Formation of disinfection by-products from microplastics, tire wear particles, and other polymer-based materials

Tire-based microplastics: Composition, detection, and impacts of advanced oxidation processes in drinking water treatment

Microplastic pollution, particularly that from tire, presents critical environmental and public health concerns. They contribute 60 % of the total microplastic pollution. Tire-based microplastics, which contain synthetic polymers and toxic chemical additives, are significant contributors to microplastic pollution in aquatic systems. They release various hazardous substances, including heavy metals, polycyclic aromatic hydrocarbons, and other persistent pollutants, which adversely affect ecosystems and pose risks to drinking water quality. Advanced oxidation processes (AOP) such as ultraviolet based treatment, ozonation and sulfate radical based processes show potential for mitigating these microplastics by fragmenting them and degrading the leached chemicals. Radicals generated during AOP (such as sulfate radicals (SO₄•-), peroxide radicals (HO₂•) and hydroxyl radicals (•OH), have also been successful in removing the transformation products associated with tire microplastics. This combined action of AOP has potential in mitigating the primary tire microplastics and the leached chemicals from it. AOP studies reported from the other microplastic researches (PP, PE, PVC etc.) shows promising results in mitigating them from drinking water sources. TMP appears to behave similarly to other microplastic polymers in terms of fragmentation. However, research is still lacking in quantifying this process due to the presence of complex chemicals additives in it. Additionally, studies focusing on their removal in DWTPs, particularly those that consider both TMP and their associated chemical leachates, remain limited. This review discusses the chemical composition, detection techniques, fragmentation of tire-related microplastics by AOP, and leaching of chemicals from them. This review also suggests modification of treatment techniques, challenges for implementing them to real world treatment and scopes in optimization of treatment conditions to mitigate tire wear particles and the associated chemicals.

Exploring the co-occurrence of microplastics, DOM and DBPs inside PVC pipes undergoing chlorination by correlation analysis and unsupervised learning

Drinking water distribution systems face a multifaceted emerging concern, including in situ microplastic (MP) generation, chemical leaching from plastic pipes, and the formation of disinfection by-products (DBPs). This study investigated the co-release of MPs and chemical leachates from polyvinyl chloride (PVC) pipes exposed to different chlorine concentrations on a lab scale, as well as the subsequent formation of DBP. Results highlighted significant evidence of PVC-derived dissolved organic matter (PVC-DOM) and microplastic (PVC-MP) leaching at higher chlorine concentrations. However, at chlorine residuals of 1 ppm, natural organic matter (NOM) retained its importance, with minimal release of PVC-DOM and PVC-MP from plastic pipes. Correlation analysis highlights the critical role of DOM, including both NOM and PVC-DOM, as a key intermediary between MPs and DBPs. This is evidenced by the strongest observed correlations within the DOM group and its significant associations with both MPs and DBPs. Conversely, the limited direct connections between MPs and DBPs further underscore the importance of DOM as the key link between these two targets. Using unsupervised learning techniques, including clustering and dimensionality reduction, further elucidated the influence of DOM in controlling the data patterns, enabling robust interpretation of complex datasets, and providing valuable insights. This study contributes to advancing understanding of the co-occurrence and behaviors of MP, DOM, and DBP within drinking water distribution systems, as well as propelling the associated risk in this intricate scenario.

Health risk assessment via ingestion of disinfection by-products in drinking water

