Degradation of chlorsulfuron and triasulfuron in alkaline soils under laboratory conditions

The degradation of chlorsulfuron and triasulfuron was investigated in alkaline soils (pH 7.1–9.4) spiked at 40 μg a.i. kg^–1 under laboratory conditions at 25 °C and a moisture content corresponding to 70% field capacity (–33 kPa), using high-performance liquid chromatography. Degradation data for the two herbicides did not follow first-order kinetics, and observed DT₅₀ values in surface soils ranged from 19 to 42 days and from 3 to 24 days for chlorsulfuron and triasulfuron respectively. Disappearance of both chlorsulfuron and triasulfuron was faster in non-sterile than in sterile soil, demonstrating the importance of microbes in the breakdown process. The persistence of chlorsulfuron increased with increasing depth, which can be attributed to the decline in the microbial populations down the profile. The DT₅₀ value for chlorsulfuron at 30–40 cm depth was nearly four times higher than that in the top-soil. The results obtained show that persistence of these herbicides in alkaline surface soils at 25 °C and at a moisture content of 70% field capacity is similar to those reported in other European and North American soils. The study shows that if these herbicides are contained in surface soil layers, the risk of residue carry-over under southern Australian conditions is small. However, the rate of their degradation in alkaline subsoils is very slow, and under conditions conducive to leaching their prolonged persistence in the soil profile is possible.     

Degradation of triasulfuron in soil under laboratory conditions

Degradation of triasulfuron in non-autoclaved and autoclaved soil incubated at different temperatures and moisture contents was evaluated in the laboratory using a maize root growth bioassay. Disappearance of triasulfuron was faster in non-autoclaved than in autoclaved soil, indicating the importance of microorganisms in the breakdown process. Degradation of the herbicide was faster at 30°C than at 10°C, with half-lives of 11–13 days at 30°C and 30–79 days at 10°C. Degradation of the herbicide was influenced more by temperature than by variation in soil moisture. Disappearance of the herbicide was rapid in the non-autoclaved soil at 30°C during the initial 30 days of incubation, but low levels of residues persisted for up to 90 days. A second application of the herbicide, to soil in which an initial dose of triasulfuron had degraded, disappeared at the same rate as herbicide added to previously untreated soil, indicating that there was no enhancement of degradation with repeated application of herbicide. Dégradation du triasulfuron dans le sol en conditions de laboratoire La dégradation du triasulfuron dans des sols non autoclavés et autoclavés, incubés à des températures et à des teneurs en humidité différentes, a étéévaluée au laboratoire en utilisant un bio essai sur la croissance d'une racine de maïs. La disparition du triasulfuron a été plus rapide en sol non autoclavé qu'en sol autoclavé, soulignant l'importance des microorganismes dans le processus de dégradation. La dégradation de l'herbicide a été plus rapide à 30°C qu'à 10°C avec des demi-vies respectives de 11–13 jours et de 30–79 jours. La dégradation de l'herbicide a été plus influencée par la température que par les variations d'humidité du sol. La disparition de l'herbicide a été rapide dans le sol non autoclavéà 30°C pendant les 30 premiers jours d'incubation, mais de faibles résidus persistaient au delà de 90 jours. Une seconde application d'herbicide sur un sol dans lequel une dose initiate de triasulfuron avait été dégradée, a disparu de la même façon qu'une dose appliquée sur un sol non traitd, montrant qu'il n'y avait pas d'augmentation de la dégradation à la suite d'une répétition d'application. Abbau von Triasulfuron im Boden unter Laborbedingungen Der Abbau von Triasulfuron in nicht sterilisiertem und sterilisiertem Boden bei verschiedener Temperatur und Bodenfeuchte wurde mit einem Maiswurzel-Wachstumstest untersucht. Die Menge des Triasulfurons nahm im nicht-sterilisierten Boden schneller ab als im sterilisierten, was auf mikrobiellen Abbau hinweist. Das Herbizid wurde bei 30 °C mit einer Halbwertszeit von 11 bis 13 Tagen schneller abgebaut als bei 10 °C mit einer von 30 bis 79 Tagen. Der Abbau wurde durch die Temperatur stärker beeinflußt als durch Änderung der Bodenfeuchte. Das Herbizid unterlag in den ersten 30 Tagen bei 30 °C im nichtsterilisierten Boden einem schnellen Abbau, doch geringe Rückstände wurden bis zu 90 Tagen gefunden. Bei einer zweiten Applikation des Herbizids auf Boden, in dem schon eine erste Dosis von Triasulfuron abgebaut worden war, nahm der Wirkstoff im selben Maße wie zuvor ab, so daß bei wiederholter Anwendung nicht mit einem verstärkten Abbau gerechnet werden kann.     

