Spectral analysis of environmental microplastic polyethylene (PE) using average spectra.

In this study, microplastic samples from surface seawater of Tokyo Bay were collected, polyethylene (PE) microplastics were used to calculate carbonyl index (CI), and average spectra of PE were analyzed and compared with a previous study applying agitation during chemical treatment. It was found that PE and polypropylene (PP) were the predominant polymer type in the samples. Among PE samples, fragments were the most commonly observed shape, with white being the dominant color. Deviations were found in the average spectra among different shapes and colors when compared to the standard PE spectrum. A comparison of the average spectra between the two datasets suggests that pronounced peaks related to oxidation are most likely resulted from agitation during the chemical treatment. Additionally, it was found a closer spectral resemblance between the sample spectra and the spectrum of standard sample of oxidized PE (PEOx) than with the standard PE spectrum, suggesting that using the oxidized PE as a reference spectrum might be more effective for identification. These findings highlight the complex factors affecting the spectral properties of microplastics and highlight the importance of understanding these variations to enhance the accuracy of microplastic identification workflows and understanding of environmental fate of microplastics.

Accessing the intrinsic factors of carbonyl index of microplastics: Physical and spectral properties, baseline correction, calculation methods, and their interdependence.

Carbonyl index (CI) is a measure of the degradation status of microplastics. While many studies address environmental factors of microplastic degradation, intrinsic factors like physical properties, spectral properties, baseline correction, and CI calculation methods are less explored. This research focused on these aspects using surface seawater samples. We found that color and shape have limited dependence on particle size or signal-to-noise ratio (SNR). Baseline correction can significantly alter CI values, with the direction of the shift depending on the methods used. Additionally, most CI values before and after baseline correction and those calculated using different methods tend to be strongly correlated. Using the selected CI calculation methods, we found that CI values varied significantly by shape and color. CI's relation to the similarity between the sample and its pristine form suggests an alternative degradation measure. Our findings emphasize the need for standardized CI calculation methods.

The pretreatment method in marine organisms and sediment for microplastics analysis by FTIR using "Cylindrical microplastics fractionator".

For the detection of microplastics (MPs) in aquatic biota using Fourier transform infrared spectroscopy (FTIR), the ability to remove organic matter (OM) in pretreatment steps is essential to increase the time efficiency of MPs measurement and method uniformity. In principle, decreasing OM can be achieved by increasing the number of pretreatment steps. However, MPs are lost in proportion to the number of transfers between each step. Therefore, we have created a "Cylindrical MPs Fractionator" composed of commercially available materials. This container allows for a six-step pretreatment process that is designed to increase the removal capacity of OM with only one transfer to prevent the loss of MPs.•Biological or sediment samples are placed in the extractor and subjected to chemical treatment and density separation.•Residues containing MPs are obtained on filters by vacuum filtration.•After additional chemical treatment of the obtained residue, the components of the residue are identified by microscopic FTIR.This method removed 99.3% of OM and recovered 88.5% of MPs. The presenting method confirmed that this can be used with the same process for 11 organisms and sediments from estuarine ecosystem in Japan as models.

Challenges of Raman spectra to estimate carbonyl index of microplastics: A case study with environmental samples from sea surface.

This study investigates the feasibility of using the carbonyl index (CI) derived from Raman spectra as an indicator of plastic degradation and its relationship with the CI calculated from Fourier transform infrared (FTIR) spectra, using microplastic samples of polyethylene (PE) from surface seawater. Multiple methods were used to calculate the CI values of FTIR spectra, while proposed methods were used to calculate the corresponding CI values of Raman spectra. Some significant relations between FTIR CI and Raman CI were observed. However, small R2 values suggest weak functional relationships, which can be attributed to the low signal-to-noise ratio (SNR) of Raman spectra. These results highlight the challenges of establishing a functional relationship between FTIR CI and Raman CI, including challenges such as the uniformity of Raman spectra, determining optimal Raman measurement parameters, selecting appropriate peaks for Raman CI calculation, deciding on spectral processing methods, and addressing the interdependence of these issues.

A beaker method for determination of microplastic concentration by micro-Raman spectroscopy.

Fourier-transform infrared (FT-IR) spectroscopy method for measuring small microplastic (SMP) concentration in marine environment is time-consuming and labor-intensive due to sample pre-treatment. In contrast, Raman spectroscopy is less influenced by water and can directly measure SMP samples in water, making it a more efficient method to measure SMP concentration. Therefore, a method that can directly estimate the concentration of SMPs in water was developed, and the relationship between SMP concentration and experimental Raman spectra were established by testing with standard polyethylene (PE) samples. It was found that average spectra acquired in water solution could reflect characteristic peaks of the plastic after baseline correction. Further investigation found that there is a significant functional relationship between correlation coefficient of sample spectra and the concentration of PE particles, and such relationship can be modelled by Langmuir model. The empirical functional relationships can be used to estimate SMP concentrations by measuring average Raman spectra. The developed methodology is helpful for developing rapid SMP identification and monitoring methods in a more complex manner.•A method of directly measuring MP concentration in water is proposed.•Experimental procedures are provided.•Data analysis methods are outlined.

