Methyl nitrate as a byproduct in advanced water treatment systems: Liquid chromatographic determination method and cause of formation.

Neutral low-molecular-weight organics such as methyl nitrate that can readily pass through reverse osmosis (RO) membranes employed in potable water reuse facilities attract interest owing to public health considerations. In this study, a novel determination method based on high-performance liquid chromatography, online photochemical conversion to peroxynitrite, and luminol chemiluminescence detection was developed for methyl nitrate measurement in treated water. The maximum photochemical conversion efficiency of methyl nitrate to peroxynitrite was found to be 6.5% using a 222-nm excimer lamp. The calibration curve for the developed method was linear between 1.0 × 10-9 and 1.0 × 10-7 M, and the limit of detection was 0.3 nM (0.03 µg/L) given an injection volume of 200 µL. The methyl nitrate concentrations in RO permeate from reclaimed wastewater and product water after subsequent treatment by a UV/H2O2 advanced oxidation process (AOP) were 2.2 and 22.5 nM (0.17 and 1.7 µg/L), respectively. UV irradiation of RO permeate in the laboratory using a low-pressure Hg lamp confirmed the formation of methyl nitrate in the permeate in the absence of H2O2 and residual chloramines. This chemiluminescent detection method for methyl nitrate will promote a greater understanding of the origin and formation of this treatment byproduct in reclaimed wastewater.

Impact of mercury discharged from submarine volcano on inner bay ecosystems.

Organic mercury, inorganic mercury and total mercury concentrations in phytoplankton (<0.1 mm) and zooplankton (>0.1 mm) collected in Kagoshima Bay, Japan were measured from 2017 to 2019 to estimate the impact of mercury discharged from submarine volcanoes on ecosystems; submarine volcanic activity continues at a depth of 200 m in the inner part of Kagoshima Bay. The total mercury concentrations in phyto- and zooplankton collected by vertical hauling at 0-200 m at just above the submarine volcano were in the range of 0.11-2.0 mg kg-1 (avg. 0.67 mg kg-1) and 0.090-0.56 mg kg-1 (avg. 0.21 mg kg-1), respectively. These values were one order of magnitude higher than the values in plankton collected in the central part of Kagoshima Bay. Organic mercury concentrations in phyto- and zooplankton were <0.010-0.071 mg kg-1 (avg. 0.028 mg kg-1) and 0.012-0.25 mg kg-1 (avg. 0.10 mg kg-1), respectively, for the inner part, and <0.010-0.040 mg kg-1 (avg. 0.010 mg kg-1) and <0.010-0.025 mg kg-1 (avg. 0.012 mg kg-1), respectively, for the central part. The values obtained in the inner part of the bay increased in summer and decreased in winter, which was consistent with changes in seawater mercury concentrations affected by volcanic activity. The organic mercury concentration in zooplankton collected just above the submarine volcano showed a size dependency, and a higher value was observed in the larger size, which suggested that the discharged mercury from the volcano was absorbed and concentrated through the ecosystem.

The distribution and dynamics of residual mercury from the Chisso chemical plant in sediments of the Yatsushiro Sea, western Kyushu, Japan: have recent sedimentations lowered surface mercury concentrations?

To determine the long-term dynamics of mercury discharged from Chisso chemical plant between 1932 and 1968, the vertical variation in mercury concentrations in Yatsushiro Sea sediments was studied from 2013 to 2020 at 31 locations and compared to the mercury concentration distribution obtained in 1996. The results suggest that new sedimentation occurred after 1996, but the mercury concentrations at the surface ranged from 0.2 to 1.9 mg kg-1, which did not decrease significantly over a 20-year period. It was estimated that approximately 17 t of mercury remained in the southern Yatsushiro Sea sediment, which is equivalent to 10-20% of the total mercury discharged between 1932 and 1968. From results of WD-XRF and TOC measurement, it was suggested that mercury in sediment had been transported with suspended particles derived from sludges from the chemical plant and further suggests that the suspended particles derived from the sediment surface layer are still slowly diffusing.

