Kinetics of heterogeneous photocatalytic decomposition of 2,4-dichlorophenoxyacetic acid over titanium dioxide and zinc oxide in aqueous solution

The photocatalytic transformation of 2,4-D in aqueous solution containing a suspension of titanium dioxide or zinc oxide leads to the formation of intermediates which are totally mineralised to carbon dioxide and hydrogen chloride (2,4-dichlorophenol and chlorohydroquinone are the major intermediates). The products at the initial stage of the reaction were 2,4-dichlorophenol (2,4-DCP), chlorohydroquinone, 4-chloropyrocatechol, 2,4-dichloropyrocatechol and 1,4-chlorobenzoquinone. The initial rate of photodegradation was studied as a function of the initial concentration of reactants by the linearised form of the Langmuir–Hinshelwood equation, by which rate constants k and equilibrium adsorption constants K were evaluated. These constants were calculated at different temperatures between 25 and 60°C. The photodegradation rate increased with increase of pH. The photocatalytic transformation of 2,4-D over titanium dioxide or zinc oxide in solution containing hydrogen peroxide was studied. The latter accelerated the reaction rate of 2,4-D significantly. It was found that chloride or bicarbonate ions slowed down the photodegradation rate of 2,4-D by scavenging hydroxyl radicals. Partial inhibition by ethanol is attributed to scavenging of the OH radicals involved in the first step of the reaction. © 1998 Society of Chemical Industry     

Kinetics of interaction of three carbamate pesticides with Indian soils: Aligarh district

The kinetics of interaction with soil of three carbamate pesticides (I, II, III) used as nematicides and herbicides was studied at four different temperatures from solutions of six soil samples of Aligarh district. The values obtained for rate constants for adsorption and desorption were in good agreement with those obtained from the Lindstrom model, which proved useful in the simultaneous evaluation of adsorption (k1) and desorption (k2) rate constants. The rate constants for pesticides were in the order III > I > II on all the six soil samples. The data for rate constants, activation energies, heats of activation, entropy of activation and thermodynamic parameters indicated a partly physical and partly chemical adsorption of pesticide on the soil surfaces. Adsorption occurred via coordination and/or protonation of the exchangeable cations with the amidic carbonyl group, and hydrogen bonding and dipole association at the crystal edge and basal surfaces. The adsorptivity of the soils may be attributed to the organic matter content and percentage clay content.     

A mechanistic analysis of penetration of glyphosate salts across astomatous cuticular membranes

Penetration of glyphosate salts across isolated poplar (Populus canescens (Aiton) Sm) cuticular membranes (CM) was studied using Na+, K+, NH4+, trimethylsulfonium+ (TMS) and isopropylamine+ (IPA) as cations. After droplet drying, humidity over the salt residues on the outer surfaces of the CM was kept constant, and cuticular penetration was monitored by sampling the receiver solution facing the inner surfaces of the CM. Glyphosate salts disappeared exponentially with time from the surfaces of the CM. This first-order process could be quantitatively described using rate constants (k) or half-times (time for 50% penetration; t1/2). Humidity strongly affected the velocity of penetration, as k increased by factors of 5.3 (K-glyphosate), 6.9 (TMS-glyphosate), 7.1 (NH4-glyphosate), 8.5 (Na-glyphosate) and 10.5 (IPA-glyphosate) when humidity was increased from 70 to 100%. Depending on the type of cation and humidity, t1/2 varied between 4 and 70h, but the humidity effect was statistically significant only at 100% humidity, when half-times were highest with IPA-glyphosate and lowest with TMS-glyphosate. Glyphosate acid penetration was measured only at 90% humidity and found to be extremely slow (t1/2 = 866 h). Adding 0.2 g litre-1 of a wetter (alkylpolyglucoside) to the donor increased IPA-glyphosate rate constants by about four times, but increasing concentration produced no further increase in k. When donors contained 0.2 g litre-1 wetter, further additions of 4 g litre-1 Ethomeen T25 did not change rate constants measured with IPA-glyphosate at 90% humidity, while Genapol C-100 and diethyl suberate increased k by only 35%. Concentration of IPA-glyphosate (1, 2 and 4 g litre-1) did not influence k at 90% humidity, and pH of donor solutions (4.0, 7.7, 9.5) had no effect on k of K-glyphosate at 90% humidity. Temperature (10 to 25 degrees C) had only a small influence on velocity of penetration of IPA-glyphosate and K-glyphosate, as energies of activation amounted to only 4.26 and 2.92 kJ mole-1, respectively. These results are interpreted as evidence for penetration of glyphosate salts in aqueous pores.     

