Occurrence and distribution of plastic particles (10-25,000 µm) and microfibers in the surface water of an urban river network in Japan.

Urban rivers remain the key conduits conveying land-sourced plastics into the ocean. However, detailed information is limited on the concurrent evaluation over a wide array of particle size-specific abundances, characteristics, and distribution patterns of plastics in riverine environments. Therefore, this study provides a comprehensive assessment of plastic pollution in an urban river network in Japan by analyzing mesoplastics (5000-25,000 µm), large microplastics (300-5000 µm), small microplastics (SMPs, 10-300 µm), and microplastic-fibers (MPFs, 10-5000 µm) concurrently, for the first time. Sampling was conducted at seven stations in the Kamo and Katsura Rivers flowing across metropolitan Kyoto City. The analytical procedures involved infrared spectroscopy and fluorescence-staining microscopy. The concentrations of plastics were moderate compared to the global reports and gradually increased along the river flow (3550-15,840 items/m3; 180-13,180 µg/m3), mostly due to urban discharges via non-point sources. The number concentrations increased with decreasing particle size, marking 99.94% of SMPs, including 50% smaller than 40 µm. Conversely, mass concentrations decreased, exhibiting 96% larger than 1000 µm (64% mesoplastics including 20% around 5000 µm), along with 2% SMPs. Polyethylene (PE) and polyvinyl alcohol were distinct among SMPs, with PE indicating higher susceptibility to fragmentation compared to polypropylene and other polymer types. MPF concentrations were homogeneous throughout the watershed (1470-3600 items/m3; 520-1060 µg/m3), with a higher proportion of fibers smaller than 1000 µm (86%), apparently originating from polyethylene terephthalate/nylon/acrylic-like textile fibers. The proportion of MPFs surpassed particles within 100-3000 µm and was considerably high around 300 µm (> 98%). The river network of Kyoto conveys billions of tiny microplastics to the Yodo River, the primary water resource downstream, within a dry day.

Quantification of microplastic by particle size down to 1.1 µm in surface road dust in an urban city, Japan.

The impact of microplastics (MPs, plastic particles ≤5 mm) on ecosystems is of great concern. Road surfaces represent a significant source of MPs where plastic fragments are physically and chemically reduced to MPs. However, the literature lacks information on fragmentation tendencies below 11 µm. This study aimed to characterize the occurrence of MPs in road dust in different size fractions down to 1.1 µm. Road dust was collected at five sites near a major road in Kusatsu city, Japan, and partitioned by size into 13 fractions (1.1-850 µm). The coarser fractions accounted for a greater proportion of the dust. The percentage of organic matter, determined by loss on ignition, increased as the fractions became finer. Pyrolysis-gas chromatography-mass spectrometry was used to quantify 12 types of polymers in each fraction. The dust was found to contain nine types of MP, namely, polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (PS), styrene/butadiene rubber (SBR), acrylonitrile/butadiene/styrene resin (ABS), polycarbonate (PC), polymethylmethacrylate (PMMA), and polyamide 66 (PA66). The total MP concentration in road dust particles by particle size fraction (concentrationf) began to increase from the 125-250 µm fraction and remained elevated in finer fractions down to 1.1 µm, indicating that MPs in the road dust micronized to at least 1.1 µm. However, for individual polymer types, the tendency for concentrationf to increase or decrease with particle size fraction varied: the concentrationf of some polymers, such as PE and PVC, remained elevated in fractions down to 1.1 µm; the concentrationf of SBR, a rubber-MP, showed a stable or decreasing trend in fractions of 7.0-11 µm and finer. Particles of PE, PVC, and some other plastics might become increasingly finer, even down to 1.1 µm. Further research is needed to understand the comminution limits of these polymers under pertinent environmental conditions.

Multimodal image and spectral feature learning for efficient analysis of water-suspended particles.

We have developed a method to combine morphological and chemical information for the accurate identification of different particle types using optical measurement techniques that require no sample preparation. A combined holographic imaging and Raman spectroscopy setup is used to gather data from six different types of marine particles suspended in a large volume of seawater. Unsupervised feature learning is performed on the images and the spectral data using convolutional and single-layer autoencoders. The learned features are combined, where we demonstrate that non-linear dimensional reduction of the combined multimodal features can achieve a high clustering macro F1 score of 0.88, compared to a maximum of 0.61 when only image or spectral features are used. The method can be applied to long-term monitoring of particles in the ocean without the need for sample collection. In addition, it can be applied to data from different types of sensor measurements without significant modifications.