Sensitive Detection of Nitrite and Nitrate in Seawater by 222 nm UV-Irradiated Photochemical Conversion to Peroxynitrite and Ion Chromatography-Luminol Chemiluminescence System.

Sensitive detection methods for nitrite (NO2-) and nitrate (NO3-) ions are essential to understand the nitrogen cycle and for environmental protection and public health. Herein, we report a detection method that combines ion-chromatographic separation of NO2- and NO3-, on-line photochemical conversion of these ions to peroxynitrite (ONOO-) by irradiation with a 222 nm excimer lamp, and chemiluminescence from the reaction between luminol and ONOO-. The detection limits for NO2- and NO3- were 0.01 and 0.03 µM, respectively, with linear ranges of 0.010-2.0 and 0.10-3.0 µM, respectively, at an injection volume of 1 µL. The results obtained by the proposed method for seawater analysis corresponded with those of a reference method (AutoAnalyzer based on the Griess reaction). As luminol chemiluminescence can measure ONOO- at picomolar concentrations, our method is expected to be able to detect NO2- and NO3- at picomolar concentrations owing to the high conversion ratio to ONOO- (>60%), assuming that contamination and background chemiluminescence issues can be resolved. This method has the potential to emerge as an innovative technology for NO2- and NO3- detection in various samples.

The dynamics of mercury around an artisanal and small-scale gold mining area, Camarines Norte, Philippines.

To elucidate the dynamics of mercury emitted and released by artisanal and small-scale gold mining (ASGM) activity and to estimate its impact on the ecosystems of the bay, the distribution of mercury in the atmosphere, soil, water, and sediment around Mambulao Bay, Camarines Norte, Philippines, was investigated. The ASGM operations use mercury to extract gold from ore and are located on the east shore side of the bay. Samplings were conducted in August 2017 and September 2018. The samples were used for determination of total mercury (T-Hg) and organic mercury (org-Hg) concentrations, total organic carbon (TOC) content, and chemical composition. The atmospheric mercury concentration on the east shore side, 6.1-25.8 ng m-3, was significantly higher than the value of 1.4-9.9 ng m-3 observed on the west shore side. The average concentrations of T-Hg in the forest soils of the west shore side and those of the east shore side were 0.081 ± 0.028 mg kg-1 and 0.496 ± 0.439 mg kg-1, respectively. In the vertical distribution of T-Hg in the soil of the east shore side, a higher concentration was observed near the surface. For the vertical variations in T-Hg in the marine sediment, higher values were observed near the estuary, and the vertical variations in core samples showed an increase in mercury concentration toward the surface. The highest concentration of T-Hg in sediment, 9.5 mg kg-1, which was 2 orders of magnitude higher than the background levels of this area, was found near the river mouth. The T-Hg, org-Hg, and TOC levels showed a positive correlation, suggesting that the rivers are the main sources of T-Hg and org-Hg in the bay. Although the fish sample containing a mercury content higher than the regulatory level for fish and shellfish of 0.4 mg kg-1 in Japan was only one of 42 samples, the percentage of org-Hg in fish samples was 91 ± 18%. Mercury released into the surroundings by the ASGM activities can be converted into methylmercury and affect the bay's ecosystem.

Distribution, alkylation, and migration of mercury in soil discharged from the Itomuka mercury mine.

The purpose of this study was to investigate the behavior of previously discharged mercury (Hg) released from the Itomuka Hg mine into the surrounding environment, especially into soil. Total-Hg (T-Hg), methylmercury (MeHg), and ethylmercury (EtHg) concentrations in the surface soil at eight sample sites around the mine were 3.8-64.2 mg/kg, 6.0-54.7 µg/kg, and undetected to 4.5 µg/kg, respectively. Core samples collected from seven of the eight sample sites showed that the vertical distribution of T-Hg was the highest in the surface soil layer and decreased rapidly in the lower layers. A strong positive correlation was observed between T-Hg and MeHg concentrations in the core samples; however, the slope of the regression line varied considerably for each core. This suggests that Hg and MeHg were not supplied from the atmosphere simultaneously, but rather that MeHg was produced on-site. Further, the formation of MeHg and EtHg in soil was considered in terms of the total organic carbon/total nitrogen ratio, which is a decomposition index of soil organic matter. The strong positive correlation between T-Hg and MeHg can be attributed to the migration of organic matter containing Hg species to the lower layers. There was no relationship between T-Hg and MeHg at the riverbed sample site because of the high T-Hg in the lower soil layers, suggesting that Hg was supplied by ore at this sample site. These assumptions of the formation change and migration of Hg in soil were supported by the results of the fractionation experiment and the elution test. To understand the current conditions in this area, measurements of Hg in the water, sediment, atmosphere, and plants were also conducted.

