Enantioselective metabolism and cytotoxicity of the chiral herbicide ethofumesate in rat and chicken hepatocytes

We investigated the metabolic kinetics and toxicity of ethofumesate (ETO) in rat and chicken hepatocytes using a chiral high-performance liquid chromatographic (HPLC) method. The metabolic of ETO in rat hepatocytes was enantioselective, whereas it was not in chicken hepatocytes. The T_1/2 of (−)-ETO was about two times longer than that of (+)-ETO after the rat hepatocytes had been incubated with 20 μM rac-ETO. There was no chiral conversion or transformation during their incubation with the hepatocytes. Toxicity differences were observed between the two enantiomers of ETO, reflected in their EC₅₀ values in rat and chicken hepatocytes. The stereoselective cytotoxicity of the two enantiomers was opposite in rat and chicken hepatocytes. We have developed a method of studying the toxicokinetics and cytotoxicity of chiral agrochemicals in hepatocytes isolated from mammals (rats) and chicken. The data presented here allow a more thorough understanding of this pesticide and should be useful in its full environmental assessment.     

Persistence and movement of ethofumesate in soil*

Persistence of ethofumesate [(±)2-ethoxy-2.3-dihydro-3,3-dimethylbenzofuran-5-yl-methansulphonate] in soil was associated with soil temperature. Ethofumesate applied at 4.5 kg/ha in November persisted about twice as long in soil as that applied the following March. In another field study, 88–91% of the herbicide had dissipated after 24 weeks in sandy loam soil, compared to 72–77% in loam soil when it was applied at rates of 2.2, 3.4, 4.5, and 9.0 kg/ha. The rate of degradation was independent of the initial rate of chemical applied. The time required for 50% of the herbicide to dissipate in sandy loam and loam soils was 7.7 and 12.6 weeks, respectively. The movement of ethofumesate in these two soils over a 24-weeks sampling period was confined mainly to the upper 7.5 cm of the soil profile.     

实验室条件下氯氰菊酯在土壤中的降解

在实验室条件下, 通过对东北黑土、华北褐土、华南红土中3 次添加氯氰菊酯的降解研究发现: 氯氰菊酯在3 种土壤中的降解是以微生物降解为主, 化学降解为辅; 土壤间理化性质的不同对化学降解速率没有明显影响, 多次施药则因较难降解的顺式异构体在土壤中积累而使半衰期延长。     

Enantioselective degradation kinetics of metalaxyl in rabbits

Metalaxyl [methyl-N-(2′-methoxyacetyl)-N-(2,6-dimethylphenyl)-d,l- alaninate] is a potent phenylamide fungicide. The (−)-(R)-isomer accounts for most of the fungicidal activity. A possible stereo and/or enantioselective kinetics of metalaxyl in rabbits was investigated by intravenous injection. The concentrations of (−)-(R)- and (+)-(S)-metalaxyl in plasma, liver, and kidney tissue were determined by HPLC with a cellulose-Tris-(3,5-dimethylphenylcarbamate)-based chiral stationary phase and gas chromatography-mass spectroscopy. After intravenous administration of racemic metalaxyl (40 mg/kg), the (+)-(S)-enantiomer levels in plasma, liver, and kidney decreased more rapidly than the (−)-(R)-isomer. The area ratio of the (−)-(R)-/(+)-(S)-enantiomer under the concentration-time curve (AUC_0 → ∞) in plasma after drug application was 1.62. The total plasma clearance value of the (+)-(S)-enantiomer was 1.53 and higher than that of the (−)-(R)-enantiomer. The [R]/[S] ratio in plasma was >1 for standard rac-metalaxyl at each time point. The other pharmacokinetic parameters of the enantiomers were also different. The results indicate substantial stereoselectivity in the degradation of metalaxyl enantiomers in rabbits.     

