In vitro synthesis of 1,N6-etheno-2'-deoxyadenosine and 1,N2-etheno-2'-deoxyguanosine by 2,4-dinitrophenol and 1,3-dinitropyrene in presence of a bacterial nitroreductase

Formation of nitrosated and nitrated aromatic products of concerns in the treatment of phenols by the combination of peroxymonosulfate and hydroxylamine

Recently, the combination of peroxymonosulfate (PMS) and hydroxylamine (HA) has been proposed as a green and efficient sulfate radical ()-based advanced oxidation process (AOP) for eliminating organic contaminants. However, we found that toxic nitrosated and nitrated aromatic compounds were generated during the treatment of phenolic compounds by PMS/HA system, indicating the involvement of reactive nitrogen species (RNS) during the interaction of PMS with HA. Specifically, considerable production of p-nitrosophenol (p-NSP) and mononitrophenol were obtained when phenol was oxidized by PMS/HA system under various conditions. At the molar ratio between HA and PMS of 1.0 and pH 5.0, sum of the yields of p-NSP and nitrophenols reached their maxima (around 50%). Moreover, production of p-NSP was inhibited while that of nitrophenols was promoted when applied NH₂OH1/2H₂SO₄ was replaced by NH₂OHHCl, which was possibly related to the formation of secondary reactive species induced by the reaction of with chloride ion. Further, formation of undesirable nitrosated and nitrated aromatic products was obtained in the treatment of other phenolic compounds including acetaminophen, bisphenol A, and bisphenol S by PMS/HA system. Considering the toxicity of nitrosated and nitrated aromatic compounds, practical application of PMS/HA system for environmental decontamination should be scrutinized.

Recent developments in DNA adduct analysis by mass spectrometry: a tool for exposure biomonitoring and identification of hazard for environmental pollutants

DNA adducts represent an important category of biomarkers for detection and exposure surveillance of potential carcinogenic and genotoxic chemicals in the environment. Sensitive and specific analytical methods are required to detect and differentiate low levels of adducts from native DNA from in vivo exposure. In addition to biomonitoring of environmental pollutants, analytical methods have been developed for structural identification of adducts which provides fundamental information for determining the toxic pathway of hazardous chemicals. In order to achieve the required sensitivity, mass spectrometry has been increasingly utilized to quantify adducts at low levels as well as to obtain structural information. Furthermore, separation techniques such as chromatography and capillary electrophoresis can be coupled to mass spectrometry to increase the selectivity. This review will provide an overview of advances in detection of adducted and modified DNA by mass spectrometry with a focus on the analysis of nucleosides since 2007. Instrument advances, sample and instrument considerations, and recent applications will be summarized in the context of hazard assessment. Finally, advances in biomonitoring applying mass spectrometry will be highlighted. Most importantly, the usefulness of DNA adducts measurement and detection will be comprehensively discussed as a tool for assessment of in vitro and in vivo exposure to environmental pollutants.

Indirect photochemistry in sunlit surface waters: photoinduced production of reactive transient species

This paper gives an overview of the main reactive transient species that are produced in surface waters by sunlight illumination of photoactive molecules (photosensitizers), such as nitrate, nitrite, and chromophoric dissolved organic matter (CDOM). The main transients (˙OH, CO3(-˙) , (1)O2, and CDOM triplet states) are involved in the indirect phototransformation of a very wide range of persistent organic pollutants in surface waters.

The role of nitrite and nitrate ions as photosensitizers in the phototransformation of phenolic compounds in seawater

Nitrite and nitrate are known to be involved in photochemical processes occurring in natural waters. In this study we have investigated the role played by these photosensitizers towards the transformation of xenobiotic organic matter in marine water, with the goal of assessing the typical transformation routes induced in seawater by irradiated nitrite/nitrate. For this purpose, phenol was chosen as model molecule. Phenol transformation was investigated under simulated solar radiation in the presence of nitrite (in the range of 1 × 10(-5)-1 × 10(-2)M) or nitrate ions, in pure water at pH 8, in artificial seawater (containing same dissolved salts as seawater but no organic matter), and in natural seawater. In all experiments, phenol degradation rate and formation of intermediates were assessed. As expected, phenol disappearance rate decreased with decreasing nitrite concentration and was slightly reduced by the presence of chloride. Other salts present in artificial seawater (e.g. HCO(3)(-), CO(3)(2-) and Br(-)) had a more marked effect on phenol transformation. Analysis of intermediates formed in the different matrices under study showed generation of hydroxyl-, nitro- and chloroderivatives of phenol, to a different extent depending on experimental conditions. 1,4-Benzoquinone prevailed in all cases, nitroderivatives were only formed with nitrite but were not detected in nitrate-spiked solutions. Competition was observed between halogenation and nitration of phenol, with variable outcome depending on nitrite concentration. The most likely reason is competition between nitrating and halogenating species for reaction with the phenoxyl radical. A kinetic model able to justify the occurrence of different intermediates under the adopted conditions is presented and discussed.

