The Indoor Air Quality (IAQ) of a hospital is very important to properly protect both patients and the staff against hospital infections. The present study aims at evaluating the efficiency of photocatalytic filters as well as the impact of important factors such as the type of UV wavelength (UVC, UVA) with different intensities and loading rates of TiO2 in HEPA Filters on reducing airborne microorganisms. For so doing, it has prepared photocatalytic filters by dipping them into 2% and 4% titanium dioxide suspensions as low and high loading, respectively. The experiments have been carried out on four species’ microorganisms, namely Epidermidis, Subtilis, Niger, and Penicillium. Fungi and bacteria suspensions have been prepared with concentrations of 106, 107 CFU/m3, respectively. In terms of microorganism removal, the efficiency of HEPA filters in both types of TiO2 loading and UVC and UVA radiations with two intensities at three times intervals (60, 90, and 120 min) have been investigated. Results show that lower penetration microorganism belong to PCO (TiO2 + UV), compared to photolysis (UV alone) at all intervals of UV radiation. TiO2 loading has no significant effect on percentage removal in all microorganisms. The percentage penetration of microorganisms under UVC radiation is lower than UVA radiation. Also, increasing the radiation intensity in both types of UV shows that it has higher effectiveness for removing bacteria and fungi. Therefore, the use of photocatalytic HEPA filters with UVC radiation can play an influential role in reduction of the microorganisms in different places such as hospitals, cleanrooms, etc.

Nitrous acid (HONO), an essential precursor of hydroxyl radicals (OH) in the troposphere, plays an integral role in atmospheric photochemistry. However, potential HONO sources remain unclear, particularly in rural areas, where long-term (including seasonal) measurements are scarce. HONO and related parameters were measured at a rural site in the North China Plain (NCP) during the winter of 2017 and summer and autumn of 2020. The mean HONO level was higher in winter (1.79 ± 1.44 ppbv) than in summer (0.67 ± 0.50 ppbv) and autumn (0.83 ± 0.62 ppbv). Source analysis revealed that the heterogeneous conversion (including photo-enhanced conversion) of NO₂ on the ground surface dominated the daytime HONO production in the three seasons (43.1% in winter, 54.3% in summer, and 62.0% in autumn), and the homogeneous reaction of NO and OH contributed 37.8, 12.2, and 28.4% of the daytime HONO production during winter, summer, and autumn, respectively. In addition, the total contributions of other sources (direct vehicle emissions, particulate nitrate photolysis, NO₂ uptake and its photo-enhanced reaction on the aerosol surface) to daytime HONO production were less than 5% in summer and autumn and 12.0% in winter. Unlike winter and autumn, an additional HONO source was found in summer (0.45 ± 0.21 ppbv h⁻¹, 31.4% to the daytime HONO formation), which might be attributed to the HONO emission from the fertilized field. Among the primary radical sources (photolysis of HONO, O₃, and formaldehyde), HONO photolysis was dominant, with contributions of 82.6, 49.3, and 63.2% in winter, summer, and autumn, respectively. Our findings may aid in understanding HONO formation in different seasons in rural areas and may highlight the impact of HONO on atmospheric oxidation capacity.

Dissolved organic matter (DOM) plays a significant role in the photochemical behavior of nano- and micro-plastic particles (NPs/MPs). We investigated the influence of DOM on the mechanism on the photoaging of NPs/MPs with different molecular structures under UV₃₆₅ irradiation in water. DOM components used in this study are mainly humic acid and fulvic acid. The results showed that DOM promoted the weathering of aliphatic NPs/MPs (polypropylene (PP)), but inhibited or had only a minor effect on the photoaging of aromatic NPs/MPs (polystyrene (PS) NPs/MPs, carboxyl-modified PS NPs, amino-modified PS NPs, and polycarbonate MPs). NPs with a large surface area may adsorb sufficient DOM on the particle surfaces through π-π interactions, which competes with NPs for photon absorption sites, thus, can delay the photoaging of PS NPs. Aromatic MPs may release phenolic compounds that quench •OH, thereby weakening the photoaging process. For aliphatic MPs, the detection of peracid, aldehyde, and ketone groups on the polymer surface indicated that DOM promoted weathering of PP MPs, which was primarily because the generation of •OH due to DOM photolysis may attack the polymer by C–C bond cleavage and hydrogen extraction reactions. This study provides insight into the UV irradiation weathering process of NPs/MPs of various compositions and structures, which are globally distributed in water.

