Domesticating aquatic plants in hydroponic systems to demonstrate and advance phytoremediation of the artificial sweetener acesulfame.

Artificial sweeteners (ASs) are ubiquitously detected in the global water system, among which acesulfame (ACE) is an emerging contaminant for its chemical and biological stability and unsatisfying removal by conventional or advanced treatment technologies. Phytoremediation is an effective and sustainable in-situ remediation technology that this study is the first to explore ACE removal by aquatic plants. The emergent plants, Scirpus Validus (S. validus), Phyllostachys heteroclada Oliver (P. heteroclada) and Acorus tatarinowii (A. tatarinowii) showed superior removal capability than eleven floating plants, and demonstrated high phytoremediation efficiencies (PEs) of up to 75 % after 28 d domestication. ACE removal by the three emergent plants increased during domestication, as the PEs after 28 d domestication were 5.6-6.5 times of 7 d domestication. Notably, the half-life of ACE was decreased from 20.0 to 33.1 d to 1.1-3.4 d in the plant-hydroponic system, compared with 481.0-1152.4 d in control water without plants. Moreover, A. tatarinowii demonstrated the highest removal capacity for ACE with 0.37 mg/g fresh biomass weight (FW), higher than S. validus (0.27 mg/g FW) and P. heteroclada (0.20 mg/g FW). It is worth noting that a mass balance analysis demonstrated that plant transpiration and plant uptake account for about 6.72 %-18.54 % and 9.69 %-21.67 % ACE removal, while hydrolysis only accounted for about 4 % and photolysis was negligible. The rest ACE may be used as a carbon source by endophytic bacteria and root microorganisms of plants. In addition, increased temperature, pH, and illumination intensity had a significant effect on phytoremediation. In the selected experimental range, the increase of temperature from 15 °C to 35 °C, illumination intensity from 1500 lx to 6000 lx, and pH from 5 to 9 generally accelerated the PEs of ACE during the domestication process. Though the mechanism still requires further investigation, the results provide scientific and feasible data for removal of ACE from water by diverse plants for the first time, and also revealed insights for in-situ treatment of ACE.

Enhanced dehalogenation of brominated DBPs by catalyzed electrolysis using Vitamin B12 modified electrodes: Kinetics, mechanisms, and mass balances.

Vitamin B12 (VB12) modified electrodes were prepared for the electrocatalytic reductive debromination of tribromoacetic acid (TBAA). Under galvanostatic conditions set as 5 mmol/L VB12 loading, 20 mmol/L Na2SO4 as electrolyte, 10.0 mA/cm2 current density, pH 3, and 298 K, the degradation efficiency of 200 µg/L TBAA at the VB12 modified electrode could reach 99.9 % after 6 h. The debromination of TBAA followed the first-order kinetic model. The masses of carbon and bromine elements were conserved before and after the reaction, together with the qualitative analysis of the degradation products showed the likely degradation pathways as TBAA→dibromoacetic acid (DBAA)→monobromoacetic acid (MBAA)→acetic acid (AA). ESR detection and quenching experiments confirmed the role of atomic H* in TBAA debromination. In-situ Raman spectroscopy showed that the Co-Br bond was strongly enriched to the electrode surface, accelerating the electron transfer. The H2O dissociation performance and transition states searching catalyzed by VB12 were calculated by Density Functional Theory (DFT) and proved that the composite electrode can effectively promote atomic H* generation. Material characterization and electrochemical performance tests showed that the VB12 modified electrode had excellent stability and atomic H* catalytic activity. The electrocatalytic debromination of TBAA at VB12 modified electrodes mainly involves two mechanisms, direct reduction by electron transfer and indirect reduction by the strongly reducing atom H*. The results provide an efficient way to achieve safe removal of brominated DBPs from drinking water after chlorination and before human consumption.

Environmental risks from consumer products: Acceptable drinking water quality can produce unacceptable indoor air quality with ultrasonic humidifier use.

