Sorption and dissipation of aged metolachlor residues in eroded and rehabilitated soils

BACKGROUND: Sorption and dissipation of aged metolachlor were characterized in rehabilitated and eroded prairie soils using sequential batch slurry (conventional) and accelerated solvent extraction (ASE). RESULTS: In spite of an almost twofold difference in soil organic carbon (OC) content, S‐metolachlor sorption coefficients (K_d) and dissipation rates (DT₅₀) were the same in soils from different landscape positions within an eroded landform. Soil was moved within the landform to increase productivity. In areas receiving topsoil addition, S‐metolachlor K_d was higher and DT₅₀ was longer than in eroded areas. The efficiency of extraction was higher for ASE than for conventional extractions. No consistent aging effect on K_d was observed. Mineralization in 8 weeks accounted for < 10% of the applied metolachlor. CONCLUSION: The results of this laboratory study support a field dissipation study. Both showed that S‐metolachlor has the same retention and dissipation rate throughout an eroded landform, which was not expected owing to the large variability in soil properties, including OC concentrations. Altering soil properties by adding topsoil increased metolachlor sorption and persistence. The method of extraction (conventional versus ASE) affected calculated sorption coefficients and dissipation rates. In all cases, groundwater ubiquity scores (GUSs) categorized metolachlor as having intermediate mobility. Published 2012 by John Wiley & Sons, Ltd.     

Adsorption,desorption and dissipation of metolachlor in surface and subsurface soils

BACKGROUND: Variations in soil properties with depth influence retention and degradation of pesticides. Understanding how soil properties within a profile affect pesticide retention and degradation will result in more accurate prediction by simulation models of pesticide fate and potential groundwater contamination. Metolachlor is more persistent than other acetanilide herbicides in the soil environment and has the potential to leach into groundwater. Reasonably, information is needed about the dissipation and eventual fate of metolachlor in subsoils. The objectives were to evaluate the adsorption and desorption characteristics and to determine the dissipation rates of metolachlor in both surface and subsurface soil samples. RESULTS: Adsorption of metolachlor was greater in the high‐organic‐matter surface soil than in subsoils. Lower adsorption distribution coefficient (K_ads) values with increasing depth indicated less adsorption at lower depths and greater leaching potential of metolachlor after passage through the surface horizon. Desorption of metolachlor showed hysteresis, indicated by the higher adsorption slope (1/n_ads) compared with the desorption slope (1/n_des). Soils that adsorbed more metolachlor also desorbed less metolachlor. Metolachlor dissipation rates generally decreased with increasing soil depth. The first‐order dissipation rate was highest at the 0–50 cm depth (0.140 week^?1) and lowest at the 350–425 cm depth (0.005 week^?1). Degradation of the herbicide was significantly correlated with microbial activity in soils. CONCLUSION: Metolachlor that has escaped degradation or binding to organic matter at the soil surface might leach into the subsurface soil where it will dissipate slowly and be subject to transport to groundwater. Copyright © 2009 Society of Chemical Industry     

Adsorption of acetanilide herbicides on soils and its correlation with soil properties

The adsorption of metolachlor, acetochlor, pretilachlor and butachlor, as a group of acetanilide herbicides, on eight soils with various physical and chemical properties was studied. The adsorption isotherms fit the Freundlich equation well. The extent of adsorption increased in the order: metolachlor < acetochlor < pretilachlor < butachlor. The product of the Freundlich adsorption constants, K_f(1/n), showed good correlation with organic matter content (OM) of soils for each of these herbicides, suggesting that the latter is the main factor controlling the adsorption process of these acetanilide herbicides. Multivariant correlation regression between K_f(1/n) and two factors, water solubility (S_w) of herbicides and OM, was also performed. K_f(1/n) correlated well with 1/S_w and OM/S_w, showing that high S_w corresponds to a weak tendency to adsorb on soils. IR spectra and ESR parameters confirmed that multifunctional H bonds and charge-transfer bonds between humic acids (HA) and the herbicides were the main adsorption mechanisms of the latter. The ability of herbicides to form these adsorption bonds with HA increased in the same order as the extent of adsorption. © 1999 Society of Chemical Industry     

