Characterization of Microplastics and Adsorbed/Dissolved Polycyclic Aromatic Hydrocarbons in the Biggest River System in Saitama and Tokyo, Japan.

This study presents a comprehensive characterization of microplastics (MPs) and adsorbed/dissolved polycyclic aromatic hydrocarbons (PAHs) in the Arakawa River, the largest river system in Saitama and Tokyo, Japan. The MPs were sampled at various points along the river, revealing an average number density of 2.21 ± 1.48 pieces/m3, with a predominant size range of 0.5-1 mm. Polymer analysis indicated that polyethylene (PE) comprised the highest proportion of MPs (55.9%), followed by polypropylene (PP) (22.4%) and polystyrene (PS) (21.7%). Seasonal fluctuations in MPs concentration were observed, with the highest values in winter and the lowest in summer. An analysis of adsorbed PAHs revealed a median partition coefficient (Kd) value of 3.58 × 104 L/kg for MPs, indicating their affinity for PAHs. Further PAHs analysis revealed that the PAHs with the highest mean values were bicyclic naphthalene, pyrene, and fluoranthene. A comparison with coastal MPs showed differences in PAH composition, with higher proportions of high-ring PAHs observed in coastal samples. The study also investigated the distribution of PAHs in the dissolved and suspended states in the river, finding that similar PAHs were distributed in both states, with the PAHs present in MPs being about 1/10,000 of those in the dissolved and suspended states. The study underscores the importance of the continued monitoring and management of MPs and associated pollutants in river ecosystems.

Mechanisms for removal of gaseous toluene in headspace using sonophysical and sonochemical effects at the gas-liquid interface.

We developed a new method for removing gaseous substances by using high frequency (200 kHz) ultrasonic irradiation of water, and the effects of ultrasonic irradiation on gas-phase toluene were evaluated quantitatively for the first time. The removal ratio of gaseous toluene increased with increasing ultrasonic power, but the reaction was inhibited by the addition of radical scavengers, indicating that ultrasonic irradiation not only accelerated the dissolution of gaseous toluene but also induced toluene decomposition. The contribution made by OH radicals to the decomposition of gaseous toluene at the gas-liquid interface was confirmed by the difference in removal ratios between addition of KI and addition of tert-butyl alcohol. The toluene removal mechanism was investigated by studying the logarithmic plots for toluene concentration at specified times. The results of this study clearly showed the promotion of gaseous toluene dissolution and the reaction via OH radicals at the gas-liquid interface by sonophysical and sonochemical effects with both effects contributing to the removal of gaseous toluene. Furthermore, the total organic carbon concentration in the aqueous phase increased with increasing reaction time, indicating that the toluene degradation products were trapped and decomposed into low-molecular-weight organic compounds in the aqueous phase.

Evaluating sewer exfiltration in groundwater by pharmaceutical tracers after the 2016 Kumamoto earthquakes, Japan.

In April 2016, a series of earthquakes (M 7.3 on the Japan Meteorological Agency scale) occurred in Kumamoto, Japan causing serious damage to underground sewerage networks. In this study, we evaluated sewer exfiltration in groundwater in the Kumamoto area after the earthquakes by using multiple tracers. We used 14 pharmaceuticals, including carbamazepine and crotamiton, and anthropogenic Gd as tracers, and we measured concentrations of these tracers from September 2016 to November 2017 seasonally. The detection frequency of caffeine, carbamazepine, crotamiton, ibuprofen, and anthropogenic Gd ranged from 29% to 45%, and the concentrations of the pharmaceuticals in the groundwater were lower than those in previous studies. The median of all pharmaceutical concentrations did not decrease, whereas the median of the sum of crotamiton and carbamazepine concentrations, which are quantitative sewage markers, decreased with time. The sewer exfiltration rates in September 2016 estimated using carbamazepine, crotamiton, and anthropogenic Gd were 0.59 ± 0.27%, 0.66 ± 0.47%, and 0.11 ± 0.18% of sewage dry weather flow, respectively, indicating that the effect of the earthquakes on sewer exfiltration was small, probably because the damaged sewers were quickly repaired. This study demonstrated that a multiple-tracer approach is useful for evaluating sewer exfiltration after major earthquakes.

Occurrence, distribution, and possible sources of microplastics in the surface river water in the Arakawa River watershed.