Membrane distillation for achieving high water recovery for potable water reuse.

Achieving high water recovery using reverse osmosis membranes is challenging during water recycling because the increased concentrations of organics and inorganics in wastewater can cause rapid membrane fouling, necessitating frequent cleaning using chemical agents. This study evaluated the potential of membrane distillation to purify reverse osmosis-concentrated wastewater and achieve 98% overall water recovery for potable water reuse. The results indicate that membrane fouling during membrane distillation treatment was low (4% reduction in permeability) until 98% water recovery. In contrast, membrane fouling during reverse osmosis treatments was high (73% reduction in permeability) before reaching 90% water recovery. Furthermore, membrane distillation showed superior performance in removing dissolved ions (99.9%) from wastewater as compared with reverse osmosis (98.9%). However, although membrane distillation removed most trace organic chemicals tested in this study, a negligible rejection (11%) was observed for N-nitrosodimethylamine, a disinfection byproduct regulated in potable water reuse. In contrast, RO treatment exhibited a high removal of N-nitrosodimethylamine (70%). Post-treatment (e.g., advanced oxidation) after reverse osmosis and membrane distillation may be needed to comply with the N-nitrosodimethylamine regulations. Overall, the membrane distillation process had the capacity to purify reverse osmosis concentrate with insignificant membrane fouling.

Potential of UV-B and UV-C irradiation in disinfecting microorganisms and removing N-nitrosodimethylamine and 1,4-dioxane for potable water reuse: A review.

The ultraviolet (UV)-based advanced oxidation process (AOP) is a powerful technology for removing pathogenic microorganisms and contaminants of emerging concern (CECs) from water. AOP in potable water reuse has been predominantly based on traditional low-pressure mercury (LP-Hg) lamps at 254 nm wavelength, supplemented by hydrogen peroxide addition. In this review, we assessed the potential of unconventional UV wavelengths (UV-B, 280-315 nm and UV-C, 100-280 nm) compared to conventional one (254 nm) in achieving the attenuation of pathogens and CECs. At the same UV doses, conventional 254 nm LP-Hg lamps and other sources such as, 222 nm KrCl lamps and 265 nm UV-LEDs, showed similar disinfection capability for viruses, protozoa, and bacteria, and the effect of hydrogen peroxide (H2O2) addition on disinfection remained unclear. The attenuation levels of key CECs in potable water reuse (N-nitrosodimethylamine and 1,4-dioxane) by 185 + 254 nm LP-Hg or 222 nm KrCl lamps were generally greater than those by conventional 254 nm LP-Hg and other UV lamps. CEC degradation was generally enhanced by H2O2 addition. Overall, our review suggests that 222 nm KrCl or 185 + 254 nm LP-Hg lamps with the addition of H2O2 would be the best alternative to conventional 254 nm LP-Hg lamps for achieving target removal levels of both pathogens and CECs in potable water reuse.

Degradation of N-nitrosamines and 1,4-dioxane using vacuum ultraviolet irradiation (UV254+185 nm or UV172 nm).

