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 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.
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•Behavior of Hg released into soil for 30 years of active Hg mining was investigated.•T-Hg vertical distribution was high in surface soil layer, and low in lower layers.•MeHg and EtHg were detected in different proportions to T-Hg at different sites.•T-Hg and MeHg were strongly positively correlated at each sampling site.•The transformation and migration of Hg in soil was considered.
Volcanic activity is one of the primary sources of arsenic in nature, and chemical forms of arsenic discharged by volcanic activity are inorganic. Kagoshima Bay has active submarine volcano located ...in the 200 m deep basin of its northern part. Since dissolved inorganic arsenic is more toxic than organic arsenic it is important to understand the dispersion of discharged arsenic in seawater. To estimate the influence of arsenic emitted from the bottom vents seasonal changes in As(III) and As(V) concentrations in seawater were studied. There are few studies on the impact of arsenic discharged by submarine volcanos in the inner bay. The total concentrations of As(III) and As(V) (T-As) in seawater at the background site in Kagoshima Bay was 1.71 ± 0.35 μg L
−1
(av. ± s.d.), similar to the world average value of 1.7 μg L
−1
. The highest T-As value at the nearest point to the submarine volcano, 3.48 μg L
−1
, was observed in summer. Since the vertical mixing of seawater cannot occur in summer due to the formation of the thermocline, the deep water is strongly affected by volcanic activity. The increase in T-As was caused by the increase in As(III) concentration suggesting the discharge of As(III) from the vents.
Wakamiko Proto-Caldera, a submarine volcano, is located at the bottom of the sea in the bay head area of Kagoshima Bay. In Kagoshima Bay, several species of fish with total mercury exceeding the ...provisional regulation value of 0.40 mg kg−1 were found in the 1970s. The effects of mercury released from submarine volcanoes are suspected. However, the path from volcanic mercury to the broader ecosystem has not yet been clarified. In this study, as the first step to elucidate the impact of volcanic activity on the ecosystems of Kagoshima Bay, seasonal changes in the concentrations of dissolved gaseous mercury (DGM), Hg(II), filtered total mercury (FT-Hg), particulate mercury (P-Hg), and mercury in suspended particulate matter (Hg in SPM) in seawater of Kagoshima Bay were tracked every two months from Feb. 2014 to Dec. 2017. The dissolved total mercury (DT-Hg) concentration was calculated by summing the DGM and FT-Hg concentrations. The DT-Hg at the location in the caldera ranged from 0.09 to 6.83 ng L−1 showing higher values in summer compared to winter, that is, in the stratified period. The P-Hg showed similar periodic variation as DT-Hg, and the highest Hg in SPM was 2.15 mg kg−1, which is one order of magnitude higher than that observed at the reference site. The high mercury concentration in SPM suggests the accumulation of dissolved mercury discharged from volcanic activity on SPM. Since mercury loaded on SPM can be taken up by suspension feeders and enter the food chain, the Hg in SPM may be a key factor affecting Hg in fishes in Kagoshima Bay.
•Submarine volcano is suspected to be the source of mercury in fish in Kagoshima Bay.•Seasonal change in Hg species in seawater of Kagoshima Bay was followed.•Accumulation of dissolved Hg discharged from volcanic activity on SPM was suggested.•The Hg in SPM may be a key factor affecting Hg in fishes of Kagoshima Bay.
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 H3O+ 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.
pH, Gibbs energy, enthalpy, and entropy windows of ethylammonium nitrate (EAN) scaled based on water. Each window opens at a similar location to that of water, which causes ethylammonium nitrate to provide a water‐like reaction field.
Attenuation of trace organic chemicals (TOrCs), including pesticides, by reverse osmosis (RO) membrane treatment is critical for ensuring public health protection in potable water reuse. This study ...aimed to elucidate the mechanisms underlying the poor rejection of small pesticides by polyamide-based RO membranes. Rejection of the selected TOrCs (four N-nitrosamines and 158 pesticides) was primarily governed by size exclusion, charge interactions, and dipolar interactions when evaluated at high water temperatures. Further investigation indicated that small and uncharged secondary amide pesticides showed low and highly variable rejections, compared to similarly sized counterparts with no amide functional groups. Remarkably, three secondary amide pesticides that have no other atoms holding a high partial negative charge showed very low rejections (34–65%), likely due to the cooperativity of hydrogen bonding which occurs between amide functional groups of the pesticides and RO membranes. In contrast, secondary amide pesticides that have an atom holding a high partial negative charge showed higher rejections (72–98%), likely due to the inducted electrostatic repulsion. This study proposed that secondary amide pesticides that have no other atoms holding a high partial negative charge can be poorly rejected. The findings are useful to predict the rejection level of unregulated TOrCs.
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•Mechanisms underlying the poor rejection of small pesticides by RO were examined.•Size exclusion, and charge & dipolar interactions play a role in pesticide rejection.•2° amides holding no high partial negative charge atoms were poorly rejected.•The low rejections were attributed to the cooperativity of hydrogen bonding.
•Hypochlorite cleaning was adopted as a fouling mitigation technique.•Hypochlorite cleaning did not alter the performance of a Cl2-resistant NF membrane.•Membrane permeability was fully restored with ...a 2000ppm NaOCl solution for 1h.•Effective flux recovery was demonstrated with three filtration cycles.
The effectiveness of hypochlorite cleaning for fouling mitigation of a prototype chlorine-resistant nanofiltration (NF) membrane was assessed for direct filtration of a secondary treated effluent. The chlorine resistance and separation performance of the prototype NF membrane were also compared to commercial NF and reverse osmosis membranes. The prototype chlorine resistant NF membrane did not show any changes in permeability and conductivity rejection after exposing a NaOCl solution for up to 5×104ppm-h. By contrast, a considerable deterioration in rejection was observed for the other two commercial membranes. Direct filtration of a secondary treated effluent by the prototype NF membrane resulted in a progressive permeability reduction by up to 25% after 10h of filtration. The membrane permeability was fully restored by hypochlorite cleaning with a 2000ppm NaOCl solution for 1h. Effective permeability recovery by hypochlorite cleaning was demonstrated with multiple hypochlorite cleaning cycles. Membrane fouling and hypochlorite cleaning were also simulated using solutions containing a model foulant (sodium alginate, humic acids or bovine serum albumin). Among them, an insufficient permeability recovery was observed for membrane fouling caused by humic acids. Further research is recommended to develop an improved hypochlorite cleaning protocol to control various membrane fouling.
To quantify the properties of protic ionic liquids (PILs) as acid–base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was ...found between the 14 pKa values of 12 compounds in EAN and in water. In other words, the pKa value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3O+ in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from −1 to 9 on the pH scale based on the pH value in water.
Tipping the pH scale: By using potentiometric acid–base titrations, a pH scale applicable to the protic ionic liquid ethylammonium nitrate (EAN) was determined. This water‐based pH scale can be employed to directly compare the differences in H+ activity between EAN and water. For example, the H+ activity in the neutral EAN corresponds to the aqueous solution with pH=4.
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.
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•Stabilized hypobromite showed more bactericidal effects than monochloramine.•Pre-disinfection by stabilized hypobromite inhibited membrane fouling at pilot scale.•NDMA formation by stabilized hypobromite in two treated wastewaters was negligible.•NDMA FP by the new chemical was 2–5 orders of magnitude lower than chloramine.
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.
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