Leaching of organic matters and formation of disinfection by-product as a result of presence of microplastics in natural freshwaters

Leaching-driven transformations of tire wear particles (TWPs): Uncovering the neglected environmental implications

Extensive research has been conducted on the leaching behavior and risks of the leachate of tire wear particles (TWPs) in aquatic environments. However, the leaching-driven transformations of TWPs and the subsequent environmental impacts have been largely overlooked. This work examines the changes in physicochemical properties of TWPs during leaching in several water bodies, thereby facilitating a more thorough assessment of the environmental impacts. The results revealed that the environmental behavior related properties of TWPs, including surface morphology, pores, contact angel, zeta potential, functional groups, and surface adsorption sites varied at different levels during leaching. The ionic strength and organic matter content of water body highly determine the above transformations. The carbon index (CI) and O/C ratio of TWPs increased by 55.40 % and 14.27 % after leached in the water for 30 days, while the adsorption capacity of the TWPs for tetracycline (TC) and oxytetracycline (OTC) decreased by 27 % and 24.63 %, respectively. Herein, the changes in the functional groups and polarity during leaching highly influenced the adsorption performance of leached-TWPs. This study provides novel insight into understanding the leaching behavior of TWPs in aquatic environments and highlights an urgent need to assess the environmental implications of leaching-driven transformations of TWPs.

Insight into the dynamic transformation properties of microplastic-derived dissolved organic matter and its contribution to the formation of chlorination disinfection by-products

Microplastics (MPs) can cause adverse effects and pose potential threats to humans and the environment. In addition, dissolved organic matter leached from MPs (MP-DOM) is also a critical issue due to its ecotoxicity and potential to form disinfection by-products (DBPs) during the disinfection process of water treatment plants. However, limited information is available on the dynamic transformation of MP-DOM during UV irradiation and subsequent disinfection, which may further influence the formation of DBPs in MP-DOM. Herein, PSMPs-DOM were leached in aqueous solutions under UV irradiation and the samples were then chlorinated. PSMPs-DOM before and after chlorination were characterized by multiple spectral technologies and methods. With prolonged irradiation time, the aromaticity, molecular weight, humic-like substances and oxygen-containing functional groups of PSMPs-DOM increased, suggesting the continuous transformation of PSMPs-DOM. After chlorination, the aromaticity, molecular weight and humic-like substances of PSMPs-DOM decreased, among which the changes of C2 and oxygen-containing functional groups were more significant. Besides, the PSMPs-DOM formed under prolonged irradiation exhibited higher chlorine reactivity, owing to the more aromatic structures and unsaturated bonds. TCM, DCBM, DBCM and TBM were detected in all chlorinated PSMPs-DOM samples, while the PSMPs-DOM formed at the later stage of irradiation exhibited lower THMs formation potential. The correlation results showed that the conversion of humic-like substances in PSMPs-DOM affected the THMs formation potential, with photo-induced humic-like substance being a more dominant factor. This study provided more information on the relationship between the compositional transformation of MP-DOM and their potential to form DBPs, which may facilitate the assessment of potential toxicity associated with MPs-containing water, as well as the development of more effective water treatment methods.

Microplastic-derived dissolved organic matter: Generation, characterization, and environmental behaviors

Microplastics (MPs) represent a substantial and emerging class of pollutants distributed widely in various environments, sparking growing concerns about their environmental impact. In environmental systems, dissolved organic matter (DOM) is crucial in shaping the physical, chemical, and biological processes of pollutants while significantly contributing to the global carbon budget. Recent findings have revealed that microplastic-derived dissolved organic matter (MP-DOM) constitutes approximately 10 % of the DOM present on the ocean surface, drawing considerable attention. Hence, this study's primary objective is to explore, the generation, characterization, and environmental behaviors of MP-DOM. The formation and characteristics of MP-DOM are profoundly influenced by leaching conditions and types of MPs. This review delves into the mechanisms of the generation of MP-DOM and provides an overview of a wide array of analytical techniques, including ultraviolet-visible (UV-Vis) spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and mass spectroscopy, used to assess the MP-DOM characteristics. Furthermore, this review investigates the environmental behaviors of MP-DOM, including its impacts on organisms, photochemical processes, the formation of disinfection by-products (DBPs), adsorption behavior, and its interaction with natural DOM. Finally, the review outlines research challenges, perspectives for future MP-DOM research, and the associated environmental implications.