Uptake and translocation of ethofumesate in sugar-beet plants

The uptake and translocation of ¹⁴C-labelled ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethylbenzofuran-5-yl methanesulphonate] was studied in sugar-beet seedlings following soil and foliar applications. After soil applications, the roots absorbed and translocated to the foliage more ethofumesate or its metabolites than did the emerging hypocotyls. Ethofumesate or its metabolites did not accumulate in either roots or hypocotyls after exposure to treated soil. When sugar-beet leaves were treated with the herbicide at the two-leaf stage, acropetal translocation was rapid but there was no translocation out of the treated leaves. Furthermore, ethofumesate or its metabolites were not translocated basipetally after either soil or foliar application.     

Translocation and degradation of pyrazosulfuron-ethyl in rice soil

BACKGROUND: Pyrazosulfuron‐ethyl {ethyl 5‐[(4,6‐dimethoxypyrimidin‐2‐ylcarbamoyl)‐sulfamoyl]‐1‐methylpyrazole‐4‐carboxylate} is a new rice herbicide belonging to the sulfonylurea group. This study reports the translocation of ¹⁴C‐pyrazosulfuron‐ethyl to rice plants and its degradation in rice‐planted and unplanted soil. RESULTS: Pyrazosulfuron‐ethyl did not show any appreciable translocation to rice shoots, as ¹⁴C‐activity translocated to the aerial portion never exceeded 1% of the initially applied ¹⁴C‐activity over a 25 day period. Results suggested that the dissipation of pyrazosulfuron‐ethyl from soils followed first‐order kinetics with a half‐life of 5.5 and 6.9 days in rice‐planted and unplanted soils respectively. HPLC analysis of the organic extract of soil samples showed the formation of three metabolites, namely ethyl 5‐(aminosulfonyl)‐1‐methyl‐1‐H‐pyrazole‐4‐carboxylate, 5‐[({[(4,6‐dimethoxy‐2 pyrimidinyl)‐amino]‐carbonyl} amino)‐sulfonyl]‐1‐methyl‐1H‐pyrazole‐4‐carboxylic acid and 2‐amino‐4,6‐dimethoxy pyrimidine, in both rice‐planted and unplanted soils. CONCLUSION: The study indicates that pyrazosulfuron‐ethyl was a short‐lived compound in the soil and was degraded relatively faster in rice‐planted soil than in unplanted soil. The herbicide did not show any appreciable translocation to rice plants. Copyright © 2011 Society of Chemical Industry     

Kinetics of linuron and metribuzin degradation in soil

The disappearance of linuron and metribuzin was studied during laboratory incubation of soil samples which had been taken from several depths at three sites, and treated with the pesticides. Temperature and water content of the soils were varied. There was a tendency for the rate of loss to be slower in soil taken from deeper horizons than in surface soil but the differences were not large. In only ten out of forty experiments did the value 1 for the apparent order of reaction fall within 95% confidence limits. In the remaining experiments the apparent reaction order was greater than 1 with eight values higher than 4. For one soil, the reaction order for linuron was markedly lower for incubation at 22°C compared with incubations at 10°C. The results could be explained on the basis that the systems were complex, involving consecutive or competing reactions. An alternative possibility is that the apparent complexities were artifacts brought about by the inherent limitations of the laboratory incubation system.     

The degradation of aldicarb and oxamyl in soil

The breakdown of oxamyl was studied in three downland chalk soils, a peat loam, a sandy loam, and the same sandy loam modified by adding peat. The kinetics of aldicarb degradation via its sulphoxide and aldoxycarb (aldicarb sulphone) were also studied in these two sandy loam soils. All the reactions followed first-order kinetics, the reaction being faster in the original than in the modified sandy loam. Rates of reaction were slower at low moisture contents, and decreased markedly when the temperature was reduced from 10 to 5°C though less so than from 15 to 10°C.     

