Degradation behaviour of pyrazosulfuron-ethyl in water as affected by pH

Pyrazosulfuron-ethyl, a new herbicide belonging to the sulfonylurea group, is used for weed control in rice crops growing in areas varying from acidic to alkaline soils. This study was undertaken to determine the degradation behaviour of pyrazosulfuron-ethyl in distilled water and buffer solutions at pH 4, 7 and 9. Degradation was pH-dependent and herbicide was least persistent in acidic pH followed by alkaline and neutral pH. The half-life of pyrazosulfuron-ethyl varied from 2.6 days (pH 4) to 19.4 days (pH 7) and half-life in distilled water was comparable to half-life at pH 7 buffer. HPLC analysis of different pH samples showed the formation of three metabolites viz., 5-(aminosulfonyl)-1-methyl-1H-pyrazole-4-carboxylic acid; ethyl 5-(aminosulfonyl)-1-methyl-1H-pyrazole-4-carboxylate and 2-amino-4,6-dimethoxy pyrimidine. The formation of pyrazosulfuron acid [5-([([(4,6-dimethoxy-2 pyrimidinyl)-amino]-carbonyl) amino]-sulfonyl)-1-methyl-1H-pyrazole-4-carboxylic acid] was not observed at any pH. The study indicated that the herbicide was least stable under acidic conditions and the predominant degradation route of pyrazosulfuron-ethyl in water is hydrolysis of sulfonamide linkage.     

Leaching and degradation of ethametsulfuron-methyl in soil

Leaching and degradation of the herbicide ethametsulfuron-methyl[methyl 2-[(4-ethoxy-6-methylamino-1,3,5-triazine-2-yl)carbamoylsulfamoyl]benzoate] in three soils were investigated under laboratory conditions. Ethametsulfuron-methyl was mobile on soils when tested using non-aged and aged soil columns; this mobility agreed reasonably well with Freundlich soil isotherm constants. It was found that ethametsulfuron-methyl was more mobile in alkaline sandy Vertisol soil and neutral loamy Alfisol soil than in acidic clayey Red soil. Degradation of ethametsulfuron-methyl in soils was pH-dependent; calculated half-life (t(1/2)) values ranged from 13 to 67 days. Ethametsulfuron-methyl was more persistent in neutral or weakly basic than in acidic soil. Five soil metabolites were isolated and identified by LC/MS/MS analysis. The degradation pathways included the cleavage of the sulfonylurea bridge, N- and O-dealkylation, and triazine ring opening.     

Kinetics and mechanism of the hydrolysis of thiamethoxam

The degradation of thiamethoxam [(EZ)-3-(2-chloro-1,3-thiazol-5-yl-methyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene (nitro) amine] insecticide in buffers at different pH and temperature levels was investigated in laboratory studies. Acidic hydrolysis under conventional heating conditions and alkaline hydrolysis under both conventional heating and microwave conditions were carried out. Different hydrolysis products were found to form under alkaline and acidic conditions. Hydrolysis of thiamethoxam in acidic, neutral and alkaline buffers followed first-order reaction rate kinetics at pH 4, 7 and 9.2, respectively. Thiamethoxam readily hydrolyzed in alkaline buffer but was comparatively stable in neutral buffer solution. The main products formed under different conditions were characterized on the basis of infrared (IR), ¹H-NMR and Mass spectroscopy. The possible mechanisms for the formation of these hydrolysis products have also been proposed.     

Fate and degradation of triasulfuron in soil and water under laboratory conditions

The behavior and fate of triasulfuron (TRS) in water and soil systems were examined in laboratory studies. The degradation of TRS in both buffer solution and soil was highly pH-sensitive. The rate of degradation could be described with a pseudo first-order kinetic and was much faster at pH 4 than at pH 7 and 9. Aqueous hydrolysis occurred by cleavage of the sulfonylurea bridge to form 2-(2-chloroethoxy) benzenesulfonamide (CBSA) and [(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] (AMMT). AMMT was unstable in aqueous solutions in any pH condition but it degraded more quickly at pH 4 and 9. CBSA did not degrade in aqueous solutions or in enriched cultures but it underwent a quick degradation in the soil. The rates of TRS degradation in sterile and non-sterile soils were similar, suggesting that microorganisms played a minimal role in the breakdown process. This hypothesis is supported by the results of studies on the degradation of TRS by enriched cultures during which the molecule underwent a prevalently chemical degradation.     