Characterization of microplastic-derived dissolved organic matter in freshwater: Effects of light irradiation and polymer types

This study investigated the impacts of light irradiation and polymer types on the leaching behavior of dissolved organic matter (DOM) from microplastics (MPs) in freshwater. Polypropylene had the highest leaching capacity of DOM after photoaging, followed by polystyrene (PS), polyamide (PA) and polyethylene terephthalate (PET). While similarly low levels of DOM were observed in the remaining 5 MP suspensions under UV irradiation and in almost all MP suspensions (except PA) under darkness. These suggest that the photooxidation of some buoyant plastics may influence the carbon cycling of nature waters. Among 9 MP-derived leachates, PET leachates had the highest chromophoric DOM concentration and aromaticity, probably owing to the special benzene rings and carbonyl groups in PET structures and its fast degradation rate. Protein-like substances were the primary fluorescent DOM in MP suspensions (except PS), especially in darkness no other fluorescent substances were found. Considering the bio-labile properties of proteins together, MPs regardless of floating or suspended in an aquatic environment may have prevalent long-term effects on microbial activities. Besides, from monomers to hexamers with newly formed chemical bonds were identified in UV-irradiated MP suspensions. These results will contribute to a deep insight into the potential ecological effects related to MP degradation.

Microplastics and associated chemicals in drinking water: A review of their occurrence and human health implications

Microplastics (MPs) have entered drinking water (DW) via various pathways, raising concerns about their potential health impacts. This study provides a comprehensive review of MP-associated chemicals, such as oligomers, plasticizers, stabilizers, and ultraviolet (UV) filters that can be leached out during DW treatment and distribution. The leaching of these chemicals is influenced by various environmental and operating factors, with three major ones identified: MP concentration and polymer type, pH, and contact time. The leaching process is substantially enhanced during the disinfection step of DW treatment, due to ultraviolet light and/or disinfectant-triggered reactions. The study also reviewed human exposure to MPs and associated chemicals in DW, as well as their health impacts on the human nervous, digestive, reproductive, and hepatic systems, especially the neuroendocrine toxicity of endocrine-disrupting chemicals. An overview of MPs in DW, including tap water and bottled water, was also presented to enable a background understanding of MPs-associated chemicals. In short, certain chemicals leached from MPs in DW can have significant implications for human health and demand further research on their long-term health impacts, mitigation strategies, and interactions with other pollutants such as disinfection byproducts (DBPs) and per- and polyfluoroalkyl substances (PFASs). This study is anticipated to facilitate the research and management of MPs in DW and beverages.

Mechanistic insight into the role of typical microplastics in chlorination disinfection: Precursors and adsorbents of both MP-DOM and DBPs

Microplastics (MPs) in drinking water are predominantly < 10 µm. The leaching of MPs derived dissolved organic matters (MP-DOM) from 5 µm polypropylene MPs (PP-MPs) and polystyrene MPs (PS-MPs) and the formation of MP-DOM derived disinfection byproducts during chlorination disinfection were first investigated. Comparably, PS-MPs are more vulnerable to chlorination and the primary attacks are on para C in aromatic side-chains via electrophilic Cl-substitution and oxidation by two-electron transfer. The O/C and Cl/C ratio of polystyrene MPs was linear and exponential versus initial available Cl2 concentrations, respectively. The significant PS-DOM leaching was observed with initial available Cl2 of 4.0 mg/L (USEPA recommended upper dose). As the initial available Cl2 concentration increased to 8.0 mg/L, the adsorption of chloro-phenolic-components of 200 Daltons in PS-DOM by 5 µm PS-MPs was observed for the first time. Trichloromethane (TCM) was identified as the dominant disinfection byproduct with a formation potential of 60.3 ± 7.8 and 73.7 ± 9.8 μg/mg for PS-DOM and PP-DOM, respectively. The derived TCM could adsorb onto PS-MPs followed the pseudo-second-order kinetic and Langmuir isotherm models. Extreme chlorination could reduce the maximal adsorption capacity of TCM on 5 µm PS-MPs from 196.68 ± 48.66 to 146.02 ± 32.98 μg/g. Thus, PS-MPs act as precursors and carriers of TCM in chlorination.

A Glow before Darkness: Toxicity of Glitter Particles to Marine Invertebrates

Glitter particles are considered a model of microplastics, which are used in a wide range of products. In this study, we evaluated the toxicity of two types of glitter (green and white, with distinct chemical compositions) dispersions on the embryonic development of the sea urchins Echinometra lucunte, Arbacia lixula, and the mussel Perna perna. The Toxicity Identification and Evaluation (TIE) approach was used to identify possible chemicals related to toxicity. Glitter dispersions were prepared using 0.05% ethanol. The tested dispersions ranged from 50 to 500 mg/L. The white glitter was composed of a vinyl chloride-methyl acrylate copolymer. The effective concentrations of green glitter to 50% embryos (EC50) were 246.1 (235.8-256.4) mg/L to A. lixula, 23.0 (20.2-25.8) mg/L to P. perna and 105.9 (61.2-150.2) mg/L, whereas the EC50 of white glitter to E. lucunter was 272.2 (261.5-282.9) mg/L. The EC50 for P. perna could not be calculated; however, the lowest effect concentration was 10 mg/L-that was the lowest concentration tested. The filtered suspension of green glitter had Ag levels exceeding the legal standards for marine waters. TIE showed that metals, volatiles, and oxidant compounds contribute to toxicity. The results showed that glitter may adversely affect marine organisms; however, further studies are necessary to determine its environmental risks.

