a single or cascade stainless steel filters with a mesh size of 100 ^m and smaller. The main advantage of such systems is the isolation of the sample in the filtration unit
in order to avoid the airborne contamination. However, pump filtration systems are typically submerged up to several meters below the surface and therefore study microplastics in the subsurface compared to surface netting. Pump filtration systems can also be used to collect large volumes of water, which is advantageous in areas where microplastic concentrations are considered to be low [23], in particular, the Arctic [22, 24-26] or Antarctic waters [27].
The aim of the study was to conduct an experiment on intercalibration of river water sampling by two methods (pump filtration system and Manta trawl) and subsequent cross-independent analysis of samples in two research laboratories. The main hypothesis was that the methodology used for sampling and particle extraction during laboratory processing affects microplastic quantification results. The model object was one of the most waterbearing rivers in the world, extremely poorly studied for microplastic pollution - the Yenisei River, Siberia, Russia.
2. Material and methods 2.1. Sampling
On August 8, 2022, water sampling from the Yenisei River was performed simultaneously by two methods at one point near the city of Minusinsk (53°39'12"N 91°33'26"E). Samples were taken during the summer low water period.
Fig. 1. Instruments used for sampling river water: A - PP-3 Manta trawl and B - HydroPuMP filter
The surface water layer (0-15 cm) was sampled by the PP-3 Manta trawl (Fig. 1A). The model was designed and manufactured at Tomsk State University (TSU) to sample river water, and then it was tested on the rivers of Eurasia [2829]. For sampling, the trawl is placed in downstream direction at a depth of 1 m and is fixed to collect plastic particles from the upper water layer for 15 min. Three water samples are taken in parallel. Particles are captured by the net with a mesh diameter of 333 ^m. The volume of the filtered river water is measured with
a flowmeter attached to the sampler (Hydro-Bios, Altenholz, Germany); the area of the intake part of the device immersed in water is also taken into account. The PP-3 Manta trawl was used to take 2 series of samples in 3 replicates (Table 1); the sample volume ranged from 3.42 m3 (samples of the M_PL series) to 3.44 m3 (samples of the M_TSU series).
Table 1
Designation and characteristics of water samples
Sample series Processing laboratory Instrument Sample volume, m3 Number of samples
F_RSHU PlasticLab, RSHU* Flow filter HydroPuMP 0.10 n = 3
M_RSHU PlasticLab, RSHU Manta trawl PP-3 0.10 n = 3
F_TSU Research centre 'Microplastic Siberia', TSU** Flow filter HydroPuMP 3.42 n = 3
M_TSU Research centre 'Microplastic Siberia', TSU Manta trawl PP-3 3.44 n = 3
Note. *RSHU lab, **TSU lab
The next sampling was performed at a depth of 30-40 cm using an autonomous filtration system HydroPuMP (HydroPump for MicroPlastics) developed at RSHU lab (PlasticLab). It consists of a battery, flowmeter and an isolated filtration unit with stainless steel replaceable filters with mesh size of 100 ^m (Fig.lB). An operator immerses the filtration unit under the water surface so that it does not touch the bottom (at a depth of at least 1 m). This filtration system can be used for both oceans and rivers; however, due to high turbidity of river water, the filtered sample volume is 0.1 m3 (while seawater sampling requires at least 1 m3 of pumped water). This procedure was used to take 2 series of samples in 3 replicates with a volume of 0.1 m3 each (F_RSHU and F_TSU, Table 1).
2.2. Laboratory Sample Processing
Laboratory sample processing to extract particles was performed in parallel in two laboratories - TSU lab and Russian State Hydrometeorological University (RSHU) lab (Table 1). The TSU lab procedure for microplastics extraction from water samples was adapted from the method by Masura et al. [2015]. The procedure includes the following steps: (1) sequential wet sieving of a water sample through a 5.0 mm stainless steel sieve and 0.33 mm net; (2) collecting sieved particles and their drying in a glass container at 85 °C; (3) thermochemical treatment with hydrogen peroxide (30%) with the addition of 0.05 M Fe (II) aqueous solution at 60 °C; (4) density separation in a saturated NaCl solution with density of 1.2 g/cm3 within 24 h; (5) vacuum filtration of the upper phase through a 1.0 ^m glass fiber filter (Pall Corporation, Ann Arbor, MI, USA), followed by quantitative and qualitative particle analysis. This procedure was previously tested on water samples taken from the Yenisei tributary, the Lower Tunguska River [30].
