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1.
This study aimed to design ecologically acceptable formulations of acetochlor by adsorbing it on montmorillonite exchanged by a small organic cation, phenyltrimethylammonium (PTMA). Adsorption of acetochlor on the clay mineral exchanged with different organic cations and its release from these complexes were determined by GC and modeled by Langmuir equation. Interactions between acetochlor molecules and the exchanged organic cation on the clay surface were studied by Fourier transform infrared spectroscopy. Leaching of acetochlor in soil was determined by a bioassay using a column technique and Setaria viridis as a test plant. The adsorbed amounts of acetochlor on montmorillonite exchanged by PTMA at a loading of 0.5 mmol/g of clay were higher than at a loading up to the cation-exchange capacity, i.e., 0.8 mmol/g, and were higher than obtained by using a clay mineral exchanged by other organic cations. Preloading montmorillonite by PTMA at 0.5 mmol/g yielded maximal shifts of the infrared peaks of the herbicide. The above formulation of acetochlor yielded slow release in water and showed improved weed control in field and greenhouse experiments in comparison with the commercial formulation. The PTMA-clay formulation of acetochlor maintained herbicidal activity in the topsoil and yielded the most significant reduction in herbicide leaching and persistence under field conditions. The application of this formulation can minimize the risk to groundwater and can reduce the applied rates.  相似文献   

2.
This study aimed to design formulations of hydrophobic herbicides, alachlor and metolachlor, by adsorbing them on the clay mineral montmorillonite preadsorbed by the small organic cation phenyltrimethylammonium (PTMA). An adsorption model that considers electrostatics and specific binding and the possibility of cation adsorption above the cation exchange capacity (CEC) could explain and yield predictions for PTMA adsorption in the presence of NaCl concentrations from 0 to 500 mM. Adsorption of alachlor and metolachlor from aqueous solution on a clay mineral preadsorbed by PTMA was determined by GC and modeled by Langmuir equation. Herbicide interactions with the organoclay were studied by Fourier transform infrared spectroscopy. Leaching of herbicides was determined by a bioassay using a column technique and Setaria viridis as a test plant. The adsorbed amounts of alachlor and metolachlor on montmorillonite preadsorbed by PTMA at a loading of 0. 5 mol/kg (Mont-PTMA0.5) were higher than at a loading up to the CEC, that is, 0.8 mol/kg, and were higher than those obtained by using several other organic cations. Herbicide formulations based on Mont-PTMA0.5 yielded the largest shifts of the infrared peaks of the herbicides. These formulations based on Mont-PTMA0.5 gave slower release and showed improved weed control in comparison with formulations based on other organoclays. These formulations maintained herbicidal activity in the topsoil and yielded the most significant reduction in herbicide leaching.  相似文献   

3.
Pesticide formulations based on organoclays have been proposed to prolong the efficacy and reduce the environmental impact of pesticides in soil. This research addressed the question of whether atrazine in organoclay-based formulations is irreversibly sorbed or is bioavailable for bacterial degradation in soil. Different cations of l-carnitine (CAR), tyramine (TYRAM), hexadimethrine (HEXADIM), phenyltrimethylammonium (PTMA), hexadecyltrimethylammonium (HDTMA), and Fe(III) were incorporated into Na-rich Wyoming montmorillonite (SWy-2) and Ca-rich Arizona montmorillonite (SAz-1) at 100% of the cation exchange capacity (CEC) of the clays as a strategy to enhance the affinity of the clay minerals for atrazine. A Buse loam soil from Becker, MN, was treated with three organoclay-based formulations of 14C-atrazine or free herbicide and incubated for 2 weeks. To determine the bioavailability of 14C-atrazine, the soil was inoculated with Pseudomonas sp. strain ADP, which rapidly mineralizes atrazine. At day 0, and after a 2 week incubation, mineralization and the amount of 14C-atrazine residues distributed between the aqueous-extractable, methanol-extractable, and bound fractions in the soil were determined to characterize the availability of nonaged and aged atrazine residues. By the end of the 2 week incubation, the microorganisms had mineralized >80% of the initial readily available (water-extractable) and >70% of the less readily available (methanol-extractable) 14C-atrazine in the soil. Bound residues increased from <4% at day 0 to ～17% after the 2 week incubation for both the formulated and free forms of atrazine. The results of these incubation experiments show that the bioavailabilities of atrazine were similar in the case of the organoclay formulations and as free atrazine. This indicated that whereas more atrazine was sorbed and less likely to be transported in soil, when formulated as organoclay complexes, it was ultimately accessible to degrading bacteria, so that the herbicide is likely to be naturally attenuated by soil microorganisms.  相似文献   

