Understanding N-nitrosodimethylamine Formation in Water: Chloramine Chemistry, Kinetics, and A Proposed Reaction Pathway

The formation of N-nitrosodimethylamine (NDMA) in drinking water systems is a concern because of its potential carcinogenicity and occurrence at toxicologically relevant levels. The postulated mechanism for NDMA formation involves a substitution between dichloramine and amine-based precursors to form an unsymmetrical dimethylhydrazine (UDMH), which is then oxidized by ground-state molecular oxygen to form NDMA. However, this latter reaction is spin forbidden, thus likely occurs at a slow rate. It is hypothesized that the reaction between monochloramine and hydroxylamine (a nitrification product) may form an intermediate, which is involved in the NDMA formation pathway. This intermediate may also be generated from dichloramine decay, in the absence of hydroxylamine. In this study, a series of batch kinetic experiments were conducted to investigate the decomposition of chloramine species at pH 8.0 to 10.0 and the concomitant formation of NDMA. Chloramine species were quantified using UV/Vis spectroscopy (Direct UV) and colorimetric methods (Hach) and compared to simulations from the unified chloramine model. NDMA was quantified using GC-MS following liquid-liquid extraction. The model captured the decay of monochloramine and dichloramine adequately, with the exception of monochloramine at pH 10.0, possibly due to an interference from a previously reported unidentified chloramine decomposition compound (UC1). NDMA formation was pH dependent with the maximum yields at pH 9.0 and the fastest kinetics at pH 10.0. A second unidentified compound (UC2), with a mass spectrum identified as UDMH, was detected only at pH 9.0 and 10.0 in batch reactors with DMA and dichloramine. Importantly, NDMA formation appeared to be insensitive to the presence or absence of UC2, suggesting UC2 was not involved in NDMA formation. Hydroxylamine accelerates the decomposition of monochloramine. The reaction between DMA and hydroxylamine formed a third unidentified compound (UC3), preliminarily identified as acetoxime, which was not observed in the presence of monochloramine. Upon addition of hydroxylamine, NDMA yields decreased by more than half in batch reactors with DMA and monochloramine. On balance, the findings suggest the existence of a NDMA formation pathway that may not involve UDMH, and points to the need for studies with scavengers and donors of short-lived species from chloramine decay

Vietnam's Trade Policy Dilemmas

Vietnam faces alternative options in opening its economy to trade. It is about to join the World Trade Organization; as a member of the ASEAN Free Trade Area it is contemplating extending the regional trade area to include China, Korea and Japan; and it has recently concluded a bilateral agreement with the United States. Opening up to trade is a two-edged sword, with the beneficial effects of improved market access and resource allocation liable to be partially or totally offset by adverse terms of trade effects and significant, albeit one-off, cost of structural adjustment. Simulations of unilateral, bilateral, regional and multilateral liberalization reform and a tariff harmonization scenario are undertaken using a general equilibrium model, GTAP. Results indicate that significant welfare benefits could be obtained from unilateral liberalization without the need to negotiate with others. Harmonization of tariffs at the current average also shows to be beneficial in raising tariff revenues with little need for adjustment. The extension of AFTA brings moderate benefits, as does a multilateral reform which reduces applied tariffs by 50 per cent. There are only limited gains in the agricultural and resources sectors, as these major exports face low tariff barriers. However, the market for Vietnam's textiles and apparel is crucially important.Vietnam, trade, WTO negotiations

Changes of benthic macroinvertebrates in Thi Vai River and Cai Mep Estuaries under polluted conditions with industrial wastewater

The pollution on the Thi Vai River has been spreading out rapidly over the two lasted decades caused by the wastewater from the industrial parks in the left bank of Thi Vai River and Cai Mep Estuaries. The evaluation of the benthic macroinvertebrate changes was very necessary to identify the consequences of the industrial wastewater on water quality and aquatic ecosystem of Thi Vai River and Cai Mep Estuaries. In this study, the variables of benthic macroinvertebrates and water quality were investigated in Thi Vai River and Cai Mep Estuaries, Southern Vietnam. The monitoring data of benthic macroinvertebrates and water quality parameters covered the period from 1989 to 2015 at 6 sampling sites in Thi Vai River and Cai Mep Estuaries. The basic water quality parameters were also tested including pH, dissolved oxygen (DO), total nitrogen, and total phosphorus. The biodiversity indices of benthic macroinvertebrates were applied for water quality assessment. The results showed that pH ranged from 6.4 – 7.6 during the monitoring. The DO concentrations were in between 0.20 – 6.70 mg/L. The concentrations of total nitrogen and total phosphorous ranged from 0.03 – 5.70 mg/L 0.024 – 1.380 mg/L respectively. Macroinvertebrate community in the study area consisted of 36 species of polychaeta, gastropoda, bivalvia, and crustacea, of which, species of polychaeta were dominant in species number. The benthic macroinvertebartes density ranged from 0 – 2.746 individuals/m2 with the main dominant species of Neanthes caudata, Prionospio malmgreni, Paraprionospio pinnata, Trichochaeta carica, Maldane sarsi, Capitella capitata, Terebellides stroemi, Euditylia polymorpha, Grandidierella lignorum, Apseudes vietnamensis. The biodiversity index values during the monitoring characterized for aquatic environmental conditions of mesotrophic to polytrophic. Besides, species richness positively correlated with DO, total nitrogen, and total phosphorus. The results confirmed the advantage of using benthic macroinvertebrates and their indices for water quality assessment