As replacements for “old” organohalides, such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), “new” organohalides have been developed, including decabromodiphenyl ethane (DBDPE), short-chain chlorinated paraffins (SCCPs), and perfluorobutyrate (PFBA). In the past decade, these emerging organohalides (EOHs) have been extensively produced as industrial and consumer products, resulting in their widespread environmental distribution. This review comprehensively summarizes the environmental occurrence and remediation methods for typical EOHs. Based on the data collected from 2015 to 2021, these EOHs are widespread in both abiotic (e.g., dust, air, soil, sediment, and water) and biotic (e.g., bird, fish, and human serum) matrices. A significant positive correlation was found between the estimated annual production amounts of EOHs and their environmental contamination levels, suggesting the prohibition of both production and usage of EOHs as a critical pollution-source control strategy. The strengths and weaknesses, as well as the future prospects of up-to-date remediation techniques, such as photodegradation, chemical oxidation, and biodegradation, are critically discussed. Of these remediation techniques, microbial reductive dehalogenation represents a promising in situ remediation method for removal of EOHs, such as perfluoroalkyl and polyfluoroalkyl substances (PFASs) and halogenated flame retardants (HFRs).

Antibiotics are a typical group of pharmaceutical and personal care products (PPCPs) with emerging pollutant effects. The presence of residual antibiotics in the environment is a prominent issue owing to their potential hazards, toxic effects, and persistence. Several treatments have been carried out in aquatic environments in order to eliminate antibiotic residues. Among these, photodegradation is regarded as an environmentally-friendly and efficient option. Indirect photodegradation is the main pathway for the degradation of residual antibiotics in natural water, as opposed to direct photodegradation. Algae, working as photosensitizers, play an important role in the indirect photolysis of residual antibiotics in natural water bodies. They promote this reaction by secreting extracellular organic matters (EOMs) and inducing the generation of active species. In order to provide a thorough understanding of the effects of algae on residual antibiotic degradation in the environment, this paper comprehensively reviews the latest research regarding algae-induced antibiotic photodegradation. The summary of the different pathways and photosensitive mechanisms involved in this process show that EOMs are indispensable to antibiotic photodegradation. The influencing factors of algae-induced photodegradation are also discussed here: these include algae species, antibiotic types, and environmental variables such as light source, ferric ion presence, temperature, and ultrasound treatment. Based on the review of existing literature, this paper also considers several pathways for the future study of algae-induced antibiotic photodegradation.

Sodium percarbonate (SPC, 2Na₂CO₃∙3H₂O₂), is a compound that can be used under multiple environmental applications. In this work, SPC was employed as oxidant in the treatment of soil contaminated with diesel oil. The soil samples were collected during the earthmoving stage of RNEST Oil Refinery (Petrobras), Brazil. Then, the samples were air-dried, mixed and characterized. Subsequently, raw soil was contaminated with diesel and treated by photo-Fenton reaction (H₂O₂/Fe²⁺/UV). SPC played a significant role in the generation of hydroxyl radicals under the catalytic effect of ferrous ions (Fe²⁺), hydrogen peroxide (H₂O₂) and radiation. These radicals provoked the photodegradation of polycyclic aromatic hydrocarbons (PAHs), in the soil remediation. A factorial design 3³ was carried out to assess the variables which most influenced the decrease in total organic carbon (TOC). The study was performed with the following variables: initial concentration of [H₂O₂] and [Fe²⁺], between 190.0 and 950.0 mmol L⁻¹ and 0.0–14.4 mmol L⁻¹, respectively. UV radiation was supplied from sunlight, blacklight lamps, and system without radiation. All experiments were performed with 5.0 g of contaminated soil in 50.0 mL of solution. The initial concentration of Fe²⁺ showed the statistically most significant effect. The oxidation efficiency evaluated in the best condition showed a decrease from 34,765 mg kg⁻¹ to 15,801 mg kg⁻¹ in TOC and from 85.750 mg kg⁻¹ to 20.770 mg kg⁻¹ in PAHs content. Moreover, the sums of low and high molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs and HMW-PAHs) were 19.537 mg kg⁻¹ and 1.233 mg kg⁻¹, respectively. Both values are within the limits recommended by the United Sates Environmental Protection Agency (USEPA) and evidenced the satisfactory removal of PAHs from contaminated soil, being an alternative to classic oxidation protocols.

