Degradation of chlortoluron in water disinfection processes: a kinetic study

Chlor(am)ination of iopamidol: Kinetics, pathways and disinfection by-products formation

The degradation kinetics, pathways and disinfection by-products (DBPs) formation of iopamidol by chlorine and chloramines were investigated in this paper. The chlorination kinetics can be well described by a second-order model. The apparent second-order rate constants of iopamidol chlorination significantly increased with solution pH. The rate constants of iopamidol with HOCl and OCl^- were calculated as (1.66 ± 0.09) × 10^-3 M^-1 s^-1 and (0.45± 0.02) M^-1 s^-1, respectively. However, the chloramination of iopamidol fitted well with third-order kinetics and the maximum of the apparent rate constant occurred at pH 7. It was inferred that the free chlorine (i.e., HOCl and OCl^-) can react with iopamidol while the combined chlorine species (i.e., NH₂Cl and NHCl₂) were not reactive with iopamidol. The main intermediates during chlorination or chloramination of iopamidol were identified using ultra performance liquid chromatography - electrospray ionization-mass spectrometry (UPLC-ESI-MS), and the destruction pathways including stepwise deiodination, hydroxylation as well as chlorination were then proposed. The regular and iodinated DBPs formed during chlorination and chloramination of iopamidol were measured. It was found that iodine conversion from iopamidol to toxic iodinated DBPs distinctly increased during chloramination. The results also indicated that although chloramines were much less reactive than chlorine toward iopamidol, they led to the formation of much more toxic iodinated DBPs, especially CHI₃.

Reactions of phenylurea compounds with aqueous chlorine: Implications for herbicide transformation during drinking water disinfection

Phenylurea herbicides have been known to contaminate surface waters serving as potable supplies. To access the potential for transformation of these compounds during drinking water treatment, reactions of phenylurea compounds with aqueous chlorine at different pHs were investigated. The effect of substitution at the amino-N on the rate of transformation depends upon pH. Under acidic conditions, all of the phenylurea studied except 3,4-dichloro-3'-N-methylphenylurea (3,4-DCMPU) exhibited third-order kinetics, second order with respect to chlorine and first order with respect to phenylurea, while the reactions of 3,4-DCMPU were first order with respect to both chlorine and the organic compound. Under neutral and alkaline conditions, all compounds exhibited second-order kinetics that was first order with respect to chlorine and the organic compound. Apparent second-order rate constants at 25°C and pH 7 were 0.76 ± 0.16, 0.52 ± 0.11, 0.39 ± 0.02, 0.27 ± 0.04 and 0.23 ± 0.05 M(-1)s(-1) for phenylurea, 3, 4-dichlorophenylurea, 3, 4-DCMPU, metoxuron and monuron, respectively. Studies of the chlorination products, monitored by LC/MS/MS, under different pH values indicated the reaction to take place at both N atoms and also at ortho- and para- positions of the phenylurea aromatic group. The main chlorinating species were found to be different in different pH ranges. Under conditions typically encountered in drinking water treatment systems, transformation of these compounds by chlorine will be incomplete.

Degradation kinetics and N-Nitrosodimethylamine formation during monochloramination of chlortoluron

The degradation of chlortoluron by monochloramination was investigated in the pH range of 4-9. The degradation kinetics can be well described by a second-order kinetic model, first-order in monochloramine (NH(2)Cl) and first-order in chlortoluron. NH(2)Cl was found not to be very reactive with chlortoluron, and the apparent rate constants in the studied conditions were 2.5-66.3M(-1)h(-1). The apparent rate constants were determined to be maximum at pH 6, minimum at pH 4 and medium at alkaline conditions. The main disinfection by-products (DBPs) formed after chlortoluron monochloramination were identified by ultra performance liquid chromatography-ESI-MS and GC-electron capture detector. N-Nitrosodimethylamine (NDMA) and 5 volatile chlorination DBPs including chloroform (CF), dichloroacetonitrile, 1,1-dichloropropanone, 1,1,1-trichloropropanone and trichloronitromethane were identified. The distributions of DBPs formed at different solution pH were quite distinct. Concentrations of NDMA and CF were high at pH 7-9, where NH(2)Cl was the main disinfectant in the solution. NDMA formation during chlortoluron monochloramination with the presence of nitrogenous salts increased in the order of nitrite<nitrate<ammonium for a given monochloramination and chlortoluron concentration.