Fate and environmental behaviors of microplastics through the lens of free radical

Microplastics (MPs), as plastics with a size of less than 5 mm, are ubiquitously present in the environment and become an increasing environmental concern. The fate and environmental behavior of MPs are significantly influenced by the presence of free radicals. Free radicals can cause surface breakage, chemical release, change in crystallinity and hydrophilicity, and aggregation of MPs. On the other hand, the generation of free radicals with a high concentration and oxidation potential can effectively degrade MPs. There is a limited review article to bridge the fate and environmental behaviors of MP with free radicals and their reactions. This paper reviews the sources, types, detection methods, generation mechanisms, and influencing factors of free radicals affecting the environmental processes of MPs, the environmental effects of MPs controlled by free radicals, and the degradation strategies of MPs based on free radical-associated technologies. Moreover, this review elaborates on the limitations of the current research and provides ideas for future research on the interactions between MPs and free radicals to better explain their environmental impacts and control their risks. This article aims to keep the reader abreast of the latest development in the fate and environmental behaviors of MP with free radicals and their reactions and to bridge free radical chemistry with MP control methodology.

The potential risks posed by micro-nanoplastics to the safety of disinfected drinking water

Micro-nanoplastics (M-NPs) have become an emerging critical issue in the environment because they migrate easily, can bioaccumulate with toxic effects, and are difficult to degrade. Unfortunately, the current technologies for removing or degrading M-NPs in drinking water are insufficient to eliminate them completely, and residual M-NPs in drinking water may pose a threat to human health by impairing human immunity and metabolism. In addition to their intrinsic toxic effects, M-NPs may be even more harmful after drinking water disinfection than before disinfection. Herein, this paper comprehensively summarizes the negative impacts of several commonly used disinfection processes (ozone, chlorine, and UV) on M-NPs. Moreover, the potential leaching of dissolved organics from M-NPs and the production of disinfection byproducts during the disinfection process are discussed in detail. Moreover, due to the diversity and complexity of M-NPs, their adverse effects may exceed those of conventional organics (e.g., antibiotics, pharmaceuticals, and algae) after the disinfection process. Finally, we propose enhanced conventional drinking water treatment processes (e.g., enhanced coagulation, air flotation, advanced adsorbents, and membrane technologies), detection of residual M-NPs, and biotoxicological assessment as promising and ecofriendly candidates to efficiently remove M-NPs and avoid the release of secondary hazards.

UV aging of microplastic polymers promotes their chemical transformation and byproduct formation upon chlorination

The presence and accumulation of microplastics (MPs) in water and wastewater is a growing concern. When released to the water bodies, microplastics can be subject to surface weathering due to ultraviolet (UV) exposure. In this study, the effects of UV aging of six MP polymers from three groups (e.g., polyamide, polyester, and polyolefin) on their chlorine reactivity, chemical transformation, and formation of disinfection byproducts (DBPs) were studied. Polyamide (e.g., polyamide 6) in both virgin and UV-aged forms showed significantly higher chlorine demands than other MP polymers (915.5-947.9 versus 7.0-21.1 μmol/g MP in 24 h), and polyolefins were relatively inert to chlorine. UV aging enhanced the destructions of functional groups of polyamide and polyester upon chlorination, promoting the chlorine demands and leaching of organics by up to 1.7- and 2.4-fold, respectively. Polymer monomer and oligomers of polyamide 6 and toxic or endocrine disrupting additives (e.g., dimethyl phthalate and butyl octyl phthalate) were identified in leachates from chlorinated MP polymers by mass spectrometry. Meanwhile, up to >10-fold increases in the yields of trihalomethane, haloacetic acid, haloacetaldehyde, haloacetonitrile, and haloacetamide were observed from 30-day UV-aged MP polymers as compared to their virgin counterparts. Overall, this study reveals that UV aging can promote the reactivity and chemical transformation of MP polymers during chlorination, especially for polyamide and polyester, increase the release of polymer monomers, oligomers, and additives, and aggravate the role of MP polymers as DBP precursors.