Advanced oxidation processes (AOPs) play a vital role in attenuating contaminants of emerging concern (CECs) during potable water reuse. AOPs are conventionally performed by irradiating with a 254-nm low-pressure (LP) mercury-vapor (Hg) ultraviolet (UV) lamp along with chemical treatment. Compared with UV-C light treatment (200-280 nm), vacuum-UV (V-UV) light treatment (100-200 nm) is advantageous in terms of hydroxyl radical generation without the requirement for chemical treatment. This study assessed the potential of V-UV (172-nm Xe2 excimer or 185 + 254-nm LP-Hg) lamps on the destruction of two major CECs in potable water reuse, namely N-nitrosodimethylamine (NDMA) and 1,4-dioxane. Direct irradiation using UV254 nm or UV185+254 nm lamps achieved ≥94% removal of N-nitrosamines, including NDMA, at a UV dose of 900 mJ/cm2. In contrast, the Xe2 excimer lamp (UV172 nm) was less effective for N-nitrosamine removal, achieving up to 82% removal of NDMA. The removal of 1,4-dioxane by V-UV lamps at a UV dose of 900 mJ/cm2 reached 51% (UV172 nm) and 28% (UV185+254 nm), both of which results were superior to that obtained using a conventional UV254 nm lamp (10%). The addition of hydrogen peroxide during UV254 nm or UV185+254 nm irradiation was found to enhance the removal of 1,4-dioxane, while UV172 nm irradiation without hydrogen peroxide addition still exhibited greater efficiencies than those UV254 nm lamps-based AOPs. Overall, this study demonstrated that the removal of both NDMA and 1,4-dioxane can be successfully achieved using either a UV254+185 nm lamp with hydrogen peroxide or a UV172 nm Xe2 excimer lamp without hydrogen peroxide.

NDMA and NDMA precursor attenuation in environmental buffers prior to groundwater recharge for potable reuse.

Natural attenuation of N-nitrosodimethylamine (NDMA) and NDMA precursors was evaluated in infiltration basins, a riverbed filtration system, and constructed wetlands operated as part of a managed aquifer recharge system. Initial NDMA concentrations up to 9.0 ng/L in infiltration basins (advanced purified, recycled water) before sunrise declined to non-detect (<1.5 ng/L) by 10:00 A.M due to natural photolysis (half-life of 33 to 86 min dependent on solar irradiance). NDMA fortified controls adjacent to the infiltration basin showed similar results, while concentrations in dark controls did not change over the basin's hydraulic retention time. NDMA precursor concentrations did not change significantly in the basin containing advanced-treated water from a potable reuse treatment plant, indicating that photolysis did not remove NDMA precursors nor did photolysis produce a significant amount of precursors. For the other environmental buffers evaluated, NDMA removal was variable through laboratory scale soil columns (22 cm height), in full-scale riverbed filtration system that pre-filters water prior to infiltration basin recharge, and in the constructed wetland. Variability in NDMA removal through the wetlands is attributed to high turbidity. In the case of the riverbed filtration system, variability is likely due to short exposure times to sunlight. For the soil columns, limited NDMA removal is attributed to inefficacy of soil aquifer treatment in removing NDMA over short travel times/distances. NDMA precursors were also ineffectively removed in these systems, with effluent concentrations occasionally exceeding influent concentrations. Overall, the removal of NDMA in environmental buffers utilized for planned or de facto indirect potable reuse is dependent on the system's capacity for photolysis, while NDMA precursors are more recalcitrant and unlikely to be removed in such systems without enhancement or sufficient hydraulic residence times.

Contamination, Decomposition, and Formation of N-Nitrosodimethylamine in Water Samples at the ng/L Level of Determination.

An ultra-sensitive analytical system that can determine the concentration of N-nitrosamines at the ng/L level without preconcentration was used to investigate the contamination, decomposition, and formation of N-nitrosodimethylamine (NDMA) and other N-nitrosamines in water samples during general analytical procedures. A preliminary experiment was performed to estimate the NDMA concentrations in ambient air. Since the air samples contained NDMA at concentrations in the range of 2.0 - 10.7 ng/m3, ambient air was identified as the source of NDMA contamination in water samples. We directly confirmed that the concentration of aqueous 10-ng/L NDMA samples stored in clear glass bottles decreased upon exposure to sunlight. Thus, to maintain the N-nitrosamine concentration, such samples must always be protected from sunlight during sampling. The existence of N-nitrosamines in experimental reagents, such as ranitidine and sodium hypochlorite solutions, was also confirmed, as was the formation of NDMA on an activated carbon solid-phase extraction cartridge.