Characterization of an AFFF impacted freshwater environment using total fluorine, extractable organofluorine and suspect per- and polyfluoroalkyl substance screening analysis.

The vast number of per- and polyfluoroalkyl substances (PFASs) that are in global commerce (n > 4700) pose immense challenges for environmental monitoring. The large discrepancy between this large number and the few PFASs usually monitored suggest that environmental exposure might be substantially underestimated. This study applied a workflow, which included analysis of total fluorine (TF), extractable organofluorine (EOF), 24 target PFASs and suspect screening. The workflow aimed to close the organofluorine mass balance and to tentatively identify overlooked PFASs in various matrices from an aqueous film forming foam (AFFF) contaminated pond and its adjacent riparian zone. PFAS target analysis revealed that water, aquatic invertebrates as well as emergent aquatic insects had high concentrations with up to 2870 ng L-1, 9230 ng g-1 dry weight (dw) and 1470 ng g-1 dw ∑24PFASs, respectively. The EOF mass balance could be explained by target PFAS analysis for most biota samples such as aquatic invertebrates, emergent aquatic insects and terrestrial spiders and earthworms (i.e. EOF ≈ ∑24PFASs). In the pond surface water, 42-58% of the EOF was not explained by target PFASs. However most new tentatively identified PFASs (n = 25) were detected in water, which could contribute to the unknown EOF. Nine suspects could be further identified, which where perfluoroalkyl sulfonamide-based compounds and derivatives that all have been found in historical AFFFs produced by electrochemical fluorination. One suspect, F5S-PFOS, was also detected for the first time in aquatic and terrestrial invertebrates.

Data-independent acquisition with ion mobility mass spectrometry for suspect screening of per- and polyfluoroalkyl substances in environmental water samples.

Per- and polyfluoroalkyl substances (PFASs) have environmentally persistent, and the various types of PFASs have been detected in water environments. Many previous studies have performed data-dependent acquisition (DDA) of mass spectra from an environmental sample by high-resolution mass spectrometry to identify PFAS suspects individually. In comparison, the data-independent acquisition (DIA) of comprehensive mass spectra of the sample is a technology which enables to know the occurrences of suspects and non-targets simultaneously. However, it is difficult to associate the fragment ions of targeted precursor ions by retention time only, because of the existence of co-eluting ions derived from environmental samples. Since the separation of ions is not enough with only the conventional DIA method, here, we attempted to support it using ion mobility mass spectrometry (IMS) to distinguish the relevant ions from co-eluting ions by drift time. Firstly, suspect screening of PFASs with eternal database resulted in determining 32-96 PFAS suspects in firefighting foam impacted groundwater samples (n = 8) by suspect screening. Among all the pairs of respective precursor ions and fragment ions of the PFAS suspects, 5%-19% (4-9 PFASs) of them were associated without considering the drift time of IMS, while 37%-49% (15-43 PFASs) of them were associated with considering the drift time. The consideration of the drift time increased the association ratios in all samples. In a sample, most precursor ions could be associated with their fragment ions (41 of 43 PFASs) because at least one probable fragment ion was observed among three of maximum intensity fragment ions. Thus, the method improved the identification by excluding the unrelated co-eluting ions by IMS. Moreover, the method can acquire a certain reliable MS/MS spectra of suspects in environmental samples in one analysis. It is not essential to conduct instrumental analyses again for samples stored for a long time even when the data sets and/or methodologies of data analyses are modified (e.g., the original database, screening list, or statistical filtering/data cleaning approach). It will be particularly useful for studies that must analyze a large number of environmental samples.

A profile analysis with suspect screening of per- and polyfluoroalkyl substances (PFASs) in firefighting foam impacted waters in Okinawa, Japan.