放牧对短花针茅草原土壤微生物和土壤养分的影响及其季节动态

研究了短花针茅草原不同季节、不同放牧梯度内土壤微生物数量、土壤养分的变化及土壤微生物与土壤养分之间的相关性,结果表明:轻度放牧区(LG)和重度放牧区(HG)内土壤微生物数量春季最高,土壤微生物数量(0-10 cm)在三个放牧区内随着季节的变化均呈下降趋势。而在10-20 cm,对照区内土壤微生物数量的高峰期出现在夏季然后开始下降,轻度放牧区和重度放牧区土壤微生物随着季节的变化而下降。土壤微生物数量到了秋季在三个放牧梯度内均呈现显著性的差异,土壤养分也是在秋季出现了显著性差异(P<0.05)。土壤微生物总数在不同放牧梯度内的变化规律是对照和轻度放牧区均大于重度放牧区。土壤微生物与土壤有机质和土壤全氮呈较强的正相关。     

Enhanced degradation of iprodione and vinclozolin in soil

Residues of iprodione and vinclozolin were measured following repeated application of the fungicides to a sandy loam soil in the laboratory. There was a progressive increase in rates of degradation with successive treatments. With iprodione, for example, the times for 50% loss of the first and second applications were about 23 and 5 days respectively. When treated for the third time, less than 10% of the applied dose remained in the soil after just 2 days. Similar results were obtained with vinclozolin in the same soil, and with both compounds in a second soil. In a third soil, which had relatively low pH, degradation of both compounds occurred only slowly and the rate of degradation of a second application was the same as that of the first. Degradation rates in this soil were increased by addition of 100 g kg^?1 of a soil in which degradation occurred more readily, and they were markedly increased by addition of 100 g kg^?1 of a soil in which enhanced degradation had been previously induced. Residues of both fungicides were also measured following repeated application in the field. When iprodione was applied to previously untreated plots, about 3% of the initial dose remained in the soil after 77 days. When applied to plots treated once before, less than 1% remained after 18 days, and when applied to plots treated twice previously less than 1% remained after 10 days. Similar results were obtained with vinclozolin. Enhanced degradation of subsequent soil treatments was also observed following a sequence of low-dosage sprays in the field.     

Factors controlling degradation of pesticides in soil

Rates of pesticide degradation in soil exhibit a high degree of variability, the sources of which are usually unclear. Combining data from incubations performed using a range of soil properties and environmental conditions has resulted in greater understanding of factors controlling such degradation. The herbicides clomazone, flumetsulam, atrazine, and cloransulam-methyl, as well as the former insecticide naphthalene offer examples of degradation kinetics controlled by coupling competing processes which may in turn be regulated separately by environmental conditions and soil properties. The processes of degradation and volatilization appear to compete for clomazone in solution; sorbed clomazone is degraded only after the solution phase is depleted. Similarly, volatilization of naphthalene is enhanced when degradation has been inhibited by high nutrient levels. Degradation of the herbicide flumetsulam has been shown to be regulated by sorption, even though the compound has a relatively low affinity for the soil. The fate pathway for cloransulam-methyl shifts from mineralization to formation of metabolities, bound residues and physically occluded material as temperature increases. Atrazine degradation in soil may be controlled in part by the presence of inorganic nitrogen, as the herbicide appears to be used as a nitrogen source by micro-organisms. New insight gained from measurement of multiple fate processes is demonstrated by these examples.     

Peroxidase activity and propanil degradation in soil*

The herbicide N-(3,4-dichloropxhenyl)-propionamide (propanil) and a metabolite of propanil, 3,4-dichloroaniline (DCA), were mixed with Nixon loam soil which was subjected to moisture and air-drying treatments. Degradation of propanil was altered by subjecting the treated soil samples to storage conditions of moisture, drying and chloroform. The peroxidase activity in fresh soil was very low when soil samples were collected during the cold season. The amount of 3,3′,4,4′- tetrachloroazobenzene (TCAB) produced from DCA increased with a simultaneous increase in the peroxidase activity in preincubated soil where carbon and nitrogen sources were added.     