Development of Human Hair Reference Material Supporting the Biomonitoring of Methylmercury.

A certified reference material, NIMD-01, was developed for the analysis of mercury speciation in human hair. We collected the hair of Vietnamese males from a barbershop in Hanoi in 2016 and prepared 1200 bottles containing 3 g of sieved and blended hair powder. The certified value was given on a dry-mass basis, with the moisture content obtained by drying at 85°C for 4 h. Certified values with the expanded uncertainties (coverage factor, k = 2) were as follows: methylmercury, 0.634 ± 0.071 mg kg-1 as mercury; total mercury, 0.794 ± 0.050 mg kg-1; copper, 12.8 ± 1.4 mg kg-1; zinc, 234 ± 29 mg kg-1; selenium, 1.52 ± 0.29 mg kg-1. An indicative arsenic concentration of 0.17 ± 0.03 mg kg-1 was measured. Extended uncertainties were estimated by sample homogeneity, long- and short-term stabilities, and a characterization from measurements made by collaborating laboratories.

Detailed investigation of methylmercury accumulation in rice grain from Hg2+-spiked non-contaminated paddy field soils.

Total-Hg (T-Hg) and methylmercury (MeHg) concentrations in rice grains were measured to understand the MeHg accumulation process. Rice plants were cultivated in Hg2+-spiked non-contaminated soils in experimental pots at three different places. Although soil MeHg concentrations in the pots changed significantly and individually during the rice-growing season, T-Hg concentration of brown rice grain was high at high soil MeHg concentration. In addition, there was no significant variation in T-Hg concentration in brown rice grains from individual panicles or among panicles obtained from the same pot, although the period of growth for each panicle was different. The highest T-Hg concentration of brown rice grains recorded for a panicle was 1.4 ± 0.1 mg kg-1 (n = 8), and the corresponding MeHg ratio was 76%. In addition, the T-Hg and MeHg concentrations in various parts of the brown rice grain-white rice (endosperm), bran, and embryo-were measured. Among the parts of the brown rice grain, the embryo had the highest Hg concentration. Furthermore, Hg concentration in the grain was constant during grain filling. These findings suggest that MeHg formed in soil accumulates in the rice plant during growth and is supplied to the rice grains continuously for the entire duration of the grain development period.

Mercury speciation in preserved historical sludge: Potential risk from sludge contained within reclaimed land of Minamata Bay, Japan.

In the latter half of the 1950s, a large amount of methylmercury (MeHg) was discharged directly into Minamata Bay, Japan by a chemical factory, resulting in the contamination of the fish and shellfish. Ultimately, an outbreak of MeHg intoxication, called Minamata disease, occurred. From 1977 to 1988, the Kumamoto Prefectural Government dredged and transferred sediments exceeding 25 µg/g of total mercury (THg, dry basis) into a strictly segregated area of the bay near the wastewater outlet, then this area was landfilled. We conducted analyses of the mercury speciation in preserved Minamata Bay sludge samples (collected from inside of the bay prior to the termination of the remediation project; n=4) and recent Minamata Bay sediments (collected outside the dredging area of the bay; n=5) to evaluate the potential risk of the sludge/sediment leakage from the reclaimed land to the Minamata Bay. Median THg (dry basis) concentrations were 241 µg/g for the preserved sludge, 6.1 µg/g for the recent Minamata Bay sediments, and 0.18 µg/g for a single control sample; median MeHg concentrations (percentage of MeHg in THg) were 108 ng/g (0.031%), 3.7 ng/g (0.12%), and 0.71 ng/g (0.41%), respectively. In all the samples, the MeHg% decreased exponentially with increasing THg concentration. The extractability of THg from each sample into seawater was shown to be much lower than that of MeHg. The extracted MeHg was 0.86% for the preserved sludge, 4.57% for the recent Minamata Bay sediments, and 7.89% for the control. The predominant chemical form of mercury in the preserved sludge containing the highest THg concentration was found to be stable ß-mercury sulfide (HgS) based on transmission electron microscopy linked with energy-dispersive X-ray spectroscopy (TEM-EDX) and X-ray absorption fine structure (XAFS) analyses.