Adsorption-desorption studies of alachlor, metolachlor, EPTC, chlorothalonil and pirimiphos-methyl in contrasting soils

Five soils with different organic matter contents ranging from 0.48 to 10.4% were used to study the adsorption and desorption of alachlor, metolachor, EPTC, chlorothalonil and pirimiphos-methyl in batch experiments. The isotherm shapes according to Giles classification were S-type for alachlor, metolachlor and chlorothalonil, changing to L-type for the latter as the level of soil organic matter increased, and L-type for EPTC and pirimiphos-methyl. The adsorption isotherms fitted the Freundlich equation x/m = KfCe1/n. The Kf values increased with the increase of organic matter content. The amounts of pesticides adsorbed over a range of concentrations of 0.1-20 mg litre-1 reached 63.1% for alachlor, 69.2% for metolachlor, 89.3% for EPTC, 98.4% for chlorothalonil and 96.3% for pirimiphos-methyl. The increase of the amounts desorbed with acetone indicated that the sorption of organic compounds onto organic matter occurred principally via weak London-type induction forces, or dispersion forces which are characteristics of the physical adsorption process.     

Influence of straw management, nitrogen fertilization and dosage rates on the dissipation of five sulfonylureas in soil

The dissipation behaviour of metsulfuron-methyl, tribenuron-methyl, thifensulfuron-methyl, triasulfuron and amidosulfuron were studied in soil following post-emergence spring applications to cereal crops. Incorporation or removal of straw and different fertilizer applications had no influence on the disappearance time (DT₅₀) of the herbicides. However, in laboratory trials dissipation of metsulfuron-methyl, triasulfuron and amidosulfuron at higher application rates was accelerated after incorporation of straw into the soil. The addition of straw decreases soil pH thereby causing faster hydrolysis of the compounds. Addition of nitrogen fertilizer increased the half-lives (t_1/2) of the herbicides. Combination of both straw and N fertilizer, however, had no effect. Neither straw nor N influenced the degradation of tribenuron-methyl and thifensulfuron-methyl.
The DT₅₀ of all herbicides investigated varied from 6 to 17 days in the field trials. Except for amidosulfuron, herbicides could not be detected 38–68 days after application. In the laboratory, t_1/2 values were higher than those in the field at 75 days (amidosulfuron), 63 days (metsulfuron-methyl), 35 days (triasulfuron) and 13 days (tribenuron-methyl). Only the t_1/2 of thifensulfuron-methyl was at 29 h faster under laboratory conditions. T_1/2 values of all herbicides were influenced by their initial concentration. The t_1/2 values of amidosulfuron and tribenuron-methyl at 1 mg a.i. kg⁻¹ soil were 2–2.5 times higher than at the recommended field application rate of 42 μg a.i. kg⁻¹ soil.     

Adsorption-desorption of metalaxyl as affecting dissipation and leaching in soils: role of mineral and organic components

Adsorption-desorption studies of metalaxyl in fifteen agricultural soil samples from Southern Portugal and Spain were performed following a batch equilibration method. Very high sorption was observed on a clay soil of high content in altered illite, but, when this soil was excluded from regression analysis, organic matter (OM) was the most important single soil property affecting sorption at low concentrations of metalaxyl. At higher concentrations, no correlation was observed with any soil property. The relevance of OM on sorption was also corroborated by the increase in sorption coefficients when soil OM was increased artificially by the addition of an organic amendment. Sorption studies with the colloidal fraction of selected soils also revealed the importance of mineral surfaces in metalaxyl sorption. Sorption of metalaxyl in most of the soil samples was hysteretic. Selected soil samples were incubated in the dark, sampled periodically and extracted for their fungicide content. Metalaxyl half-lives increased with sorption and OM content of the soil, and were specially high in the amended soil. Leaching studies in hand-packed columns under saturated/unsaturated flow conditions showed an inverse relation between leaching and sorption. Recoveries from the soil columns were close to 80% of the metalaxyl applied, except for the soil which OM was artificially increased, in which recovery was lower and this has been attributed to the much higher irreversibility of metalaxyl sorption in the amended soil.     