The atmospheric microplastics deposition contributes to microplastic pollution in urban waters

Identifying and understanding the potential sources delivering microplastics into the urban water environment is imperative for microplastic pollution control. However, how atmospheric deposition contributes to microplastic pollution in the urban water environment is unclear. Therefore, this study investigated the contribution of atmospheric deposition to microplastic pollution in urban waters based on the analysis of the atmospheric deposition characteristics in the urban area. The results showed that microplastic deposition fluxes during wet weather and dry weather varied from 1.1 × 10³±0.06×10³ to 3.5 × 10³±0.3 × 10³ particles/m²/day and 0.91×10³±0.09×10³ to 1.6 × 10³±0.1 × 10³ particles/m²/day, respectively. The microplastics deposition flux showed moderate to strong correlations to atmospheric particulate matter concentrations, especially the PM2.5 concentration (R² = 0.76-0.93), suggesting the regularly monitored PM2.5 concentration might be served as an indicator for microplastics deposition flux estimation. The deposited microplastics were mainly transparent fragments with an average size of 51-67 μm. Polyethylene and polypropylene were the most abundant plastic polymer, followed by polyethylene terephthalate and polyamide. The comparison of microplastics collected during different weather conditions suggested that rain events could increase microplastics deposition fluxes when air quality conditions are similar. Particularly, rains promoted the deposition of fibrous microplastics as well as smaller microplastics. The estimated daily microplastics deposition in the whole city region suggested more microplastics were deposited in summer and winter. The total quantity of microplastics deposited in the urban environment could reach 1.7-12 times of those discharged from treated wastewater. Among them, 10% would directly deposit to urban waters in the studied city region, while the others may also enter the urban waters through runoff. The results of this study highlighted that the atmospheric microplastics deposition is an important source for microplastics, especially smaller ones, to enter the urban waters, which could not be ignored during microplastics pollution control.

Quantitative assessment of interactions of hydrophilic organic contaminants with microplastics in natural water environment

The interaction between microplastics (MPs) and hydrophilic organic contaminants (HOCs) in natural water environment has recently raised great public attentions due to the potential toxicity to humans. However, the quantitative assessment is less studied. In this study, the interaction between ciprofloxacin (CIP) and ofloxacin (OFL) (two important HOCs) and virgin and aged polystyrene (PS) was investigated. The aged PS showed higher adsorption rate and capacity than the virgin PS, due to its larger surface area and more O-containing groups. The pH-dependent adsorption of CIP was higher than OFL on both virgin and aged PS; the maximum adsorption for both HOCs occurred at pH 5. The sequential orders of functional groups for the adsorption were discovered according to the study by the 2D correlation Fourier transform infrared spectroscopy. Several mechanisms existed for the interaction: (1) at 3.0 < pH < 5.0, the electrostatic attraction (EA) was inhibited while H-bond (HB) was dominant, accounting for > 60% of the total uptake; (2) at 5.0 < pH < 8.0, the contribution of EA increased to around 50-60% while HB decreased to 30-40%; (3) at 8.0 < pH < 10.0, EA, HB and π-π conjugation caused 30-40%, 25-40% and 20-45% of the total uptake, respectively; (4) at 10.0 < pH < 12.0, π-π conjugation accounted for 90-100%. Notably, higher adsorption of CIP was mainly attributed to the presence of secondary amino groups and its higher pK_a value, correspondingly leading to the additional ordinary HB and negative charge-assisted HB, and EA interactions with PS. This study further provides clear evidences on the risk of MPs and HOCs on humans and aqueous living organisms.

The effects of polypropylene microplastics on the DBP formation under the chlorination and chloramination processes

With the increased use of microplastics in modern society, tonnes of various microplastics (MPs) end up in natural and engineered water systems if not properly handled. Being a class of organics, the role of MPs during the disinfection of water treatment systems is still unclear at this stage. In the current experimental study, the formation of 6 typical disinfection by-products (DBPs) was investigated using varying concentrations of polypropylene (PP) MPs under various aquatic chemistry conditions and disinfectants. All investigated DBPs were detected, during the chlorination of PP, with an average CHCl₃ concentration of 378 μg/g, and other DBPs, including CHCl₂Br, TCA, DCAN, 1,1-DCP, and TCNM, were present in less than 60 μg/g, on average. When PP coexisted with Suwannee River Fulvic acid (SRFA), a suppression of DBP formation was observed with a 56% net reduction compared with a condition of PP alone. The dynamic balance of being a DBP precursor, or a scavenger, by absorbing the organics of PP is subjected to aquatic chemistry. Increasing the pH decreases the HOCl concentrations, reducing the PP oxidation capacity and DBP formation. As salinity increases, the aggregation of PP can reduce the reaction sites on the surface of PP and enhance the adsorption of SRFA, hence lowering the formation of DBPs.