Application of stabilized hypobromite for controlling membrane fouling and N-nitrosodimethylamine formation.

Chloramination is a conventional and successful pre-disinfection approach to control biological fouling for reverse osmosis (RO) treatment in water reuse. This study aimed to evaluate the possibility of using a new disinfectant-stabilized hypobromite-in controlling membrane fouling and the formation of a particular carcinogenic disinfection byproduct (DBP)-N-nitrosodimethylamine (NDMA). Our accelerated chemical exposure tests showed that the new disinfectant reduced the permeability of a polyamide RO membrane permeability from 6.7 to 4.1 L/m2hbar; however, its treatment impact was equivalent to that of chloramine. The disinfection efficacy of stabilized hypobromite was greater than that of chloramine when evaluated with intact bacterial counts, which suggests its potential for mitigating membrane biofouling. Additional pilot-scale tests using synthetic wastewater demonstrated that pre-disinfection with the use of stabilized hypobromite inhibits membrane fouling. Among 13 halogenated DBPs evaluated, the formation of bromoform by stabilized hypobromite was higher than that by chloramine at a high dose of 10 mg/L, thus suggesting the need for optimizing chemical doses for achieving sufficient biofouling mitigation. NDMA formation upon stabilized hypobromite treatment in two different types of actual treated wastewaters was found to be negligible and considerably lower than that by chloramine treatment. In addition, NDMA formation potential by stabilized hypobromite was 2-5 orders of magnitude lower than that by chloramine. Our findings suggest the potential of using stabilized hypobromite for controlling NDMA formation and biofouling, which are the keys to successful potable water reuse.

Proton Thermodynamics in a Protic Ionic Liquid, Ethylammonium Nitrate.

In order to investigate the proton solvation state in protic ionic liquids (PILs), ten acid dissociation enthalpies and entropies of eight compounds were determined in ethylammonium nitrate (EAN). Regardless of the nature of the compound, 24 kJ mol-1 larger enthalpy and 65 J mol-1 K-1 larger entropy than those in water, respectively, were observed. These values were reasonably explained by the differences in the proton solvation structure in EAN and water. Namely, protons in EAN exist as HNO3 , having a higher reaction energy than that of H3 O+ in water, undergo entropic stabilization as a result of the less-structured solvation. As such, the entropic effect of the proton solvation structure on the acid-base property is possibly applicable to all PILs. In addition, based on these proton thermodynamics, enthalpy and entropy windows were proposed as a novel perspective for the characterization of solvents. Use of this concept enabled the visualization of similarities and differences between EAN and water.

A surrogate-based approach for trace organic chemical removal by a high-rejection reverse osmosis membrane.

Public confidence in the safety of recycled water for potable water reuse can be improved by providing assurance regarding high removal of trace organic chemicals (TOrCs) by reverse osmosis (RO) treatment. This pilot-scale study assessed the effectiveness of a surrogate indicator-N-Nitrosodimethlyamine (NDMA)-for ensuring a high level of TOrC removal by a high-rejection RO membrane. The pilot-scale tests showed that the rejection of 23 TOrCs by the high-rejection RO membrane was consistently greater than NDMA rejection. In addition, NDMA rejection was highly correlated with TOrC rejection across varied operating conditions, indicating that NDMA can be used as a conservative surrogate indicator for TOrC removal. The RO treatment at a permeate flux of 20 L/m2 h and feed temperature of 13-27 °C resulted in as high as 75-87% NDMA rejection, which was considerably greater than a conventional low-pressure RO membrane (26-47%). However, the high-rejection RO membrane required a transmembrane pressure that was greater than that of the low-pressure RO membrane. Despite this disadvantage, this study suggests that the high-rejection RO membrane can effectively ensure a high level of TOrC removal (≥65%) when NDMA is used as a surrogate indicator, which cannot be ensured by assessing conventional conductivity rejection.

Transport of mercury species by river from artisanal and small-scale gold mining in West Java, Indonesia.