Microplastic pollution in the gastrointestinal tract of giant river catfish Sperata seenghala (Sykes, 1839) from the Meghna River, Bangladesh.

Freshwater rivers are considered the major route for microplastics (MPs), yet limited studies have been reported on MPs in freshwater river fish, especially in Bangladesh. This research reveals the intake of MPs by the giant river catfish Sperata seenghala, collected from the Meghna River, which is the only outlet of the Ganges-Brahmaputra River. Three locations, namely, Chandpur Sadar, Bhola Sadar, and Char Fasson, along the Meghna River, were selected in order to investigate the gastrointestinal tracts (GIT) of the fish. Ninety percent (n=27) of fish (n=30) were contaminated, with fragment-shaped MPs (65%) as the most abundant among the four types. A total of 179 MP particles were detected using micro-Fourier transformed infrared spectroscopy (µ-FTIR), with an average of 5.96 ± 1.32 MP particles per fish. Among the four size groups, the highest proportion of MPs (54%) occurred in the 45-100 µm group; the dominant color among the seven color groups was white (30%). The highest quantity of MPs was found in the relatively densely populated Chandpur Sadar region. Polypropylene-polyethylene copolymer (PP-PE, 23%) was proportionally dominant among the 15 types. No significant relationship was found between the total number of observed MPs and the GIT weight. This study will help us to understand MP pollution in S. seenghala that may transmit to the human body through the food chain.

Coumarin 6 staining method to detect microplastics.

Microplastics have contaminated the ocean in large quantities and are widely distributed throughout the world. Thus, our understanding of the concentration of microplastics in various environments should be increased. However, current methods to detect microplastics require considerable effort and expensive equipment. In this study, we developed a fluorescence staining technique using coumarin 6 and examined its effectiveness. A mixture of acetone and ethanol was used as the solvent, and 10 different types of plastics were able to be stained with coumarin 6. The fluorescence peak for coumarin 6 staining was approximately 500 nm for each plastic type. The optimal immersion time and coumarin 6 concentration for staining were determined to be 60 min and 1 mg L-1, respectively. Using this technique, we were able to stain all of the microplastics obtained from samples collected in Tokyo Bay seawater.

Development of automated microplastic identification workflow for Raman micro-imaging and evaluation of the uncertainties during micro-imaging.

In this study, an automated identification workflow for Raman micro-imaging (RMI) was developed, and the performance was evaluated by artificial samples of microplastic (MP) microsphere with different sizes and types. Theoretical detection rate and estimated particle size were derived and compared with experimental data. Results show that the proposed workflow can identify plastic types and estimate the size of the MP microspheres under different conditions for most cases. However, size of laser spot and discrepancy between sample surface and focal plane can influence RMI results in two ways. Firstly, small particles are more likely to be detected. Secondly, estimated sizes of particles are more likely to be overestimated. The derived uncertainties can serve as a reference for future experimental design and further investigation of more complex situations. The workflow is accessible online, and interested researchers can adjust the parameter values as necessary to suit their specific circumstances.

A double sliding-window method for baseline correction and noise estimation for Raman spectra of microplastics.

When measuring microplastics of environmental samples, additives and attachment of biological materials may result in strong fluorescence in Raman spectra, which increases difficulty for imaging, identification, and quantification. Although there are several baseline correction methods available, user intervention is usually needed, which is not feasible for automated processes. In current study, a double sliding-window (DSW) method was proposed to estimate the baseline and standard deviation of noise. Simulated spectra and experimental spectra were used to evaluate the performance in comparison with two popular and widely used methods. Validation with simulated spectra and spectra of environmental samples showed that DSW method can accurately estimate the standard deviation of spectral noise. DSW method also showed better performance than compared methods when handling spectra of low signal-to-noise ratio (SNR) and elevated baselines. Therefore, DSW method is a useful approach for preprocessing Raman spectra of environmental samples and automated processes.

Comparative evaluation of the carbonyl index of microplastics around the Japan coast.

