Contribution of organic matter to metolachlor adsorption on some soils

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除草剂乙草胺、异丙甲草胺的光降解及其致突变性

对两种常见的酰胺类除草剂乙草胺、异丙甲草胺的光降解进行了研究,采用Ames试验方法对母体及其光降解产物的致突变性进行了检验．结果表明,初始ｐＨ值的变化对这两种除草剂的光降解速率无明显影响,异丙甲草胺比乙草胺更易于发生光降解．乙草胺在光降解前后均表现出无致突变性;异丙甲草胺本身具有致突变性,在光降解过程中未表现出有其它致突变性物质产生．     

Fate of the herbicide metolachlor in aerobic and anaerobic soils

The fate of the herbicide metolachlor in aerobic and anaerobic soils with repeated applications of the metolachlor over a period of 5 years was studied. After 12 weeks incubation, cumulative 14CO2 evolution from the soil accounts for 8.01% in aerobic condition versus 1.5% of 14CO2 in the soil had not been treated with metolachlor. The total 14C recovery in the methanol-water extract and in the non-extractable portion of this aerobic soil accounted for 73.1% and the total metolachlor recovery in the methanol-water extract was 46.7% but 86.9% of 14C was accounted for in the γ-irradiated control soil. There axe no differences in the recovery of 14C between non-sterile and γ-irradiated control soil under anaerobic conditions. The results show that there was some active metolachlor-degrading population in the Virginia soil which had been previously received repeated applications of the metolachlor but only under aerobic condition.     

Fate of metolachlor under subirrigation in a sandy soil: A lysimeter study

Abstract

A three‐year field lysimeter study was conducted to investigate the role of subirrigation systems in reducing the risk of water pollution from metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methlphenyl)‐N‐(2‐methoxy‐l‐methylethyl)acetamide). Nine large PVC lysimeters, 1 m long x 0.45 m diameter, were packed with a sandy soil. Three water table management treatments, i.e. two subirrigation treatments with constant water table depths of 0.4 and 0.8 m, respectively, and a free drainage treatment in a completely randomized design with three replicates were used. Corn (Zea mays L.) was grown in each lysimeter, and at the beginning of summer of each year metolachlor was applied, at the locally recommended rate of 2.75 kg a.i./ha. Soil and water samples were collected at different time intervals after each natural or simulated rainfall event. Metolachlor was extracted from these samples and analyzed using Gas Chromatography.

Results obtained in this three year study, (1993–1995), lead to the conclusion that metolachlor is quite mobile since it leached to a depth of 0.85 m below the soil surface quite early in the growing season. Metolachlor concentrations decreased with depth as well as with time. The shallower water table in the 0.4 m subirrigation treatment showed less residues in the soil solution than that of other treatments. However, a mass balance study, supported by an independent laboratory investigation, shows that water table management, statistically, has no significant effect on the reduction of metolachlor residues in sandy soils.     

几种酰胺类除草剂的光降解及其致突变性

对３种常见的酰胺类除草剂乙胺,异丙甲草胺,丁草胺的光降解进行了研究,采用Ａｍｅｓ试验方法对母体和光降解产物的致突变性进行了检验,结果表明,在紫外灯照射下,这３种除草剂的光降解均较符合一级动力学,其降解速率次序为：异丙草胺〉乙草胺〉丁草胺。     

异丙甲草胺对蚯蚓体重及酶活性的影响

采用自然土壤法,研究了异丙甲草胺对蚯蚓体重及体内纤维素酶、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)活性的影响.结果表明,蚯蚓体重及纤维素酶活性在异丙甲草胺作用下均受到抑制;蚯蚓体内SOD、CAT、POD活性对异丙甲草胺响应不同,CAT活性受影响最大,POD次之,SOD最小.异丙甲草胺浓度对蚯蚓体重及体内纤维素酶和CAT活性影响显著,对SOD和POD则无显著性影响;处理时间对蚯蚓体重及体内纤维素酶、SOD、CAT和POD活性均有极显著影响;而异丙甲草胺浓度和处理时间二者交互作用对蚯蚓体内CAT和POD活性有极显著影响,对蚯蚓体重及体内纤维素酶和SOD活性则影响不大.     