The RSHU lab procedure is a modification of the protocol that implies peroxide oxidation of organic matter and particle density separation [31]. It includes the
following steps: (1) wet sieving onto an 82 ^m nylon filter; (2) density separation of particles with a ZnCh solution with density of 1.7-1.8 g/cm3 within a day;
(3) thermochemical treatment to dissolve organic matter in a water bath with hydrogen peroxide (30%), with a ferrous sulfate catalyst at 60 °C; (4) cooling at room temperature with the addition of 10 ml hydrochloric acid (1:1) until complete dissolution of the organic material (up to 12 h); (5) rinsing with distilled water onto the filter, drying at room temperature, and further quantitative and qualitative analysis of the filter with suspension. This procedure was tested for extraction of microplastics from water samples taken from the Russian Arctic seas [26, 32].
In both laboratories, after visual analysis, the particles were examined using the hot needle method, which enables highly accurate identification of synthetic polymer particles based on the plastic-non plastic principle [33]. A heated needle was brought to the detected particle under microscopic control; plastic particles melted, while organic particles darkened or burned. The method is one of the easiest and cheapest for microplastic identification unless it is used to determine the polymer composition [33-34]. Identified polymer particles were photographed, and their size, shape, and color were recorded as described in section 2.3.
2.3. Data Processing and Analysis
Detection of microplastics from three independent samples of the Yenisei surface water was carried out in parallel. Based on the data obtained, the arithmetic mean and standard deviation were calculated for each sampling site. A non-parametric Mann-Whitney U test [35] was used to compare differences in total microplastic counts and morphology between results from different series (in items/m3), with results considered statistically significant at p < 0.01.
The microplastic particles were classified into four groups by shape as described by Frias and Nash [36]: (1) fibers, (2) fragments of irregular shape, (3) films, and
(4) spheres. During analysis in TSU lab, the particles were classified by the largest size using ToupView 3.7.6273 software (ToupTek, Hang-zhou, China) and categorized by groups: (1) 150-300 ^m, (2) 300-1,000 ^m, (3) 1,000-2,000 ^m, (4) 2,000-3,000 ^m, (5) 3,000-4,000 ^m, and (6) 4,000-5,000 ^m. In RSHU lab, the particles were measured and categorized by similar size groups using a Leven-huk stereo microscope, a built-in camera, and software. Percentage of the different shapes, sizes, and color of the particles was determined. To identify differences between the methods for sampling and laboratory preparation of samples, the particles counted in two different laboratories were grouped as follows: (1) 100-300 ^m, (2) 300-1,000 ^m, and (3) 1,000-5,000 ^m.
2.4. Quality Assurance and Control
Materials and equipment used for in-situ and laboratory processing were made of stainless steel, glass, and aluminum whenever possible to prevent sample contamination by external microplastics; cotton clothing was used during sampling and laboratory testing. Laboratory processing of samples was performed in a laminar
flow unit to prevent air contamination with prefiltration of the reagent/solution using glass membrane filters with a pore size of 1.0 ^m. Filters with collected microplastic particles were stored in closed, clean Petri dishes until microscopic analysis.
External contamination of samples during collection, preparation, and storage was monitored using blank negative controls (n = 3 for each set of three samples) as recommended by Koelmans et al. [37]. Filter examination revealed 0 to 2 mi-crofibers per empty filter. For laboratory-contaminated samples, the results were adjusted by excluding fibers of similar morphology from further analysis.
3. Results
In total, we detected and analyzed 131 microplastic particles (total for all water samples taken from the Yenisei River). Table 2 summarizes the data on quantitative assessment of microplastic particles in different sample series. The table shows the number of particles in samples obtained from each individual water sample, and the amount of microplastics of different shapes and sizes. The data obtained were used to assess differences in the total particle content per cubic meter of water taken from the Yenisei River and differences in the extraction and counting of microplastics of different shapes and sizes performed by different methods of sampling and laboratory processing.
3.1. Microplastic Count Differences
In pump samples, from 5 to 18 particles were detected in RSHU lab, and from 8 to 11 in TSU lab (Table 2). Conversion to cubic meter of river water and averaging in each sample series revealed that both laboratories found approximately equal total number of microplastic particles, 107 ± 66.6 and 93.0 ± 15.3 items/m3, respectively. Statistical analysis did not show significant differences in values (Table 3). Manta trawl sampling performed by RSHU and TSU labs in complience with different protocols revealed no significant differences in the number of microplastics either - 4.85 ± 2.50 versus 2.04 ± 0.88 items/m3 were found, respectively (Table 2).