The commonly used consumer product of an ultrasonic humidifier (e.g., cool mist humidifier) emits fine particles containing metals from tap water used to fill the humidifier. The objectives are: 1) predict emitted indoor air inhalable metal concentrations produced by an ultrasonic humidifier filled with tap-water containing As, Cd, Cr, Cu, Mn, and Pb in 33 m3 or 72 m3 rooms with varying air exchange rates; 2) calculate daily ingestion and 8-h inhalation average daily dose (ADD) and hazard quotient (HQ) for adults and children (aged 0.25-6 yr); and 3) quantify deposition in respiratory tract via multi-path particle dosimetry (MPPD) model. Mass concentrations of indoor air metals increase proportionally with aqueous metal concentrations in fill water, and are inversely related to ventilation. Inhalation-ADDs are 2 magnitudes lower than ingestion-ADDs, using identical water quality for ingestion and fill-water. However, in the 33 m3, low 0.2/h ventilated room, inhalation-HQs are >1 for children and adults, except for Pb. HQ inhalation risks exceed ingestion risks at drinking water regulated levels for As, Cd, Cr, and Mn. MPPD shows greater dose deposits in lungs of children than adults, and 3 times greater deposited doses in a 33 m3 vs 72 m3 room. Rethinking health effects of drinking water and consumer products to broaden consideration of multiple exposure routes is needed.

Exposure at the indoor water-air interface: Fill water constituents and the consequent air emissions from ultrasonic humidifiers: A systematic review.

This systematic review investigates the emissions from ultrasonic humidifiers (e.g., cool mist humidifiers) within indoor air environments, namely soluble and insoluble metals and minerals as well as microorganisms and one organic chemical biocide. Relationships between ultrasonic humidifier fill water quality and the emissions in indoor air are studied, and associated potential adverse health outcomes are discussed. Literature from January 1, 1980, to February 1, 2022, was searched from online databases of PubMed, Web of Science, and Scopus to produce 27 articles. The results revealed clear positive proportional relationships of the concentration of microorganisms and soluble metals/minerals between fill water qualities and emitted airborne particles, for both microbial (n = 9) and inorganic (n = 15) constituents. When evaluating emissions and the consequent health outcomes, ventilation rates of specific exposure scenarios affect the concentrations of emitted particles. Thus, well-ventilated rooms may alleviate inhalation risks when the fill water in ultrasonic humidifiers contains microorganisms and soluble metals/minerals. Case reports (n = 3) possibly due to the inhalation of particles from ultrasonic humidifier include hypersensitivity pneumonitis in adults and a 6-month infant; the young infant exhibited nonreversible mild obstructive ventilator defect. In summary, related literature indicated correlation between fill water quality of ultrasonic humidifier and emitted particles in air quality, and inhalation of the emitted particles may cause undesirable health outcomes of impaired respiratory functions in adults and children.

Occurrence and modeling of disinfection byproducts in distributed water of a megacity in China: Implications for human health.

Disinfection byproducts (DBPs) are initially formed in the process of chlorination in the drinking water treatment plants (DWTPs), then further formed in the distribution system due to the presence of residual chlorine and reactive organic matters. However, in China, DBPs are monitored in the effluent from the DWTPs, but less is known about concentrations of DBPs in tap water since they are usually monitored once per half a year. The smart water service system is establishing real-time monitoring of water indices, although DBPs are an urgent need, they are difficult to monitor in real-time due to their diversity and complicated detection methods. If the correlation between DBP concentration and routinely real-time monitored water quality parameters (e.g., pH value, residual chlorine, ammonia) can be evaluated, the concentration of DBPs can be predicted, which will strengthen the control of tap water safety. This article comprehensively assessed the physicochemical parameters and the occurrence of DBP formation in the tap water with an 18-month investigation in Z city (China). DBP formation in tap water of different seasons and different water sources were compared. Based on the relationship between DBPs and physicochemical parameters, linear prediction and nonlinear prediction models of trihalomethanes (THMs), haloacetonitriles (HANs) and haloacetic acids (HAAs) were established, and the accuracy of these models was verified by measured data. Finally, the toxicity and carcinogenic and non-carcinogenic health risk assessment of DBPs in tap water were analyzed.