双氟磺草胺在不同类型土壤中的吸附与淋溶特性研究

农药在土壤中的吸附和淋溶特性是评价其环境行为的重要指标。采用批量平衡法和土柱淋溶法,研究了双氟磺草胺在小麦种植区3种代表性土壤中的吸附和淋溶特性。结果表明:双氟磺草胺在安徽黏土、山东砂质壤土和河南砂质黏壤土中的吸附规律均可以较好地用Freundlich方程描述,其吸附系数(Kf)在0.39~0.62之间;土壤有机碳归一化吸附系数(Koc)在66.91~81.35之间,表明双氟磺草胺在3种土壤中均属于难吸附型;吸附自由能(ΔG)在-10.90~-10.42kJ/mol之间,均属于物理吸附。双氟磺草胺在3种土壤中的淋出率在71.7%~74.1%之间,说明其在3种土壤中的淋溶性均较强。双氟磺草胺初始添加量和腐殖酸对淋出率具有一定影响。综合试验结果,认为双氟磺草胺在3种土壤中的吸附和淋溶可能受土壤有机质含量、黏粒含量、阳离子交换量和土壤pH值等多个因素的综合影响,其对地下水的污染风险较大,因此应引起高度重视。     

Structure–degradability relationships for propyzamide analogues in soils

The kinetics of the degradation in soil of propyzamide and nine analogues have been measured at two temperatures (28 and 60°C). The degradation rates of propyzamide were determined in sterilised soil and in soil perfusates. The results obtained are in agreement with a chemical degradation of propyzamide and its analogues. Relationships were established between degradation rate constants and physicochemical parameters of the compounds: log k = ?aσ+bπ + c where σ = Hammett constant, π = hydrophobic constant, a, b, c are constants.     

Synthesis of 1,2,4-triazole compounds related to the fungicides flutriafol and hexaconazole

Triazole and imidazole compounds are important both as pharmaceutical and agrochemical fungicides. It has been demonstrated that they exhibit this activity because they inhibit the 14 α-demethylase enzyme involved in the biosynthesis of fungal sterols. A knowledge of the mode of action of the triazoles paclobutrazol, diclobutrazol and propiconazole has made it possible to devise inhibitors of the 14 α-demethylase enzyme somewhat more readily, using computer graphic techniques. These techniques were used in the discovery of flutriafol, one of the first examples of a triazole tertiary alcohol structure. They also assisted in identifying other triazole tertiary alcohol structures for testing as fungicides. Hexaconazole is one example of a highly active broad-spectrum fungicide. Modification of the hexaconazole structure has produced many other active fungicides, many of which can be conveniently synthesised by the addition of organometallic (e.g. lithium, magnesium, aluminium, titanium or zinc) reagents to α-1,2,4-triazol-1-yl ketones or α-haloketones. Alternatively, they can be prepared by the reaction of nucleophiles such as mercaptans, nitrogen heterocycles or organometallic (e.g. magnesium) reagents with epoxides.     

三氟苯嘧啶在5种土壤中的吸附与解吸附行为

为研究三氟苯嘧啶的吸附-解吸附特性,采用振荡平衡法研究了三氟苯嘧啶在采集于吉林通化、江苏扬州、江西萍乡、广西南宁和海南海口等地的5种土壤中的吸附-解吸附行为及其环境影响因素。结果表明:三氟苯嘧啶在土壤中的吸附动力学符合Elovich模型,吸附和解吸附等温线符合Freundlich模型,吸附常数在1.886~7.626。温度的升高更有利于吸附,土壤对三氟苯嘧啶的吸附主要是物理吸附;随着溶液中pH值的升高,土壤对三氟苯嘧啶的吸附能力逐渐下降。除广西南宁黏壤土外,三氟苯嘧啶在5种土壤中的解吸附过程中存在滞后现象,不易在土壤中长期积累,具有一定的迁移特性。     

Alcoholysis and chemical hydrolysis of bensulfuron-methyl

Alcoholysis (methanol or ethanol) and hydrolysis (pH ≤ 8) of the herbicide bensulfuron-methyl at 30 or 50^C involve only the breakdown of the urea part of the molecule. A high yield of the pyrimidinamine is always obtained, along with the corresponding carbamate (alcoholysis) or benzylsulfonamide (hydrolysis). The latter compound was easily cyclized (pH ≥ 6). In alkaline solution, the carbomethoxy substituent of the aromatic ring was preferentially hydrolysed. In all cases, the alcoholysis and hydrolysis rates could be described well with first-order kinetics. Alcoholysis rate constants of bensulfuron-methyl and bensulfuron ranged from 0.08 to 0.15 d^?1 at 30^C. Hydrolysis rate constants of bensulfuron-methyl, bensulfuron and benzylsulfonamide varied strongly with pH. The hydrolysis rate constant of bensulfuron-methyl was minimal around pH 8. The hydrolysis rate constant of bensulfuron decreased with increasing pH, whereas that of benzylsulfonamide increased with increasing pH.     

