Microplastics and volatile organic compounds released from face masks after disinfection: Layers and materials differences.

Effective disinfection methods are critical for ensuring the reusability of masks, yet these methods may inadvertently introduce health concerns associated with microplastics (MPs) and volatile organic compounds (VOCs). This study investigated the impact of ultraviolet germicidal irradiation (UVGI) and sodium hypochlorite (NaClO) bleaching on mask filter layers composed of four distinct materials. Our results revealed that UVGI induced more pronounced damage compared to bleaching, leading to the significant release of both MPs and VOCs. After UVGI treatment at conventional disinfection doses, meltblown (MB) fabrics released MPs reaching 864 ± 182 µg/g (92 ± 19 particles/g). For all filter layers, the quantity of released MPs followed the order: MB > HDPE>PU ≈ NW. These MPs were identified as degraded debris from the mask filter layers. The specific VOCs generated varied depending on the material composition. Non-woven (NW) and MB fabrics, both comprised of polypropylene, predominantly produced various branched aliphatic hydrocarbons and their derivative oxides. The cotton-like fabric, composed of high-density polyethylene, primarily emitted different linear aliphatic hydrocarbons and oxygenates. In contrast, the polyurethane filter layer of reusable masks released aromatic compounds, nitrogenous compounds, and their oxidation products. The formation of VOCs was primarily attributed to bond breakage and oxidative damage to the filter structure resulting from the disinfection process. In summary, as UVGI induced higher yields of MPs and VOCs compared to bleaching, the latter would be a safer option for mask disinfection.

Characteristics and ecological risks of microplastic pollution in a tropical drinking water source reservoir in Hainan province, China.

Microplastic (<5 mm) pollution has become a pressing environmental concern in recent years. The present study investigated the occurrence characteristics and assessed the ecological risk of microplastics in the surface water and sediment of the Chitian Reservoir, a drinking water source in Hainan province (China). The results indicated that microplastics were detected in the surface water and sediment of the Chitian Reservoir and its surrounding areas. The overall abundance of microplastics in the water was 3.05 ± 1.16 items per L and in the sediment was 0.15 ± 0.06 items per g dry weight, which is relatively low compared to other reservoirs in China. The dominant components of microplastics detected in the Chitian Reservoir were polypropylene (PP), rayon, and polyester. Physical morphology analysis of microplastics showed that fibers with small particle sizes (<1 mm) and white color were the predominant characteristics in both the surface water and sediment. The domestic sewage from surrounding residents and agricultural wastewater may be the primary sources of microplastics in the reservoir. Ecological risk assessment revealed that the overall pollution load index (PLI) in the surface water (0.65) and sediment (0.51) of the Chitian Reservoir and its surrounding area is at a low level. The potential ecological hazards (RI) of microplastics (0.13 to 336.78 in water; 0.23 to 465.93 in sediment) in most sites fall within the scope of level I, but those in a few sites are at level II due to the presence of polyvinyl chloride (PVC). This study enriches the data on microplastic pollution in inland reservoir systems, providing fundamental reference information for future ecotoxicological studies and the management of microplastic pollution control.

Modifications to microplastics by potassium ferrate(VI): impacts on sorption and sinking capability in water treatment.

Pre-treatment (oxidation) may induce potential modifications to microplastics (MPs), further affecting their behaviors and removal efficiency in drinking water treatment plants. Herein, potassium ferrate(VI) oxidation was tested as a pre-treatment for MPs with four polymer types and three sizes each. Surface oxidation occurred with morphology destruction and oxidized bond generation, which were prosperous under low acid conditions (pH 3). As pH increased, the generation and attachment of nascent state ferric oxides (FexOx) gradually became dominant, making MP-FexOx complexes. These FexOx were identified as Fe(III) compounds, including Fe2O3 and FeOOH, firmly attaching to the MP surface. Using ciprofloxacin as the targeted organic contaminant, the presence of FexOx enhanced MP sorption dramatically, e.g., the kinetic constant Kf of ciprofloxacin raised from 0.206 (6.5 µm polystyrene) to 1.062 L g-1 (polystyrene-FexOx) after oxidation at pH 6. The sinking performance of MPs was enhanced, especially for small MPs (< 10 µm), which could be attributed to the increasing density and hydrophilicity. For instance, the sinking ratio of 6.5 µm polystyrene increased by 70% after pH 6 oxidation. In general, ferrate pre-oxidation possesses multiple enhanced removals of MPs and organic contaminants through adsorption and sinking, reducing the potential risk of MPs.

Volatile organic compounds generation pathways and mechanisms from microplastics in water: Ultraviolet, chlorine and ultraviolet/chlorine disinfection.