Formation of Reactive Nitrogen Species During Dichloramine Decay and Their Impact on N Nitrosodimethylamine Formation Under Drinking Water Conditions

NDMA occurrence and formation pathways in drinking water systems are reviewed and NDMA yields are compared on the basis of disinfectant type, water chemistry, and precursor category. In chloramination, despite monochloramine being the predominant species between pH 7-9, evidence suggests that dichloramine is the primary species involved in NDMA formation. This is somewhat confounding as NDMA yields are maximal at pH 9, yet at pH 9 dichloramine decays faster than it forms and hence is present at trace levels; additionally, the proposed mechanism involves a spin-forbidden incorporation of dissolved oxygen as a triplet, which is presumably kinetically slow. This review reveals that kinetic data for NDMA formation is lacking, and its influence on chloramine chemistry has not been carefully considered. In pH 7-10 waters amended with 10 μM total dimethylamine and 800 μeq Cl2.L–1 dichloramine (NHCl2), NDMA, nitrous oxide (N2O), dissolved oxygen (DO), NHCl2, and monochloramine (NH2Cl) were kinetically quantified. NHCl2, N2O, and DO profiles indicated reactive nitrogen species (RNS) formed during NHCl2 decomposition, including nitroxyl/nitroxyl anion (HNO/NO−) and peroxynitrous acid/peroxynitrite anion (ONOOH/ONOO–). Experiments with uric acid (an ONOOH/ONOO– scavenger) implicated ONOOH/ONOO– as a central node for NDMA formation, which was further supported by concomitant N-nitrodimethylamine formation. A kinetic model accurately simulated NHCl2, NH2Cl, NDMA, and DO concentrations and included (1) the unified model of chloramine chemistry revised with HNO as a direct product of NHCl2 hydrolysis, (2) HNO/NO− then reacting with (i) HNO to form N2O, (ii) DO to form ONOOH/ONOO–, or (iii) NHCl2 or NH2Cl to form nitrogen gas, and (3) NDMA formation via ONOOH/ONOO– or their decomposition products reacting with (i) dimethylamine (DMA) and/or (ii) chlorinated unsymmetrical dimethylhydrazine (UDMH-Cl), the product of NHCl2 and DMA. The role of DO was further examined at pH 9 by assessing kinetic profiles of NHCl2 and NDMA under ambient DO (~280 μM) and low-DO (\u3c 20 μM) conditions in the presence and absence of 10 μM TOTDMA. Uric acid completely shut down NDMA formation under the low-DO condition, validating ONOOH/ONOO− as the central node in NDMA formation. Yield experiments with initial NHCl2 of 200-, 400-, and 800 μeq Cl2.L–1 tracked the formation of NH3/NH4+, NH2Cl, N2O, N2, NO2−, and NO3−. NH3/NH4+ yields were 20–40% greater under the low-DO condition, implying a reaction occurred between NH3/NH4+ and ONOOH/ONOO− or its decomposition products. NH2Cl yields were 16–20% lower under the low-DO condition, revealing a previously unknown NH2Cl formation reaction. Under ambient DO conditions, about 80% of the nitrogen was accounted for compared to the low-DO conditions in which nitrogen recoveries were 90- and 100% in the absence and presence of 10 μM TOTDMA, respectively. An existing mechanistic model accurately predicted NH3/NH4+, NH2Cl, and N2 under ambient conditions but underpredicted N2O and overpredicted NO2− and NO3−. The results provide a framework to guide future experiments with ONOOH/ONOO− generators and revise the mechanistic model to better capture the nitrogenous end-products

Climate Change through the Studies of Volcano Rocks and Blue Icebergs

The investigation, by advanced physical methods, allows us to identify the chemical composition of volcano stones propelled from the deepness of the globe in various countries on the world and the blue icebergs detached from secular glaciers of Antarctic and Arctic poles. The stones and ashes of Island contain more elements than those of other volcanos, especially compared to those of Mediteranean countries. This confirms that the earthquake is much important and deeper under eastern Atlantic. Similarly, Sumatra volcano eruptions indicate pronounced tectonics under Western Pacific ocean. As a primary consequence, the planet temperature increases and induced the melting of thousands years glaciers at the North and South poles, rejecting in the oceans blue icebergs as big as Portugal or Vietnam. Nevertheless the sea level rising is not a great danger compared to its local sudden elevations, tsunamis, which cause tremendous damages. I have calculated the areas immerged by tsunamis, applied in particular for the deltas of North and South Vietnam, Indonesia; Malaysia and some European countries. The results will be presented in hope to prevent sudden damages and in long term, the effects on lands, environments and on the health of humanit