Degradation of the herbicide flamprop-isopropyl in soil under laboratory conditions

The degradation of the wild-oat herbicide flamprop-isopropyl, [isopropyl (±)-N-benzoyl-N-(3-chloro-4-fluorophenyl)alaninate], in four soils has been examined under laboratory conditions with sampling times of up to 45 weeks after treatment. The major degradation product of [¹⁴C]flamprop-isopropyl in all soils at up to 10 weeks after treatment was the carboxylic acid (±)-N-benzoyl-N-(3-chloro-4-fluorophenyl)alanine. This compound in turn underwent degradation by loss of the benzoyl group and the propionic acid moiety, with evolution of [¹⁴C]carbon dioxide to form 3-chloro-4-fluoroaniline (CFA). The CFA was formed slowly in soil and occurred mainly as a bound form. There was evidence to show that the CFA was subsequently converted into other polar products. The time for depletion of 50% of the applied herbicide was approximately 10 weeks in sandy loam and medium loam soils, 11 weeks in a clay loam soil and 23 weeks in a peat soil.     

Efficacy of different steam distribution systems against five soilborne pathogens under controlled laboratory conditions

The efficacy of three steam application techniques (steam injection, iron pan and sheet steaming) was evaluated against five soilborne pathogens under controlled laboratory conditions. Injection and pan steam systems proved to be efficient and feasible alternatives to traditional sheet steaming for suppressing Fusarium oxysporum f. sp. basilici at 60% moisture field capacity in sandy-loam soil. Injecting steam was the best technique to suppress F. oxysporum f. sp. basilici, F. oxysporum f. sp. raphani, F. oxysporum f. sp. conglutinans, Rhizoctonia solani and Phytophthora capsici. The mycelia of R. solani and P. capsici were very sensitive to heat and were effectively killed by injection of steam and by the pan steam system at 80% and 40% moisture field capacity.     

Degradation of the herbicide flamprop-methyl in soil under anaerobic conditions

The degradation of the wild oat herbicide flamprop-methyl [MATAVEN, methyl (±)-N-benzoyl-N-(3-chloro-4-fluorophenyl)-2-aminopropionate] was studied in soils stored under anaerobic conditions. Comparative experiments were carried out in which soil was either covered with water or stored in an atmosphere of nitrogen. Under these anaerobic conditions, the major product was the carboxylic acid analogue (II) of flamprop-methyl, which was also a major degradation product formed in soil stored under aerobic conditions. However, the 2-, 3-, and 4-hydroxy-benzoyl analogues of II were also detected in soils stored under nitrogen or water and they were present in highest concentrations in the waterlogged soil. A further new product was also detected in waterlogged soil and it was shown to be N-benzoyl-N-(3-chloro-4-hydroxyphenyl)-2-aminopropionic acid. Although no hydroxylated derivatives of flamprop-methyl were detected in soils stored under aerobic conditions, it is possible that they were formed but underwent further degradation.     