萘磺酸甲醛缩合物分散剂在氟铃脲颗粒表面的吸附性能研究

采用残余质量浓度法、ζ电位仪、红外光谱(IR)和X射线光电子能谱(X-Photoelectron spectroscopy, XPS)系统地研究了萘磺酸甲醛缩合物(NNO)分散剂在氟铃脲颗粒表面的吸附量、吸附状态、ζ电位、吸附作用力、吸附层厚度等性能。结果表明:NNO在氟铃脲表面的饱和吸附量、Langmuir吸附平衡常数k和ζ电位均随NNO相对分子质量增加而增大, NNO分散剂在氟铃脲表面呈多点吸附,吸附了NNO的氟铃脲的IR谱具有明显的"红移"现象,说明氢键是分散剂NNO与氟铃脲表面结合的重要作用力, NNO在氟铃脲颗粒表面的吸附层厚度为5.97 nm, 分析认为,NNO在氟铃脲颗粒表面吸附后具有静电排斥和空间位阻双重作用,可以较好地维持氟铃脲悬浮剂的分散稳定性。     

苜蓿轮枝菌的生物学特性分析及ATMT遗传转化体系的建立

 为了揭示苜蓿轮枝菌Verticillium alfalfae的生物学特性及其致病机理,在室内条件下测定不同温度、pH值、碳源和氮源对菌株Ms198的生长速率和产孢量的影响,同时利用农杆菌转化法(Agrobactirium tumfacience-mediated transformant,ATMT)将带有潮霉素(Hygromycin,Hyg)抗性标记和绿色荧光蛋白(green fluorescent protein,GFP)报告基因的双元载体转入苜蓿轮枝菌的分生孢子,获得147株阳性转化子,以野生型菌株为对照,对挑取的15株阳性转化子的菌落形态、生长速率、产孢量、孢子萌发率、粗毒素分泌量和致病力进行研究。结果表明,苜蓿轮枝菌具有较宽的温度和酸碱度适应范围,最适生长和产孢温度分别为25 ℃和20 ℃,最适生长pH值为6 ~ 9,最适产孢pH值为9。可以利用多种碳、氮源,最适生长的碳、氮源分别为可溶性淀粉和牛肉膏,最适产孢的碳、氮源分别为D-牛乳糖和胰蛋白胨。与野生型菌株相比,15株供试转化子中有66.67%的转化子在菌落形态方面与野生型菌株无明显差别,而其生长速率、产孢量和孢子萌发率均有不同程度的降低。在产毒能力和致病力方面,1株转化子的粗毒素分泌量显著高于野生型菌株,9株显著低于野生型菌株,其余5株与野生型菌株无显著差异;4株转化子的致病力显著低于野生型菌株,其余11株转化子的致病力与野生型菌株均无显著差异。研究结果表明,转化子的生物学特性以及产毒能力和致病力,随外源基因插入位点的随机性而有所变化。     

Kinetic Study of the Degradation of Ethiofencarb in Aqueous Solutions

A kinetic study of the hydrolysis of ethiofencarb (α-ethylthio-o-tolyl methylcarbamate) in pure water and in aqueous solutions at pH 2, 6, 9 and 12 and at three different temperatures (4, 20 and 50(±1)°C) has been carried out using a gas chromatographic nitrogen-phosphorus detection method. The values of the first-order rate constants (k) for the degradation reaction were calculated. The values for k were found to be dependent on pH and temperature. No acid hydrolysis was observed in any case. Complete degradation of ethiofencarb was observed at pH 12 at all three temperatures; it was practically instantaneous at room temperature. Ethiofencarb was also completely degraded at pH 9 at 20 and 50°C, while in pure water (pH 6) degradation took place at 50°C but not at 20°C. Ethiofencarb was not degraded in pure water at lower temperatures and, due to the reversible nature of the reaction, at equilibrium about 80% of the pesticide remained undegraded at room temperature. © 1997 SCI.     