Disinfection is a critical process to ensure the safety of drinking water. To curb the spread of various bacteria and viruses, disinfectants are extensively employed in communities, hospitals, sewage treatment plants, and other settings. However, disinfectants can produce disinfection by-products (DBPs) that threaten human health. Despite their importance, research and systematic analyses of these risks remain limited. This study monitored DBPs in drinking water across 13 districts and counties in Hangzhou, conducting a risk assessment based on the health risk assessment model recommended by the United States Environmental Protection Agency. Concentrations of 12 DBPs ranged from 0.01 µg/L to 120 µg/L, with levels in 2020-2022 generally exceeding those in 2018-2019. Notably, median concentrations of trichloromethane peaked at 18.00 µg/L in 2021. Most DBPs are detected at higher concentrations in the central and northern parts. However, the spatial distribution of DBPs in drinking water was determined to be random. The health risks associated with most DBPs were higher in 2021 compared to other years. Cancer risks of DBPs ranged between 10- 6 and 10- 4 and noncarcinogenic risks were below 1. This study demonstrates that increased disinfectant use during water treatment may elevates DBPs concentrations.

Distribution characteristics and relationship of microplastics, phthalate esters, and bisphenol A in the Beiyun River basin of Beijing

Urban rivers are closely related to human life, and due to the widespread use of plastic products, rivers have become important carriers of pollutants such as microplastics (MP), phthalate esters (PAEs), and bisphenol A (BPA). However, our understanding of the distribution characteristics and relationships of MP, PAEs, and BPA in rivers is limited. In this study, MP, six PAEs and BPA were detected in the water and sediments of the Beiyun River basin. Polyvinyl chloride (PVC) was the most abundant type of microplastic, while di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) were the most abundant PAEs. MP, PAEs, and BPA in both water and sediment showed positive correlations, with stronger correlations and higher pollution levels in sediment than in water. The tendency for PAE congeners to partition into sediments increased with a higher octanol-water partition coefficient (Kow). There was a significant positive correlation between the distribution tendency of ∑6PAEs and TOC in sediments with a pearson correlation coefficient of 0.717. Rivers with more frequent human activities and higher levels of urbanization in the vicinity had a higher abundance of various pollutants and a greater diversity of MP types.

Quantifying the effects of chlorine disinfection on microplastics by time-resolved inductively coupled plasma-mass spectrometry

Using current water treatment systems, significant amounts of microplastics (MPs) are passing through and being released into the aquatic environment. However, we do not clearly know what effects disinfection processes have had on these particles. In this study, we applied inductively coupled plasma-mass spectrometry (ICP-MS) operating in time-resolved analysis (TRA) mode for quantifying changes in the chlorine (Cl) content of MPs under a variety of water treatment scenarios. Our results illustrated that time-resolved ICP-MS offers a potential method for sensitive and direct analysis of Cl content, including Cl mass and chlorine association (%Cl/C), of discrete particles in the MP suspension by the fast sequential measurements of signals from 35Cl1H2 and 12C1H. Our research, across various water treatment scenarios, also showed that polystyrene (PS) MPs exhibited greater reactivity to Cl disinfectant after being pre-disinfected with UV light and in mildly acidic to neutral pH environments. It is noteworthy that about half of the particles in MP suspension exposed to 10 mg Cl2/L, a typical Cl dose applied in water treatment, were chlorinated, and had a Cl content comparable to that of particles subjected to extreme conditions. Of even greater concern is the fact that our cell viability tests revealed that chlorinated MPs induced considerably higher rates of cell death in both human A549 and Caco-2 cells, and that the effects were Cl dose- and polymer type-dependent. Overall, this study demonstrates the potential of time-resolved ICP-MS as a valuable technique for quantifying the Cl content of MP particles, which is crucial to assessing the fate and transformation of MPs in our water supply and treatment systems.

A comprehensive review of urban microplastic pollution sources, environment and human health impacts, and regulatory efforts