Nowadays, efforts for complementing data concerning microplastics (MPs) in freshwater systems are required as MPs exist in many populated areas. The goal of this study is to investigate the distribution and profiles of riverine MPs along the Arakawa River watershed, which runs through the Tokyo Metropolitan area. The MPs were found in 10 of the 12 sampling sites in the watershed with the mean of 1.8 pieces/m3. Also, the spatial distribution of the MPs displayed the accumulation in the downstream and in the tributary areas with high populations, reflecting the levels of the local anthropogenic activities. In contrast to the heterogeneity of the floating concentrations, polymer type compositions were consistent with the predominance of polyethylene compared with polypropylene and polystyrene. Moreover, the size distributions of the particles were consistent among samples with the predominance of the relatively smaller size fractions. These results suggest that the sources of fragmented plastic debris are likely spread over terrestrial areas and that reducing burden from these land-based MPs is necessary for mitigating MPs pollution in urban aquatic environments.

Improved ultrasonic degradation of hydrophilic and hydrophobic aldehydes in water by combined use of atomization and UV irradiation onto the mist surface.

Ultrasonic irradiation of 430 kHz, which induces both the chemical effect of pyrolysis and the physical effect of atomization, was carried out to achieve highly effective decomposition of organic substances in water with UV254 irradiation and H2O2 addition. To investigate the influence of physicochemical properties of the substrate on the degradation rate, three different aldehydes, namely, formaldehyde, acetaldehyde, and benzaldehyde, were selected as model substrates. Upon ultrasonic irradiation alone, the removal ratio of the hydrophobic substrate benzaldehyde reached 100% after 120 min, whereas the removal ratios of the hydrophilic substrates formaldehyde and acetaldehyde were only 21.1% and 53.0%, respectively. By combining ultrasonic atomization and UV254 irradiation, formaldehyde and acetaldehyde underwent effective gas-phase decomposition on the surfaces of the mist particles. Photolysis by UV254 irradiation mainly affected for the decomposition of aldehydes on the mist surface rather than the reaction of hydroxyl radicals derived from H2O2 made by water sonolysis. However, the addition of H2O2 effectively improved the decomposition and mineralization rates for both hydrophilic and hydrophobic aldehydes owing to the generation of hydroxyl radicals on the surfaces of the mist particles, which greatly contributed to the gas-phase decomposition. Consequently, the effective decomposition of organic pollutants was achieved regardless of their physicochemical properties in aqueous media.

Aqueous photochemical degradation of mefenamic acid and triclosan: role of wastewater effluent matrices.

In this study, photochemical degradation of two emerging pharmaceutical chemicals, mefenamic acid (MF) and triclosan (TCS), was investigated to clarify the role of treated wastewater effluent matrices on their environmental photolysis. Target compounds were individually exposed to simulated sunlight in different media: ultrapure buffered water and synthetic field water with treated municipal wastewater effluent. The results in ultrapure buffered water showed that the direct photolysis processes in aquatic environments are not relevant to the elimination of MF. However, in samples containing treated wastewater effluent, photochemical degradation of MF was clearly enhanced. Our results indicate that MF undergoes indirect photolysis by reactive intermediates produced in an effluent matrix. Further quenching experiments suggested that photochemically produced hydroxyl radicals and excited triplet state dissolved organic matter drive the degradation of MF. In contrast to MF, TCS photochemical degradation proceeds through rapid direct photolysis. TCS was quickly degraded in ultrapure buffered water but it is considerably hampered in samples containing wastewater effluent. The declined degradation of TCS in the synthetic field water was discussed in terms of underlying optical filter effects by coexisting chromophoric substances. Results emphasize the importance of taking local water chemistry into consideration when predicting natural attenuation of pharmaceutical chemicals in receiving areas.

Dynamics of dissolved organic matter in a wastewater effluent-impacted Japanese urban stream: characteristics, occurrence and photoreactivity of fluorescent components.

We report the results of using the excitation-emission matrix (EEM) method combined with parallel factor analysis (PARAFAC) to investigate the characteristics and occurrence of dissolved organic matter (DOM) in an urban stream impacted by effluent from a wastewater treatment plant (WWTP). The PARAFAC model divides the bulk EEM spectra into six individual fluorescent components with three humic-like components (C1-C3), two protein-like components (C4 and C5) and a wastewater-derived component (C6). In general, intensities of fluorescent components are abundant in WWTP effluent impacted samples, thus showing that such an effluent is a major source of DOM in urban rivers, but C5 is considered to have autochthonous sources within the stream. In areas where the effluent is released, the fluorescent intensity from components (except C5) gradually decreases as these components are transported downstream. However, concentrations of dissolved organic carbon remain almost constant downstream of the release area. These results would be attributed to degradation and/or modification of fluorophore. Photolysis experiments confirmed that fluorescent intensities can decrease with increase of irradiation times. C6 particularly showed a rapid photodegradation, remaining only 24.1% after 48 h photolysis. These findings would be important when assessing DOM source and water quality in aquatic environments by EEM-PARAFAC.

Combined sonochemical and short-wavelength UV degradation of hydrophobic perfluorinated compounds.