Table 2
Data of quantitative assessment of microplastic particles in the series of water samples taken from the Yenisei River obtained by different methods of sampling and laboratory processing
Sample series Sample No. MP number in the sample Abundance of each particle shape, items/m3 Particle size range, ^m MPs, items/m3 MPs, items/m3 (mean ± SE)
Fiber Fragment Sphere Film
F RSHU 1 9 70.0 20.0 0.00 0.00 235-2,150 90.0 107 ± 66.6
2 5 50.0 0.00 0.00 0.00 1,254-3,336 50.0
3 18 80.0 100 0.00 0.00 158-2,112 180
M RSHU 1 27 0.87 6.98 0.00 0.00 131-2,337 7.85 4.85 ± 2.50
2 13 0.00 3.78 0.00 0.00 186-2,813 3.78
3 10 0.00 2.91 0.00 0.00 335-2,409 2.91
The end of table 2
Sample Sample MP number Abundance of each particle shape, items/m3 Particle size MPs, MPs, items/m3 (mean ± SE)
series No. in the sample Fiber Fragment Sphere Film range, ^m items/m3
1 11 0.00 40.0 0.00 70.0 150-1,000 110
F TSU 2 8 50.0 20.0 0.00 10.0 150-1,000 80.0 93.0 ± 15.3
3 9 10.0 50.0 0.00 30.0 150-4,000 90.0
1 4 0.00 0.87 0.00 0.29 150-2,000 1.16
M TSU 2 7 0.58 1.17 0.29 0.00 150-2,000 2.04 2.04 ± 0.88
3 10 0.88 1.75 0.00 0.29 300-3,000 2.92
Significant differences were found between the microplastic content in samples taken by two different sampling techniques. Significantly greater number (p < 0.01) of microplastics was detected via the filtration pump compared to that obtained by the Manta trawl (Tables 2, 3).
In pump samples, RSHU and TSU labs detected 107 ± 66.6 and 93.0 ± ± 15.3 items/m3, which is several fold higher compared to the data of quantitative assessment of particles in net samples (only 4.85 ± 2.50 and 2.04 ± 0.88 items/m3 in RSHU lab and TSU lab, respectively).
Table 3
Differences in the total amount of microplastics found (items/m3) in the series of samples
Sample series F RHSU F TSU M RHSU M TSU
F RSHU
F TSU No
M RSHU 0.01 0.01
M TSU 0.01 0.01 No
Note. No - no statistically significant differences, 0.01 - statistically significant differences (p < 0.01).
Thus, significant differences (p < 0.01) were found for microplastics detected in samples taken using the filtration pump versus the Manta trawl. The laboratory processing protocol used did not affect the analysis results (p > 0.01).
3.2. Microplastic Morphology Differences
The shape distribution of microplastics found in water samples from the Yenisei River (n = 131) was as follows: fragments of irregular shape (56.3%) > fibers (30.5%) > films (12.0%) > spheres (1.2%). The abundance of different shaped MPs (items/m3) is shown in Table 2.
Differences were observed in the proportions of fibers and fragments in the F_RSHU/F_TSU series compared to the M_RSHU/M_TSU series. Significantly more fibers were detected (p < 0.01) in the F_RSHU sample series compared to the two Manta trawl series (Table 4). Moreover, more fragments were detected in trawl samples compared to pump samples (p < 0.01). As seen from Table 4, the M_RSHU series revealed a significantly higher number of fragments compared to the M TSU series.
In contrast to samples processed in RSHU lab, water samples processed in TSU lab exhibited a diverse morphology of particles - fibers, fragments, microfilms, and spheres (in one mesh sample) (Fig. 2). The number of the detected films was higher in both series processed in TSU lab (p < 0.01) and significantly higher in the F_TSU series compared to the M_TSU series (Table 4). The differences between the absolute content of spheres on filters with concentrated microplastics were not significant for different sample preparation protocols.
Fig. 2. Shape distribution of microplastics in the series of samples
Table 4
Differences in the amount of particles of different shapes in the series of samples
Sample series F RSHU F TSU M RSHU M TSU
Fibers
F RSHU
F TSU No
M RSHU 0.01 No
M TSU 0.01 No No
Fragments
F RSHU
F TSU No
M RSHU No 0.01
M TSU No 0.01 0.01
Spheres
F RSHU
F TSU No
M RSHU No No
M TSU No No No
The end of table 4
Sample series F RSHU F TSU M RSHU M TSU
Fibers
Films
F RSHU
F TSU 0.01
M RSHU No 0.01
M TSU No 0.01 No
Note. No.- no statistically significant differences, 0.01 - statistically significant differences (p < 0.01).
Fig. 3 presents the samples that contained microplastics of different size (100300, 300-1,000 and 1,000-5,000 ^m), except for one sample in the F_RSHU series (only particles > 1,000 ^m) and four samples in the TSU series (only particles < 1,000 ^m). The size distribution of microplastics found in the Yenisei River (n = 131) was as follows: 300-1,000 ^m (54.0%) > 1,000-5,000 (24.1%) > 150300 ^m (21.9%).
The proportion of particles larger than 1,000 ^m was significantly higher in one sample of the F_RSHU series, compared to the remaining three series (Table 5). More microplastics 300-1,000 ^m in size were found in both series processed in TSU lab compared to RSHU lab (p < 0.01). Of the two sample series processed in RSHU, the proportion of particles 300-1,000 ^m in size was significantly higher in trawl samples (Table 5). No differences in the absolute content of the smallest particles (100-300 ^m) were found either in samples obtained by different sampling methods or different laboratory processing protocols used to extract microplastic particles.
