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.     

Kinetics of chemical degradation of organophosphorus pesticides; hydrolysis of chlorpyrifos and chlorpyrifos-methyl in the presence of copper(II)

The kinetics of the hydrolysis reactions of chlorpyrifos-methyl and chlorpyrifos, in the presence of copper(II), have been measured in buffered aqueous solutions. For each reaction, a rate law of the type -d[pesticides]/dt= k₂[pesticides][Cu²⁺] was observed. As the concentration of copper(II) increased, a corresponding increase in the rate of hydrolysis was observed until the concentration of copper(II) reached about 1.0 × 10^?2_M. At this point, the rate of hydrolysis became independent of the concentration of copper(II) in both reactions. Using the experimental data, a mechanism for each reaction is proposed, in which the copper(II) ion forms a six-membered ring complex with the nitrogen in the ring structure and the sulphur of the phosphorothioate moiety. The rate of hydrolysis increased with increasing pH. At higher pH values, precipitation of Cu²⁺ was observed and general base-hydrolysis reactions became more and more important. The differences in the rate constant observed is explained using the inductive effect theory of the alkyl group.     

Kinetics of hydrolysis of atrazine in aqueous fulvic acid solution

The hydrolysis of atrazine in aqueous fulvic acid solution followed first-order kinetics with respect to the herbicide concentration. The half-life of atrazine, calculated from first-order plots, was lowest at low pH and increased as the pH of the reaction mixture increased. Increase in fulvic acid concentration resulted in a higher hydrolysis rate constant and a shortened half-life but had no effect on the activation energy. However, the latter increased with increase in pH of the reaction mixture. The only product identified after hydrolysis in fulvic acid solution was 2-ethylamino-4-hydroxy-6-isopropylamino-1,3,5-triazine.     

莠去津在土壤中的残留动态和淋溶动态

利用HPLC法对土壤中莠去津的残留动态、淋溶动态进行了研究。结果显示,莠去津以有效成分2.25 kg/hm2和4.50 kg/hm2的剂量施用时,在土壤中的半衰期分别为19.1 d和18.1 d,即其半衰期与莠去津的施用浓度无关,属于典型的一级动力学反应。在120 d的玉米生长期中,土壤中莠去津在不断降解代谢的同时,逐渐向深层土壤中淋溶,多数莠去津持留在表层土壤中。施用莠去津27 d后,高浓度处理小区莠去津的淋溶深度超过30 cm,深度为10~15 cm处的土壤在施用后27 d莠去津的浓度最大。同一土壤深度,莠去津在高浓度处理小区的残留量要远高于低浓度处理小区。这些结果显示,减小莠去津的用量可以减少莠去津在土壤中的移动,表明低剂量施用莠去津是保护地下水免受污染的一种有效措施。影响莠去津的淋溶作用的主要因素包括使用量和土壤的理化特性。     

喹草酮与莠去津复配防除杂草效果及对高粱的安全性

为明确对羟基丙酮酸双氧化酶抑制剂类新型除草剂喹草酮应用于高粱田的可行性,于2018-2019年在温室和田间测定喹草酮与莠去津复配的除草效果及对高粱的安全性。温室试验结果表明,喹草酮与莠去津复配对狗尾草Setaria viridis和苘麻Abutilon theophrasti均有很好的防除效果,两者按有效成分用量比1：4~1：7配比对狗尾草的GR₅₀在134.40~168.92 g （a.i.）/hm²之间,明显好于喹草酮和莠去津单独施用时的GR₅₀,分别为150.53g （a.i.）/hm²和589.30g （a.i.）/hm²;两者复配对狗尾草的共毒系数在234.80~311.03之间,远大于120.00,显示出明显的增效作用;对苘麻的共毒系数在140.16~168.38之间,也表现出增效作用;对马唐Digitaria sanguinalis也有较好的防除效果;喹草酮与莠去津按有效成分用量比1：5复配的制剂在最高用量3 600g （a.i.）/hm²处理下,3个高粱品种生长均正常,且对高粱和杂草之间的选择性指数远大于6.59,对高粱的安全性高。田间试验结果表明,喹草酮与莠去津复配应用于高粱田对高粱安全,且对田间杂草野稷Panicum ruderale、虎尾草Rabdosia eriocalys、稗Echinochloa crus-galli、反枝苋Amaranthus retroflexus和藜Chenopodium album等均有极好的防除效果,2018-2019年对高粱田杂草的总株防效分别为94.2%和92.8%,鲜重防效分别为95.6%和94.2%,明显高于药剂对照50%异甲·莠去津悬浮剂土壤处理和37%二氯·莠去津悬浮剂茎叶处理的防除效果。表明喹草酮与莠去津复配应用于高粱田防除杂草效果良好。     