Fate and degradation of triasulfuron in soil and water under laboratory conditions

The behavior and fate of triasulfuron (TRS) in water and soil systems were examined in laboratory studies. The degradation of TRS in both buffer solution and soil was highly pH-sensitive. The rate of degradation could be described with a pseudo first-order kinetic and was much faster at pH 4 than at pH 7 and 9. Aqueous hydrolysis occurred by cleavage of the sulfonylurea bridge to form 2-(2-chloroethoxy) benzenesulfonamide (CBSA) and [(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] (AMMT). AMMT was unstable in aqueous solutions in any pH condition but it degraded more quickly at pH 4 and 9. CBSA did not degrade in aqueous solutions or in enriched cultures but it underwent a quick degradation in the soil. The rates of TRS degradation in sterile and non-sterile soils were similar, suggesting that microorganisms played a minimal role in the breakdown process. This hypothesis is supported by the results of studies on the degradation of TRS by enriched cultures during which the molecule underwent a prevalently chemical degradation.     

Hydrolysis and soil sorption of insecticide pyraclofos

The hydrolysis of the insecticide pyraclofos in buffered solutions at pH 5.0, 7.0 and 9.0, and its sorption on four soils of different physicochemical properties were investigated. The results showed that the degradation of pyraclofos in buffered solutions followed pseudo-first-order kinetics. At 40 degrees C, the rate constants for the hydrolysis of pyraclofos at pH 5.0, 7.0 and 9.0 were 0.0214, 0.1293, and 2.1656 d(-1), respectively. Pyraclofos was relatively stable under both acidic and neutral conditions, while it was readily hydrolyzed under basic conditions. The sorption of pyraclofos on four soils was well described by the Freundlich equation. The sorption constant, K(f), increased with an increase in soil organic carbon content, suggesting that organic carbon content was an important factor affecting sorption. The K(oc) values for Xiaoshan clay loam soil, Hangzhou I clay loam soil, Hangzhou II soil, and Fuyang silt loam soil were 30.4, 6.7, 5.3, and 7.1, respectively. These results suggest that the sorption of pyraclofos on the tested soils was relatively weak.     

Hydrolysis and photolysis of oxytetracycline in aqueous solution

Oxytetracycline ((2Z,4S,4aR,5S,5aR,6S,12aS)-2-(amino-hydroxy-methylidene)-4-dimethylamino-5,6,10,11,12a-pentahydroxy-6-methyl-4,4a,5,5a-tetrahydrotetracene-1,3,12-trione) is a member of tetracycline antibiotics family and is widely administered to farm animals for the purpose of therapeutical treatment and health protection. Increasing attention has been paid to the environmental fate of oxytetracycline and other veterinary antibiotics with the occurrence of these antibiotics in the environment. The hydrolysis and photolysis degradation of oxytetracycline was investigated in this study. Oxytetracycline hydrolysis was found to obey the first-order model and similar rate constant values ranging from 0.094 ± 0.001 to 0.106 ± 0.003 day^{? 1} were obtained at different initial concentration ranging from 10 to 230 μ M. Solution pH and temperature were shown to have remarked effects on oxytetracycline hydrolysis. The hydrolysis in pH neutral solution appeared to be much faster than in both acidic and alkaline solutions. Oxytetracycline half-life decreased from 1.2 × 10² to 0.15 day with the increasing temperature from 4 ± 0.8 to 60 ± 1°C. The presence of Ca^{2 +} made oxytetracycline hydrolytic degradation kinetics deviate from the simple first-order model to the availability-adjusted first-order model and greatly slowed down the hydrolysis. Oxytetracycline photolysis was found to be very fast with a degradation rate constant at 3.61 ± 0.06 day^{? 1}, which is comparable to that of hydrolysis at 60°C. The presence of Ca^{2 +} accelerated oxytetracycline photolysis, implying that oxytetracycline become more vulnerable to sunlight irradiation after chelating with Ca^{2 +}. The photolysis may be the dominant degradation pathway of oxytetracycline in shallow transparent water environment.     