Microplastic (MP) pollution in urban environments is a pervasive and complex problem with significant environmental and human health implications. Although studies have been conducted on MP pollution in urban environments, there are still research gaps in understanding the exact sources, regulation, and impact of urban MP on the environment and public health. Therefore, the goal of this study is to provide a comprehensive overview of the complex pathways, harmful effects, and regulatory efforts of urban MP pollution. It discusses the research challenges and suggests future directions for addressing MPs related to environmental issues in urban settings. In this study, original research papers published from 2010 to 2024 across ten database categories, including PubMed, Google Scholar, Scopus, and Web of Science, were selected and reviewed to improve our understanding of urban MP pollution. The analysis revealed multifaceted sources of MPs, including surface runoff, wastewater discharge, atmospheric deposition, and biological interactions, which contribute to the contamination of aquatic and terrestrial ecosystems. MPs pose a threat to marine and terrestrial life, freshwater organisms, soil health, plant communities, and human health through ingestion, inhalation, and dermal exposure. Current regulatory measures for MP pollution include improved waste management, upgraded wastewater treatment, stormwater management, product innovation, public awareness campaigns, and community engagement. Despite these regulatory measures, several challenges such as; the absence of standardized MPs testing methods, MPs enter into the environment through a multitude of sources and pathways, countries struggle in balancing trade interests with environmental concerns have hindered effective policy implementation and enforcement. Addressing MP pollution in urban environments is essential for preserving ecosystems, safeguarding public health, and advancing sustainable development. Interdisciplinary collaboration, innovative research, stringent regulations, and public participation are vital for mitigating this critical issue and ensuring a cleaner and healthier future for urban environments and the planet.

Effect of microplastics on sodium hypochlorite disinfection and changes in its toxicity on zebrafish

The presence of microplastics (MPs) in water may affect the efficacy of the disinfection process and induce toxicity changes to MPs themselves during disinfection. Therefore, this study evaluated the two-way effects of polyethylene microplastic (MP) particles in water and wastewater during sodium hypochlorite (NaClO) disinfection. On the one hand, it has been confirmed that the presence of MPs reduced the disinfection efficiency of NaClO. The required CT (concentration of the disinfection × contact time) for a 2-4-log inactivation of Escherichia coli (E. coli) in different water samples was in the order of deionized water < turbid water (1 NTU) < water with MPs (1 mg/L) < turbid water (10 NTU). On the other hand, although exposure to MPs did induce significant changes in the activities of superoxide dismutase and glutathione, compared to pristine MPs, the MPs treated by NaClO at current conditions (0.3 and 3.0 mg/L for 30 min) did not show significant changes in their toxicity on zebrafish, at an MP exposure concentration of 1 mg/L. There was no significant difference in the survival rate and weight growth rate, neither as in the activities of the oxidative stress-related enzymes (superoxide dismutase, catalase, glutathione, glutathione peroxidase, and glutathione s-transferase) in both gut and muscle tissues of the zebrafish, between exposure to the pristine and NaClO-treated MPs. It is indicated that NaClO disinfection commonly applied for water and wastewater treatment would not pose a serious concern to effluent safety in the presence of mild levels of MPs.

Differences of microplastics and nanoplastics in urban waters: Environmental behaviors, hazards, and removal

Microplastics (MPs) and nanoplastics (NPs) are ubiquitous in the aquatic environment and have caused widespread concerns globally due to their potential hazards to humans. Especially, NPs have smaller sizes and higher penetrability, and therefore can penetrate the human barrier more easily and may pose potentially higher risks than MPs. Currently, most reviews have overlooked the differences between MPs and NPs and conflated them in the discussions. This review compared the differences in physicochemical properties and environmental behaviors of MPs and NPs. Commonly used techniques for removing MPs and NPs currently employed by wastewater treatment plants and drinking water treatment plants were summarized, and their weaknesses were analyzed. We further comprehensively reviewed the latest technological advances (e.g., emerging coagulants, new filters, novel membrane materials, photocatalysis, Fenton, ozone, and persulfate oxidation) for the separation and degradation of MPs and NPs. Microplastics are more easily removed than NPs through separation processes, while NPs are more easily degraded than MPs through advanced oxidation processes. The operational parameters, efficiency, and potential governing mechanisms of various technologies as well as their advantages and disadvantages were also analyzed in detail. Appropriate technology should be selected based on environmental conditions and plastic size and type. Finally, current challenges and prospects in the detection, toxicity assessment, and removal of MPs and NPs were proposed. This review intends to clarify the differences between MPs and NPs and provide guidance for removing MPs and NPs from urban water systems.

