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 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.     

Degradation of fluridone in submersed soils under controlled laboratory conditions

The experimental, aquatic herbicide fluridone (1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone) was degraded in two submersed soils and in the water above those soils to one acidic metabolite (identified as 1,4-dihydro-1-methyl-4-oxo-5-[3-(trifluoromethyl)phenyl]-3-pyridinecarboxylic acid by mass spectrometry). A sandy and a silt loam soil were treated with [¹⁴C]fluridone, immersed in water, and analyzed after 1, 3, 5, 7, 9, and 12 months. Seven to fifteen percent of the ¹⁴C applied to the soils was recovered in the water on each of the various collection dates. The acidic metabolite accounted for 86 to 93% of the radioactivity in the water fraction 7 months after treatment. The metabolite was absorbed strongly by both soils and comprised about 60% of the total ¹⁴C in each soil after 12 months. The remainder of the ¹⁴C in the soils after 12 months was either the parent compound (～30%) or an undefined insoluble residue (～10%).     

Degradation of the sulfonylurea herbicides chlorsulfuron and triasulfuron in a high-organic-matter volcanic soil

The degradation rates of two sulfonylurea herbicides, chlorsulfuron and triasulfuron, were determined at two application rates, 15 and 30 g a.i. ha^–1, in a sandy loam soil of volcanic origin under controlled environment and field conditions. Residues were measured using a modified gas chromatographic (gc) determination method. Both herbicides degraded rapidly in the acidic soil (pH 5.7) with high organic matter levels (7.3% o.m.), generally according to first-order rate kinetics. The respective half-lives ranged from 22 to 38 d for chlorsulfuron and from 31 to 44 d for triasulfuron under five controlled temperature/soil moisture regimens, ranging from 10 to 30 °C and between 40% and 80% maximum water-holding capacity. Half-lives in the field were considerably shorter (13 d for chlorsulfuron and 12–13 d for triasulfuron). The degradation rates of the herbicides were influenced more by soil temperature than by soil moisture content. Bioassays using white mustard ( Sinapis alba L.) and forage sorghum [ Sorghum bicolor (L.) Moench] were also used to determine the persistence of phytotoxic residues of both herbicides in the field, and the results showed that the effects of chlorsulfuron disappeared within 8 weeks. Triasulfuron residues disappeared within 9 and 14 weeks for the 15 and 30 g a.i. ha^–1 rates respectively.     

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 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     

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.     

Investigations on the metabolic fate of prochloraz in soil under field and laboratory conditions

The degradation of prochloraz in different soils was investigated in field and laboratory experiments. In laboratory degradation experiments in the dark, initial prochloraz concentrations decreased to 30–64% within 56 days, depending on temperature and soil pH. In neutral to basic soils, formation of up to 3.7% of the metabolite prochloraz-urea was observed. The rate of mineralization was strongly pH-dependent, not exceeding 3.2% in the acidic and 18.3% in the neutral to basic soils. Amounts of non-extractable residues ranged from 14 to 31%. Under field conditions, prochloraz disappeared much more rapidly with DT₅₀ values of 11–43 days. The metabolites prochloraz-formylurea and prochloraz-urea were found in significant concentrations. Laboratory experiments with fresh and sterilized soils under UV irradiation confirmed the enhancing effect of light on the formation of the primary metabolite, prochloraz-formylurea. The latter is hydrolysed to prochloraz-urea predominantly by microbial degradation. © 1999 Society of Chemical Industry     

实验室条件下威百亩及异硫氰酸甲酯在土壤中的降解特性

在实验室条件下,利用高效液相色谱研究了威百亩及其降解产物异硫氰酸甲酯在土壤中的降解特性及影响因素。结果表明:威百亩在土壤中的降解与土壤绝对含水量、环境温度和土壤有机质含量均密切相关。25 ℃下,威百亩在绝对含水量为0、20%、40%、60%的土壤中的半衰期分别为5.0、1.2、4.1和4.3 d,绝对含水量约为20%的土壤最有利于其降解。威百亩的降解速率还随温度的升高和土壤有机质含量的增加而加快。异硫氰酸甲酯的降解趋势与威百亩基本相同。研究结果可为威百亩的田间安全、合理施用提供参考。     