The carbonyl index (CI) of polyethylene and polypropylene microplastics (MPs) (2950 particles) collected in coastal waters around Japan was investigated. The CI of MPs was calculated by the specified area under band technique. The mean MP CI in all samples (regardless of shape and color) was 0.69 ± 0.34 and 0.70 ± 0.34 for polyethylene and polypropylene, respectively, and there was no significant difference in the color or shape of the MPs. The polyethylene, white, and fragment MPs CI was negatively (p < 0.05) correlated with the major length of the MPs. Large MPs with relatively little deterioration were distributed along the west coast of the Sea of Japan, whereas small MPs were distributed along the east coast. Our findings of this gradual change in the deterioration of MPs, based on geographical distribution, are in accordance with literature CI-size and MP degradation hypotheses.

Microplastics pollution in the river Karnaphuli: a preliminary study on a tidal confluence river in the southeast coast of Bangladesh.

Bangladesh is a deltaic country in Asia, and its riverine systems ultimately drain into the Bay of Bengal. Plastic is a severe environmental issue for coastal-marine ecosystems due to the indiscriminate usage and discarding of plastic items in the upstream river that eventually find their route into the Bay of Bengal. Microplastics (MPs) are widespread pollutants in almost all environmental compartments, including aquatic environments. This study aimed to quantify and understand the distribution of microplastics in surface water and sediments of the river Karnaphuli, a tidal confluence river adjacent to the Chattogram seaport city of Bangladesh, a highly inhabited and industrial area on the southeast coast of the Bay of Bengal. A manta trawl net (300-µm mesh size) was used to collect surface water samples, while an Ekman dredge was used to collect sediment samples. The concentrations of microplastics in the surface water of the river Karnaphuli during late monsoon, winter, and early summer were recorded to be 120,111.11, 152,222.22, and 164,444.44 items/km2, respectively, while in sediments, those were recorded to be 103.83, 137.50, and 103.67 items/kg, respectively. A higher abundance of microplastics was observed in downstream surface water (228,888.88 items/km2) and sediments (164.17 items/kg). Smaller sizes (0.3 to 0.5 mm) of microplastics were predominant, fibers or threads were the frequent types, and black was the most common color in the river Karnaphuli. The Fourier transform infrared analysis revealed that polyethylene terephthalate (surface water: 22%, sediments: 19%), polyamide (surface water: 15%, sediments: 13%), polyethylene (surface water: 12%, sediments: 18%), polystyrene (surface water: 13%, sediments: 11%), and alkyd resin (surface water: 13%, sediments: 10%) were the most prevalent polymers in the river Karnaphuli. Moreover, there was a moderate positive correlation between MPs abundance in surface water and sediments. Therefore, improved long-term research (in different seasons with horizontal and vertical monitoring) is necessary in order to accurately determine the flux of microplastics from the river Karnaphuli to the Bay of Bengal.

Contamination of sea surface water offshore the Tokai region and Tokyo Bay in Japan by small microplastics.

A nested double neuston net was prepared and used to collect samples from the surface of coastal waters around Japan to obtain information about the properties of both small microplastics (SMPs; <350 µm) and large microplastics (LMPs; >350 µm). The SMP concentrations ranged from 1000 to 5900 pieces m-3 in the open ocean and averaged approximately 3000 pieces m-3 in the inner part of Tokyo Bay. The SMP concentrations were around 20-60 times greater than the LMP concentrations. By analyzing the seawater, we obtained a microplastic size distribution that spanned 50-5000 µm. The LMPs mainly comprised packaging-related plastics, such as polyethylene (PE) and polypropylene, while the SMPs were dominated by paint-related plastics. SMPs derived from packaging materials (e.g., PE) may have gradually sank down from the sea surface when they were smaller than 600 µm.

Influence of suspended inorganic particles (kaolinite) on eggs and larvae of the pelagic shrimp Lucensosergia lucens.

The pelagic shrimp Lucensosergia lucens is a commercially important species in Japan, predominantly harvested in Suruga Bay. It has been suggested that a marked decrease in the wild population over recent years is associated with an increased concentration of suspended particles. We tested the hypothesis that suspended inorganic particles (kaolinite) negatively affect the hatching ratio of fertilized eggs, and the survival, growth, and metamorphosis of nauplius and elaphocaris larvae. The relative hatching ratio of eggs decreased from 100 to 57.7% at 139 mg L-1 of kaolinite particles. Similarly, the relative survival ratio of nauplius larvae progressively decreased from 100% in filtered seawater to 73.6% after 72 h of exposure to 139 mg L-1 of kaolinite particles. Consequently, the survival ratio of elaphocaris larvae was greatly reduced at high particle concentrations. Exponential growth in the standard lengths of elaphocaris larvae occurred at particle concentrations < 6.9 mg L-1, but growth was inhibited at kaolinite concentrations > 20 mg L-1.

Contamination of sea urchin Mesocentrotus nudus by radiocesium released during the Fukushima Daiichi Nuclear Power Plant accident.