Influence of biodegradable plastics on the generation of disinfection byproducts in the chlorination process

Biodegradable plastics (BPs) have seen a continuous increase in annual production and application due to their environmentally sustainable characteristics. However, research on the formation of disinfection byproducts (DBPs) from biodegradable microplastics (BMPs) during chlorination is limited, and the effects of aqueous solution chemistry on this process have yet to be explored. Therefore, two biodegradable microplastics, polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT), were investigated in this study to examine the changes in their physicochemical properties before and after chlorination, and the formation of DBPs under different environmental conditions. The results showed that PLA was more chlorine-responsive, and generated more DBPs. The pH converted some of the intermediates into more stable DBPs by affecting the concentration of HClO and base-catalyzed reactions, whereas ionic strength slightly reduced DBP concentration by ion adsorption and promoting the aggregation of BMPs. Finally, since PLA has a slightly greater volume of mesopores and micropores compared to PBAT, it may more effectively adsorb DBP precursors beyond natural organic matter (NOM), such as some anthropogenic pollutants, thus potentially decreasing the formation of chlorinated DBPs in surface water. This research explored the potentiality for DBP formation by BMPs under different water quality conditions during the disinfection process, which is useful for assessing the environmental hazards of BMPs.

Microplastics removal in wastewater treatment plants: A review of the different approaches to limit their release in the environment

In last 10 years, the interest about the presence of microplastics (MPs) in the environment has strongly grown. Wastewaters function as a carrier for MPs contamination from source to the aquatic environment, so the knowledge of the fate of this emerging contaminant in wastewater treatment plants (WWTPs) is a priority. This work aims to review the presence of MPs in the influent wastewater (WW) and the effectiveness of the treatments of conventional WWTPs. Moreover, the negative impacts of MPs on the management of the processes have been also discussed. The work also focuses on the possible approaches to tackle MPs contamination enhancing the effectiveness of the WWTPs. Based on literature results, despite WWTPs are not designed for MPs removal from WW, they can effectively remove the MPs (up to 99 % in some references). Nevertheless, they normally act as "hotspots" of MPs contamination considering the remaining concentration of MPs in WWTPs' effluents can be several orders of magnitude higher than receiving waters. Moreover, MPs removed from WW are concentrated in sewage sludge (potentially >65 % of MPs entering the WWTP) posing a concern in case of the potential reuse as a soil improver. This work aims to present a paradigm shift intending WWTPs as key barriers for environmental protection. Approaches for increasing effectiveness against MPs have been discussed in order to define the optimal point(s) of the WWTP in which these technologies should be located. The need of a future legislation about MPs in water and sludge is discussed.

Molecularly imprinted polymers and porous organic frameworks based analytical methods for disinfection by-products in water and wastewater

Disinfection by-products (DBPs) with heritage toxicity, mutagenicity and carcinogenicity are one kind of important new pollutants, and their detection and removal in water and wastewater has become a common challenge facing mankind. Advanced functional materials with ideal selectivity, adsorption capacity and regeneration capacity provide hope for the determination of DBPs with low concentration levels and inherent molecular structural similarity. Among them, molecularly imprinted polymers (MIPs) are favored, owing to their predictable structure, specific recognition and wide applicability. Also, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) with unique pore structure, large specific surface area and easy functionalization, attract increasing interest. Herein, we review recent advances in analytical methods based on the above-mentioned three functional materials for DBPs in water and wastewater. Firstly, MIPs, MOFs and COFs are briefly introduced. Secondly, MIPs, MOFs and COFs as extractants, recognition element and adsorbents, are comprehensively discussed. Combining the latest research progress of solid-phase extraction (SPE), sensor, adsorption and nanofiltration, typical examples on MIPs and MOFs/COFs based analytical and removal applications in water and wastewater are summarized. Finally, the application prospects and challenges of the three functional materials in DBPs analysis are proposed to promote the development of corresponding analytical methods.