Photochemical transformation of anionic 2-nitro-4-chlorophenol in surface waters: laboratory and model assessment of the degradation kinetics, and comparison with field data

Anionic 2-nitro-4-chlorophenol (NCP) may occur in surface waters as a nitroderivative of 4-chlorophenol, which is a transformation intermediate of the herbicide dichlorprop. Here we show that NCP would undergo efficient photochemical transformation in environmental waters, mainly by direct photolysis and reaction with OH. NCP has a polychromatic photolysis quantum yield Φ(NCP)=(1.27±0.22)·10(-5), a rate constant with OH k(NCP,)(OH)=(1.09±0.09)·10(10) M(-1) s(-1), a rate constant with (1)O(2)k(NCP,1O2)=(2.15±0.38)·10(7) M(-1) s(-1), a rate constant with the triplet state of anthraquinone-2-sulphonate k(NCP,3AQ2S*)=(5.90±0.43)·10(8) M(-1) s(-1), and is poorly reactive toward CO(3)(-). The k(NCP,3AQ2S*) value is representative of reaction with the triplet states of chromophoric dissolved organic matter. The inclusion of photochemical reactivity data into a model of surface-water photochemistry allowed the NCP transformation kinetics to be predicted as a function of water chemical composition and column depth. Very good agreement between model predictions and field data was obtained for the shallow lagoons of the Rhône delta (Southern France).

Theoretical and experimental evidence of the photonitration pathway of phenol and 4-chlorophenol: a mechanistic study of environmental significance

Light-induced nitration pathways of phenols are important processes for the transformation of pesticide-derived secondary pollutants into toxic derivatives in surface waters and for the formation of phytotoxic compounds in the atmosphere. Moreover, phenols can be used as ˙NO(2) probes in irradiated aqueous solutions. This paper shows that the nitration of 4-chlorophenol (4CP) into 2-nitro-4-chlorophenol (NCP) in the presence of irradiated nitrate and nitrite in aqueous solution involves the radical ˙NO(2). The experimental data allow exclusion of an alternative nitration pathway by ˙OH + ˙NO(2). Quantum mechanical calculations suggest that the nitration of both phenol and 4CP involves, as a first pathway, the abstraction of the phenolic hydrogen by ˙NO(2), which yields HNO(2) and the corresponding phenoxy radical. Reaction of phenoxyl with another ˙NO(2) follows to finally produce the corresponding nitrated phenol. Such a pathway also correctly predicts that 4CP undergoes nitration more easily than phenol, because the ring Cl atom increases the acidity of the phenolic hydrogen of 4CP. This favours the H-abstraction process to give the corresponding phenoxy radical. In contrast, an alternative nitration pathway that involves ˙NO(2) addition to the ring followed by H-abstraction by oxygen (or by ˙NO(2) or ˙OH) is energetically unfavoured and erroneously predicts faster nitration for phenol than for 4CP.

Modeling phototransformation reactions in surface water bodies: 2,4-dichloro-6-nitrophenol as a case study

The anionic form of 2,4-dichloro-6-nitrophenol (DCNP), which prevails in surface waters over the undissociated one, has a direct photolysis quantum yield of (4.53 ± 0.78) × 10(-6) under UVA irradiation and second-order reaction rate constants of (2.8 ± 0.3) × 10(9) M(-1) s(-1) with •OH, (3.7 ± 1.4) × 10(9) M(-1) s(-1) with (1)O(2), and (1.36 ± 0.09) × 10(8) M(-1) s(-1) with the excited triplet state of anthraquinone-2-sulfonate, adopted as a proxy for the photoactive dissolved organic compounds in surface waters. DCNP also shows negligible reactivity with the carbonate radical. Insertion of the data into a model of surface water photochemistry indicates that the direct photolysis and the reactions with •OH and (1)O(2) would be the main phototransformation processes of DCNP, with •OH prevailing in organic-poor and (1)O(2) in organic-rich waters. The model results compare well with the field data of DCNP in the Rhône river delta (Southern France), where (1)O(2) would be the main reactive species for the phototransformation of the substrate.

Enhancement by anthraquinone-2-sulphonate of the photonitration of phenol by nitrite: implication for the photoproduction of nitrogen dioxide by coloured dissolved organic matter in surface waters

Anthraquinone-2-sulphonate (AQ2S) under UVA irradiation is able to oxidise nitrite to (·)NO(2) and to induce the nitration of phenol. The process involves the very fast reactions of the excited triplet state (3)AQ2S(*) and its 520-nm absorbing exciplex with water, at different time scales (ns and μs, respectively). Quinones are ubiquitous components of coloured dissolved organic matter (CDOM) in surface waters and AQ2S was adopted here as a proxy of CDOM. Using a recently developed model of surface-water photochemistry, we found that the oxidation of nitrite to (·)NO(2) by (3)CDOM(*) could be an important (·)NO(2) source in water bodies with high [NO(2)(-)] to [NO(3)(-)] ratio, for elevated values of column depth and NPOC.