Persistence of tebufenozide in aquatic ecosystems under laboratory and field conditions

The persistence and dissipation behaviour of tebufenozide, an ecdysone agonist, were investigated: (1) under laboratory conditions in aquatic models set up in glass aquaria, and (2) under field conditions in in-situ aquatic enclosures deployed in a mixed-wood boreal forest lake. Two models were set up in the laboratory study (Study I), which was conducted at constant conditions of temperature, water pH and photoperiod. In Model I, partitioning of tebufenozide from sediment, treated at a concentration of 1400 μg kg^-1, into untreated water was examined. The results showed that the chemical moved very little from the treated sediment into water. The concentration in sediment and water decreased gradually during the 90-day incubation period. Tebufenozide disappeared faster from the top layer of sediment than from the middle and bottom layers. The half-lives of disappearance were 64 days for the top layer but >90 days for the middle and bottom layers respectively. In Model II, partitioning from water, treated at a concentration of 350 μg litre^-1, into untreated sediment was investigated. The results showed that the chemical moved from treated water into sediment due to adsorption. Little vertical downward movement of the adsorbed residues from the top layer of sediment occurred into layers beneath. The adsorbed residues were also not released readily back into water. The concentration in water and sediment decreased gradually during the 90-day incubation period. The half-life of dissipation from water was 67 days. The field microcosm study (Study II), conducted under fluctuating conditions of temperature, water pH and photoperiod, involved application of tebufenozide onto aquatic enclosures at four concentrations of 0·05, 0·10, 0·26 and 0·5 mg litre^-1. This study also showed that the chemical moved downwards from the applied location and was adsorbed onto sediment. The chemical persisted longer in Study II than in Study I. Tebufenozide, being photo-labile, probably degraded faster after constant exposure to light in Study I than after exposure to fluctuating light in Study II. At 90 days after treatment in Study I, only about 55% of the applied material persisted in the sediment, and there was little accumulation. In Study II, the material not only persisted but also was accumulated in the sediment, since at 92 days post-treatment the residues were about 25 times higher than the applied concentration level. Residues in water also decreased more rapidly in Study I than in Study II, because the concentration at 90 days post-treatment was about 41% of the applied value. In Study II, however, about 65% of the applied chemical persisted in water at 92 days post-treatment. While the long persistence of tebufenozide in both the laboratory and field studies was attributable to its low vapour pressure, low water solubility, high octanol/water partition coefficient etc., the differences in the persistence characteristics observed in the two studies were due to the fluctuating environmental conditions and water pH encountered in the field study, compared with the constant environmental conditions and water pH utilized in the laboratory study. © 1997 SCI.     

Leaching potential and decomposition of fluroxypyr in Swedish soils under field conditions

The mobility and decomposition of the herbicide fluroxypyr (4-amino-3,5-dichloro-6-fluoro-2-pyridyloxyacetic acid) was studied under field conditions in a sandy soil and a clay soil. Leachate was collected in lysimeters with undisturbed soil (sand) and in tile-drained plots (clay). Soil samples to a depth of one metre were also collected in both soils to characterize the temporal depth distribution of fluroxypyr in the profiles. The herbicide was applied as the I-methylheptyl ester of fluroxypyr at two rates, 187.5 and 375.0 g a.e. ha^?1, representing the normal and double the dose of the compound used for spring cereals. Some lysimeters received supplementary watering. Only two leachate samples (one from each soil) had concentrations of fluroxypyr above the detection limit (1 μg litre^?1), i.e. 2 and 5 μg litre^?1. Both samples were collected within two months after application, when less than 2 mm of drainage had been collected. The methylheptyl ester of fluroxypyr was not found in any of the samples. Fluroxypyr levels above the detection limit in soil (5 μg kg^?1 dry soil), were never found below the topsoil (0.2 m) in the clay profile, while, in the sandy profile, levels just above the detection limit were found occasionally in deeper soil layers. Concentrations were reduced to undetectable or very low levels within three months after spraying.     