Insights for booster chlorination strategy based on DBPs control in a large-scale water supply system.

Based on a one-year field investigation of disinfection by-products (DBPs) in large scale water distribution system (LSWDS), the various characteristics of DBPs together with their correlation with booster chlorination were elaborated through ArcGIS model. Furthermore, the effects of booster chlorination on DBP formation were investigated through simulated experiments. Residual chlorine showed a strong relationship with occurrence of different DBPs in LSWDS, and the yield of DBPs increased significantly after booster chlorination. The simulated chlorination experiments showed that diminution of the ratio of primary to secondary (booster) chlorination dosage, and delaying the secondary chlorine addition reduced the generation of DBPs during water conveyance. The yield concentrations of THMs and HAAs obviously increased after booster chlorination. The correlation between HAAs and chlorine dosage is weaker in the field research than in the simulation experiment while THMs had a positive correlation with the chlorine addition in both field research and simulation experiment.

Insights into metal-organic frameworks HKUST-1 adsorption performance for natural organic matter removal from aqueous solution.

Natural organic matter (NOM) has rich halogenation reactive sites, therefore acts as the main precursor of disinfection byproducts (DBPs) in the chlorine disinfection process during drinking water treatment. In this research, high-quality metal-organic framework HKUST-1 is rapidly synthesized by a solvothermal method, and we are the first to report adsorption of aqueous humic acid (HA), representing NOM, and its adsorption behavior, influencing factors, and recycling capability. The crystalline HKUST-1 possessed a microporous framework with a high 1385 m2/g specific surface area, and three-dimensional structure as characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM). 99% removal of 5 mg/L HA was observed at pH 5.8, room temperature, and 0.6 g/L HKUST-1. The maximum capacity was 14.42 mg HA/g HKUST-1 at room temperature. The Langmuir adsorption isotherm, quasi-second-order kinetic model, and thermodynamic parameters accurately describe the spontaneous and disorderly endothermic adsorption of HA by HKUST-1. The desorption regeneration process was accomplished by washing HKUST-1 with NaOH and calcination; it showed that HKUST-1 was viable in three regeneration cycles. The mechanism of HA adsorption by HKUST-1 is electrostatic and synergistic interaction between π-π bonding, and hydrogen bonding. HKUST-1 is a potential treatment strategy to remove NOM.

Degradation of saccharin by UV/H2O2 and UV/PS processes: A comparative study.

Artificial sweeteners have raised emerging concern due to their potential threats to human health, which were frequently detected in aquatic environment with median concentrations. Although current researches have widely reported that ultraviolet light-activated persulfate process (UV/PS) was superior to UV/H2O2 process for the degradation of refractory organic contaminants, UV/H2O2 process presented a more satisfactory saccharin (SAC) removal efficiency than UV/PS process, completely degraded 20 mg/L SAC within 45 min. Hence, quenching and probe experiments were employed to investigate the difference between hydroxyl radical (OH)- and sulfate radical (SO4-)-mediated oxidation mechanisms, which revealed the higher reactivity of OH (1.37-1.56 × 109 M-1 s-1) toward SAC than SO4- (3.84-4.13 × 108 M-1 s-1). A combination of density functional theory calculation and transformation products identification disclosed that OH preferred to attack the benzene ring of SAC via hydrogen atom transfer pathway, whereas SO4- oxidation was conducive to the cleavage of -C-NH2 bond. Increasing oxidant concentration significantly accelerated SAC degradation in both processes, while UV/H2O2 process consumed lower electrical energy with respect to UV/PS process. Additionally, UV/H2O2 system presented excellent adaptability and stability under various water matrices parameters (e.g. pH, anions and humic acid). While both UV/H2O2 and UV/PS processes promoted the generation of disinfection by-products (DBPs) during subsequent chlorination, and prolonging pretreatment time posed positive effect on reducing the formation of DBPs. Overall, the results clearly demonstrate the high efficiency, economy and practicality of UV/H2O2 process in the remediation of SAC-contaminated water.