Secondary oxidation of cyclic 1,N2-propano and 1,N2-etheno-2'-deoxyguanosine DNA adducts. Consequences in oxidative stress biomarker development

This work is an attempt to investigate the chemical stability of 1,N2-propano-2'-deoxyguanosine (pdG-HNE) and 1,N2-etheno-2'-deoxyguanosine (epsilondG) DNA adducts against hydrolysis and upon oxidation reactions. It includes both kinetic issues together with proposed degradation pathways. While both chemicals are stable in the 3.5-9 pH range, the results suggest that pdG-HNE adduct is less prone to in vitro oxidative transformation than epsilondG adduct. EpsilondG and pdG-HNE behave differently upon hydroxyl radical and one electron oxidation reactions. The exocyclic ring of epsilondG is mainly affected by oxidative processes leading to the regeneration of 2'-deoxyguanosine (dG) while the integrity of the exocyclic ring is preserved for pdG-HNE. Consequently, pdG-HNE might be a better biomarker than epsilondG for monitoring oxidative stress during environmental or occupational exposures to chemicals. Understanding the in vitro routes of etheno and propano DNA adduct degradation would probably help to guide the development of analytical methodologies for the reliable detection of these endogenous adducts.

UVA irradiation induces direct phototransformation of 2,4-dinitrophenol in surface water samples

Lake water samples spiked with 2,4-dinitrophenol (24DNP) were irradiated under artificial UVA irradiance. It was found that the direct photolysis is the main photodegradation pathway of 24DNP in lake water. On the lake water samples it was also determined the formation and consumption rates of *OH, by means of the transformation reaction of benzene into phenol. It was found that the rate of direct photolysis prevails over the *OH phototransformation rate by one-two orders of magnitude. Moreover, the excited triplet states of chromophoric dissolved organic matter and singlet oxygen are expected to play a negligible role in the photodegradation of 24DNP. By modelling the direct photolysis of 24DNP in surface water bodies, one gets a half-life time of 2-10 summer sunny days for water-column depths up to 10 m. This would make the direct photolysis a major pathway for the transformation of 24DNP in freshwaters.

Nitration processes of acetaminophen in nitrifying activated sludge

This work is an attempt to elucidate the quantitative significance of acetaminophen (APAP) nitration in nitrifying activated sludge and to propose a reaction mechanism for this process. The link between nitrification and nitration of APAP was investigated at different scales. Results from field studies showed the occurrence of 3-nitro-APAP and to a lesser extent 3-chloro-5-nitro-APAP at concentration levels in the 50-300 ng/L range in effluents of a full scale wastewater treatment plant (WWTP) operated with nitrogen removal, whereas 3-hydroxy-APAP was eliminated after the nitrification step. Batch experiments with nitrifying activated sludge confirmed APAP transformation by nitration and suggested that nitrifying bacteria may play a role in this transformation process through the release of reactive nitrogen species. In vitro assays provided evidence that nitration through the production of nitrous acid is a very unlikely pathway. In contrast, nitric oxide (*NO) produced by nitrifying bacteria is probably involved in APAP nitration through the formation of peroxynitrite in presence of superoxide anion. The production of 3-nitro-APAP would only account for a few percents of the total transformation rate of APAP in WWTPs. The production of nitrated derivatives is highly relevant because of the potential ecotoxicological risks of these compounds.

Pesticide by-products in the Rhône delta (Southern France). The case of 4-chloro-2-methylphenol and of its nitroderivative

A field monitoring campaign for pesticides and their transformation intermediates was carried out in the Rhône delta (Southern France). It was evidenced the following transformation sequence: MCPA-->4-chloro-2-methylphenol (CMP)-->4-chloro-2-methyl-6-nitrophenol (CMNP). Interestingly CMP disappeared about as quickly as MCPA, while CMNP was environmentally more persistent than the parent molecules. This is very relevant to the environmental risk associated with the occurrence of these compounds, because the nitration of chlorophenols reduces their acute toxicity but the nitroderivatives could have more marked long-term effects, associated with their genotoxicity. Irradiation experiments suggested that the photonitration of CMP into CMNP involves nitrogen dioxide, generated from the photolysis of nitrate and from the photooxidation of nitrite by ()OH. The photochemistry of Fe(III) species could also play a significant role, but its contribution is still difficult to be quantified. Another important intermediate of CMP transformation is methylnitrophenol (MNP), produced via a dechlorination/nitration pathway, with ortho-cresol as the most likely reaction intermediate.

Spectroscopic properties of some derivatives of polycyclic aromatic hydrocarbons

The aim of this paper is to provide a general picture of the spectral characteristics of some polycyclic aromatic hydrocarbon (PAH) derivatives. A great deal of data concerning PAHs has been reported in the literature, but there is lack of comprehensiveness about important parameters in the same experimental conditions for their nitro (NO(2)) and amino (NH(2)) derivatives such as absorption and emission characteristics. Thus, important parameters such as the molar extinction coefficient, absorption maxima, fluorescence maxima, and fluorescence quantum yield are reported here. The efficiencies of the reduction of NO(2)-PAHs to their corresponding amino compounds were also verified by means of high-performance liquid chromatography (HPLC). This class of derivatives represents one of the most toxic groups of carcinogenic substances and therefore the data reported here should be useful for toxicological research.