Persistence of gamma-BHC and beta-BHC in Indian rice soils under flooded conditions

The relative persistence of [¹⁴C]-gamma-BHC and [¹⁴C]-beta-BHC in Indian rice soils under flooded conditions was studied. In alluvial, laterite and pokkali (acid sulphate, saline) soils, rapid degradation of both isomers occurred; in sandy and kari (acid sulphate, saline) soils, both isomers persisted even after 41 days of flooding. The rapid degradation of BHC isomers in the former three soils was related to highly negative redox potentials within 20 days of flooding in contrast to oxidised conditions in sandy and kari soils even after 41 days. During the degradation in the soils, beta-BHC showed longer lag than gamma-BHC. Results suggest that the degradation of beta-BHC commences at a potential lower than that required for gamma-BHC degradation. Greater decomposition of gamma-BHC occurred in rice straw-amended soils than in unamended soils when the insecticide was incorporated to the soils in an aqueous solution. Addition of BHC isomers to the soils in ethanol resulted in comparable rates of rapid decomposition in both rice straw-amended and unamended soils, since ethanol was as effective as rice straw in lowering the redox potentials of the soils favouring BHC decomposition in unamended soil as well.     

Persistence of pyrazosulfuron in rice-field and laboratory soil under Indian tropical conditions

BACKGROUND: Pyrazosulfuron ethyl, a new rice herbicide belonging to the sulfonylurea group, has recently been registered in India for weed control in rice crops. Many field experiments revealed the bioefficacy of this herbicide; however, no information is available on the persistence of this herbicide in paddy soil under Indian tropical conditions. Therefore, a field experiment was undertaken to investigate the fate of pyrazosulfuron ethyl in soil and water of rice fields. Persistence studies were also carried out under laboratory conditions in sterile and non‐sterile soil to evaluate the microbial contribution to degradation. RESULTS: High‐performance liquid chromatography (HPLC) of pyrazosulfuron ethyl gave a single sharp peak at 3.41 min. The instrument detection limit (IDL) for pyrazosulfuron ethyl by HPLC was 0.1 µg mL^?1, with a sensitivity of 2 ng. The estimated method detection limit (EMDL) was 0.001 µg mL^?1 and 0.002 µg g^?1 for water and soil respectively. Two applications at an interval of 10 days gave good weed control. The herbicide residues dissipated faster in water than in soil. In the present study, with a field‐soil pH of 8.2 and an organic matter content of 0.5%, the pyrazosulfuron ethyl residues dissipated with a half‐life of 5.4 and 0.9 days in soil and water respectively. Dissipation followed first‐order kinetics. Under laboratory conditions, degradation of pyrazosulfuron ethyl was faster in non‐sterile soil (t_1/2 = 9.7 days) than in sterile soil (t_1/2 = 16.9 days). CONCLUSION: Pyrazosulfuron ethyl is a short‐lived molecule, and it dissipated rapidly in field soil and water. The faster degradation of pyrazosulfuron in non‐sterile soil than in sterile soil indicated microbial degradation of this herbicide. Copyright © 2012 Society of Chemical Industry     

噻虫嗪在棉花和土壤中的残留动态研究

采用超高效液相色谱一电喷雾串联质谱法测定噻虫嗪和高效氯氟氰菊酯·噻虫嗪混剂中噻虫嗪在棉叶和土壤中的残留.结果表明,噻虫嗪在土壤中平均回收率为88.8％～97.9％,变异系数为3.1％～6.2％;噻虫嗪在棉叶中的平均回收率为84.4％～95.8％,变异系数为1.3％～5.2％.噻虫嗪在棉叶和土壤中的消解动态表明:噻虫嗪在棉叶中的降解比在土壤中快,单剂中噻虫嗪在山东省和河南省两地土壤中的消解半衰期分别为2.9d和4.8d,棉叶中的消解半衰期为1.4d和1.9d.混剂中的噻虫嗪在山东省和河南省两地棉叶中的消解半衰期分别为1.4d和1.6d.     