Disinfection in water treatments induces microplastics (MPs) to produce various derivative products, among which the volatile organic compounds (VOCs) are still poorly understood. Ultraviolet (UV), chlorine and UV/chlorine disinfections were used to treat polypropylene (PP), polystyrene (PS) and polyvinylchloride (PVC) in this study. Modifications were observed on the MP surfaces, including melting, cracks, folds, and even forming oxygen-containing structures, resulting in the release of a diversity of VOCs. The polymer types of MPs influenced the VOCs characteristics. PP released alkanes, alkenes and aldehydes, while PVC released alkanes, alkenes and halogenated hydrocarbons. VOCs from PS were dominated by unique aromatic alkanes, alkenes and aldehydes. These derived VOCs are generated during different disinfections with distinct mechanisms. UV-C at 254 nm induced direct scission and radical oxidation on MPs. The derived VOCs were mainly bond-breaking fragments. Chlorination relied on HOCl/OCl- electrophilic reactions, resulting fewer VOCs since C-C skeleton MPs have strong resistance to electrophilic reactions. UV/chlorination promotes the generation of chlorine radicals and hydroxyl radicals, thereby causing oxidative damage. Various oxidized VOCs, such as benzaldehyde and acetophenone, were formed. The disinfection reactions can produce various VOCs from MPs, posing potential risks to the ecological environment and human beings.

Gaseous products generated from polyethylene and polyethylene terephthalate during ultraviolet irradiation: Mechanism, pathway and toxicological analyses.

The generation of various degradation products from microplastics (MPs) has been confirmed under ultraviolet (UV) irradiation. The gaseous products, primarily volatile organic compounds (VOCs), are usually overlooked, leading to potential unknown risks to humans and the environment. In this study, the generation of VOCs from polyethylene (PE) and polyethylene terephthalate (PET) under UV-A (365 nm) and UV-C (254 nm) irradiation in water matrixes were compared. More than 50 different VOCs were identified. For PE, UV-A-derived VOCs mainly included alkenes and alkanes. On this basis, UV-C-derived VOCs included various oxygen-containing organics, such as alcohols, aldehydes, ketones, carboxylic acid and even lactones. For PET, both UV-A and UV-C irradiation induced the generation of alkenes, alkanes, esters, phenols, etc., and the differences between these two reactions were insignificant. Toxicological prioritization prediction revealed that these VOCs have diverse toxicological profiles. The VOCs with the highest potential toxicity were dimethyl phthalate (CAS: 131-11-3) from PE and 4-acetylbenzoate (3609-53-8) from PET. Furthermore, some alkane and alcohol products also presented high potential toxicity. The quantitative results indicated that the yield of these toxic VOCs from PE could reach 102 µg g-1 under UV-C treatment. The degradation mechanisms of MPs included direct scission by UV irradiation and indirect oxidation induced by diverse activated radicals. The former mechanism was dominant in UV-A degradation, while UV-C included both mechanisms. Both mechanisms contributed to the generation of VOCs. Generally, MPs-derived VOCs can be released from water to the air after UV irradiation, posing a potential risk to ecosystems and human beings, especially for UV-C disinfection indoors in water treatments.

Differential physiological response of marine and freshwater microalgae to polystyrene microplastics.

Effects of microplastics on microalgae have not been compared from different habitat. To answer this question, three marine microalgae species (Chlorella marined, Nannochloropsis oculate, and Phaeodactylum tricornutum) and two freshwater species (Chlorella vulgaris and Tetradesmus obliquus) were selected and exposed to the environment relevant concentrations of polystyrene microplastics. The results indicated that microplastics have a significant concentration effect on the growth of microalgae. The attachment of microalgae to microplastics surface and the aggregation of microalgae with each other were observed. Under exposure of microplastics, the photosynthesis of microalgae was inhibited while the antioxidant system was activated, indicating that microplastics had a negative impact on microalgae. At the end of exposure, the oxidative stress status caused by microplastics in marine microalgae were alleviated, but the antioxidant system of freshwater microalgae was still at high levels, indicating a stress response. In addition, integrated biomarker response (IBR) indicated that the effects of microplastics on freshwater microalgae were severer than marine microalgae, which might relate to their differences in removing reactive oxygen species (ROS) effectively and membrane structure. Our study provides a reliable data for understanding the complex effects of microplastics on microalgae, and especially for comparing the differential effects of microplastics among different microalgae.

Modifications of microplastics in urban environmental management systems: A review.

Microplastics (MPs) are a worldwide environmental pollution issue. Besides the natural environmental stresses, various treatments in urban environmental management systems induce modifications on MPs, further affecting their environmental behavior. Investigating these modifications and inherent mechanisms is crucial for assessing the environmental impact and risk of MPs. In this review, up-to-date knowledge regarding the modifications of MPs in urban environmental management systems was summarized. Variations of morphology, chemical composition, hydrophilicity and specific surface area of MPs were generalized. The aging and degradation of MPs during drinking water treatment, wastewater treatment, sewage sludge treatment and solid waste treatment were investigated. A high abundance of MPs occurred in sewage sludge and aging solid waste, while digestion and composting contributed to significant decomposition and reduction of MPs. These treatments have become converters for MPs before entering the environment. Several novel technologies for MPs removal were listed; However, no appropriate methods can be put into actual application by now, except the membrane separation. The corresponding effects of degradation on the behaviors of MPs, including adsorption, sinking and contaminant leakage, were discussed. Finally, three priorities for research were proposed. This critical review provides viewpoints and references for risk evaluation of MPs after treatments in urban environmental management systems.