Spatio-temporal variability of halogenated disinfection by-products in a large-scale two-source water distribution system with enhanced chlorination.

Distributions of halogenated disinfection byproducts (DBPs) in a two-source water distribution system (WDS) with enhanced chlorination were investigated. The WDS was divided into different sub-service areas based on different electrical conductivity of two water sources. Results clearly show that the principal halogenated DBPs were trihalomethanes (THMs) (5.06-82.69 µg/L), varying within the concentration range as 2-5 times as the levels of haloacetic acids (HAAs) (1.41-61.48 µg/L) and haloacetonitriles (HANs) (0.21-15.13 µg/L). Different water sources, treatment trains, and enhanced chlorination within the WDS had significant effects on seasonal and spatial variations of the DBP distributions over water conveyance. THM and HAA formation followed the sequence of summer > autumn > winter > spring. On the other hand, the DBP spatial distributions were visualized using the ArcGIS enabled Inverse distance weighting technique. The superposition of different DBP spatial distributions allowed for the identification of the high-risk THMs and HAAs areas based on the average values of THMs (27.49 µg/L) and HAAs (14.06 µg/L). Beyond the comprehensive analyses of DBP distribution in a municipal WDS, the project proposed and validated an innovative methodology to locate the DBP high-risk areas and to reveal the effects of different factors on DBPs distribution in a two-source WDS.

Data Analytics Determines Co-occurrence of Odorants in Raw Water and Evaluates Drinking Water Treatment Removal Strategies.

A complex dataset with 140 sampling events was generated using triple quadrupole gas chromatography-mass spectrometer to track the occurrence of 95 odorants in raw and finished water from 98 drinking water treatment plants in 31 cities across China. Data analysis identified more than 70 odorants with concentrations ranging from not detected to thousands of ng/L. In raw water, Pearson correlation analysis determined that thioethers, non-oxygen benzene-containing compounds, and pyrazines were classes of chemicals that co-occurred, and geosmin and p(m)-cresol, as well as cyclohexanone and benzaldehyde, also co-occurred, indicating similar natural or industrial sources. Based on classification and regression tree analysis, total dissolved organic carbon and geographical location were identified as major factors affecting the occurrence of thioethers. Indoles, phenols, and thioethers were well-removed through conventional and advanced treatment processes, while some aldehydes could be generated. For other odorants, higher removal was achieved by ozonation-biological activated carbon (39.3%) compared to the conventional treatment process (14.5%). To our knowledge, this is the first study to systematically identify the major odorants in raw water and determine suitable treatment strategies to control their occurrence by applying data analytics and statistical methods to the complex dataset. These provide informative reference for odor control and water quality management in drinking water industry.

Risks to children from inhalation of aerosolized aqueous manganese emitted from ultrasonic humidifiers can be greater than for corresponding ingestion.

The essential trace element manganese (Mn) can cause neurotoxicity with inhalation acknowledged as a more severe health and cognition threat than ingestion. METHODS: Over a range of aqueous Mn concentrations present in tap water, this research characterizes exposures and risks for adults and 0.25, 1, 2.5, and 6 yr old children who ingest the water and inhale respirable particles produced by a room-sized ultrasonic humidifier filled with the same water. Aqueous Mn concentrations evaluated included 50 µg/L USEPA esthetic guideline, 80 µg/L WHO infant guideline, and 120 µg/L Canadian regulatory level. Airborne-particle-bound Mn concentrations were generated for water filling an ultrasonic humidifier under four realistic room conditions (33 m3 small or 72 m3 large) with varying ventilation rates from 0.2/h -1.5/h. Average daily doses (ADD) and reference intake doses were calculated for ingestion and 8-h inhalation of humidified air. Hazard quotients (HQ) compared the intake doses and reference doses. Multi-path particle dosimetry (MPPD) model quantified the particle deposition and deposited dose in children's and adults' respiratory tracts. RESULTS: At only 11 µg/L Mn, the resulting humidified air Mn exceeds USEPA's reference concentration of 0.05 µg/m3 Mn in small room with low, energy-efficient ventilation. Inhalation ADD are 2 magnitudes lower than ingestion ADD for identical water Mn concentrations and daily exposure frequency. Even so, ingestion HQs are approximately 0.2 but inhalation risk is significant (HQ>1) for children and adults when breathing Mn-humidified air under most small room conditions at 50, 80 or 120 µg/L Mn. MPPD model indicates inhaled Mn deposits in head and pulmonary regions, with greater Mn dose deposits in children than adults. CONCLUSION: Inhalation of Mn-particles produced from ultrasonic humidifiers can pose greater risks than ingestion at the same water concentration, especially for children. Aqueous Mn concentration and room size influence risks. Limiting manganese exposures and setting regulations requires consideration of both ingestion and inhalation of water.