Light-induced transformation of tribenuron-methyl on glass, soil, and plant surface

Photolysis of tribenuron-methyl (methyl 2-[[[[N-(4-methoxy-6-methyl-1,3,5triazin-2-yl)methylamino]carbonyl]amino]sulfonyl]benzoate), a sulfonylurea herbicide, was studied as thin film on glass surface, soil surface, and plant surface. A number of photoproducts such as 4-methoxy-6-methyl-2-aminomethyl-1,3,5-triazine; methyl-2-(aminosulfonyl) benzoate; N-(2-carbomethoxyphenyl)-N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N'-methylurea; N-(2-carbomethoxyphenyl sulfonyl)-N-methyl urea; o-benzoic sulfimide and 4-methoxy-6-methyl-2-amino-1,3,5-triazine were identified by comparison of their GC-MS with the authentic standards. The rate of degradation in all the cases followed first-order kinetics with a statistically significant correlation coefficient. Rate of photodegradation was greater on glass surface than on soil surface.     

水胺硫磷工业废水的酸性水解处理研究

水胺硫磷工业废水中 ,有机磷和硫化物含量均 >10 0 0 0mg/L ,COD高达 5 5 0 0 0mg/L左右 ,NH3 N在 4 0 0 0 0mg/L左右 ,BOD/COD仅为 0 .0 5 ,属典型难生物降解废水。本文采用常压酸性水解和脱氨除磷工艺处理该废水 ,有机磷、硫化物、NH3 N和总磷等去除率均 >90 % ,COD去除率达到 5 0 %以上 ,废水可生化性提高 ;同时 ,可回收得到硫氢化钠、氨水等物质 ,使废水资源得到了综合利用     

Biodegradation of nicosulfuron by the bacterium Serratia marcescens N80

By enrichment culturing of the sludge collected from the industrial wastewater treatment pond, we isolated a highly efficient nicosulfuron degrading bacterium Serratia marcescens N80. In liquid medium, Serratia marcescens N80 grows using nicosulfuron as the sole nitrogen source, and the optimal temperature, pH values, and inoculation for degradation are 30-35°C, 6.0-7.0, and 3.0% (v/v), respectively. With the initial concentration of 10 mg L?1, the degradation rate is 93.6% in 96 hours; as the initial concentrations are higher than 10 mg L?1, the biodegradation rates decrease as the nicosulfuron concentrations increase; when the concentration is 400 mg L?1, the degradation rate is only 53.1%. Degradation follows the pesticide degradation kinetic equation at concentrations between 5 mg L?1 and 50 mg L?1. Identification of the metabolites by the liquid chromatography/mass spectrometry (LC/MS) indicates that the degradation of nicosulfuron is achieved by breaking the sulfonylurea bridge. The strain N80 also degraded some other sulfonylurea herbicides, including ethametsulfuron, tribenuron-methyl, metsulfuron-methyl, chlorimuron-ethyl,and rimsulfuron.     

Light induced transformation of tribenuron-methyl

To study the photostability of sulfonylurea herbicide tribenuron-methyl (methyl 2-[[[[ N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl) methylamino] carbonyl]amino]sulfonyl]benzoate), in the field, model experiments with organic solvents were performed. Irradiation of tribenuron-methyl in methanol, isopropanol and cyclohexane yielded 4-methoxy-6-methyl-2-aminomethyl-1,3,5-triazine; methyl-2-(aminosulfonyl) benzoate; N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N-methyl urea; N-(2-carbomethoxy phenyl)-N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N'-methyl urea; 2-(aminosulfonyl) benzoic acid, N-methyl saccharin and saccharin in considerable amounts. The rate of degradation in different solvents followed first-order kinetics with a statistically significant correlation coefficient.     