Co‐solvent effects on the adsorption of carbofuran by two Indian soils

The adsorption of carbofuran on soils from water‐methanol mixtures has been evaluated by batch shake testing. Two uncontaminated soils having different physicochemical properties were used in these experiments. The volume fraction of methanol in the liquid phase (f_s) was varied from 0.25 to 1.0. Higher adsorption of carbofuran was observed in medium black (silt loam) soil than in alluvial (sandy loam) soil; calculated values of the Freundlich constant (K^m) and distribution coefficient (K_d) showed that adsorption of carbofuran in both soils decreased with increase in f_S values. The decreased carbofuran adsorption in methanol–water mixtures meant a greater potential of ground‐water contamination through leaching from potential sites. The data have been used to evaluate the co‐solvent theory for describing adsorption of carbofuran in methanol–water mixtures. The aqueous phase partition coefficient K_dw (mol g⁻¹) normalized with respect to f_oc and the aqueous phase adsorption constant K_w for carbofuran were evaluated by extrapolating to f_S = 0. © 2000 Society of Chemical Industry     

Hydrolysis of triasulfuron,metsulfuron‐methyl and chlorsulfuron in alkaline soil and aqueous solutions

The hydrolysis of triasulfuron, metsulfuron‐methyl and chlorsulfuron in aqueous buffer solutions and in soil suspensions at pH values ranging from 5.2 to 11.2 was investigated. Hydrolysis of all three compounds in both aqueous buffer and soil suspensions was highly pH‐sensitive. The rate of hydrolysis was much faster in the acidic pH range (5.2–6.2) than under neutral and moderately alkaline conditions (8.2–9.4), but it increased rapidly as the pH exceeded 10.2. All three compounds degraded faster at pH 5.2 than at pH 11.2. Hydrolysis rates of all three compounds could be described well with pseudo‐first‐order kinetics. There were no significant differences (P = 0.05) in the rate constants (k, day⁻¹) of the three compounds in soil suspensions from those in buffer solutions within the pH ranges studied. A functional relationship based on the propensity of nonionic and anionic species of the herbicides to hydrolyse was used to describe the dependence of the ‘rate constant’ on pH. The hydrolysis involving attack by neutral water was at least 100‐fold faster when the sulfonylurea herbicides were undissociated (acidic conditions) than when they were present as the anion at near neutral pH. In aqueous buffer solution at pH > 11, a prominent degradation pathway involved O‐demethylation of metsulfuron‐methyl to yield a highly polar degradate, and hydrolytic opening of the triazine ring. It is concluded that these herbicides are not likely to degrade substantially through hydrolysis in most agricultural alkaline soils. © 2000 Society of Chemical Industry     

Photolysis of fluchloralin in aqueous methanol

The photodegradation of fluchloralin by UV irradiation or sunlight in aqueous methanolic solution has been examined. In the presence of titanium dioxide five photoproducts were obtained, but only four in its absence. One photoproduct, 2, 2'-azoxy-bis(alpha,alpha,alpha-trifluoro-6-nitro-p-toluidine) is reported for the first time as a metabolite of fluchloralin. In natural sunlight the rate of degradation was higher than in UV light and titanium dioxide had almost no effect on the rate of degradation.     

Kinetics and hydrolysis mechanism of chlorsulfuron and metsulfuron-methyl

In acidic media, hydrolysis of chlorsulfuron and metsulfuron-methyl occurs via two consecutive reactions which were followed by ultraviolet spectrophotometry. For these two reactions, the pseudo-first-order rate constants increase proportionally to the concentration of hydronium ion in the more acidic media and to the square of this concentration at higher pH values. A kinetic study by HPLC shows that the first reaction leads to the formation of 4-methoxy-6-methyl-1,3,5-triazin-2-amine and (o-chlorophenylsulfonyl) carbamic acid for chlorsulfuron or (o-methoxycarbonylphenylsulfonyl) carbamic acid for metsulfuronmethyl. The second reaction is the conversion of these sulfonylcarbamic acids to sulfonamides and carbon dioxide. The complete lack of saccharin and of o-sulfamoyl benzoic acid proves that the ester function of the methoxycarbonyl group is stable. The lack of general acid-base catalysis and a solvent deuterium isotope effect less than unity are consistent with a rate-determining cleavage of the protonated substrate. In the basic pH range (10–14) a single reaction occurs, the nucleophilic substitution of the methoxy group on the triazine by a hydroxide group.     