噻菌茂在稻田土壤中的微生物降解及对土壤细菌种群数量的影响

采用模拟土壤生态系统,研究了噻菌茂(2-苯甲酰肼-1,3-二噻茂烷)在不同稻田土壤中的消解规律及其对土著细菌种群数量的影响。结果表明,0.2和100 mg/kg的噻菌茂在未灭菌处理的淹水及不淹水土壤中的消解半衰期分别为2.6、4.0 d和5.5、7.3 d,而在经灭菌处理未淹水土壤中的消解半衰期分别为7.5和11.0 d,表明微生物是土壤中噻菌茂消解的主要影响因子。同时,噻菌茂对土壤中的微生物尤其是稻田土壤细菌也具有一定的影响,低浓度(0.2 mg/kg)下,噻菌茂对土壤中细菌生长的影响是暂时性的,7 d后菌群生长即可基本恢复至对照水平;而高浓度(100 mg/kg)噻菌茂则对土壤中细菌的生长具有明显的持续抑制作用,28 d后菌群生长仍未能恢复。     

Measuring cysteine biosynthesis activity from serine in extracts from sorghum, corn and grass weeds, and their metolachlor susceptibility

In vitro assay procedures for measuring the activity of cysteine biosynthesis from serine (CBS), which is a coupled reaction catalyzed by serine acetyltransferase and cysteine synthase, were developed using crude extracts from sorghum shoots. Cysteine biosynthesis from serine activity was dependent on acetyl‐CoA concentrations (up to 1.5 mmol L^?1), serine (at least up to 20 mmol L^?1) and sulfide (up to 0.25 mmol L^?1), respectively, and was proportional to the protein concentration in the reaction mixture below 0.4 mg mL^?1. The reaction rate was 6.6 nmol min^?1 per mg of protein during the first 5 min, but increased to 45.6 nmol min^?1 per mg of protein between 30 and 45 min after reaction initiation. Sorghum had the highest CBS total activity (222.4 nmol min^?1 per g of fresh weight), and large crabgrass had the lowest CBS total activity (4.7 nmol min^?1 per g of fresh weight) when CBS activity in shoots was extracted from sorghum, corn, johnsongrass, barnyardgrass, goosegrass, green foxtail and large crabgrass. Similar results were obtained for CBS specific activity (nmol min^?1 per mg of protein). There was no correlation between total CBS activity and susceptibility to metolachlor; however, when corn was excluded, a correlation of R² = 0.690 was found. Flurazole seed treatment (1.25 g per kg of seed) conferred metolachlor resistance by sorghum, and enhanced total CBS activity and non‐protein thiol content by 27 and 61%, respectively. The increase in thiol content presumably contributed to metolachlor tolerance in sorghum. From these results, the difference in CBS activity partially contributes to the selectivity to metolachlor among certain grass species, and to the safening action of flurazole by increasing thiol content.     

Evidence for 2,4‐D mineralisation in Mediterranean soils: impact of moisture content and temperature

BACKGROUND: The 2,4‐D degradation ability of the microbiota of three arable Mediterranean soils was estimated. The impact of soil moisture and temperature on 2,4‐D degradation was investigated. RESULTS: The microbiota of the three soils regularly exposed to 2,4‐D were able rapidly to mineralise this herbicide. The half‐life of 2,4‐D ranged from 8 to 30 days, and maximum mineralisation of ¹⁴C‐2,4‐D ranged from 57 to 71%. Extractable ¹⁴C‐2,4‐D and ¹⁴C‐bound residues accounted for less than 1 and 15% respectively of the ¹⁴C‐2,4‐D initially added. The highest amounts of ¹⁴C‐2,4‐D bound residues were recorded in the soil with the lowest 2,4‐D‐mineralising ability. Although all three soils were able to mineralise 2,4‐D, multivariate analysis revealed that performance of this degrading microbial activity was dependent on clay content and magnesium oxide. Soil temperature affected the global structure of soil microbial community, but it had only a moderate effect on 2,4‐D‐mineralising ability. 2,4‐D‐mineralising ability was positively correlated with soil moisture content. Negligible 2,4‐D mineralisation occurred in all three soils when incubated at 10 or 15% soil moisture content, i.e. within the range naturally occurring under the Mediterranean climate of Algeria. CONCLUSION: This study shows that, although soil microbiota can adapt to rapid mineralisation of 2,4‐D, this microbial activity is strongly dependent on climatic parameters. It suggests that only limited pesticide biodegradation occurs under Mediterranean climate, and that arable Mediterranean soils are therefore fragile and likely to accumulate pesticide residues. Copyright © 2009 Society of Chemical Industry     