Photolysis and hydrolysis of rimsulfuron

The degradation in the liquid phase of rimsulfuron and its commercial 250 g kg⁻¹ WG formulation (Titus®) was investigated. Photolysis reactions were carried out at 25 °C by a high-pressure mercury arc (Hg-UV) and a solar simulator (Suntest), while the hydrolysis rate was determined by keeping aqueous buffered samples in the dark. The effects of solvent and water pH on reaction kinetics were studied, and the results compared to literature data. Photoreactions of the commercial product in organic solvents were faster than pure rimsulfuron. Under simulated sunlight in water, the half-life for the photolysis reaction ranged from one to nine days at pH 5 and 9, respectively. The hydrolysis rate was as high as the photolysis rate, but decreased on increasing water pH. The main metabolite identified in neutral and alkaline conditions as well as in acetonitrile was N-[(3-ethylsulfonyl)-2-pyridinyl]-4,6-dimethoxy-2-pyridinamine, while N-(4,6-dimethoxy-2-pyrimidinyl)-N-[(3-(ethylsulfonyl)-2-pyridinyl)]urea and minor metabolites prevailed in acidic conditions. © 1999 Society of Chemical Industry     

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.     

Hydrolysis of the pyrethroid insecticide fenpropathrin in aqueous media

The hydrolysis of [¹⁴C] fenpropathrin ( I ) [(RS)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate] was studied in buffer solutions at pH 1.9–10.4, and in natural river and sea water at 25, 40, 55 and 65°C under laboratory conditions. The hydrolysis of I proceeded predominantly through neutral (pH independent) and base-catalysed processes in the regions below pH 3.9 and above pH 7.0, respectively, whereas both reactions occurred between pH 3.9 and 7.0. The rates of hydrolysis of I in buffer solutions were similar to those in one sample of river and one sample of sea water. If this obtains generally, it may be expected that the half-life of I in natural waters, normally within the range pH 5–9, will range from 1.54 to 1080 days at 40°C, 11.3 to 8520 days at 25°C and, by extrapolation of the data obtained in buffer solutions, 106 to 83 000 days at 10°C. The rate constants for hydrolysis of I in aqueous media can be expressed by: Where log k_N = 9.60–(5.56 × 10³ T^?1) and log k_B = 7.32–(2.56 × 10³ T^?1). The calculated rate constants were in good accord with the observed values in buffer solutions. Cleavage of the ester linkage was more rapid than hydration of the cyano group at any pH and temperature tested.     

Mechanism of hydantoin ring opening in iprodione in aqueous media

The hydrolysis kinetics of iprodione in alkaline solutions of pH 8.3 to 12 at 25°C have been determined by ultraviolet spectrophotometry. Under these conditions, iprodione leads quantitatively and irreversibly to N-(3,5-dichloroanilinocarbonyl)-N-(isopropylaminocarbonyl)glycine. The reaction is not subject to a general basic catalysis and the rate law takes the form K_obs = K_OH- [OH^?1]. The activation entropy of -77 J mol^?1deg^?1, the value of the kinetic solvent isotope effect k_OH?/k_OD? of 0.79 and the value of 0.60 for the Hammett parameter σ, obtained for the hydrolysis of a series of 3-aryl-N-isopropyl-2,4-dioxoimidazolidine-1-carboxamides are all in agreement with the rate-determining attack by the hydroxyl ion on the carbonyl in the 4-position of the hydantoin ring of the fungicide.     