Fig. 3. Size distribution of microplastics in different sample series
Table 5
Differences in the content of particles of different sizes in the series of samples
Sample series F RSHU F TSU M RSHU M TSU
100-300 ^m
F RSHU
F TSU No
M RSHU No No
M TSU No No No
300-1,000 ^m
F RSHU
F TSU 0.01
M RSHU No 0.01
M TSU No 0.01 No
1,000-5,000 ^m
F RSHU
F TSU 0.01
M RSHU 0.01 No
M TSU 0.01 No No
Note. No - no statistically significant differences, 0.01 - statistically significant differences (p < 0.01).
Fig. 4. Color distribution of microplastic particles in the F_RSHU and M_RSHU series
The color of microplastic particles was determined in samples analyzed in RSHU lab. The color range of particles detected in pump samples was different from that in trawl samples (Fig. 4). In both series, transparent, black and brown particles were identified. Yellow and red microplastics were found only in the F_RSHU series, and gray, blue and cyan were detected only in the M_RSHU series (Fig. 4).
4. Discussion
Adequate quantification of microplastics in natural waters requires large sampling volumes [38-39]. In-situ filtration and sieving enable such sampling volumes while reducing the volume in the final sample (sample concentration). These methods are more suitable for natural water samples since they provide a small
sample volume with no need to transport it to the laboratory [18]. The methods also include techniques that employ the HydroPuMP filter and the PP-3 Manta trawl. It should be noted that we collected much (p < 0.01) more microplastics during water sampling at a depth of 30-40 cm using the filter with a mesh diameter of 100 ^m compared to the Manta trawl equipped with a 333 ^m net collecting particles from the upper layer of 0-15 cm. In pump samples, microplastics were detected in both laboratories in the amount of 93.0 ± 15.3 to 107 ± 66.6 items/m3. In trawl samples, the amount of microplastics attained 4.85 ± 2.50 to 2.04 ± 0.88 items/m3, which is on average 30-fold less than that in pump samples.
Numerous publications report that mesh size or pore diameter and the amount of microplastics found in surface waters are interrelated. In the previous study, the amount of microplastics <2.00 mm collected by the Neuston net with a 333 ^m mesh size significantly exceeded that collected by the net with a 1,000 ^m mesh size [40]. In the Marne and the Seine rivers, the amount of microplastics collected using the net with a 80 ^m mesh size 250-fold exceeded that collected by a conventional net with a 330 ^m mesh size [41]. Water sampling from the Danube River showed an inverse logarithmic dependence of the number of the recorded microplastics and the pore diameter of the filtration system [42]. Thus, when using nets with 105, 95 and 20 ^m meshes, a total of 46, 95 and 2,677 items of microplastics per liter of river water were recorded, respectively. The same conclusions were drawn for marine water net tows when using a 100 ^m mesh that resulted in the collection of 2.5-fold and 10-fold greater microplastics compared to that when using 333 and 500 ^m meshes [43].
Interestingly, we did not find significant differences in the number of microplastics of the smallest size range (100-300 ^m) in river water samples taken by different sampling methods. A number of studies into marine ecosystems show that finer nets result in the collection of smaller particles (thinner, shorter fibers) [43]. We also expected to collect a greater amount of small microplastics in river water using the filtration system with a finer mesh of 100 ^m compared to that collected by the Manta net with a 333-^m mesh, but we failed. Significant differences in the absolute content of the smallest particles (up to 300 ^m) were not found either in the Yenisei River water samples obtained by different sampling methods, or in different laboratory processing protocols used to extract microplastic particles.
Some researchers consider mini-microplastics (<330 ^m) to be the most common fraction of microplastics in freshwaters which pose the greatest threat to biota [44-46]. Thus, in the water of Lake Baikal, microplastics <330 ^m accounted for 88% of all detected plastic particles in the size range of 20-5,000 ^m [46]. The data obtained using the above methods show that particles in the size range of 100-300 ^m were not dominant in water samples taken from the Yenisei River. In general, microplastics with sizes of 300-1,000 ^m along the largest axis predominated in water samples (54% of the collected and analyzed particles).