环酰菌胺在土壤中的吸附及降解特性

为评价环酰菌胺在土壤中的生态风险,采用超高效液相色谱-串联质谱(UPLC-MS/MS)方法测定了土壤和水中环酰菌胺的残留量,研究了该农药在红壤和水稻土中的吸附及降解特性,并对其淋溶特性进行了分析,评估了该农药对地下水的污染风险。结果表明:环酰菌胺在红壤和水稻土中的吸附符合Freundlich吸附等温线方程,KOC值分别为373.69和726.86 mL/g,水稻土对环酰菌胺的吸附能力强于红壤。好氧条件下,环酰菌胺在红壤和水稻土中的降解半衰期分别为0.63和5.06 d,积水厌氧条件下的降解半衰期分别为6.80和9.24 d,表明环酰菌胺在好氧条件下降解较快。环酰菌胺在红壤和水稻土中的地下水污染指数(groundwater ubiquity score)分别为1.19和1.10,表明其对地下水的污染风险较低。结果可为环酰菌胺的生态风险评估提供参考。     

土壤中花蓟马蛹的检测方法

本文对花蓟马属（Frankliniella）蛹期在土壤中存在的状态以及存在的时间进行了描述,并用直接镜检、干燥漂浮镜检、生物饲养检测等方法对土壤中蓟马蛹的检测方法进行了初步研究.生物饲养法能有效检出存在于土壤中的花蓟马蛹.     

Time effect on bentazone sorption and degradation in soil

Previous sorption/desorption batch experiments have indicated that bentazone is weakly sorbed by soils. In addition, field experiments have shown that 4% of the bentazone sprayed can be leached to drainage water. In order to complete bentazone characterisation, we have assessed the effect of time on its behaviour in contrasting soils. In laboratory studies, bentazone was added to three topsoils (sandy, loamy and clay soils). Bentazone degradation, sorption/desorption kinetics and isotherm measurements were carried out at different times. At 160 days after treatment, bentazone mineralisation amounts varied from 2.1% (sandy soil) to 14% (clay soil). The extractable amounts became lower (from 97% after treatment to 12% after 160 days for the clay soil) and a greater number of desorption series was needed to obtain these products. Nevertheless, at the end of the experiments, a small amount of bentazone was still extracted by water. At the same time, bound residues of bentazone reached 65% in clay soil. Statistical analysis indicated effects of both residence time and soil type on bentazone behaviour.     

Sulcotrione versus atrazine transport and degradation in soil columns

A soil column experiment under outdoor conditions was performed to monitor the fate of 14C-ring-labelled sulcotrione, 2-(2-chloro-4-mesylbenzoyl)cyclohexane-1,3-dione and atrazine, 6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine, in water leachates and in the ploughed horizon of a sandy loam soil. Two months after treatment, the cumulative amounts of herbicide residues leached from the soil were 14.5% and 7% of the applied radioactivity for sulcotrione and atrazine, respectively. Maximum leachate concentrations for each herbicide were observed during the first month following application: 120 and 95 microg litre(-1) for sulcotrione and atrazine respectively. After 2 weeks, 78% of the sulcotrione and atrazine was extractable from the soil, whereas after two months only 10 and 4%, respectively, could be extracted. The maximum sulcotrione content in the first 10 cm of soil was identical with that of atrazine. For both molecules, the content of non-extractable residues was low, being around 15%. Sulcotrione seems to be more mobile than atrazine but the consequences for water contamination are similar since lower doses are used.     