Chemical hydrolysis of 2-chloro-4,6-bis(alkylamino)-1,3,5-triazine herbicides and their breakdown in soil under the influence of adsorption

The determination of rate constants and the calculation of the activation parameters [activation energy (E_a), free energy of activation(ΔG^≠)and entropy of activation (ΔS^≠)] demonstrated the identity of the reaction kinetics of chemical hydrolysis of the chlorinated triazine herbicides simazine, atrazine, propazine and terbuthylazine. Persistence in soil could be estimated, from the hydrolytic half-life time, only in pH regions where these compounds were also sensitive to chemical hydrolysis. In general, the rate of hydrolysis increased in the presence of soil as the result of a catalysing effect of the soil in their breakdown. When half-lives in soil of these triazine herbicides were compared with adsorption constants, a functional relationship was observed in both soil types; as adsorption increased the half-life in soil also increased.     

Studies on organophosphorus impurities in technical malathion: Inhibition of carboxylesterases and the stability of isomalathion

Four organophosphorus esters found as impurities in technical malathion were synthesized, and their abilities to inhibit monomeric and oligomeric carboxylesterases from rabbit liver, as well as type I and type II esterases from porcine liver, were studied. The equilibrium dissociation constant (K_d), phosphorylation constant (k₂), and bimolecular rate constant (k_i) were determined in the presence of substrate. Inhibition, as judged by the k_i, was in the following order: isomalathion > O,S,S-trimethyl phosphorodithioate > O,O,S-trimethyl phosphorothioate > O,O,S-trimethyl phosphorodithioate. All of the k₂ values were relatively small, indicating that the k_d values contribute most to the overall inhibitory power. Rabbit liver carboxylesterases are more sensitive to inhibition by isomalathion than porcine liver esterases, reflecting a species difference. Isomalathion undergoes nonenzymatic degradation in the presence of fluoride ions, producing diethyl thiomalate. A kinetic investigation of the nonenzymatic degradation of isomalathion was conducted, and reaction rate constants were determined in phosphate buffer at various molarities, temperatures, and pH values.     

A field tracer study of attenuation of atrazine,hexazinone and procymidone in a pumice sand aquifer

A field tracer experiment, simulating point source contamination, was conducted to investigate attenuation and transport of atrazine, hexazinone and procymidone in a volcanic pumice sand aquifer. Preliminary laboratory incubation tests were also carried out to determine degradation rates. Field transport of the pesticides was observed to be significant under non‐equilibrium conditions. Therefore, a two‐region/two‐site non‐equilibrium transport model, N3DADE, was used for analysis of the field data. A lump reduction rate constant was used in this paper to encompass all the irreversible reduction processes (eg degradation, irreversible adsorption, complexation and filtration for the pesticides adsorbed into particles and colloids) which are assumed to follow a first‐order rate law. Results from the field experiment suggest that (a) hexazinone was the most mobile (retardation factor R = 1.4) and underwent least mass reduction; (b) procymidone was the least mobile (R = 9.26) and underwent the greatest mass reduction; (c) the mobility of atrazine (R = 4.45) was similar to that of rhodamine WT (R = 4.10). Hence, rhodamine WT can be used to delimit the appearance of atrazine in pumice sand groundwater. Results from the incubation tests suggest that (a) hexazinone was degraded only in the mixture of groundwater and aquifer material (degradation rate constant = 4.36 × 10^?3 day^?1); (b) procymidone was degraded not only in the mixture of groundwater and aquifer material (rate constant = 1.12 × 10^?2 day^?1) but also in the groundwater alone (rate constant = 2.79 × 10^?2 day^?1); (c) atrazine was not degraded over 57 days incubation in either the mixture of aquifer material and groundwater or the groundwater alone. Degradation rates measured in the batch tests were much lower than the total reduction rates. This suggests that not only degradation but also other irreversible processes are important in attenuating pesticides under field conditions. Hence, the use of laboratory‐determined degradation rates could underestimate reduction of pesticides in field conditions. © 2001 Society of Chemical Industry     

烟嘧磺隆在土壤中的吸附及与土壤性质的相关性研究

采用平衡振荡法研究了烟嘧磺隆在8种不同类型土壤中的吸附,结果表明,其吸附过程均符合经典的Freundlich模型,最大吸附常数为6.891,最小吸附常数为0.798。根据土壤有机吸附常数和吸附自由能的大小对该除草剂的移动性能进行了评价,认为其在8种土壤中均以物理吸附为主,且具有中等或较高的移动性能。通过对吸附常数Kf与土壤有机质含量、粘土含量和pH值的关系进行分析,发现土壤有机质含量、粘土含量和pH值在吸附过程中均属支配因素,Kf与土壤有机质含量、粘土含量呈正相关,而与土壤pH值呈负相关。