The size, density, and shape of microplastics, as well as the river hydrodynamics, determine whether the particle will be transported through the surface layer or in suspension [47-48]. Obviously, the considered instruments enable collection
of microplastics transported in different layers of the river flow. This can be attributed to the fact that the Manta trawl and the filtration pump take samples from different depths; therefore, they collect microplastics of different morphology and their quantitative assessment cannot be interchanged. This is evidenced by differences in the morphology of particles found in different series. Our study identified much more fibers (p < 0.01) in the F_RSHU sample series obtained using the filtration pump compared to the two series obtained via the Manta trawl. In this case, more fragments were captured when using the Manta sampler compared to the filtration system (p < 0.01). The observed differences in the color range of particles in samples obtained by two different sampling methods and analyzed in RSHU lab provide additional evidence that different microplastics are captured by these sampling methods. Similar results were previously obtained in the study into the coastal waters of the Norwegian fjords and open ocean waters in the Central Atlantic [49]. The authors of this study concluded that different sampling techniques (neuston nets to collect particles from the upper layer of 0-20 cm and the filtration system to collect microplastics from deeper horizons of 3-5 m) complicate the comparison of the data obtained. In this study, different morphology of microplastic particles found in the Yenisei River, including shape and color, were apparent already at depths of 0-15 cm (M_RSHU and M_TSU series) and 30-40 cm (F_RSHU and F_TSU series).
Different laboratory protocols for sample processing used independently in two laboratories, which were based on wet peroxide oxidation and particle density separation, but differed in the details and reagents used for particle extraction, did not affect the result of microplastics quantification. However, the analysis of the morphology of particles recorded in different series of samples showed that the protocol used can affect the result quality. It is assumed that despite the availability of NaCl and recommendations for its use [31], it does not allow the detection of all plastic particles and should be replaced in protocols with salts that produce denser solutions [16]. Yet, the results of this study obtained for river water are not in compliance with the above data. Despite the use of NaCl with a lower density (1.20 g/cm3) compared to ZnCk (1.7-1.8 g/cm3), the samples processed in TSU lab exhibited a more diverse particle morphology compared to those processed in RSHU lab. This can be due to the features of microplastics taken from the Yenisei River and due to the fact that other stages of laboratory sample preparation can also significantly affect quantitative assessment of microplastic particle.
5. Conclusion
The study results showed that the consistency of quantitative analysis of riverine microplastics depends primarily on sampling techniques but not on different laboratory protocols for sample processing. It was shown that the use of different methods for sampling and analyzing microplastics lead to incompara-bility of the obtained quantitative estimates. On average, from 93.0 to 107 items of microplastics per cubic meter were found in the Yenisei River using the filtration pump, while the amount of microplastics detected using the Manta trawl was
significantly lower (p < 0.01) and amounted to 2.04-4.85 items/m3. Differences in the morphology of the detected particles suggest that different microplastics are transported through the surface and subsurface layers of river water, which enter the samples taken with the appropriate instrument.
Standardization of sampling techniques and laboratory analysis will be relevant for further development of a more reliable riverine microplastics monitoring strategy. This study shows that direct filtration of subsurface particles and net sampling, which captures particles floating on the surface, cannot be considered interchangeable methods for quantitative assessment of riverine microplastics. We argue that these methods are not alternative, and they must be used complementary for microplastic surveys. This will contribute to better acquisition of data on distribution and characteristics of riverine microplastics.
References
1. Sharma S., Chatterjee S. Microplastic pollution, a threat to marine ecosystem and human
health: A short review // Environ. Sci. Pollut. Res. 2017. 24. pp. 21530-21547. doi: 10.1007/s11356-017-9910-8.
2. Du S., Zhu R., Cai Y., Xu N., Yap P.S., Zhang Y., He Y., Zhang Y. Environmental fate and
impacts of microplastics in aquatic ecosystems: a review // RSC Adv. 2021. 11. pp. 1576215784. doi: 10.1039/d1ra00880c.
3. Huang W., Song B., Liang J., Niu Q., Zeng G., Shen M., Deng J., Luo Y., Wen X., Zhang Y.
Microplastics and associated contaminants in the aquatic environment: A review on their ecotoxicological effects, trophic transfer, and potential impacts to human health // J. Hazard. Mater. 2021. 405. 124187. doi: 10.1016/j.jhazmat.2020.124187/.
4. Khan F.R., Oliveria M., Walker T.R., Panti C., Hardiman G. Ecotoxicological Impacts of
Micro(Nano)plastics in the Environment: Biotic and Abiotic Interactions // Microplastics. 2023. 2. pp. 215-218. doi: 10.3390/microplastics2030017.
5. Skalska K., Ockelford A., Ebdon J.E., Cundy A.B. Riverine microplastics: Behaviour, spa-
tio-temporal variability, and recommendations for standardised sampling and monitoring // J. Water Process. Eng. 2020. 38. e101600. doi: 10.1016/j.jwpe.2020.101600/.
6. van Emmerik T., Mellink Y., Hauk R., Waldschlager K., Schreyers L. Rivers as plastic
reservoirs // Front. Water. 2022. 3. 786936 p. doi:10.3389/frwa.2021.786936/.
7. Horton A.A., Dixon S.J. Microplastics: An introduction to environmental transport processes //
WIREs Water. 2017. 5. e1268. doi: 10.1002/wat2.1268.