Children and adults are exposed to dual risks from ingestion of water and inhalation of ultrasonic humidifier particles from Pb-containing water.

Room-sized ultrasonic humidifiers are exposure pathways to aerosolized metals, with dose positively associated with increased concentrations of metals in fill water. This study innovatively quantifies water ingestion along with inhalation doses from humidifiers for 10-1000 µg/L dissolved lead (Pb) in tap water. The subsequent indoor air Pb concentrations, average daily doses, and inhalation deposited respiratory fractions were predicted under four room scenarios for 3-mo, 12-mo, 28-mo, and 6-yr children and adults. Elevated blood Pb levels (BLLs) in children were modeled using USEPA's Integrated Exposure Uptake Biokinetic (IEUBK) model. Indoor air Pb exceeds the USEPA ambient air standard of 0.15 µg/m3 when humidifier fill water contains 33 µg/L Pb in the small room of 33.5 m3 and 0.2 h-1 air exchange rate (AER). For this room, ~40-46% inhaled Pb-containing humidifier particles deposit in children's respiratory tracts; inhaling humidifier particles from ≥500 µg/L Pb water results in >1 µg/dL BLL in 2-7 yr children. For adults, ~23% of particles deposit in the respiratory tract; 8-h inhalation exposure with ≥17 µg/L Pb water exceeds the California EPA reproductive toxicity guideline of 0.5 µg/day. Larger rooms and higher AER decrease Pb inhalation exposure under the same water Pb concentration.

Derivates variation of phenylalanine as a model disinfection by-product precursor during long term chlorination and chloramination.

Dissolved nitrogenous organic matter in water can contain precursors of disinfection by-products (DBPs), especially nitrogenous DBPs (N-DBPs). Amino acids are ubiquitous as dissolved nitrogenous organic matter in source water and can pass through drinking water treatment processes to react with disinfectants in finished water and in the distribution system. Phenylalanine (Phe) was selected as a model amino acid precursor to investigate its derived DBPs and their variations during a chlorination regime that simulated water distribution with residue chlorine. The 7-day DBPs formation potential (DBPsFP) test with chlorine revealed chlorination by-products of phenylalanine including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and halonitromethanes (HNMs), but not trichloronitromethane (TCNM) which was a significant N-DBP detected during the first 48 h of chlorine contact. The formation of most carbonaceous DBPs (C-DBPs) increased with chlorination time; however N-DBPs and non-chlorinated byproducts of phenylacetonitrile and phenylacetaldehyde reached their highest concentration after 2 h of reaction, and then gradually decreased until below detection after 7 days. The chlorination influencing factors indicated that light enhanced the peak yield of DBPs; the pH value showed different influences associated with corresponding DBPs; and the presence of bromide ions (Br-) generated a variety of bromine-containing DBPs. The DBPsFP test with chloramine reduced C-DBPs generation to about 1/3 of the level observed for chlorine disinfection and caused an increase in dichloroacetonitrile. Surveillance of DBPs during drinking water distribution to consumers should consider the varying contact times with disinfectants to accurately profile the types and concentrations of C-DBPs and N-DBPs present in drinking water.