Chlorination of chlortoluron: kinetics, pathways and chloroform formation

Chlortoluron chlorination is studied in the pH range of 3-10 at 25 ± 1°C. The chlorination kinetics can be well described by a second-order kinetics model, first-order in chlorine and first-order in chlortoluron. The apparent rate constants were determined and found to be minimum at pH 6, maximum at pH 3 and medium at alkaline conditions. The rate constant of each predominant elementary reactions (i.e., the acid-catalyzed reaction of chlortoluron with HOCl, the reaction of chlortoluron with HOCl and the reaction of chlortoluron with OCl(-)) was calculated as 3.12 (± 0.10)×10(7)M(-2)h(-1), 3.11 (±0.39)×10(2)M(-1)h(-1) and 3.06 (±0.47)×10(3)M(-1)h(-1), respectively. The main chlortoluron chlorination by-products were identified by gas chromatography-mass spectrometry (GC-MS) with purge-and-trap pretreatment, ultra-performance liquid chromatography-electrospray ionization-MS and GC-electron capture detector. Six volatile disinfection by-products were identified including chloroform (CF), dichloroacetonitrile, 1,1-dichloropropanone, 1,1,1-trichloropropanone, dichloronitromethane and trichloronitromethane. Degradation pathways of chlortoluron chlorination were then proposed. High concentrations of CF were generated during chlortoluron chlorination, with maximum CF yield at circumneutral pH range in solution.

Photocatalytic degradation of phenyl-urea herbicides chlortoluron and chloroxuron: characterization of the by-products by liquid chromatography coupled to electrospray ionization tandem mass spectrometry

The first stages of the photocatalytic degradation of the compounds chlortoluron [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea] and chloroxuron [3-[4-(4-chlorophenoxy)phenyl]-1,1-dimethylurea], belonging to the class of phenyl-urea herbicides, were investigated using high-performance liquid chromatography (HPLC) coupled to electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS). Degradation was accomplished under solar radiation, using TiO2 embedded into a polyvinylidene fluoride (PVDF) transparent matrix as a heterogeneous photocatalyst. Aliquots of the chlorinated herbicide solutions were withdrawn at different times and subjected to gradient elution, reversed-phase HPLC separations, specifically optimized to obtain the highest resolution between peaks related to the herbicide degradation by-products. The latter were then investigated using MS detection; in particular, MS/MS measurements were made and structural information was obtained from the interpretation of fragmentation data. Several by-products were identified; the most important ones are hydroxylated compounds arising from the interaction between the two chlorinated herbicides and OH radicals generated at the TiO2 surface under irradiation. Other by-products were generated by slightly different processes, namely demethylation, dearylation and dechlorination, eventually followed by interaction with OH radicals.

Evaluation of Chlorinated By-Products in Drinking Waters of Clentral Friuli (Italy)

Drinkable water supplied by aqueducts undergoes preliminar potabilization which, in Italy, is mainly accomplished by chlorine addition. The bactericidal action involved in this process is always accompanied by chlorination and oxidation of organic species (mainly humic and fulvic acids) naturally present in treated waters, so that many disinfection by-products (DBPs) are formed, such as trihalomethanes (THMs) and halo-acetic acids (HAA), which can represent a chemical risk for public health. The aim of this study was the monitoring of DBPs in drinking water disinfected by chlorination, supplied by four different aqueducts of Central Friuli (Italy). DBP evaluations were performed in water samples consisting of both input and output of disinfection plants. The results of analytical determinations were worked out to provide the THM and HAA parameters for disinfected waters, while in feeding waters the following different conventional parameters were adopted: (i) trihalomethanes formation potential (THMFP), (ii) halo-acetic acids formation potential (HAAFP) and (iii) UV absorbance at 254 nm (UV254). The quite moderate content of chlorinated products found in all samples considered highlighted the excellent quality of potabilized waters available in Central Friuli. Moreover, our results confirmed that the majority of DBPs formed when chlorine is used for water disinfection consists of THMs, while chlorites and chlorates prevailed when potabilization is accomplished by using chlorine dioxide. Finally, simple UV254 monitoring turned out to be a profitable approach for the determination of chlorinated by-products only when THMs prevail among DBPs.

Photocatalytic degradation of the herbicide isoproturon: characterisation of by-products by liquid chromatography with electrospray ionisation tandem mass spectrometry

By-products arising from immobilised TiO2-catalysed photodegradation of the herbicide isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] in aqueous solution under solar radiation were analysed by reversed-phase liquid chromatography combined with electrospray ionisation ion trap mass spectrometry. Structural information on by-products, formed at different degradation times, was then obtained from interpretation of the relevant MS/MS spectra. Several species were identified through this approach, and in many cases several isomers were found. As expected, most by-products resulted from single or multiple hydroxylation (by photo-generated OH* radicals) of the isoproturon molecule at different positions. However, substitution of some functional groups of the herbicide (isopropyl or methyl) by OH* was also observed. A possible degradation scheme is hypothesised.