Countless marine organisms were polluted with radioactive materials that were dispersed when the Fukushima Daiichi Nuclear Power Plant (FDNPP) was damaged in 2011 by the Great East Japan Earthquake. The aim of this study was to determine the degree to which marine herbivorous sea urchins, Mesocentrotus nudus, were contaminated with radiocesium because of the accident. We collected samples of sea urchins from four locations in Fukushima prefecture (at the coast and offshore from the Yotsukura and Ena stations) and investigated how the 137Cs activity concentrations changed. The biological half-life (Tbio) of 137Cs in the individual sea urchins was between 121 and 157 days. The ecological half-life (Teco) of 137Cs was 181-423 days and was high in places close to the FDNPP. The Teco values in the sea urchins were longer than previously reported. The results infer that the food sources of the sea urchins around the Fukushima coast strongly influenced their uptake of 137Cs.

Determining the appropriate number of particles on a filter to allow small microplastics to be analyzed by microscopy.

The concentrations of small microplastics (diameter < 350 µm) on filters are usually determined by microscopy or micro Fourier-transform infrared spectroscopy. The presence of too many particles on a filter will cause the measured number of particles and particle sizes to be incorrect because of overlapping particles. In this study, the appropriate quantity of particles on a filter to allow effective particle analysis to be performed was determined by performing numerical experiments. The larger the number of particles and the larger the particles, the smaller the proportion of isolated particles. An isolation ratio of 99% requires a particle density on the filter of 1.28 particles mm-2 if the particle size is 50 µm or of 0.351 particles mm-2 if the particle size is 100 µm.•Appropriate number of particles for small plastic particle analysis was determined.•Numerical experiments to determine particle distributions on a filter were performed.•Particle number for a 99% isolation ratio was determined.

Inclusion of shape parameters increases the accuracy of 3D models for microplastics mass quantification.

As microplastics may bring about adverse effects on living organisms, it is important to establish more precise quantification approaches to better understand their dynamics. One method to determine the concentration of microplastics is to estimate their mass using three-dimensional (3D) models, but its accuracy is not well known. In this study, we evaluated the shape of the particles and verified the accuracy of a 3D model-based mass estimation using samples from a tidal flat facing Tokyo Bay. The particle shape evaluation suggested that the microplastics were flat and irregular in shape; based on these data, we created two types of models to estimate their mass. As a result, an accuracy of mass estimation by our model was higher than other models that consider the slenderness and flatness of particles. The optimization of mass estimation methods based on 3D models may improve the reliability of microplastic evaluation in monitoring studies.

Reevaluation of microplastics identification based on Neuston net survey data.

To verify data accuracy regarding microplastics (MPs), the effects of chemical preprocessing and optical identification with Fourier transform infrared spectroscopy (FTIR) were examined using survey data. We aimed to clarify the cause of overestimation of the number concentration of MPs without FTIR by focusing on shape types. The proportion of fragments (foam) decreased (increased) after FTIR analysis. Although significant difference was found in terms of the size distribution of fragments (after FTIR > before FTIR), no such difference was found with regard to foam. These findings indicate that impurities categorized as fragments via visual confirmation, especially those measuring <1000 µm, were removed using the FTIR technique. Although previous studies recommended the use of data on MPs measuring >1000 µm, this threshold should be applied only to fragments and not to foam.

Radiocesium concentrations in shallow water sediments (Matsukawa-ura Lagoon, Fukushima, Japan) from a compact NaI(Tl) scintillation spectrometer.

We collected continuous sedimentary 137Cs concentration data from a shallow fishery ground (Matsukawa-ura Lagoon, Fukushima, Japan) in 2016 using a new compact underwater NaI(Tl) scintillation spectrometer and a quantitative technique. 137Cs concentrations in sediments were low (approx. 40 Bq/kg DW) at the lagoon mouth and high (641.2 Bq/kg DW) at the head of the lagoon. Some areas of locally elevated 137Cs concentrations (>500 Bq/kg DW) were also found.

Microplastics on the sea surface of the semi-closed Tokyo Bay.

Microplastics (MPs) pollution surveys were conducted in Tokyo Bay using neuston nets (May 2019 and January 2020). Although the pollution level in Tokyo Bay was high (3.98 pcs/m3, May), it was lower than reported in other semi-closed bays because of differences in the Enclosed Index. It was found that polyethylene fragments dominated the retrieved MPs; the mode of MPs size was 800 µm. As MPs abundance in rivers had the same seasonality as found in the inner bay, rivers were considered the main source of MPs. The seawater residence time is shorter than the time required for the density of MPs to become greater than that of seawater; therefore, it was considered that MPs are transported out of the bay instead of sinking. MPs were aggregated into a convergence zone by residual currents (the thermohaline front) in May (January). These findings will improve understanding of MPs pollution in other bays.