8. Xu X., Hou Q., Xue Y., Jian Y., Wang L. Pollution characteristics and fate of microfibers
in the wastewater from textile dyeing wastewater treatment plant // Water Sci Technol. 2018. 78. pp. 2046-2054. doi: 10.2166/wst.2018.476.
9. Lofty J., Ouro P., Wilson C.A.M.E. Microplastics in the riverine environment: Meta-analysis
and quality criteria for developing robust field sampling procedures // Sci. Total Environ. 2023. 863. 160893 p. doi: 10.1016/j.scitotenv.2022.160893.
10. Bai M., Lin Y., Hurley R., Zhu L., Li D. Controlling Factors of Microplastic Riverine Flux and Implications for Reliable Monitoring Strategy // Environ. Sci. Technol. 2022. 56. pp. 48-61. doi: 10.1021/acs.est.1c04957.
11. Eerkes-Medrano D., Thompson R.C., Aldridge D.C. Microplastics in freshwater systems: A review of the emerging threats, identification of knowledge gaps and prioritisation of research needs // Water Res. 2015. 75. pp. 63-82. doi: 10.1016/j.watres.2015.02.012/.
12. Li J., Liu H., Paul Chen J. Microplastics in freshwater systems: A review on occurrence, environmental effects, and methods for MPs detection // Water Res. 2018. 137. pp. 362374. doi: 10.1016/j.watres.2017.12.056.
13. Stock F., Kochleus C., Bansch-Baltruschat B., Brennholt N., Reifferscheid G. Sampling techniques and preparation methods for microplastic analyses in the aquatic environment -A review // Trends Anal. Chem. 2019. 113. pp. 84-92. doi: 10.1016/j.trac.2019.01.014.
14. Campanale C., Savino I., Pojar I., Massarelli C., Uricchio V.F. A Practical overview of methodologies for sampling and analysis of microplastics in riverine environments // Sustainability. 2020. 12. 6755 p. doi: 10.3390/su12176755.
15. Frank Y., Ershova A., Batasheva S., Vorobiev E., Rakhmatullina S., Vorobiev D., Fakhrullin R. Microplastics in Freshwater: A Focus on the Russian Inland Waters // Water. 2022. 14. 3909 p. doi: 10.3390/w14233909.
16. Prata J.C., da Costa J.P., Duarte A.C., Rocha-Santos T. Methods for sampling and detection of microplastics in water and sediment: A critical review // Trends Anal. Chem. 2019. 110. pp. 150-159. doi: 10.1016/j.trac.2018.10.029.
17. Bellasi A., Binda G., Pozzi A., Galafassi S., Volta P., Bettinetti R. Microplastic contamination in freshwater environments: A review, focusing on interactions with sediments and benthic organisms // Environments. 2020. 7. pp. 30. doi: 10.3390/environments7040030.
18. Razeghi N., Hamidian A.H., Wu C., Zhang Y., Yang M. Microplastic sampling techniques in freshwaters and sediments: a review // Environ Chem. Lett. 2021. 19. pp. 4225-4252. doi: 10.1007/s10311-021-01227-6.
19. Andrady A.L. The plastic in microplastics: A review. Mar. Pollut. Bull. 2004. 119, 12-22. doi: 10.1016/j.marpolbul.2017.01.082.
20. Lusher A.L., Primpke S. Finding the Balance between Research and Monitoring: When Are Methods Good Enough to Understand Plastic Pollution? // Environ. Sci. Technol. 2023. 57. pp. 6033-6039. doi: 10.1021/acs.est.2c06018.
21. Rist S., Vianello A., Winding M.H.S., Nielsen T.G., Almeda R., Rodriguez Torres R., Vol-lertsen J. Quantification of plankton-sized microplastics in a productive coastal Arctic marine ecosystem // Env. Pol. 2020. 266. 115248 p. doi: 10.1016/j.envpol.2020.115248.
22. Yakushev E., Gebruk A., Osadchiev A., Pakhomova S., Lusher A., Berezina A., van Bavel B., Vorozheikina Е., Chernykh D., Kolbasova G., Razgon I., Semiletov I. Microplastics distribution in the Eurasian Arctic is affected by Atlantic waters and Siberian rivers // Commun. Earth Environ. 2021. 2. pp. 23. doi: 10.1038/s43247-021-00091-0.
23. Crawford C., Quinn B. Microplastic collection techniques. In: Crawford, B.; Quinn, B. (eds) Microplastic Pollutants. 2017. Elsevier Inc, Amsterdam.
24. Lusher A., Tirelli V., O'Connor I., Officer R. Microplastics in Arctic polar waters: the first reported values of particles in surface and sub-surface samples // Sci. Rep. 2015. 5. 14947 p. doi: 10.1038/srep14947.
25. Ershova A., Makeeva I., Malgina E., Sobolev N., Smolokurov A. Combining citizen and conventional science for microplastics monitoring in the White Sea basin (Russian Arctic) // Mar. Poll. Bull. 2021. 173, Part A. 112955 p. doi: 10.1016/j.marpolbul.2021.112955.