Perfluorochemicals (PFCs), which are common in the aquatic environment, are toxic substances that have high chemical and heat resistance because of their strong C-F bonds. We investigated the effect of ultrasonication and short-wavelength UV irradiation on the degradation of perfluorooctane, perfluoropropionic acid, and perfluorooctanoic acid, which are examples of hydrophobic, hydrophilic, and intermediate PFCs, respectively. The results confirmed that ultrasonication was more effective for decomposing hydrophobic PFCs and UV irradiation was more effective for decomposing hydrophilic PFCs. Therefore, defluorination of the degradation intermediates was improved by a combination of ultrasonication and UV irradiation. Our results can be applied to the decomposition treatment of PFCs that have various levels of water solubility in the aquatic environment.

Effect of ultrasonic frequency on size distributions of nanosized mist generated by ultrasonic atomization.

Ultrasonic atomization is used to produce fine liquid mists with diameter ranges below 100nm. We investigated the effect of the frequency on the size distribution of ultrasonic mist. A bimodal distribution was obtained for the mist generated by ultrasonic atomization with a wide-range particle spectrometer. The peak diameter decreased with increasing frequency, and the number concentration of the mist increased in the smaller range. We determined the relation between the size distribution of the mist and the ultrasonic frequency, and we proposed a generation mechanism for the ultrasonic nanosized mist based on the amount of water vapor around the liquid column. Increasing the power intensity and density by changing the surface diameter of the ultrasonic oscillator affected the number concentration and size distribution of the nanosized mist. Using this technique, the diameter of the mist can be controlled by changing the frequency of the ultrasonic transducer.

Aqueous secondary formation of brominated, chlorinated, and mixed halogenated pyrene in presence of halide ions.

We examined the secondary production of halogenated derivatives of polycyclic aromatic hydrocarbons (PAHs) in surface seawater. Pyrene was selected as the model compound and exposed to UV irradiation in synthetic seawater for various irradiation times. Pyrene underwent rapid photochemical reactions that produced various halogenated derivatives including 1-chloropyrene, 1-bromopyrene, three unidentified dichloropyrenes, and three unidentified bromochloropyrenes. The production of 1-chloropyrene (220-360 nM) was higher than that of 1-bromopyrene (7.3-12 nM), reflecting the high chlorine content of seawater. A pilot field survey was conducted to test the environmental implications of these results, and fresh, brackish, and seawater samples were collected in southwestern Japan. The variation in the concentration ratios between 1-chloropyrene and pyrene implied the presence of a specific source of 1-chloropyrene in coastal water, which can be partly explained by the secondary production observed in our photolysis experiments. In sum, the photochemical reactions of PAHs are a potential secondary source of halogenated PAHs, especially in marine environments heavily contaminated with PAHs.

Size distribution and sources of 37 toxic species of particulate polycyclic aromatic hydrocarbons during summer and winter in Baoshan suburban area of Shanghai, China.

The objectives of this study were to assess the size-segregated distribution and sources of 37 different species of particulate polycyclic aromatic hydrocarbons (PAHs) in a suburban area of Shanghai metropolitan City, China. The ambient particulate sampling was carried out on the rooftop of a five-stories building in Baoshan campus of Shanghai University. An Andersen high-volume air sampler was employed to collect ambient size-segregated particulate matter during summer of August to September and winter of November to December 2015. The high toxic PAHs were determined by a gas chromatography mass spectrometry. The concentrations of total PAHs in suspended particulate matter (SPM) and PM1.1 (suspended particulate matter below 1.1µm in diameter) in the suburban area of Shanghai were 4.58-14.5ng/m(3) and 1.82-8.56ng/m(3), respectively in summer, and 43.6-160ng/m(3) and 23.2-121ng/m(3), separately in winter. 1,8-Naphthalic anhydride (1,8-NA) showed the highest concentration among 37 different species of PAHs in the suburban area of Shanghai. The concentrations of high molecular PAHs (e.g. 5-6 ring PAHs) followed a nearly unimodal size distribution with the highest peaks in PM1.1. The diagnostic ration qualitatively indicated that PAHs in SPM of Shanghai were mainly derived from motor-vehicle or petroleum combustion in summer and from coal and biomass combustion in winter. According to the calculated toxicity equivalency factors based on the methods of Nisbet and Lagoy and the potency equivalency factors (PEF) recommended by U.S. EPA, the highest contributors in the total carcinogenicity of the PAHs in SPM and PM1.1 were dibenzo[a,h]pyrene (46.2% and 45.0% in summer), benzo[a]pyrene (44.4% and 43.8% in winter) and benz[j]aceanthrylene (80.2% and 83.1% in summer and 83.1% and 84.0% in winter), respectively. Therefore, benzo[a]pyrene seemed to be a lower contributor than other carcinogenic PAHs.