Differentiated Instruction And The Need To Integrate Teaching And Practice

Differentiated instruction is becoming critical in higher education due to student diversity and background knowledge. Differentiated instruction does not mean matching teaching styles with learning styles as suggested by the learning styles theory. Findings in recent research studies have proved the lack of credible evidence for the utility of the learning styles theory. As not scientifically proven, the theory serves to perpetuate the learning styles mythology in the educational psychology world. This paper will emphasize students’ readiness levels as a critical part of differentiated instruction that teachers should refer to rather than sticking to student preferences and/or learning styles. The paper also suggests strategies to differentiate instruction effectively. These strategies include, but are not limited to, identifying student readiness; making modifications of the instructional content, process, and product; and enhancing collaboration and autonomy in learning. The last part of the paper places an emphasis on the integration of teaching and practice. Differentiated instruction, at its best, should reflect a new pedagogy that can promote practical integration and knowledge transformation. If implemented thoroughly, differentiated instruction can demonstrate institutional effectiveness and equip students with diverse learning experiences to highly respond to increased challenges in the global society

Nutritional state and organic matter diagenesis in an ecotone of halophyte and planted mangrove in Bac Lieu province, Vietnam

Mangroves play many significant roles in human life and socio-economical activities. However, their coverage has seriously declined worldwide due to various reasons while understanding of the roles and functions of this ecosystem is still insufficient. With a vast area of mangroves along the coast line, several studies on this ecosystem have been done in Viet Nam. Notwithstanding, the knowledge of nutrient and organic matter dynamics in the mangroves of Viet Nam, in general, and in the Mekong Delta, in particular, is still a gap. This study was conducted to understand the nutrient dynamics in a mangrove replanted in an abandoned salt-pan in Ganh Hao, Bac Lieu province â a coastal area in the South of Viet Nam. Sediments and fresh leaves were collected from 8 different landscapes along a transect which was ca. 700 m in length. Sampling was conducted in the dry and rainy season in 2009. The nutrient contents (NH4 , NO2-, NO3- and available P for plant uptake), total organic carbon and total nitrogen were determined to assess the nutritional state in the study area. The composition and concentration of the amino acids in the sediments were quantified to understand the organic matter diagenesis in the area. Glucosamine, galactosamine and amino acids in the fresh leaves were analyzed to find the source of the organic matter. The chitin content in the sediments was determined by 2 methods to calculate the contribution of chitin to the N pool. Chitin was directly quantified through the binding of N-acetylglucosamine and WGA-FITC. On the other hand, chitin was calculated from the concentration of glucosamine in the sediments. The study area was subject to a serious deficiency of nutrients, especially nitrogen. The deficiency of nitrogen resulted in the deficiency of phosphorus in the sediments. The nitrogen and phosphorus contents in the sediments were controlled by the physico-chemical properties of the sediments and the vegetation. The carbon-to-nitrogen ratios showed that the organic matter in the deep sediments (30-35 cm) mostly derived from marine sources. The organic matter derived from terrestrial plants was found mostly in the surface sediments. The forestation and the invasion of Sesuvium portulacastrum, therefore, have recently contributed to the pool of organic matter in the sediments. The organic matter content in the study area was lower compared to other coastal areas, probably due to the higher turnover rate in the sediments, which resulted from the high temperature and the aeration in the sediment. The composition and contents of the sedimentary amino acids were affected by the composition and contents of the amino acids in leaves. In general, the contents of sedimentary amino acids decreased with depth. However, the soil preparation for mangrove plantation resulted in a disturbance in the variation trend with depth in the amino acid contents under the planted mangrove. The chitin content directly quantified through the binding between N-acetylglucosamine and WGA-FITC exceeded the organic carbon content in the sediments. However, these chitin data revealed an ecological relationship between chitin and the diatom frustules. The content of chitin calculated from glucosamine concentration showed that chitin contributes less than 2% to the OC pool and less than 3% to the N pool. In the deep sediments (30-35 cm), the crustacean sheaths was the major source of chitin while in the shallow sediments, chitin mostly derived from diatoms. In conclusion, this study showed that the nutritional state and the organic matter dynamics in a mangrove planed in extreme conditions was driven by tides, vegetation and the physico-chemical properties of the sediments. These effects might relate to the activities of sediment bacteria functioning in the nitrogen and phosphorus mineralization and solubilization. Improving the sediment conditions by irrigational solutions will help to maximize the bacterial activities and enhance the efficiency of mangrove plantation in abandoned salt-pans