26. Jones-Williams K., Galloway T.S., Peck V.L., Manno C. Remote, but Not Isolated— Microplastics in the Sub-surface Waters of the Canadian Arctic Archipelago // Front. Mar. Sci. 2021. 8. 666482. doi: 10.3389/fmars.2021.666482.
27. Pakhomova S., Berezina A., Lusher A.L., Zhdanov I., Silvestrova K., Zavialov P., Bavel B., Yakushev E. Microplastic variability in subsurface water from the Arctic to Antarctica // Env. Pol. 2022. 298. 118808 p. doi: 10.1016/j.envpol.2022.118808.
28. Frank Yu., Vorobiev E., Rakhmatullina S., Trifonov A., Vorobiev D. Screening of Microplastic Content in Surface Waters of Russian Rivers // Ecol. Ind. Russia. 2022. 26. pp. 6771. doi: 10.18412/1816-0395-2022-9-67-71.
29. Frank Y., Khusanov A., Yuldashov M., Vorobiev E., Rakhmatullina S., Rednikin A., Tash-baev S., Mamatkarimova S., Ruchkina K., Namozov S., Turaev L., Sobirov J., Yuldashev A., Vorobiev D. Microplastics in the Syr Darya River tributaries, Uzbekistan // Water. 2023. 15. 3698 p. doi: 10.3390/w15203698.
30. Frank Y.A., Vorobiev D.S., Kayler O.A., Vorobiev E.D., Kulinicheva K.S., Trifonov A.A., Soliman Hunter T. Evidence for microplastics contamination of the remote tributary of the Yenisei River, Siberia—The pilot study results // Water. 2021. 13. 3248 p. doi: 10.3390/w13223248.
31. Masura J., Baker J., Foster G., Arthur C. Laboratory Methods for the Analysis of Microplastics in the Marine Environment: Recommendations for Quantifying Synthetic Particles in Waters and Sediments; NOAA Technical Memorandum NOS-OR&R-48; NOAA Marine Debris Division: Silver Spring, MD, USA. 2015. 39 p.
32. Ershova A.A., Eremina T.R., Dunayev A.L., Makeeva I.N., Tatarenko Y.A. Study of microplastic pollution in the seas of the Russian Arctic and the Far East // Arctic: Ecology and Economy. 2021. 11. pp. 164-177. doi: 10.25283/2223-4594-2021-2-164-177 (in Russian).
33. Lusher A.L., Brâte I.L.N., Munno K., Hurley R.R., Welden N.A. Is it or isn't it: The importance of visual classification in microplastic characterization // Appl. Spectrosc. 2020. 74. pp. 1139-1153. doi: 10.1177/0003702820930733.
34. Lusher A.L., Welden N.A., Sobral P., Cole M. Sampling, isolating and identifying microplastics ingested by fish and invertebrates // Anal. Methods. 2017. 9. pp. 1346-1360. doi: 10.1039/C6AY02415G.
35. Mann H.B., Whitney D.R. On a test of whether one of two random variables is stochastically larger than the other // Ann. Math. Stat. 1947. 18. pp. 50-60. doi: 10.1214/aoms/1177730491.
36. Frias J.P.G.L., Nash R. Microplastics: Finding a consensus on the definition // Mar. Pollut. Bull. 2019. 138. pp. 145-147. doi: 10.1016/j.marpolbul.2018.11.022.
37. Koelmans A.A., Mohamed Nor N.H., Hermsen E., Kooi M., Mintenig S.M., De France J. Microplastics in freshwaters and drinking water: Critical review and assessment of data quality // Water Res. 2019. 155. pp. 410-422. doi: 10.1016/j.watres.2019.02.054.
38. Huppertsberg S., Knepper T.P. Instrumental analysis of microplastics—benefits and challenges. Anal. Bioanal. Chem. 2018. 410. pp. 6343-6352. doi: 10.1007/s00216-018-1210-8.
39. Karlsson T., Kärrman A., Rotander A., Hassellöv M. Comparison between manta trawl and in situ pump filtration methods, and guidance for visual identification of microplastics in surface waters // Environ. Sci. Pollut. Res. 2020. 27. pp. 5559-5571. doi: 10.1007/s11356-019-07274-5.
40. Tokai T., Uchida K., Kuroda M., Isobe A. Mesh selectivity of neuston nets for microplastics //Mar. Pollut. Bull. 2021. 165. 112111 p. doi: 10.1016/j.marpolbul.2021.112111.
41. Dris R., Gasperi J., Rocher V., Tassin В. Synthetic and non-synthetic anthropogenic fibers in a river under the impact of Paris Megacity: sampling methodological aspects and flux estimations // Sci. Total Environ. 2018. 618. pp. 157-164. doi: 10.1016/j.scitotenv.2017.11.009.