Check-if-apply approach for consumers and utilities to communicate about drinking water aesthetics quality.

Globally, consumers judge their drinking water through its aesthetic qualities because tastes, odors, and appearances are readily detectable by untrained consumers. Consumer feedback is critical to the water industry for efficient resolution of aesthetic water quality issues, although consumer descriptions of taste and odor issues can sometimes be unfocused or confusing. A user-friendly approach can facilitate consumer communications to utilities in the challenging task of describing drinking water taste and odor issues. The purpose of this study was to develop a list of taste and odor descriptors and test a novel "check-if-apply" approach to describe drinking water quality. The final list contained 28 individual and/or groups of descriptors. 75 participants tested water samples impacted by various tastants or odorants: duplicate samples of chloraminated tap water, tap water with heptanal, tap water with 2-methylisoborneol (MIB), tap water with NaCl, bottled water, and bottled water with CuSO4. Participants used a 9-point hedonic scale (1 = 'dislike extremely'; 9 = 'like extremely') to rate overall liking of each sample, and they used the check-if-apply list to describe the taste or odor. Participants also answered a brief questionnaire and used a 5-point scale (1 = 'very difficult'; 5 = 'very easy') to evaluate their experience using the check-if-apply list. Significant differences were observed in acceptability and sensory profile of samples (p-value <0.05). Tap water with MIB had the lowest acceptability mean score (3.43 ± 1.74), while flavorless bottled water had the highest acceptability mean score (6.23 ± 1.47). 'Salty', 'metallic', 'chemical' and 'musty/earthy' were the dominant descriptors for NaCl, CuSO4, heptanal, and MIB, respectively. Most participants (81%) found the check-if-apply list as 'somewhat easy' to 'very easy' to use (mean = 3.44 ± 1.07) and suggested it as a user-friendly lexicon for consumers and utilities to communicate about water quality.

Aqueous degradation of artificial sweeteners saccharin and neotame by metal organic framework material.

The artificial sweeteners (ASs) saccharin (SAC) and neotame (NEO) are widely used across the globe and are considered as emerging contaminants in surface, ground, and drinking waters. To degrade SAC and NEO, the metal organic framework material Co-based bio-MOF-11 was prepared by hydrothermal reaction and used with peroxymonosulfate (PMS) activator. The effects of the initial concentration of SAC and NEO, bio-MOF-11-Co dosage, PMS concentration, initial pH, temperature, and competitive anions were determined. The results revealed that bio-MOF-11-Co effectively catalyzed the degradation of SAC and NEO and possessed good stability and recycling efficiency. The degradation reaction was effective from pH 3.6-9.8 and followed quasi-first-order kinetics with degradation rate constants of 0.001-0.013 min-1 for SAC and 0.03-0.52 min-1 for NEO. Increased temperature was conducive to the degradation of both artificial sweeteners. The presence of Cl- inhibited the degradation of SAC and NEO, while the presence of CO32- promoted their degradation. Electron paramagnetic resonance (EPR) and free radical quenching demonstrated that the primary free radicals were sulfate radicals ( [Formula: see text] ) and hydroxyl radicals (HO). The change of cobalt oxidation state and electron transfer in bio-MOF-11-Co mainly induces the production of [Formula: see text] . A plausible mechanism for degradation is [Formula: see text] and HO attack on CS bonds, NS bonds, and benzene rings.

An overlooked route of inhalation exposure to tap water constituents for children and adults: Aerosolized aqueous minerals from ultrasonic humidifiers.