Hydrolysis and soil sorption of insecticide pyraclofos

The hydrolysis of the insecticide pyraclofos in buffered solutions at pH 5.0, 7.0 and 9.0, and its sorption on four soils of different physicochemical properties were investigated. The results showed that the degradation of pyraclofos in buffered solutions followed pseudo-first-order kinetics. At 40°C, the rate constants for the hydrolysis of pyraclofos at pH 5.0, 7.0 and 9.0 were 0.0214, 0.1293, and 2.1656 d^?1, respectively. Pyraclofos was relatively stable under both acidic and neutral conditions, while it was readily hydrolyzed under basic conditions. The sorption of pyraclofos on four soils was well described by the Freundlich equation. The sorption constant, K _f, increased with an increase in soil organic carbon content, suggesting that organic carbon content was an important factor affecting sorption. The K _oc values for Xiaoshan clay loam soil, Hangzhou I clay loam soil, Hangzhou II soil, and Fuyang silt loam soil were 30.4, 6.7, 5.3, and 7.1, respectively. These results suggest that the sorption of pyraclofos on the tested soils was relatively weak.     

The degradation of endocrine disruptor di-n-butyl phthalate by UV irradiation: a photolysis and product study

The direct photolysis of an important endocrine disruptor compound, di-n-butyl phthalate (DBP), has been investigated under monochromatic UV irradiation at 254 nm over a wide pH range (3-11). The investigation was carried out under idealized conditions and has considered both reaction kinetics and the degradation mechanism. It was found that more than 90% of DBP can be degraded within an hour of irradiation in water. A simple model has been developed and used to predict the initial DBP photolysis rate constant at different pH values and initial DBP concentrations. The major decomposition mechanism of DBP is believed to involve the hydrolytic photolysis of the carbon in the alpha and/or beta-position of the ester chain with the production of aromatic carboxylic derivatives. Additionally, multi-degradation pathways are proposed for acid-catalyzed hydrolytic photolysis (pH 3-5), which was found to be useful in explaining the photo-degradation of DBP under acidic conditions. The use of 254 nm UV to photo-degrade DBP was found to be a relatively fast and clean process, especially in neutral to basic conditions.     

Detection of methylquinoline transformation products in microcosm experiments and in tar oil contaminated groundwater using LC-NMR

N-heterocyclic compounds are known pollutants at tar oil contaminated sites. Here we report the degradation of methyl-, and hydroxy-methyl-substituted quinolines under nitrate-, sulfate- and iron-reducing conditions in microcosms with aquifer material of a former coke manufacturing site. Comparison of degradation potential and rate under different redox conditions revealed highest degradation activities under sulfate-reducing conditions, the prevailing conditions in the field. Metabolites of methylquinolines, with the exception of 2-methylquinolines, were formed in high amounts in the microcosms and could be identified by ¹H NMR spectroscopy as 2(1H)-quinolinone analogues. 4-Methyl-, 6-methyl-, and 7-methyl-3,4-dihydro-2(1H)-quinolinone, the hydrogenated metabolites in the degradation of quinoline compounds, were identified by high resolution LC-MS. Metabolites of methylquinolines showed persistence, although for the first time a transformation of 4-methylquinoline and its metabolite 4-methyl-2(1H)-quinolinone is described. The relevance of the identified metabolites is supported by the detection of a broad spectrum of them in groundwater of the field site using LC-NMR technique. LC-NMR allowed the differentiation of isomers and identification without reference compounds. A variety of methylated 2(1H)-quinolinones, as well as methyl-3,4-dihydro-2(1H)-quinolinone isomers were not identified before in groundwater.     

Acid generation upon thermal concentration of natural water: The critical water content and the effects of ionic composition