Revealing the long-term impact of photodegradation and fragmentation on HDPE in the marine environment: Origins of microplastics and dissolved organics

The extensive usage of high-density polyethylene (HDPE) materials in marine environments raises concerns about their potential contribution to plastic pollution. Various factors contribute to the degradation of HDPE in marine environments, including UV radiation, seawater hydrolysis, biodegradation, and mechanical stress. Despite their supposed long lifespans, there is still a lack of understanding about the long-term degradation mechanisms that cause weathering of seawater-exposed HDPE products. In this research, the impact of UV radiation on the degradation of HDPE pile sleeves was studied in natural as well as laboratory settings to isolate the UV effect. After nine years of exposure to the marine environment in natural settings, the HDPE pile sleeves exhibited an increase in oxygen-containing surface functional groups and more morphological changes compared to accelerated UVB irradiation in the laboratory. This indicated that combined non-UV mechanisms may play a major role in HDPE degradation than UV irradiation alone. However, UVB irradiation was found to release dissolved organic carbon and total dissolved nitrogen from HDPE pile sleeves, reaching levels of up to 15 mg/L and 2 mg/L, respectively. Our findings underscore the significance of taking into account both UV and non-UV degradation mechanisms when evaluating the role of HDPE in contributing to marine plastic pollution.

Deterioration of single-use biodegradable plastics in high-humidity air and freshwaters over one year: Significant disparities in surface physicochemical characteristics and degradation rates

More single-use plastics are accumulating in the environment, and likewise biodegradable plastics (BPs), which are being vigorously promoted, cannot escape the fate. Currently, studies on the actual degradation of BPs in open-air and freshwaters are underrepresented despite they are potentially headmost leakage and contamination sites for disposable BPs. Herein, we compared the degradation behavior of six BP materials and non-degradable polypropylene (PP) plastics over a 1-year in situ suspension in the high-humidity air, a eutrophic river, and an oligotrophic lake. Moreover, a 3-months laboratory incubation was performed to detect the release of dissolved organic carbon (DOC) from BPs. In both air and freshwaters, poly(p-dioxanone) (PPDO) degraded significantly while PP and polylactic acid (PLA) showed no signs of degradation. The average degradation rates of three poly(butylene adipate-co-terephthalate) (PBAT)-based films varied: 100% in river, 55% in lake, and 10% in air. In addition to PLA, surface chemical groups, hydrophilicity, and thermal stability of BPs changed, and microplastics were found on their surfaces. Correspondingly, BPs with faster degradation rates released relatively higher amounts of DOC. Environmental microbial and chemical characteristics may contribute to differences in BP degradation besides polymer specificity. Altogether, our results indicate the need for appropriate monitoring of BPs.

Impact of source water quality on total organic carbon and trihalomethane removal efficiency in a water treatment plant: A case study of Upper Awash, Ethiopia

This study addresses the limited understanding of factors affecting the efficiency of water treatment plants in reducing trihalomethane (THM) formation through total organic carbon (TOC) removal, highlighting significant challenges in improving treatment effectiveness. The aim of this study was to examine the influence of water quality on the efficiency of water treatment plants to remove TOC and reduce THM formation. Linear regression and correlation analyses were conducted to examine the relationship between water quality parameters and THM concentrations. The results showed that there was a negative relationship between turbidity, metals, and TOC concentration with TOC removal efficiency. Positive correlations were found between parameters and the formation of THMs in water. Of these parameters, water temperature was observed to have relatively less influence on THM formation. It was observed that seasonal variations in water quality affect the efficiency of TOC removal and THM content in treated water. THM levels in chlorinated water were found to be within the permissible range of the World Health Organization's drinking water quality guidelines. However, it is still important to maintain continuous monitoring and take measures to reduce THMs. The model demonstrated a strong correlation (R2 = 0.906) between predicted and measured THM values.