Influence of Soil Moisture on Long-Term Sorption of Diuron and Isoproturon by Soil

Long-term sorption of diuron and isoproturon by a clay loam soil was investigated for nine weeks at two herbicide doses (0·6 or 3 mg kg⁻¹) and two soil moisture contents (35 or 62% w/w, i.e. 3·16 or 1 kPa) by measuring changes in herbicide concentrations in the soil solution sampled by means of glass microfibre filters in presence of sodium azide (200 mg litre⁻¹) which inhibited biodegradation for more than four weeks. After the first day equilibration period, where adsorption mainly occurred (>70% adsorbed), herbicide concentrations in the soil solution decreased (about 50% for diuron; up to 38% for isoproturon) for two weeks but equilibration required about one month. Small amounts of herbicides were sorbed during this process (<10% of the initial (24-h) adsorption). These were similar for both herbicides, although diuron was initially more adsorbed. Values of the partition coefficients of herbicides between soil and soil solution were increased (75–125% for diuron; 29–67% for isoproturon). High soil moisture enhanced sorption speed for both herbicides and increased final sorption only for diuron. Sodium azide inhibited long-term sorption of the more stable diuron and this effect was reversed by low temperature only at the low soil moisture. Sodium azide action might be complex (competition, effect on soil micro-organisms) and was not elucidated.     

丙炔氟草胺在大豆和土壤中的残留及消解动态

通过在山东德州、黑龙江哈尔滨和辽宁海城2年3地的田间试验,采用QuEChERS-高效液相色谱-串联质谱 (QuEChERS-HPLC-MS/MS) 法,研究了丙炔氟草胺在大豆和土壤中的残留及消解动态。结果表明: 在0.000 3、0.01和0.1 mg/kg添加水平下,丙炔氟草胺在大豆植株、青大豆、大豆籽粒和土壤中的日内平均添加回收率为89%~112%,日内相对标准偏差(RSD) (n = 5) 为1.3%~5.3%;日间平均添加回收率为85%~110%,日间RSD (n = 15) 为0.40%~4.8%。丙炔氟草胺在大豆植株、青大豆、大豆籽粒和土壤中的定量限 (LOQ) 均为0.000 3 mg/kg,能够满足农药残留限量标准的要求。丙炔氟草胺在大豆植株和土壤中的消解动态均符合一级反应动力学方程,在大豆植株和土壤中的消解半衰期分别为 5.8~11.8 d和 15.8~24.8 d。采用480 g/L丙炔氟草胺悬浮剂按推荐高剂量 (有效成分60 g/hm2) 及其1.5倍推存剂量 (有效成分90 g/hm2) 于播后苗前施药1次,收获期采样时,丙炔氟草胺在大豆植株、青大豆、大豆籽粒和土壤中的最终残留量均低于中国国家标准中规定的丙炔氟草胺在大豆上的最大残留限量 (0.02 mg/kg)。     

Sorption of atrazine and dicamba in Delaware coastal plain soils: a comparison of soil thin layer and batch equilibrium results