Abiotic persistence of atrazine and simazine in water

Hydrolysis and photolysis experiments have been undertaken to investigate the abiotic persistence of atrazine and simazine in a variety of waters. Hydrolysis only occurs to a significant extent at pH values at the lower limit of those found in the natural aquatic environment (pH 4.0 or less). Photolysis was initiated by a wide range of wavelengths in waters at pH 4.0, but only by more energetic wavelengths of less than 300 nm at higher pH values (pH 6 to 8). Based on these data, the aquatic half-life of atrazine and simazine in well-lit acidic upland waters will be typically six days. In lowland rivers with higher pH (7 to 8.5), these triazines are likely to exhibit half-lives of months rather than days. In groundwaters, atrazine and simazine will have half-lives in the order of years, due to the exceedingly slow rate of hydrolysis. © 1999 Society of Chemical Industry     

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     

Bioefficacy and leaching of controlled-release formulations of triazine herbicides

Conventional formulations of atrazine and simazine were compared with controlled-release formulations of these two herbicides for bioefficacy, leaching and crop safety in laboratory and field experiments. Three light-textured soils with a pH range of 5.8–8.5 were used for this work. An oat bioassay (Avena sativa L.) was used to quantify soil concentrations of the herbicides. Comparison of the initial bioefficacy of controlled-release formulations of atrazine and simazine showed their respective relative potencies to conventional formulations to be 0.51–0.85. The results indicated that the controlled-release formulations maintained an entrapped reserve of active ingredient after delivery with a conventional boomsprayer. In laboratory trials, the controlled-release formulations showed a reduction in leaching compared with conventional formulations. A controlled-release formulation and a conventional formulation of atrazine were tested further in a field trial. A higher concentration of atrazine in topsoil from the controlled-release formulation was observed 11 weeks after application after 107 mm of rainfall. It was deduced that this was caused by reduced leaching of the controlled-release formulation, as observed in laboratory trials. EWRC scores for the control of a range of grass and broad-leaved weeds were identical for both formulations. This indicated that, while the controlled-release formulation could inhibit leaching of the active ingredient, it did not hinder the level of potency necessary for early weed control. EWRC crop safety ratings of chickpeas (Cicer arietinum L.) sown at application were higher for the controlled-release formulation 10 weeks after sowing, and subsequent harvest yields were 50% higher. It was inferred that this resulted from a favourable interaction between crop growth and the timing of the release of the active ingredient from the controlled-release formulation. Altogether, the controlled-release formulations displayed the necessary prerequisites for their further development for large-scale use under arable regimes.     

Hydrolyse chimique acide du metsulfuron méthyle

Chemical acidic hydrolysis of metsulfuran methyl The chemical degradation of metsulfuron methyl in acidic aqueous solution involved two pathways: hydrolysis of the urea function and hydrolysis of methoxy radical. Decrease of pH (6 to 1) strongly increased activity but selectivity remained unchanged. Increase of temperature (25 to 55°C) enhanced the rate of reaction (E_A= 84 kj mol^?1) and favoured the urea function hydrolysis. Other factors (presence of various transition metals cations, humic acids or clays) were generally of limited effect, sometimes the rate of reaction was affected.     

Residualwirkung von Chlortriazin-Herbiziden im Boden an drei rumänischen Standorten. I. Prognose der Persistenz von Simazin und Atrazin im Boden

Residual effects of chlorotriazine herbicides in soil at three Rumanian sites. I. Prediction of the persistence of simazine and atrazine Persistence of simazine and atrazine in the top 10 cm soil was measured at three sites in Rumania with variations in climate and soil conditions. Both herbicides were applied at 1 and 3 kg ai ha^?1 to uncropped plots and to plots cropped with maize (Zea mays L.). Rates of residue decline were independent of application rate and crop cover but varied between sites. The time for 50% loss of atrazine varied from 36 to 68 days and that of simazine from 48 to 70 days. Laboratory studies were made with atrazine to characterize degradation rates under standard conditions and to measure adsorption and leaching behaviour in the different soils. Weather records for the periods of the field experiments were used in conjunction with appropriate constants derived from the laboratory results, or from data in the literature, in a computer program to simulate persistence in the field. Results from the model were in reasonable agreement with the observed soil residues although there was a tendency to overestimate rates of loss on some occasions. The results suggest that the model of persistence was sufficiently accurate for practical purposes, and that its use could preclude the need for extensive analytical measurements of residues.     