Thermal evaporation of a variety of simulated pore waters from the region of Yucca Mountain, Nevada, produced acidic liquids and gases during the final stages of evaporation. Several simulated pore waters were prepared and then thermally distilled in order to collect and analyze fractions of the evolved vapor. In some cases, distillates collected towards the end of the distillation were highly acidic; in other cases the pH of the distillate remained comparatively unchanged during the course of the distillation. The results suggest that the pH values of the later fractions are determined by the initial composition of the water. Acid production stems from the hydrolysis of magnesium ions, especially at near dryness. Near the end of the distillation, magnesium nitrate and magnesium chloride begin to lose water of hydration, greatly accelerating their thermal decomposition to form acid. Acid formation is promoted further when precipitated calcium carbonate is removed. Specifically, calcium chloride-rich pore waters containing moderate (10–20 ppm) levels of magnesium and nitrate and low levels of bicarbonate produced mixtures of nitric and hydrochloric acid, resulting in a precipitous drop in pH to values of 1 or lower after about 95% of the original volume was distilled. Waters with either low or moderate magnesium content coupled with high levels of bicarbonate produced slightly basic fractions (pH 7–9). If calcium was present in excess of bicarbonate, waters containing moderate levels of magnesium produced acid even in the presence of bicarbonate, due to the precipitation of calcium carbonate. Other salts such as halite and anhydrite promote the segregation of acidic vapors from residual basic solids. The concomitant release of wet acid gas has implications for the integrity of the alloys under consideration for containers at the Yucca Mountain nuclear waste repository. Condensed acid gases at very low pH, especially mixtures of nitric and hydrochloric acid, are capable of corroding even alloys, such as nickel-based Alloy 22, which are considered to be corrosion-resistant under milder conditions.     

Identification of a novel fluorescent adduct formed in the reaction of malonaldehyde with adenosine

Malonaldehyde was reacted with adenosine in aqueous solution at acidic conditions and the reaction mixtures were analysed by HPLC. Four major product peaks were observed in the chromatogram recorded by the UV detector at 320 nm. Two of the peaks could be deduced to the previously characterised malonaldehyde-adenosine reaction product 9-(beta-D-ribofuranosyl)-6-(5,7-diformyl-2H-3,6-dihydro-2,6-methano-1,3-oxazocin-3-yl)purine (M3A) and to the ribose analogue of the 2'-deoxy adduct 9-(2'-deoxy-beta-D-ribofuranosyl)-6-(3,5-diformyl-4-methyl-1,4-dihydro-1-pyridyl)purine (M2AA-dA). The two other peaks were due to previously uncharacterised adducts. Upon isolation of these adduct peaks it was found that the peaks are interconverted to each other, one adduct peak dominating over the other one. On the basis of data recorded by UV, fluorescence and 1H NMR spectroscopy, and mass spectrometry, the structure of the major adduct could be determined as 9-(beta-D-ribofuranosyl)-6-(3,5-diformyl-4-etanal-1,4-dihydro-1-pyridyl)purine (3M-A). The adduct is most likely formed by reaction of adenosine with a malonaldehyde condensation product consisting of three units of malonaldehyde. The highest yield of 3M-A was obtained in the reaction performed at pH 4.6 and 80 degrees C for 75 h. The minor form of the interconverting peaks could not be characterised on the basis of the spectral data. However, it is concluded that the minor peak most likely represents the hydrated form of 3M-A. Since these adducts are formed only in trace amounts at neutral pH and 37 degrees C and the formation requires high amounts of malonaldehyde, it is likely that the adducts are not formed in DNA in vivo and thus not contribute to the malonaldehyde genotoxicity.     

Electrochemical monitoring of methylparathion degradation in an acid aqueous medium in presence of Cu(II)

A study was undertaken to determine the effect of Cu(II) in degradation of methylparathion (o,o-dimethyl o,4-nitrophenyl phosphoriotioate) in acid medium. Initial electrochemical characterization of Cu(II) and methylparathion was done in an aqueous medium at a pH range of 2-7. Cu(II) was studied in the presence of different anions and it was observed that its electroactivity depends on pH and is independent of the anion used. Methylparathion had two reduction signals at pH < or = 6 and only one at pH > 6. The pesticide's transformation kinetic was then studied in the presence of Cu(II) in acid buffered aqueous medium at pH values of 2, 4, and 7. Paranitrophenol appeared as the only electroactive product at all three pH values. The reaction was first order and had k values of 5.2 x 10(-3) s(-1) at pH 2, 5.5 x 10(-3) s(-1) at pH 4 and 9.0 x 10(-3) s(-1) at pH 7. It is concluded that the principal degradation pathway of methylparathion in acid medium is a Cu(II) catalyzed hydrolysis reaction.     