Adsorption of chloroacetanilide herbicides on soil and its components Ⅲ. Influence of clay acidity, humic acid coating and herbicide structure on acetanilide herbicide adsorption on homoionic clays

Adsorption of chloroacetanilide herbicides on homoionic montmorillonite, soil humic acid, and their mixtures was studied by coupling batch equilibration and FT-IR analysis. Adsorption isotherms of acetochlor, alachlor, metolachlor and propachlor on Ca2 + -, Mg2 + -. Al3 + -and Fe3 + -saturated clays were well described by the Freundlich equation. Regardless of the type of exchange cations, Kf decreased in the order of metolachlor ＞ acetolachlor ＞ alachlor ＞ propachlor on the same clay. FT-IR spectra showed that the carbonyl group of the herbicide molecule was involved in binding, probably via H-bond with water molecules in the clay interlayer. The type and position of substitutions around the carbonyl group may have affected the electronegativity of oxygen, thus influencing the relative adsorption of these herbicides. For the same herbicide, adsorption on clay increased in the order of Mg2+ ＜ Ca2+ ＜ Al3+ ≤ Fe3+ which coincided with the iucreasing aciditv of homoionic clays. Acidity of cations may have affected the protonation of water, and thus the strength of H-bond between the clay water and herbicide. Complexation of clay and humic acid resulted in less adsorption than that expected from independent adsorption by the individual constituents. The effect varied with herbicides, but the greatest decrease in adsorption occurred at a 60:40 clay-to-humic acid ratio for all the herbicides. Causes for the decreased adsorption need to be characterized to better understand adsorption mechanisms and predict adsorption from soil compositions.     

Concurrent Exposure Assessments of Atrazine and Metolachlor in the Mainstem, Major Tributaries and Small Streams of the Chesapeake Bay Watershed: Indicators of Ecological Risk

The goals of this study were to: (1) measure atrazine and metolachlor concentrations during both high and low use periods in the Chesapeake Bay's mainstem/major tributaries, smaller tributaries and representative small agricultural streams during 1995 and 1996; (2) compare these exposure data with toxicity benchmarks for each herbicide to predict ecological risk and (3) use in-stream fish community data collected in the streams to provide supportive data for ecological risk characterization. Spatially, atrazine (<0.10–98 g/L) and metolachlor (<0.10–68 g/L) concentrations were highest in the streams, followed by the small tributaries (<0.10–11 g/L atrazine; <0.10–8.6 g/L metolachlor) with the lowest concentration in the mainstem Bay/larger tributaries (<0.10–0.22 g/L atrazine; <0.10–0.24 g/L metolachlor). Temporally, concentrations of both herbicides were greatest in all three types of habitats in the late spring and early summer. Concentrations of atrazine and metolachlor were very low or non-detectable in all habitats sampled from early August to mid-April. Toxicity benchmarks of 20 g/L for atrazine based on an ecological No Observed Effect Concentration (NOEC) for microcosm/mesocosm studies and an acute 10th percentile of 53 g/L for metolachlor (protection of ninety % of the species) based on laboratory toxicity data were selected to assess annual and seasonal ecological risk. Both of these toxicity benchmarks were conservative estimates of ecological risk designed to protect the trophic group (plants) most sensitive to these herbicides. Based on a comparison of these toxicity benchmarks with two years of exposure data, the ecological risk from both atrazine and metolachlor exposure in the mainstem Chesapeake Bay/large tributaries, small tributaries and representative agriculturally dominated streams was generally judged to be low. During one 72-h stream rain event in 1995, the atrazine toxicity benchmark (20 g/L) was exceeded during part of the event. However, long-term permanent ecological effects are not expected based on the documented recovery potential of the most sensitive trophic group (plant communities) to the concentrations of atrazine reported and the transient nature of the atrazine pulses. Fish communities at the stream sites receiving the highest concentrations of both herbicides were judged to be healthy based on an Index of Biotic Integrity (IBI) developed for Maryland's coastal plain.     

Analytical methods for the determination of alachlor,metolachlor, simazine and atrazine mobility in soils

Abstract

A method for the determination of the mobility of the herbicides, alachlor, metolachlor, simazine and atrazine in soil is described . The method is based on the use of soil thin‐layer chromatography (TLC) and does not require the use of radiolabelled compounds. Soil on the TLC plate after development was separated into various bands, the material in each band was extracted with solvents and analyzed by gas chromatography.     

Field calibration of surface: A model of agricultural chemicals in surface waters

Abstract

Agricultural chemicals sporadically occur at detectable levels in the surface waters of intensively farmed watersheds. HSPF, a previously released model of agricultural chemicals in surface water, had been used to predict concentrations which were much higher (10 X) than those actually observed during monitoring studies. A new model, SURFACE, is described here which is much simpler than HSPF and gives better predictions of surface water concentrations. SURFACE uses PRZM, an EPA model, to calculate edge‐of‐field runoff losses and simple hydraulic routing algorithms to determine concentrations at the bottom of large river basins. In water systems sampled during 1985 and 1986, SURFACE predictions of annualized mean concentrations for alachlor, atrazine, cyanazine and metolachlor were within 0.09 ppb half of the time.