Natural aeolian dust (AD) particles are potential carriers of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. The heterogeneous interaction between them may lead to worsened air quality and enhanced cytotoxicity and carcinogenicity of ambient particulates in downwind areas, and this topic requires in-depth exploration. In this study, AD samples were collected from four Asian dust sources, and their physical properties and compositions were determined, showing great regional differences. The physical and chemical interactions of different AD particles with naphthalene (Nap; model PAH) were observed in aqueous systems. The results showed that AD particles from the Loess Plateau had weak adsorption to Nap, which was fitted by the Langmuir isotherm. There was no obvious adsorption to Nap found for the other three AD samples. This difference seemed to depend mainly on the specific surface area and/or the total pore volume. In addition, the Nap in the aqueous solution did not undergo chemical reactions under dark conditions and longwave ultraviolet (UV) radiation but degraded under shortwave UV radiation, and 2-formylcinnamaldehyde and 1,4-naphthoquinone were the first-generated products. The degradation of Nap in the aqueous solution was probably initiated by photoionization, and the reaction rate constant (between 1.44 × 10⁻⁴ min⁻¹ and 8.55 × 10⁻⁴ min⁻¹) was much lower than that of Nap with hydroxyl radicals. Instead of inducing or promoting the chemical change in Nap, the AD particles slowed photodegradation due to the extinction of radiation. Therefore, it is inferred that natural AD particles have no substantial effect on the transportation and transformation of PAHs in the atmosphere.

Antibiotics in the environment usually co-exist with their transformation products with retained toxicity, raising concerns about environmental risks of their combined exposure. Herein, we reported a novel predictive approach for evaluating the individual and combined toxicity for photodegradation products of fluoroquinolone antibiotics (FQs). Quantitative structure-activity relationship (QSAR) models with promising predictive performance were constructed and validated using experimental data obtained with 13 FQs and 78 mixtures towards E. coli. A structural descriptor reflecting the interaction among FQ molecules and the target protein was employed in the QSAR models, which was obtained through molecular docking and thus provided a rational mechanistic explanation for these models. The predicted results indicated that the degradation products displayed varying degrees of changes compared to the parent FQs, while the combined toxicity of FQs and their degradation products was mostly additive. Furthermore, following UV irradiation the degradation products displayed elevated capacity of inducing resistance mutations in E. coli, though their overall toxicity was reduced. This result highlights the implications of antibiotic degradation products on resistance development in bacteria and stresses the importance of considering such impacts during environmental risk assessments of antibiotics.

The carbon dots (C-dots) mediated Sn₂Ta₂O₇/SnO₂ heterostructures with spongy structure were successfully assembled by simple hydrothermal route. The photocatalytic removal efficiency of amoxicillin (AMX, 20 mg L⁻¹) over C-dots/Sn₂Ta₂O₇/SnO₂ was estimated to reach up 88.3% within 120 min simulated solar light irradiating. Meanwhile, the HPLC-MS/MS analysis and density functional theory (DFT) computation were examined to clarify the photo-degradation pathway of AMX. The mechanism investigation proposed that with the modification of C-dots, the photocatalysts improves the utilization of solar energy by harvesting the long wavelength solar light due to their unique up-converted photoluminescence (UCPL). In addition, the porous spongy structure and plenty of tiny C-dots promote the ability of adsorption by enlarged specific surface area. Furthermore, the C-dots mediated Z-type heterojunction of Sn₂Ta₂O₇/SnO₂ facilitates the efficient separation and transfer of photo-induced carriers. Our work affords a promising approach for the design of the high-efficient photocatalysts to remedy poisonous antibiotics in aqueous environment.

Foamed plastic debris in aquatic systems has become one of the emerging global contaminants. In this study, the behavior of polystyrene foam (PSF) and microplastics (MPs) adhered on the PSFs were investigated on the Tuul River shore in Ulaanbaatar, the capital city of Mongolia. The micro-sized (<5 mm) PSF, which was the dominant PSF over 600 pieces in 100 m², have accumulated along the shoreline of Tuul River. Carbonyl index (CI) was calculated to evaluate the surface oxidation of macro-sized (20–100 mm), meso-sized (5–20 mm), and micro-sized PSFs and confirm the relative aging depending on photodegradation. CI ranged from 0.00 to 1.09 in the sampled PSFs, whereby the degraded PSFs with high CI were distributed on the shore of downstream of sewer drainage. Micro-sized PSFs showed a wide range of CI and a relatively high average value of CI as compared to those of meso- and macro-sized PSFs. Most of PSFs aggregated with MPs and the adhered MPs have been ubiquitously detected from the surface of PSFs. Adhered micro-sized plastics explored from the surface of PSFs with various sizes, except for mega-sized (>100 mm) PSF, ranged from 5 to 141 items per piece of PSF fragment. The aggregates of PSFs and MPs were common status of PSFs during their transportation. The present findings, which indicated a high concentration of adhered MPs, raise an environmental concern about the widespread aquatic plastic pollution.