Surface characteristic and sinking behavior modifications of microplastics during potassium permanganate pre-oxidation.

Microplastics (MPs) occur in the source water of worldwide drinking water treatment plants (DWTPs). Pre-oxidation treatments become the initial stage for MPs treatment in DWTPs. Investigating the modifications of MPs after pre-oxidations is important to understand their fate in DWTPs. In this study, potassium permanganate oxidation (PPO) was applied to treat four high abundant MPs in DWTPs, including polyethylene (PE), polyethylene terephthalate (PET), polyvinylchloride (PVC) and polystyrene (PS). Influences of polymer types, sizes and pH were considered. After 10 mg L-1 PPO, only slight corrosions were observed on all MPs. Whereas, the appearances of O-Mn spectrum and the observation of nano-scale particles indicated the generation of nascent state Mn-oxides (MnO2) on MPs surface. This adhesion of MnO2 contributed to increasing density and hydrophilicity. As a result, the sinking performance of MPs was enhanced, e.g. the sinking ratio of 6.5 µm MPs increased 30% (PET), 20% (PVC) and 30% (PS) compared with pristine ones upon pH 7 PPO. These results implied that the practical PPO can enhance the sinking behavior of MPs. Of note, PE seems to be persistent and requires special concern.

Modifications of ultraviolet irradiation and chlorination on microplastics: Effect of sterilization pattern.

Chlorination and ultraviolet disinfection in drinking water treatment plants (DWTPs) may be highly destructive for microplastics (MPs). Investigating the effect of sterilization patterns on MPs behavior modifications can provide useful information to evaluate their potential risk to drinking water safety. In this study, aged polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS) and polyvinyl chloride (PVC) were applied, and five well-designed sterilization patterns with low and high doses disinfection were performed. Especially, a combining sterilization pattern including ultraviolet disinfection, low-dose chlorination and high-dose chlorination was designed to simulate the actual disinfection processes in environmental engineering systems. Different sterilization patterns contributed various chlorinated and oxidized modifications on the MPs surface, resulting in distinct effects on their sinking and adsorption performance. After combining sterilization (180 mJ cm-2 UV-C irradiation +9675 mg min L-1 chlorination), the adsorption capacities of ciprofloxacin by PET and PVC were slightly improved, and the one by PS was inhibited. Yet, PET, PVC and PS tend to sink (>95%) after this combining sterilization, implying that these MPs would be retained in DWTPs or water supply pipes. For PE, even though it maintained floating on water, its adsorption of ciprofloxacin was inhibited by combining sterilization (Kf reduced from 0.142 L g-1 to 0.069 L g-1). In general, multiple sterilization patterns can enhance the sinking and inhibit the adsorption performance of MPs, reducing their potential to become vectors of organic contaminants and risk to drinking water users.

Coastal zone use influences the spatial distribution of microplastics in Hangzhou Bay, China.

Microplastic pollution in estuarine and coastal environments has recently been characterised in several countries but few researchers have addressed the influence of different forms of coastal zone use on the distribution of microplastic. Here, microplastic particles were sampled in Hangzhou Bay, which is heavily influenced by a range of human activities, and their abundance, size, and polymer type characterised. The abundance of microplastics was 0.14 ± 0.12 items/m3 in water, 84.3 ± 56.6 items/kg dry weight of sediment, and between 0.25 ± 0.14 and 1.4 ± 0.37 items/individual in biota. These results show that Hangzhou Bay has a low level of microplastic contamination compared to other coastal systems in China, although abundance was spatially variable within the bay; relatively higher microplastic abundances were found in the southern area of the bay, which has adjacent industrial and urban land-use zones, while lower abundances were observed in the central and northern bay areas where mariculture, fisheries, and mineral and energy industries are most common. The relatively low microplastic abundance observed in the biota samples is consistent with the generally low values for the seawater and sediment samples. Pellets were the most common of four particle-shape classes (fibres, fragments, films, and pellets) in surface seawater, while fibres were most abundant in sediment and biota. Smaller-sized microplastics (<1.0 mm) were dominant in all samples. Microplastics in the surface seawater were dominated by low-density polypropylene and polyethylene particles, while rayon was dominant in the sediment and biota samples. Our results demonstrate that regional variability in anthropogenic activity and land-use are important controls on the spatial pattern of microplastic pollution in Hangzhou Bay.