The degradation of methazole in soil. I. Effects of soil type,soil temperature and soil moisture content

[¹⁴C]-Labelled methazole was incubated in six soils at 25°C and with soil moisture at field capacity. Under these conditions, methazole was unstable, the concentration declined following first-order kinetics with half-life values in the soils ranging from 2.3 to 5.0 days. The main degradation product was 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) which was more stable than the parent compound. After about 160 days, DCPMU accounted for 30 to 45% of the initial methazole concentration. Degradation of methazole and DCPMU was affected by soil temperature and moisture content. With methazole, half-lives in one soil at field capacity moisture content and temperatures of 25, 15 and 5°C were 3.5, 8.7 and 31.1 days respectively. The half-life at 25°C was increased to 5.0 days at 50% of field capacity and 9.6 days at 25% of field capacity. A proportion of the initial radioactivity added to the soil could not be extracted and this proportion increased with time. After 160 days this unextractable radioactivity accounted for up to 70% of the amount applied.     

Global Assessment of Human-Induced Soil Degradation

Soil is a valuable natural resource that in the short - term is nonrenewable and is difficult to reclaim when degraded. The use of soils on a sustainable basis requires that their capability to withstand the demands upon them is not exceeded. Those people concerned with conservation should be aware of the vital importance of soil for maintaining food supplies for an increasing world population. Increasing demands place a greater strain upon the soil. If the demands become too great, the soil becomes degraded. As soil is the basis of all terrestrial ecosystems, a degraded soil means lower fertility, reduced biodiversity, and human poverty. To provide basic information on soil degradation worldwide, a survey of soil loss through erosion, physical deterioration, and chemical pollution was made. Digital databases are not available to hold information necessary to monitor and combat soil degrada tion at global and national scales. Soil degradation is recognized as a serious and widespread problem, so in September 1987 the International Soil Reference and Information Centre was commissioned to make a survey for a map at a scale of 1:10,000,000 entitled "Global Assessment of Human - Induced Soil Degradation" (GLASOD). Until it was published in 1990, there was no uniformly collected body of information on soil degradation worldwide. The GLASOD survey provides basic data on the world distribution and intensity of erosional, chemical, and physical types of degradation. The original purpose of GLASOD was to provide factual information, to replace sweeping statements about soil and land degradation, and to raise awareness of policy makers and governments for the continuing need for soil conservation. The GLASOD survey also enables comparisons to be drawn between degraded soils of different continents, and the methodology used can be a basis upon which plans for restoration of degraded lands can be based.     

Bromoxynil degradation in a Mississippi silt loam soil

BACKGROUND: The objectives of these laboratory experiments were: (1) to assess bromoxynil sorption, mineralization, bound residue formation and extractable residue persistence in a Dundee silt loam collected from 0–2 cm and 2–10 cm depths under continuous conventional tillage and no‐tillage; (2) to assess the effects of autoclaving on bromoxynil mineralization and bound residue formation; (3) to determine the partitioning of non‐extractable residues; and (4) to ascertain the effects of bromoxynil concentration on extractable and bound residues and metabolite formation. RESULTS: Bromoxynil K_d values ranged from 0.7 to 1.4 L kg^?1 and were positively correlated with soil organic carbon. Cumulative mineralization (38.5% ± 1.5), bound residue formation (46.5% ± 0.5) and persistence of extractable residues (T_1/2 < 1 day) in non‐autoclaved soils were independent of tillage and depth. Autoclaving decreased mineralization and bound residue formation 257‐fold and 6.0‐fold respectively. Bromoxynil persistence in soil was rate independent (T_1/2 < 1 day), and the majority of non‐extractable residues (87%) were associated with the humic acid fraction of soil organic matter. CONCLUSIONS: Irrespective of tillage or depth, bromoxynil half‐life in native soil is less than 1 day owing to rapid incorporation of the herbicide into non‐extractable residues. Bound residue formation is governed principally by biochemical metabolite formation and primarily associated with soil humic acids that are moderately bioavailable for mineralization. These data indicate that the risk of off‐site transport of bromoxynil residues is low owing to rapid incorporation into non‐extractable residues. Published 2009 by John Wiley & Sons, Ltd