Fine particulates and aerosols emitted by commonly used, room-sized ultrasonic humidifiers may pose adverse health effects to children and adults. The literature documents adverse effects for children exposed to minerals emitted from humidifiers. This study performs novel and comprehensive characterization of bivariate particle size and element concentrations of emitted airborne aerosols and particles from ultrasonic humidifiers filled with tap water, including size distribution from 0.014 to 10 µm by scanning mobility particle sizer and AeroTrak; corresponding metal and elemental concentrations as a function of particle size by inductively coupled plasma mass spectrometer; and calculations of deposition fraction in human lungs for age-specific groups using the multi-path particle dosimetry model (MPPD). Deposition fraction is the ratio of mass deposited to total mass inhaled. When filled with tap water, water evaporated from emitted aerosols to form submicron particles that became essentially "dried tap water" with median size 146 nm and mean concentration of 211 µg-total elements/m3-air including 35 µg-calcium/m3-air in a room of 33.5 m3 and air exchange rate at ∼0.8 hr-1. Approximately 90% of emitted particles deposited in human lungs were <1 µm as shown by MPPD model. The smaller particles contained little water and higher concentration of minerals, while larger particles of >1 µm consisted of lower elemental concentrations and more water due to low evaporation. Deposition fraction in pulmonary region was ∼2-fold higher, and deposited particulate mass was 3.5-fold higher for children than adults, indicating greater inhalation exposure to children compared to adults. Modeled data of total particles mass per body weight (BW) that will deposit in adult and child lungs after 8-h humidifier exposure were respectively 2.8 µg/kg-BW and 9.8 µg/kg-BW, where calcium contributes 0.4 µg/kg-BW and 1.6 µg/kg-BW. This comprehensive study of bivariate inorganic chemical composition as a function of particle size expanded, quantified, and modeled exposure for children and adults to aerosolized calcium and other inorganic constituents in water.

Human exposure to particles at the air-water interface: Influence of water quality on indoor air quality from use of ultrasonic humidifiers.

Ultrasonic humidifiers provide indoor relief to symptoms caused by dry air and produce aerosols containing both water and minerals that are present in the water that fills the humidifier. This study investigated the spatial distributions, concentrations, and metal and mineral composition of aerosols emitted when an ultrasonic humidifier was filled with deionized water (DI), low mineral tap water (LL), high total dissolved solids (TDS)/high hardness water (HH), and high TDS/low hardness water (HL). Aerosol/particle sizes and counts were obtained at six horizontal distances in both the plume and near floor for each water quality. Results are that water quality significantly affects particle size distributions which become uniform after 0.9 m from the humidifier outlet, and are independent of vertical distance from the humidifier. The mean count median diameters were 64 nm for DI, 129 nm for LL, 234 nm for HH, and 260 nm for HL; the particle counts and total mineral solids concentrations were 2,194 #/cm3 (16 µg/m3) for DI, 21,070 #/cm3 (113 µg/m3) for LL, 38,353 #/cm3 (438 µg/m3) for HH, and 43,880 #/cm3 (521 µg/m3) for HL. The µg/m3 values for LL, HH, and HL exceeded PM2.5 ambient air standards. Model predictions are that the deposition mass in the human respiratory system from inhaling particles emitted from HH and HL water exceed 135 µg for a 1 to 3-month old child and 600 µg for an adult over an 8-hr period. Mineral water quality significantly affects the distribution and concentration of emitted and inhaled indoor air particles. Consumers may unknowingly be degrading their indoor air quality when using tap water of acceptable drinking water quality as humidifier fill water.

Pyrazines: A diverse class of earthy-musty odorants impacting drinking water quality and consumer satisfaction.