Seasonal and diurnal variation of organic ultraviolet filters from personal care products used along the Japanese coast.

This study aimed to investigate the behavior of organic ultraviolet (UV) filters released by recreational activities along the Japanese coastline. Seasonal variations of organic UV filters in seawater were investigated at four different recreational beaches (Mogushi, Wakamiya, Tsurugahama, and Otachimisaki beaches) in both summer (July through August) and winter (December). Moreover, short time scale diurnal changes were monitored at Otachimisaki beach in summer. Of the four sunscreen agents tested in this study, two agents-2-ethylhexyl-4-methoxycinnamate (EHMC) and 2-ethylhexyl salicylate (EHS)-were detected in all samples, whereas octyl-dimethyl-p-aminobenzonic acid and 3-(4-methylbenzylidene)-camphor were lower than detection limits. In particular, EHMC, one of the most popular organic UV filters, was dominant. The highest concentration of EHMC was observed at 1,080 ng L(-1), a level that exceeds those of previous studies. Both EHMC and EHS concentrations showed significant (p < 0.05) seasonal variations with advancing summer suggesting direct input from recreational activities. The subsequent examination showed short time scale diurnal changes of organic UV filters on the beach. The results showed that diurnal changes in EHMC concentrations were correlated to the number of bathers. EHMC concentrations increased during the afternoon and decreased during the night, although complete attenuation during the night did not occur. EHMC persists along the coast due to low mobility and may persist the next day. This is the first study to show the natural attenuation behavior of organic UV filters along recreational beaches.

Occurrence and source of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) in tidal flats of the Ariake Bay, Japan.

In this study, we hypothesize that natural photochemical reactions of polycyclic aromatic hydrocarbons (PAHs) in tidal flats are responsible for the occurrence of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs). This study aims to survey the impact of photochemical reactions using a combination of field surveys and lab-scale experiments. Concentrations and profiles of PAHs and Cl-PAHs in road dust and sediments collected from seven tunnels and two watersheds, respectively, were determined. In the lab-scale experiments, anthracene was irradiated with ultraviolet (UV) light under various salinity conditions. No detectable Cl-PAHs were found in the road dust. However, Cl-PAHs were detected in the sediments from 700 to 6.1 × 10(3) pg g(-1) and specifically from downstream sites. 2-Monochloroanthracene (2-Cl-ANT) and 9,10-dichloroanthracene (9,10-di-Cl-ANT) were dominant in the sediments. In the Domen River watershed, the ∑Cl-PAHs and the salinity showed a significant positive correlation (p < 0.01) in the sediments, while such a correlation was not found for PAHs. 2-Cl-ANT, 9-monochloroanthracene, and 9,10-di-Cl-ANT were identified as transformation products in the UV irradiation experiments. Production of these Cl-PAHs was dependent on the solution salinity. These results support our hypothesis, and we conclude that photochemical reactions significantly contribute to the occurrence of Cl-PAHs in the studied tidal flats.

Evidence for in situ production of chlorinated polycyclic aromatic hydrocarbons on tidal flats: environmental monitoring and laboratory scale experiment.

This study investigated environmental distributions and production mechanisms of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) in the sediments from some tidal flats located in Asia. Cl-PAHs were found in sediments taken from Arao tidal flat, Kikuchigawa River and Shirakawa River. The range of ∑Cl-PAHs was from 25.5 to 483 pg g(-1) for Kikuchigawa River and Arao tidal flat, respectively. Concentrations of PAHs and Cl-PAHs showed no significant correlations (r=0.134). This result suggests that the origins of these compounds differ. In the identified Cl-PAH isomers, the most abundant Cl-PAH isomer was 9,10-dichloroanthracene (9,10-di-Cl-ANT) in the three sites. In general, concentrations of Cl-ANTs in the coastal environment are about 3-5 orders of magnitude lower than those of anthracene (ANT). However, concentration ratios between Cl-ANTs and ANT (Cl-ANTs/ANT) in the sediments ranged from 4.1% to 24.6%. This result indicated that Cl-PAHs were not generated under industrial processes but the high concentration ratios have resulted from the contribution of photochemical production of Cl-ANTs in the sediments because ANT is known to have high photochemical reactivity. For examining this phenomenon, ANT adsorbed onto glass beads was irradiated with UV under the mimicked field conditions of tidal flats. As a result, it was noticed that, while chlorinated derivatives were negligible in a light-controlled group, production of 2-Cl-ANT, 9-Cl-ANT and 9,10-diCl-ANT on the irradiated surface were found in this study. These results suggest that photochemical reaction of PAHs can be a potential source of the occurrence of Cl-PAHs in the coastal environment.