42. Kiefer T., Knoll M., Fath A. Comparing methods for microplastic quantification using the Danube as a model //Microplastics. 2023. 2. pp. 322-333. doi: 10.3390/microplastics2040025.
43. Lindeque P.K., Cole M., Coppock R.L., Lewis C.N., Miller R.Z., Watts A.J.R., Wilson-McNeal A., Wright S.L., Galloway T.S. Are we underestimating microplastic abundance in the marine environment? A comparison of microplastic capture with nets of different mesh-size // Env. Pol., Part A. 2020. 265. 114721 p. doi: 10.1016/j.envpol.2020.114721.
44. Brandon J.A., Freibott A., Sala L.M. Patterns of suspended and salp-ingested microplastic debris in the North Pacific investigated with epifluorescence microscopy // Limnol. Oceanogr. Lett. 2020. 5. pp. 46-53. doi: 10.1002/lol2.10127.
45. Cable R.N., Beletsky D., Beletsky R., Wigginton K., Locke B.W., Duhaime M.B. Distribution and modeled transport of plastic pollution in the Great Lakes, the world's largest freshwater resource // Front. Environ. Sci. 2017. 5. pp. 45. doi: 10.3389/fenvs.2017.00045.
46. Moore M.V., Yamamuro M., Timoshkin O.A., Shirokaya A.A., Kameda Y. Lake-wide assessment of microplastics in the surface waters of Lake Baikal, Siberia // Limnology. 2021. 23. pp. 265-274. https://doi.org/10.1007/s10201-021-00677-9.
47. Khatmullina L., Isachenko I. Settling velocity of microplastic particles of regular shapes // Mar. Pollut. Bull. 2017. 114. pp. 871-880. doi: 10.1016/j.marpolbul.2016.11.024.
48. Waldschlager K., Schuttrumpf H. Effects of particle properties on the settling and rise velocities of microplastics in freshwater under laboratory conditions // Environ. Sci. Technol. 2019. 53. pp. 1958-1966. doi: 10.1021/acs.est.8b06794.
49. Pakhomova S., Zhdanov I., Berezina A., Yakushev E. Difference in the fate of surface and subsurface microplastics: an example for open and coastal waters, EGU General Assembly, Vienna, Austria, 24-28 Apr. 2023. EGU23-16273. doi: 10.5194/egusphere-egu23-16273.
Information about the authors:
Frank Yulia A. - Cand. Sci. (Biol.), Associate Professor, Department of Ichthyology and Hydrobiology, Biological Institute, Tomsk State University (Tomsk, Russia). E-mail: yulia.a. [email protected]
Ershova A.A. - Cand. Sci. (Geographical), Associate Professor, Russian State Hydrometeoro-logical University, Plastic Pollution Research Laboratory PlasticLab (Saint-Petersburg, Russia). E-mail: [email protected]
Vorobiev Egor D. - Master's student, Biological Institute, Tomsk State University (Tomsk, Russia). E-mail: [email protected]
Vorobiev Danil S. - Doct. Sci. (Biol.), Director of the Institute, Biological Institute, Tomsk State University (Tomsk, Russia). E-mail: [email protected]
Contribution of the authors: the authors contributed to this article as follows: Yulia A. Frank (40%), Alexandra A. Ershova (40%), Egor D. Vorobiev (10%), Danil S. Vorobiev (10%). The authors declare no conflicts of interests.
Информация об авторах:
Франк Юлия Александровна - кандидат биологических наук, доцент кафедры ихтиологии и гидробиологии Биологического института Томского государственного университета (Томск, Россия). ORCID: https://orcid.org/0000-0001-6347-4009. E-mail: yulia.a. frank@gmail .com
Ершова Александра Александровна - кандидат географических наук, лаборатория ПластикЛаб Российского государственного гидрометеорологического университета (Санкт-Петербург, Россия); кафедра ихтиологии и гидробиологии Биологического института Томского государственного университета (Томск, Россия). ORCID: https://orcid.org/0000-0003-3634-7009. E-mail: [email protected]
Воробьев Егор Данилович - магистрант Биологического института Томского государственного университета (Томск, Россия). ORCID: https://orcid.org/0000-0001-5764-6134. E-mail: [email protected]
Воробьев Данил Сергеевич - доктор биологических наук, директор Биологического института Томского государственного университета (Томск, Россия). ORCID: https://or-cid.org/0000-0003-4397-4406. E-mail: [email protected]
Вклад авторов: Ю.А. Франк - 40%, А.А. Ершова - 40%, Е.Д. Воробьев -10%, Д.С. Воробьев -10%. Авторы заявляют об отсутствии конфликта интересов.
The article was submitted 18.07.2024; accepted for publication 16.08.2024 Статья поступила в редакцию 18.07.2024; принята к публикации 16.08.2024