Persistence and mobility of tebufenozide in forest litter and soil ecosystems under field and laboratory conditions

A field microcosm study was conducted to determine persistence of tebufenozide, an insect growth regulator, in sandy litter and soil. Litter and soil plots (c. 4·5 m² each) were sprayed with an aqueous suspension concentrate formulation of tebufenozide at rates of 35, 70 and 140 g AI ha^-1. Samples were collected at intervals up to 408 days after spraying, and analyzed for tebufenozide residues. The data were subjected to regression analysis and half-life (DT₅₀, the time required for 50% of the initial residues to disappear) values were computed. The DT₅₀ was c. 62 days for both substrates treated with the two lower dosage rates. At the highest dosage rate, the DT₅₀ was 115 days for the litter and c. 52 days for the soil, indicating irregular variations in persistence. Downward movement in soil occurred only in trace amounts, suggesting strong adsorption. Laboratory microcosm studies were conducted to investigate the relative importance of rainfall, exposure to light and volatilization on persistence. Vertical movement occurred in litter and soil (both sandy and clay types) during rainfall. The amount moved increased with the amount of rainfall, but decreased with the rain-free period. The larger the rain droplets, the greater the downward movement. When the rainwater could move laterally along the surface of the substrate (as would occur on a slope), more lateral movement than vertical movement of tebufenozide occurred. The photolysis study indicated that disappearance of tebufenozide was directly related to the duration of exposure to radiation and radiation intensity. Volatilization of tebufenozide depended upon the ambient temperature and the duration of air passing through the substrates. Nonetheless, the amount lost by volatilization was much lower than the amount lost after rainfall or exposure to radiation, thus indicating the greater influence of rainfall and sunlight on persistence. In the laboratory microcosm studies, more tebufenozide was lost from the sandy substrates than from the clay substrates. This behaviour was attributed to the greater adsorptive capacity of the clay substrates, thus providing a greater protection against downward mobility and loss due to radiation. © 1997 SCI     

The relative movement and persistence in soil of chlorsulfuron, metsulfuron-methyl and triasulfuron

Summary. Adsorption and degradation rates of triasulfuron in 8 different soils were negatively correlated with soil pH and were generally lower in subsoils than in soils from the plough layer. The half-life at 20°C varied from 33 days in a top soil at pH 5·8 to 120 days in a subsoil at pH 7·4. Adsorption distribution coefficients in these two soils were 0·55 and 0·19, respectively. Movement and persistence of residues of chlorsulfuron, triasulfuron and metsulfuron-methyl were compared in a field experiment prepared in spring 1987. Triasulfuron was less mobile in the soil than the other two compounds. Residues of all three herbicides were largely confined to the upper 40–50 cm soil 148 days after application. With an initial dose of 32 g ha⁻¹, residues in the surface soil layers were sufficient to affect growth of lettuce and sugar-beet sown approximately one year after application. Laboratory adsorption and degradation data were used with appropriate weather data in a computer model of herbicide transport in soil. The model gave good predictions of total soil residues during the first five months following application, and also predicted successfully the maximum depth of penetration of the herbicides into the soil during this period. However, more herbicide was retained close to the soil surface than was predicted by the model. The model predicted extensive movement of the herbicides in the soil during winter but did not predict that residues sufficient to affect crop growth could be present in the upper 15–20 cm soil after one year.     

Photodegradation of herbicide triasulfuron

Triasulfuron was degraded in aqueous solution by ultraviolet irradiation to yield 2-chloroethoxybenzene and (4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea. The reaction followed first-order kinetics. In sunlight, the reaction was slower and afforded these two photoproducts together with 2-amino-4-methoxy-6-methyltriazine and 2-(2-chloroethoxy)benzenesulfonamide. The latter compounds arise from hydrolytic cleavage of the sulfonylurea bridge of triasulfuron because of the acidity of the reaction medium due to the loss of sulfur dioxide. A mechanism which accounts for the formation of the photoproducts is proposed. © 1999 Society of Chemical Industry     

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.     

Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil-applied pethoxamid [2-chloro- N -(2-ethoxyethyl)- N -(2-methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice ( Oryza sativa cv. Kiyohatamochi ) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.     

Behaviour of fipronil in soil under Sahelian Plain field conditions

The behaviour of fipronil, a phenylpyrazole insecticide used for locust control, was studied under sub-Saharan conditions in soils of the Niamey region of Niger. A formulation of fipronil (Adonis^®) was applied to uncultivated soils at Banizoumbou and Saguia. Soil was sampled at 0–10, 10–20 and 20–30 cm depths for up to two months after treatment. Residues were analysed by gas chromatography using electron capture and mass detectors. For both soils, a rapid initial decrease of fipronil was observed, with rapid formation for the most part of a photodegradate. Three other metabolites of fipronil were also detected throughout the study. These metabolites displayed different dissipation kinetics. Fipronil and its metabolites did not move beyond 10 cm depth, except for the amide, which is not considered a toxicologically significant metabolite. © 1998 SCI.     

不同水分条件下作物蒸腾效率的比较研究

通过盆栽试验,研究了三种土壤水分下(高水、中水、低水,分别占田间持水量的80%~85%、70%~75%、60%~65%)小麦、高粱、玉米、谷子的生物量、耗水量、蒸腾效率(TE)及干物质分配的特点。结果表明,随土壤含水量的降低,作物的生物量、耗水量降低,单株蒸腾效率(TE单株)升高,其中高粱的TE单株升高幅度最大为53.6%。随土壤水分的降低,作物的净光合速率、蒸腾速率降低,作物通过大幅度降低蒸腾速率来维持较高的叶片蒸腾效率(TE叶片)。作物全生育期的TE叶片呈单峰趋势,小麦、玉米的TE叶片在开花期均达到最大值,谷子和高粱的分别在灌浆期和抽穗期达到最大值。相关分析表明,作物的TE产量与收获指数显著正相关(小麦:R2=0.632,玉米:R2=0.994,高粱:R2=0.920,谷子:R2=0.949)。谷子在低水环境中具有更合理的干物质分配机制,小麦在中、低水环境中能够保持较高的收获指数和TE产量,它对水分的变动不敏感,适宜生长的水分条件较广泛。     

Survival of Tilletia indica teliospores under European soil conditions

As part of developing a European Pest Risk Analysis (PRA) for Tilletia indica , the causal agent of Karnal bunt of wheat, teliospore survival studies were done outside under quarantine containment at three European sites (Norway, UK, Italy). At each site, experiments were set up in three consecutive years (Experiments 1, 2 & 3) to determine teliospore survival over time (1–3 years) at 5, 10 and 20 cm depths. Experiments were sampled annually and survival assessed in relation to teliospore recovery and to germination at recovery (T0) and 3 months after recovery in case of burial-induced dormancy ( T3 ). Teliospores survived at all three sites at all depths over all the time periods studied. At each site, there was no evidence of a marked decline in teliospore recovery between sampling years, except in one set of years in one Norwegian experiment. There was no consistent effect of depth on recovery. In general there was little evidence for a marked decline in teliospore germination between sampling years. There was some evidence of a decrease in germination with increasing depth in the UK, and for some time-depth interactions. After 3 years' incubation (Experiment 1), mean teliospore recovery and mean germination were: UK: 61% recovery and 31% ( 33% ) germination for T0 (and T3 ); Italy: 30% recovery and 36% ( 29% ) germination; and Norway: 12% recovery and 19% ( 49% ) germination. Germination for laboratory controls ranged from 20–59% (UK), 18–41% (Italy) and 28–59% (Norway). There was no evidence for burial-induced dormancy except in Norway. Teliospores of T. indica can survive for at least three years in European soils. This prolonged period of survival could support establishment of the pathogen if it were introduced into areas of European cereal production.     

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