Arsenic release from iron rich mineral processing waste: Influence of pH and redox potential

This paper presents the effect of pH and redox potential on the potential mobility of arsenic (As) from a contaminated mineral processing waste. The selected waste contained about 0.47 g kg(-1) of As and 66.2 g kg(-1) of iron (Fe). The characteristic of the waste was identified by acid digestion, X-ray diffraction and sequential extraction procedures. Less than 2% of the total As was acid extractable with the remaining 98% associated with Fe-oxyhydroxides and oxides. Batch leaching tests at different pH conditions showed a strong pH dependence on arsenic and iron leaching. Arsenic leaching followed a "V" shaped profiles with significant leaching in the acidic and alkaline pH region. Acid extractable phases dissolved at acidic pH, while desorption of arsenic due to increase in pH resulted in high arsenic concentration at alkaline pH. Under aerobic conditions and pH 7, As solubility was low, probably due to its precipitation on Fe-oxyhydroxides. Maximum As solubilization occurred at pH 11 (3.59 mg l(-1)). Similarity in the As and Fe leaching profiles suggested that the release of As was related to the dissolution of Fe in the low pH region. In general, redox potential did not play a significant role in arsenic or iron solubilization. It was thus concluded that for this solid waste, desorption was the predominant mechanism in arsenic leaching. A simple thermodynamic model based on arsenic and iron redox reactions was developed to identify the more sensitive redox couple.     

Kinetics and mechanism of oxidation of tetrachloroethylene with permanganate

The kinetics, reaction pathways and product distribution of oxidation of tetrachloroethylene (PCE) by potassium permanganate (KMnO4) were studied in phosphate-buffered solutions under constant pH, isothermal, completely mixed and zero headspace conditions. Experimental results indicate that the reaction is first-order with respect to both PCE and KMnO4 and has an activation energy of 9.3+/-0.9 kcal/mol. The second-order rate constant at 20 degrees C is 0.035+/-0.004 M(-1) s(-1), and is independent of pH and ionic strength (I) over a range of pH 3-10 and I approximately 0-0.2 M, respectively. The PCE-KMnO4 reaction may proceed through further oxidation and/or hydrolysis reaction pathways, greatly influenced by the acidity of the solution, to yield CO2(g), oxalic acid, formic acid and glycolic acid. Under acidic conditions (e.g., pH 3), the further oxidation pathway will dominate and PCE tends to be directly mineralized into CO2 and chloride. Under neutral (e.g., pH 7) and alkaline conditions (e.g., pH 10), the hydroxylation pathway dominates the reaction and PCE is primarily transformed into oxalic acid prior to complete PCE mineralization. Moreover, all chlorine atoms in PCE are rapidly liberated during the reaction and the rate of chloride production is very close to the rate of PCE degradation.     

Reproductive status, blood chemistry, gill histology and growth of perch (Perca fluviatilis) in three acidic lakes

Perch (Perca fluviatilis L.) were sampled soon after spawning in three small acidic lakes (pH 4.3-6.1, Al(lab) 5-106 microg litre(-1), Ca2+ 0.01-0.08 mmol litre(-1)) and in one circumneutral lake (pH 5.9-6.4, Al(lab) 4-12 microg litre(-1), Ca2+ 0.06-0.07 mmol litre(-1)) in southern Finland. Due to the delayed spawning of perch in the acidic lakes, sampling in those lakes was performed later than in the reference lake. In spite of that, the gonadosomatic index (GSI) of males in all the acidic lakes was significantly greater than in the reference lake. Of the two lakes with similar low water pH, the effects on reproduction were more prominent in the lake with higher water Al content. The plasma Ca2+ concentrations of females in the acidic lakes were significantly smaller than in the females of the reference lake. The low female:male plasma Ca2+ ratio (1.0-1.32) depicted delay of spawning. Stress in perch in acidic water was also seen in elevated blood haematocrit values, especially in females. On the other hand, a low plasma Cl- level, a common response to acidic water in salmonids, was not detected in perch in the most acidic lakes. The amount of Al accumulated in the gill epithelium was highest in the most acidified lake with high Al concentration, but was also pronounced in a lake with low pH and low Al concentration.