Comparison of monochloramination and chlorination of 1,3-diphenylguandine (DPG): Kinetics, transformation products, and cell-based in-vitro testing

As a widely used secondary vulcanization accelerator in the rubber industry, 1,3-diphenylguanidine (DPG) poses risks to human health and the environment. To compare and comprehend the disinfection process of DPG, this work investigates the reaction kinetics, toxicity, and transformation products (TPs) of DPG during chlorination and monochloramination. It has been revealed that the reactivity of monochloramine is significantly slower compared to chlorination of DPG, with the maximum efficiency observed at pH 7 to pH 8. Cytotoxicity assessment using HepG2 and THP-1 cells reveals that cytotoxicity hierarchy is as follows: chlorine TPs > monochloramine TPs > DPG. Moreover, oxidant-to-DPG molar ratios 10 and 20 lead to higher cytotoxicity in both chlorination and monochloramination compared to ratio 5 and 100. Additionally, cell bioenergetics experiments demonstrate that chlorine and monochloramine TPs induce mitochondrial dysfunction and enhance glycolytic function in HepG2 cells. The genotoxic response from p53 signaling further suggested genotoxic effects of certain TPs. Furthermore, analysis of TPs using high-resolution mass spectrometry (HRMS) identifies ten TPs, with chlorination yielding more TPs than monochloramination. Generally, a chlorine or monochloramine molar ratio to DPG of 10-20 results in an increased formation of TPs and heightened cytotoxicity. Notably, higher oxidant molar ratios increased the formation of monoguanidine TPs and DPG hydroxylation during chlorination, whereas monochloramination lead to DPG substitution predominantly generating chlorinated DPG due to weaker oxidation effects. These findings provide valuable information for the appropriate treatment of DPG and disinfection processes in water facilities to mitigate potential risks to human health and the ecosystem.

Releases of microplastics and chemicals from nonwoven polyester fabric-based polyurethane synthetic leather by photoaging

The nonwoven PET fabrics are chemically, mechanically and thermally treated fiber aggregate without weaving, knitting or braiding, which could be used as a base to make polyurethane (PU) synthetic leather through a series of processing. Our research systematically compared the photoaging behaviors of pure non-woven PET base fabric (NPET-P) and PU synthetic leather (nonwoven PET-base fabrics with PU coating, NPET-U), and their possibilities for microplastic fibers (MPFs) generation and chemical transformation in water. NPET-U was photoaged to a higher oxidation degree with higher O/C ratios and more distinct changes in chemical structures. The amount of MPFs released from NPET-U (1.98 × 107 g/fibers) was significantly lower than that from NPET-P (4.76 × 107 g/fibers) after 360 h light irradiation (p value <0.05) with a slower degradation rate and delayed MPFs release. The lengths and diameters of released MPFs from NPET-U varied within a smaller range than that from NPET-P exposed to UV light irradiation. Natural sunlight aging of fabrics for 365 days was found to be equivalent to approximately 85.3-127.2 h UV aging in the laboratory, which indicated the lab accelerated experiments was extraordinarily intense to simulate natural sunlight aging. Furthermore, abundant calcium and sulfur-contained chemicals were detected in original fabrics and the leachate of 360 h light-aged fabrics using the inductively coupled plasma optical emission spectrometer (ICP-OES). The organic components of the leachate were separated according to their molecular weight with the changes of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and the UV response over aging time. UV stimulation aggravated the role of plastic polymers as disinfection by-product (DBP) precursors. Nevertheless, although NPET-U could produce more nitrogen-contained chemicals, it had similar formation potentials of nitrogen-containing DBPs as NPET-P. The discussion lucubrated the potential risks of the production of MPFs and chemical release in the leachate with regard to combined plastic pollution.