Per- and polyfluoroalkyl substances (PFASs) are a group of persistent contaminants detected in firefighting foam impacted waters. Previous studies have performed suspect and non-target screening by high-resolution mass spectrometry (HRMS) to determine the composition of PFAS contamination and to discover unknown PFASs. Here, we performed a profile analysis with suspect screening against two lists in the NORMAN Suspect List Exchange in firefighting foam impacted environmental and drinking water (n = 18) collected in Okinawa, Japan, in April 2019. Samples were analyzed by liquid chromatography (LC) quadrupole time-of-flight (QTOF) MS in electron spray ionization mode. Suspect screening returned 116 candidate PFASs with their molecular weights, functional groups, and perfluoroalkyl chain lengths. Long-chain perfluoroalkyl acids (PFAAs) and some of their precursors were specifically found around the firefighting training area. Short-chain PFAAs were assumed to be formed from precursors by environmental processes. Perfluoroalkyl sulfonamide precursors were found to be transformed to perfluoroalkyl sulfonic acids (PFSAs) in the drinking water treatment process. In contrast, biological activated carbon filtration formed perfluoroalkyl carboxylic acids (PFCAs). The PFAS profile showed that a large number of different substances needs to be considered.

Occurrence and characteristics of microplastics in surface road dust in Kusatsu (Japan), Da Nang (Vietnam), and Kathmandu (Nepal).

Microplastics (MPs, plastics < 5 mm) are a growing concern in ecosystems, being found in the soil and water environment. One of the primary sources of MPs has been suspected to be road dust in urban areas as it can flow into waters with runoff. To understand the occurrence of MPs (100 µm-5 mm) in surface road dust of three cities (Kusatsu, Shiga, Japan; Da Nang, Vietnam; and Kathmandu, Nepal), we collected surface road dust samples. The samples were pretreated (organic matter decomposition and gravity separation), and all MP candidates were individually observed by microscope for color, shape, and size; and analyzed their polymer types using fourier transform infrared spectrometry. The abundances of MPs 100 µm to 5 mm in size were 2.0 ±â€¯1.6 pieces/m2 (13 polymer types) in Kusatsu, 19.7 ±â€¯13.7 pieces/m2 in Da Nang (14 types), and 12.5 ±â€¯10.1 pieces/m2 in Kathmandu (15 types). We classified the MPs into two groups; containers/packaging-MPs and rubber-MPs. Among all MPs, the containers/packaging-MPs accounted for 55 ±â€¯5% of the polymer types composition. In contrast, the rubber-MPs accounted for 16 ±â€¯6% of all MPs which were higher than those previously published for environmental water and sediment samples. The containers/packaging-MPs were fragments of various colors while most of the rubber-MPs were fragments or granules in black. The number-size distributions of MPs showed that the mode of formation explains the differences between their polymer types (tearing for containers/packaging-MPs and abrasion for rubber-MPs). In Da Nang and Kathmandu, the abundance of containers/packaging-MPs and rubber-MPs were correlated so that those MPs might be micronized from the originated materials in the sources with the similar composition (e.g. dump points). It was indicated that the characteristics of MPs pollution in surface road dust might be different depending on waste management practices.

A new method to search for per- and polyfluoroalkyl substances (PFASs) by linking fragmentation flags with their molecular ions by drift time using ion mobility spectrometry.

Per- and polyfluoroalkyl substances (PFASs) are a group of anthropogenic organic fluorinated compounds that have been detected widely. To discover unknown PFASs, previous researchers have applied high-resolution mass spectrometer using fragmentation flagging approach with common fragment ion at the same retention time as the flags. However, it was difficult to search for their molecular ion from co-eluting peaks in the full-scan spectrum at a specific retention time. Here, we attempted to utilize drift time acquired by ion mobility spectrometry for making linkages between fragment ions and their molecular ions. For validating the process, standard solution spiked with PFASs were analyzed by liquid chromatography/ion mobility - quadrupole time-of-flight mass spectrometry (LC/IM-QTOF-MS). Fluorinated fragment ions (fragmentation flags) were categorized into three classes: Class 1 (120 types of [CxFy]-), Class 2 (123 types of [CxFyO]-), Class 3 (131 types of [CxFyO3S]-) and all overlapping fragmentation flags detected at an identical retention time were bundled together as a "flag set". Injecting standard mixed solution of 20 types of PFASs resulted in picking up 20 flag sets by fragmentation flagging. All the fragmentation flags were detected within a designated range of drift time, and their molecular ion was confirmed as a PFAS spiked in the standard solution even when co-eluting compounds were found at almost same retention time. This method was applied to a household fire extinguisher liquid, resulting in finding out nine molecular ions. Therefore, the new linking method achieved rapid searching for the prospective molecular ions using LC/IM-QTOF-MS.