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     

DIFFERENTIAL PHYTOTOXICITY OF ATRAZINE AND AMETRYNE TO BANANAS*

Summary. In field screening trials for bananas (Musa acuminata var. Dwarf Cavendish) in Hawaii, ametryne (2-methylthio-4-ethylamino-6-isopropylamino-s-triazine) was less phytotoxic to bananas than atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine). Sand culture experiments showed that both herbicides were equally injurious to banana plants. Differential degradation of the herbicides by the plants did not account for the phytotoxicity observed. Both herbicides were partly metabolized by the plant to their common hydroxyl derivative (hydroxyatrazine) and two other unidentified metabolites after 3 and 7 days of exposure to nutrient solution containing ¹⁴C-labelled ametryne and atrazine. Phytotoxicity was directly related to leachability of the herbicides and negatively related to adsorption capacity of each soil for the herbicides. Organic matter content seemed to be correlated to the response observed. It was postulated that phytotoxicity in the field may have been attributed to differential location of the herbicide in relation to the roots.     

Hydrolysis of 1, 3-dichloropropene in dilute aqueous solution

Hydrolysis of [¹⁴C]-radiolabeled 1, 3-dichloropropene (1, 3-D) was studied at pH 5, 7 and 9 at 10, 20 and 30°C in sterile buffered water. The rate of hydrolysis was independent of pH at each temperature, with measured half-lives of 3-1 (±0.l), 11.3 (±0.5) and 51 (±2.3) days at 30, 20 and 10°C, respectively. The activation energy for the hydrolysis reaction was determined to be 23.9 kcal mol^?1 deg^?1. One hydrolysis product was formed during the course of the study and was identified by co-chrornatography with analytical standards, using h.p.l.c., to be 3-chloroallyl alcohol. The alcohol appeared to be stable to further hydrolytic conversion and was formed in the same cis: trans ratio as in the initial 1, 3-D starting material, indicating essentially identical rates of hydrolysis for the cis and trans isomers of 1, 3-D.     

Etude des phénomènes de sorption entre deux triazines herbicides et des acides humiques

A study of sorption phenomena between two triazine herbicides and humic acids Terbutryne is very readily adsorbed by humic acids while atrazine is only slightly adsorbed and this only in an acid environment. The influence of pH on adsorption and the competitive effect of the cations Ca²⁺, Al³⁺ and Fe³⁺ shows that the proton form of the molecules of the two herbicides can be adsorbed by an ion exchange-type mechanism; the neutral form of terbutryne molecules could be adsorbed by other mechanisms. Desorption of terbutryne is accompanied by a more marked hysteresis phenomenon in the case of neutral molecules, and, in an acid environment, calcium shows a weak capacity for displacement in relation lo the adsorbed herbicide.     

Removal of paraquat and atrazine from water by montmorillonite‐(Ce or Zr) phosphate cross‐linked compounds

The adsorption of paraquat (1,1′‐dimethyl‐4,4′‐bipyridilium dichloride) and atrazine (6‐chloro‐N ²‐ethyl‐N ⁴‐isopropyl‐1,3,5‐triazine‐2,4‐diamine) from aqueous solution onto two montmorillonite‐(Ce or Zr) phosphate cross‐linked compounds at different temperatures (288 K and 308 K) has been studied using batch experiments. The adsorption isotherms obtained for paraquat on both adsorbents may be classified as H‐type of the Giles classification, which suggests that paraquat molecules are strongly adsorbed on the samples. For the adsorption of atrazine, L‐type isotherms were obtained for both montmorillonite‐(Ce or Zr) phosphate compounds, which suggests that these compounds have a medium affinity for this herbicide. The increase in temperature from 288 K to 308 K did not have any clear effect on the adsorption process of paraquat on either adsorbent whereas atrazine adsorption decreased slightly as temperature increased, possibly due to a mainly physical process. Fourier transform infrared (FTIR) spectroscopic studies revealed that at the pH generated by the adsorbents, the cationic herbicide interacted to a greater extent with the negatively charged surface of the adsorbents than did atrazine. For both herbicides, the Ce‐montmorillonite adsorbent showed a higher adsorption capacity than the Zr‐montmorillonite adsorbent. © 2000 Society of Chemical Industry