双唑草腈在3种典型土壤中的降解

为明确双唑草腈在环境中的降解行为特性,采用室内模拟试验方法,分别研究了积水厌气、好氧和灭菌条件下,双唑草腈在紫色土、水稻土及红壤3种典型土壤中的降解特性。结果表明:双唑草腈在3种土壤中的降解均符合一级反应动力学方程,好氧条件下,其在紫色土、水稻土及红壤中的降解半衰期分别为13.4、10.1和31.1 d,且降解速率与土壤中有机质和黏粒含量呈正相关;不同条件下的降解速率依次为积水厌气 > 好氧 > 灭菌,说明双唑草腈在土壤中的降解一定程度上受水解和微生物活性的影响;在一定的土壤持水量范围内,双唑草腈在土壤中的降解速率随土壤含水量增加而加快。研究表明,双唑草腈在稻田淹水条件下施用降解较快,残留期较短。所得结果可为双唑草腈的合理使用及其环境安全性评价提供科学依据。     

Note: Toxicity of some insecticides onBracon hebetor under laboratory conditions

Insecticides which were environmentally friendly and the least toxic, were screened against a laboratory strain ofBracon hebetor (Say) (Hymenoptera: Braconidae) for their suitability for release in IPM of cotton. Concentrations ranging from 1 to 1000 ppm of the formulated insecticides in acetone were applied in glass vials and also by a leaf method, whereby cotton leaves were dipped in aqueous solutions of the same concentrations of insecticides. Adult parasitoids were exposed in both methods. According to the LC₅₀ at 24 h exposure, Λ-cyhalothrin and spinosad were the most (7 and 5 ppm) and least (263 and 225 ppm) toxic in the vial and the leaf method, respectively, toB. hebetor. The possible use of the parasitoid for IPM of cotton is discussed. http://www.phytoparasitica.org posting July 20, 2006.     

Residual activity of clomeprop and its downward movement under laboratory conditions

The relationship between the behavior of clomeprop ([ RS ]-2-[2,4-dichloro- m -tolyloxy]propionanilide) and its residual phytotoxic activity in the soil was investigated in the laboratory with special emphasis on the concentration in the soil water. The phytotoxic activity of clomeprop on radish seedlings ( Raphanus sativus L. var. radicula cv. Akamaruhatsukadaikon), as the test plant, became greater with time after application but the inhibition was different between the two soils, which had different properties. The amount of 2-(2,4-dichloro-3-methylphenoxy)propionic acid (DMPA), a hydrolyzed and active metabolite of clomeprop, in the soil water and total soil increased with time, corresponding to the decrease in the amount of clomeprop under non-water leakage conditions. The residual phytotoxic activity of clomeprop in the soil was more highly correlated with the concentration of DMPA in the soil water than with the amount of DMPA in the total soil. In addition, a leaching column test was conducted with clomeprop and DMPA. The DMPA easily moved downward and the concentration in the soil water in the upper layer decreased with time after application. It is supposed that the downward movement of DMPA was one of the factors influencing the lasting effect of clomeprop in the field.     

Disappearance of endosulfan residues from seawater and sediment under laboratory conditions

The dissipation rate of endosulfan isomers (α and β) in seawater and sediment was studied. The disappearance rate of both isomers from seawater and pure water was compared, and the same measurements were made in both sterile and unsterile marine sediment. Flasks of water and sediment, fortified with a dispersion of a commercial endosulfan 350 g litre⁻¹ EC, Protodan 35®, were incubated under laboratory light at room temperature for 82 days. A micro on‐line extraction method and GC‐ECD was used to determine the pesticide and its metabolites. The dissipation of endosulfan (in two phases of first‐order kinetics) occurred more rapidly in seawater than in pure water. At the end of the experiment, the concentration of α‐endosulfan in sterile sediment was four times greater than in unsterile sediment, while the dissipation rate of β‐endosulfan in unsterile sediment was approximately double that observed in sterile sediment. The dissipation of both forms in sediment occurred in a single stage. Endosulfan β‐isomer was more persistent than α‐isomer in both sterile and unsterile sediment. Dissipation of endosulfan sum of α‐ and β‐isomers in sediment at the end of the experiment ranged from 80% (sterile) to 95% (unsterile). Endosulfan sulfate was detected in water and sediment as the main metabolite. © 2000 Society of Chemical Industry     