To estimate the impact of mercury discharged from artisanal and small-scale gold mining (ASGM) activity, variations in the concentrations of elemental mercury (Hg0), mercury ion (Hg2+), particulate mercury (P-Hg), and total mercury in filtered river water (FT-Hg) were investigated from sampling locations extending from 10 km upstream to 30 km downstream of ASGM operations in West Java, Indonesia. The average of the annual concentrations at the ASGM site from 2013 to 2017 were 0.14-0.85 µg L-1, 0.27-12.9 µg L-1, 4.3-49.5 µg L-1, and 1.2-12.5 µg L-1 for Hg0, Hg2+, P-Hg, and FT-Hg, respectively. The concentration of mercury species decreased as the distance from the ASGM site increased, while the ratio of P-Hg increased towards the lower reaches of the river system, with the percentage of P-Hg estimated at 90% of Hg at the sample location furthest downstream. A high mercury concentration of 600 mg kg-1 was observed for suspended particulate matter (SPM) at the ASGM site. The SPM maintained a high concentration of mercury, even in the downstream area. In the annual variations of the mercury species from 2013 to 2017, FT-Hg and P-Hg concentrations tended to decrease from 2016, which suggested a decline of ASGM activity in this area. However, SPM and river sediment showed no apparent changes in their mercury concentrations over this period, indicating that the contamination in the river system is persistent and does not recover quickly.

Validation of pH Standards and Estimation of the Activity Coefficients of Hydrogen and Chloride Ions in an Ionic Liquid, Ethylammonium Nitrate.

We selected and validated the pH values of three standard materials that function in the protic ionic liquid, ethylammonium nitrate (EAN). The pH values of 0.05 mol kg-1 phthalate, oxalate, and phosphate buffers were 4.93 (0.04), 2.12 (0.04), and 7.13 (0.06), respectively (the values in the parentheses denote the standard deviation). Because the pH of EAN ranges from 0 to 10, with a neutral pH of 5, these materials are usable as acidic, basic, or neutral standards. The standard electrode potential of silver-silver chloride in EAN was 127.2 (1.7) mV. The activity coefficients of hydrogen and chloride ions remain equal to unity in EAN of a wide concentration range, which indicates that the effective ionic strength is independent of the solute ion concentration. In addition, the estimated value of the transfer activity coefficient of chloride ion suggests a weaker solvation in EAN compared with water in spite of a ubiquitous cation (C2H5NH3+). These behaviors of ions in EAN can be explained by the unique solvation in the ionic liquid through direct ion-ion electrostatic interactions.

An inline ion-exchange system in a chemiluminescence-based analyzer for direct analysis of N-nitrosamines in treated wastewater.

A newly developed, ion exchange-based inline pretreatment system was used to mitigate the effect of background constituents in natural water and treated wastewater to achieve rapid, reliable, and sensitive analysis of N-nitrosamines. The pretreatment system (anion exchange module, AEM) was incorporated into a high-performance liquid chromatograph (HPLC) coupled with a photochemical reactor (PR) and chemiluminescence (CL) detector (HPLC-PR-CL), which can analyze four hydrophilic N-nitrosamines at ng/L levels. This system requires no pre-concentration of the water sample nor the use of deuterated surrogates, unlike other conventional N-nitrosamine analytical techniques. The AEM converted anions in the eluent to hydroxide ions after HPLC separation and increased eluent pH, allowing for the subsequent photochemical reactions, which are otherwise achieved by pH conditioning with an additional dosing pump of basic chemical. The AEM also removed anionic interfering compounds (e.g. nitrate) from the samples, allowing for improved N-nitrosamine analysis in treated wastewater. The operating conditions of the AEM and PR were optimized to obtain sensitive and stable analytical performance. As a result, the lowest-concentration minimum reporting levels of N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N- nitrosopyrrolidine using the optimized system were 0.42, 0.54, 0.58, and 1.4 ng/L, respectively. The improved analytical method was validated by comparing the results with a conventional method based on gas chromatography coupled with a mass spectrometric ion trap detector. These results indicated that HPLC-PR-CL equipped with an inline AEM can be competitively applied as a rapid analytical technique for the determination of N-nitrosamines in various water matrices.