The mobility and retention of atrazine and dicamba in six Atlantic Coastal Plain soils were estimated by soil thin-layer chromatography (soil-TLC). The soils studied were representative of the major agricultural regions in Delaware and were sampled, by horizon, to the water table. Four horizons from each profile were leached simultaneously with distilled water on one soil-TLC plate. Two values were obtained from each plate: the ratio of the distance traveled by the herbicide center of mass over that traveled by the solvent front (R_m), and a sorption distribution coefficient (K_d). The R_m values ranged from 0·06 to 0·94 for atrazine and from 0·80 to 0·94 for dicamba. Herbicide mobility was found to be greatest in coarse-textured soil horizons that contained low levels of organic matter, clay, and Fe and Al oxides. Correlation analysis indicated that effective cation exchange capacity, exchangeable acidity, exchangeable aluminum, and clay were useful predictive variables or both atrazine mobility and sorption. Organic matter was not useful for predicting soil-TLC derived sorption estimates; however, it was correlated to K_d-batch estimates. Distribution coefficients calculated from soil-TLC data were found to be in general agreement with K_d values obtained for the same soils by batch equilibrium techniques. The average K_d-soil-TLC values for atrazine and dicamba were 2·09(±2·24) and 0·03(±0·02), respectively. The ratio of the batch K_d to the soil-TLC K_d ranged from 0·1 to 19 (x̄=1·6, SD=3·8) for atrazine and from 2·9 to 38 (x̄=12·6, SD=8·7) for dicamba. Thus, although for some horizons agreement between the two methods was good, for other horizons significant discrepancies existed. It is suggested that the soil-TLC gives results under non-equilibrium conditions, whereas the batch procedure is, by definition, at quasi-equilibrium. These fundamental differences may account for the observed differences between the two methods. It is also suggested that, due to this difference, the soil-TLC procedure can provide additional information relevant to herbicide partitioning in the field environment that is not provided by traditional batch equilibrium techniques. © 1998 Society of Chemical Industry     

丙硫菌唑及代谢物硫酮菌唑在土壤中的残留分析方法及消解

初步研究了土壤中丙硫菌唑及代谢物硫酮菌唑的残留分析方法及其在北京和安徽两地土壤中的消解情况。样品经乙腈超声提取,盐析后取上清液,经高效液相色谱-紫外检测器（HPLC-UVD）测定,外标法定量。结果表明:在0.05、0.3和1 mg/kg 3个添加水平下,丙硫菌唑和硫酮菌唑的平均回收率在75%~97%之间,相对标准偏差（RSD）在1.0%~7.8%之间,定量限（LOQ）均为0.05 mg/kg,丙硫菌唑在土壤提取液及前处理过程中会部分转化成代谢产物硫酮菌唑。北京和安徽两地喷施到土壤中的丙硫菌唑会迅速转化为代谢物硫酮菌唑,且硫酮菌唑的残留浓度随时间的延长呈现先升高后降低的趋势。     

噻虫胺在番茄和土壤中的残留及消解动态

通过两年3地的田间试验,采用分散固相萃取-液相色谱-串联质谱法,研究了50%噻虫胺水分散粒剂在番茄和土壤中的残留及消解动态。结果表明:在0.005、0.01和0.05 mg/kg添加水平下,噻虫胺在番茄中的回收率为90%～121%,相对标准偏差（RSD）为4.0%～4.5%（n=5）,在土壤中的回收率为88%～92%,RSD为3.6%～5.8%（n=5）,番茄和土壤中噻虫胺的定量限均为0.005 mg/kg,可满足现有限量标准的要求。噻虫胺在番茄中的消解动态符合准一级动力学方程,半衰期为3.5～17.3 d。当50%噻虫胺水分散粒剂以推荐剂量（有效成分）60 g/hm2在番茄生长到成熟个体一半大小时施药3次,施药间隔7 d时,噻虫胺在番茄上的最终残留量在< LOQ～0.32 mg/kg之间,远低于日本规定的最大允许残留量（MRL）值3 mg/kg,推荐采收安全间隔期为1 d。     

Pencycuron dissipation in soil: effect of application rate and soil conditions

Dissipation of the fungicide pencycuron was examined under controlled laboratory conditions in clay loam soils from rice cultivated fields of alluvial soil (Typic udifluvent) and coastal saline soil (Typic endoaquept) at field rate, twice the field rate and 10 times the field rate with and without decomposed cow manure maintained at 60% of maximum water-holding capacity (WHC) and waterlogged soil condition. The half-life values depended on the initial concentrations of pencycuron. Pencycuron, in general, degraded fastest in coastal saline soil and in soil amended with decomposed cow manure at 60% of maximum WHC of soil.     