Behaviour of ddt in three soils exposed to solar radiations under different conditions

Volatilization, mineralization, degradation and binding of soil-applied [¹⁴C]DDT were studied in three different soils from a tropical region of southern India subjected to solar irradiation and flooding for a period of 42 days. The soil types–red cotton soil, nursery soil and canal bank soil–differed in their organic carbon content, pH and texture. Under unflooded conditions, volatile losses were highest in the sandy canal bank soil. Flooding significantly enhanced volatilization, and this effect was maximal in the nursery soil, which had the highest organic carbon. The soils fully exposed to solar radiations in quartz tubes registered 1.5-1.8 times greater volatility. The volatilized organics contained appreciable quantities of DDE under both flooded and unflooded conditions. In addition, greater quantities of DDD volatilized from the flooded systems. The rate of formation of DDE was faster when soils were irradiated in quartz tubes. Mineralization remained minimal throughout the period of exposure and flooding the soil appeared to reduce further the [¹⁴C]carbon dioxide evolution. Canal bank soil exhibited the least mineralization and degradation. The data indicate that volatilization was significantly influenced by solar radiation and flooding to a much greater degree than by the differences in soil properties. Binding of DDT to soil was significantly increased by flooding the soil, thus leaving up to 33% of the initial DDT as bound residues in the nursery soil.     

An experimental study of salt expansion in sodium saline soils under transient conditions

Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.     

Degradation of the herbicide [14C]-diclofop-methyl in soil under different conditions

The degradation of the herbicide diclofop-methyl, ( ± )-methyl 2-[4-(2,4-dichloro-phenoxy)phenoxy]propionate, was investigated in two agricultural soils under aerobic and anaerobic conditions. Using two differently labelled forms of [¹⁴C]-diclofop-methyl the qualitative as well as the quantitative formation of extractable metabolites was followed for 64 days. The mineralisation of the uniformly labelled aromatic rings was pursued by monitoring the ¹⁴CO₂ generated for 25 weeks. As a first step of the degradation a very rapid hydrolysis of the ester bond was detected under all conditions. Diclofop, the corresponding substituted propionic acid formed, was extensively degraded under aerobic conditions, the final product being ¹⁴CO₂. As an intermediate, a compound later identified by GLC/MS to be 4-(2,4-dichlorophenoxy)phenol, was found in the extracts. Furthermore, traces of six other unknown metabolites were detected. Under anaerobic conditions the degradation proceeded to a small extent. At most 3% of the applied radioactivity was accounted for by the degradation product 4-(2,4-dichlorophenoxy)phenol. No other metabolite, including ¹⁴CO₂, was observed, implying lack of any further degradation.     

Fecundity ofEurydema ornatum feeding on a variety of seeds under laboratory conditions

The egg parasitoidTrissolcus spp. is the natural enemy of the cabbage bug,Eurydema ornatum L. (Het., Pentatomidae), a destructive pest of cultivated and wild Crucifera. Its preferred host is the wheat bugEurygaster integriceps Put., the most important pest of wheat. In order to rear the parasite for biological control purposes, mass production of its hostE. ornatum is suggested. In a laboratory study, the fecundity ofE. ornatum feeding on garden cress and radish was significantly higher than on red cabbage, white cabbage, rape or cauliflower. The oviposition period was significantly longer on garden cress and radish than on the other Crucifera. There was no difference among the various Crucifera in terms of length of postoviposition period or number of eggs laid per female per day.