The presence of earthy-musty odors in drinking water is a major concern for water suppliers and consumers worldwide. While geosmin and 2-methylisoborneol are the most studied earthy-musty odor-causing compounds, pyrazine and its alkyl and methoxy compounds possess similar odors and are widely distributed in nature, foods, and beverages. In this study, odor characteristics of pyrazines and their presence in natural and treated waters were determined. Pyrazine, 2,6-dimethyl-pyrazine (DMP), 2,3,5-trimethyl-pyrazine (TrMP), 2-ethyl-5(6)-methyl-pyrazine (EMP), 2,3,5,6-tetramethyl-pyrazine (TeMP), 2-isobutyl-3-methoxy-pyrazine (IBMP) and 2-isopropyl-3-methoxy-pyrazine (IPMP) were measured in source and finished drinking water across China. 2-Methoxy-3,5-dimethyl-pyrazine (MDMP), IBMP, and IPMP were investigated in rivers in Virginia, USA. The results showed that "musty" and "sweet" were the most common descriptors for pyrazine, DMP, MDMP, TrMP, and TeMP. While IBMP and IPMP were never detected in 140 source or drinking water samples from across China, pyrazine, DMP, MDMP, TrMP, and TeMP occurred throughout with concentrations of n.d.-62.2 ng/L-aq in source water and n.d.-39.6 ng/L-aq in finished water. IBMP, IPMP, and MDMP were present in two Virginia rivers; MDMP occurred in 18% of the samples with concentrations of n.d.-4.4 ng/L, many of which were above the aqueous odor threshold of 0.043 ng/L MDMP. The removal efficiencies through conventional water treatment were poor, ranging from negative removals to ∼10%. Advanced oxidation water treatment could only remove EMP and TrMP. The widespread presence of earthy-musty-sweet pyrazines in source and drinking waters on two continents, their poor removal during water treatment, and ng/L odor threshold concentrations confirm their potential to be T&O issues for consumers.

A review: The challenge, consensus, and confusion of describing odors and tastes in drinking water.

Documentation exists for many chemicals that cause tastes and odors in water, however, water suppliers do not routinely monitor for these chemicals. Effective management of a taste-and-odor (T&O) problem in drinking water often requires good verbal description of the offending sensory experience. Experience demonstrates that obtaining verbal descriptions is challenging. To improve our understanding of communications, sensory science literature was reviewed to obtain descriptors for twenty-one chemicals acknowledged to cause T&O issues in drinking water. The review focused on pure chemicals above their odor threshold concentrations. Results reveal that descriptors follow four general categories. For select chemicals, strong consensus exists around a single or very few appropriate descriptors. Examples are "salty" for sodium and "chlorinous" for free chlorine. The next category has moderate agreement for several descriptors, with at least one major descriptor. For example the microbiological metabolite 2-methylisoborneol is most commonly described as "earthy/musty/moldy" but also "camphor, grass, and sweet". Some chemicals have weak agreement on their descriptors, but overall associate words with similar meaning. An example is the chemical toluene with descriptors of "solvent-like" words including "solvent", "gasoline", "paint-like", "cleaning fluid", and "etherish", but also "vinegar" and "sweet". The last chemical category possesses diverse descriptors with no consensus. For example, the oxylipin n-heptanal is described as "oily, fatty, chemical, musty/earthy/moldy, rancid, sweaty, grass, sickening, and stale". While descriptor diversity for select chemicals may not identify the cause of T&O, understanding that certain chemicals are perceived very differently aids in effective communications and eliminates confusion from expecting consumers or utility personnel to respond with consensus.

Emission of iron and aluminum oxide particles from ultrasonic humidifiers and potential for inhalation.

Ultrasonic humidifier use is a potential source of human exposure to inhalable particulates. This research evaluated the behavior of insoluble iron oxide and aluminum oxide particles in water used to fill room-sized ultrasonic humidifiers. Solutions of 10 mg/L Fe, as iron oxide particles, or 5 mg/L Al, as aluminum oxide suspension, were added into tap water used to fill ultrasonic humidifiers. The humidifiers were operated for 14 h; samples were obtained over time and monitored for soluble and particulate Fe and Al, as well as particle sizes in the humidifier reservoir and emitted in aerosols. Denser, settleable particles of approximately 1.5 µm diameter of iron or aluminum oxides accumulated at the bottom of the humidifier reservoir. Smaller, suspended metal oxide particles of 0.22-0.57 µm diameter were emitted as aerosols from the humidifier. Soluble anions and cations in tap water were also present in the aerosols emitted from humidifiers. The results indicate that a typical 1.6 MHz ultrasonic humidifier can emit 0.22-0.57 µm particles and dissolved minerals from fill water into breathable air.