5种除草剂对土壤蔗糖酶和脲酶活性的影响

采用室内培养法,研究了土壤中添加5种除草剂(氟磺胺草醚、甲咪唑烟酸、乳氟禾草灵、扑草净和噻吩磺隆)对土壤蔗糖酶和脲酶活性的影响。结果表明:在0.05、0.5和5 mg/kg的甲咪唑烟酸、乳氟禾草灵、扑草净和噻吩磺隆作用下,在3~40 d内对土壤蔗糖酶活性表现为抑制-激活-恢复效应,其中0.5mg/kg的乳氟禾草灵处理,3 d时土壤蔗糖酶被显著抑制,6、9、25和40 d时被激活;而0.05、0.5和5 mg/kg的氟磺胺草醚处理,前9 d土壤蔗糖酶活性被显著抑制,25和40 d时被激活。在用0.05、0.5和5mg/kg的甲咪唑烟酸、噻吩磺隆和5 mg/kg扑草净处理的3~40 d内,对土壤脲酶活性均表现为抑制-激活-抑制效应;0.05和0.5 mg/kg的扑草净及0.05和5 mg/kg的乳氟禾草灵处理,土壤脲酶在3~40 d内虽然也出现上述变化趋势,但到40 d时已恢复到对照水平;低浓度(0.05和0.5 mg/kg)氟磺胺草醚处理对土壤脲酶表现为抑制-激活效应,而高浓度(5 mg/kg)处理则表现为抑制-激活-抑制作用。     

Fate of the herbicides glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron in two Finnish arable soils

The fate of five herbicides (glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron) was studied in two Finnish sugar beet fields for 26 months. Soil types were sandy loam and clay. Two different herbicide-tolerant sugar beet cultivars and three different herbicide application schedules were used. Meteorological data were collected throughout the study and soil properties were thoroughly analysed. An extensive data set of herbicide residue concentrations in soil was collected. Five different soil depths were sampled. The study was carried out using common Finnish agricultural practices and represents typical sugar beet cultivation conditions in Finland. The overall observed order of persistence was ethofumesate > glyphosate > phenmedipham > metamitron > glufosinate-ammonium. Only ethofumesate and glyphosate persisted until the subsequent spring. Seasonal variation in herbicide dissipation was very high and dissipation ceased almost completely during winter. During the 2 year experiment no indication of potential groundwater pollution risk was obtained, but herbicides may cause surface water pollution.     

氟环唑在小麦及土壤中的残留及消解动态

为了评价氟环唑在小麦生产上使用的残留安全性,建立了气相色谱-电子捕获检测器检测氟环唑在小麦植株、小麦籽粒及土壤中残留的分析方法,并对氟环唑在小麦植株、小麦籽粒和土壤中的最终残留量及小麦植株和土壤中的消解动态进行了研究。结果表明:在添加水平为0.01、0.1和2 mg/kg（小麦籽粒和土壤）和0.01、0.1和10 mg/kg（小麦植株）下,氟环唑的回收率为82%~93%,相对标准偏差为3.0%~9.7%。氟环唑在小麦植株、小麦籽粒和土壤中的定量限均为0.01 mg/kg。氟环唑在小麦植株和土壤中的消解半衰期分别为3.5~8.4和10~30 d。当以有效成分112.5 g/hm2的剂量施药2次、采收间隔期为21 d时,小麦籽粒中氟环唑的残留量为<0.05 mg/kg,低于中国制定的小麦中氟环唑的最大残留限量值（0.05 mg/kg）。建议氟环唑在小麦上使用时最大剂量为有效成分112.5 g/hm2,施药2次,安全间隔期为21 d。