4.
Slow release formulations of the anionic herbicide sulfosulfuron (SFS) were prepared by incorporating it in micelles of an organic cation octadecyltrimethylammonium, which adsorb on the clay-mineral montmorillonite. The fraction of SFS adsorbed on the micelle-clay complex reached 98%, whereas for monomer-clay complexes, its adsorption was insignificant. Fluorescence studies showed surface contact between the micelles and the clay surface. The rate of SFS release from the micelle-clay formulations in aqueous suspensions was slow (<1%, 72 h). Spraying SFS formulations on a thin soil layer in a funnel, followed by irrigations (50 mm), resulted in complete elution of SFS from the commercial formulation (dispersible granular) versus 4% from the micelle-clay formulation. A plant bioassay in Rehovot soil showed that these respective formulations yielded 23 and 65% of shoot growth inhibition of foxtail. Consequently, the slow release micelle-clay formulations of SFS yield significantly reduced leaching and enhanced biological activity, thus providing environmental and agricultural advantages.  相似文献   

5.
采用批处理恒温振荡法,利用气相色谱一质谱联用仪研究了人工添加不同吸附物质对土壤中乙草胺的吸附／解吸作用。结果表明,人工添加不同吸附物质对土壤中乙草胺的吸附强度和吸附容量不同,不同的添加剂对土壤中乙草胺的吸附／解吸作用均呈现明显的非线性关系,可用Freundlich模型描述。并且随着土壤中添加量的增大,吸附强度增大、吸附容量增大、所得吸附等温线的非线性也逐步增大;另外,添加剂对乙草胺的解吸迟滞作用也随添加剂含量的增高而更加明显。但是不同添加剂对土壤中乙草胺的吸附能力有明显差异,其中煤粉的吸附能力最大,其次是壳聚糖,沸石最小。  相似文献   

6.
Adsorption of the chloroacetanilide herbicides acetochlor, alachlor, metolachlor, and propachlor was determined on soils and soil components, and their structural differences were used to explain their sorptivity orders. On all soils and soil humic acids, adsorption decreased in the order: metolachlor > acetochlor > propachlor > alachlor. On Ca(2+)-saturated montmorillonite, the order changed to metolachlor > acetochlor > alachlor > propachlor. FT-IR differential spectra of herbicide-clay or herbicide-humic acid-clay showed possible formation of hydrogen bonds and charge-transfer bonds between herbicides and adsorbents. The different substitutions and their spatial arrangement in the herbicide molecule were found to affect the relative sorptivity of these herbicides by influencing the reactivity of functional groups participating in these bond interactions. It was further suggested that structural characteristics of pesticides from the same class could be used to improve prediction of pesticide adsorption on soil.  相似文献   

7.
Controlled-release formulations of the herbicide acetochlor were prepared by using carboxylmethylcellulose (CMC) gel and different types of clay, which were obtained by acid activation, pillared with metal hydroxides, or saturated with organic cations. The effect of formulation parameters (amount and type of clay used, cross-linking time, and drying of the hydrogel formulations) on the acetochlor release rate from different formulations was evaluated by water-release studies. The time taken for 50% of acetochlor to be released, t 50, showed a wide variation (151-522 h) for dried gel formulations, the largest value corresponding to the formulation incorporating aluminum hydroxide pillared clay into CMC gels. The release rate of acetochlor from clay/CMC hydrogel formulations decreased with the increase of the hydrogels' cross-linking time (t50 values ranged from 2.18 to 14.0 h for cross-linking times ranging from 2.0 to 120 min). The performance of inorganic clays in dried gel formulations on slowing the release of acetochlor is related to their sorption capacities, but the addition of organic clay did not lead to the slowest release despite its highest sorption capacity. According to the parameters of an empirical equation used to fit herbicide-release data, the release of acetochlor from clay/CMC gel formulations is controlled by diffusion mechanism.  相似文献   

8.
The risk of ground water contamination resulting from rapid leaching of highly soluble pesticides can be minimized through the application of the pesticide adsorbed on a matrix or carrier, which limits the amount of pesticide immediately available for undesirable losses. The use of natural materials for this purpose is of special interest in terms of economy and sustainability. In this work the adsorption of the herbicide hexazinone by two montmorillonites saturated with various inorganic and organic cations was determined and the ability of the two clays displaying the highest adsorption capacities [Fe(3+)-saturated Wyoming montmorillonite, (Fe-SW) and hexadecyltrimethylammonium-saturated Arizona montmorillonite (HDTMA-SA)] to act as carriers for slow release of hexazinone and to reduce herbicide leaching losses was evaluated. Hexazinone formulations based on Fe-SW and HDTMA-SA displayed slow release properties in water and soil/water suspensions, reduced herbicide leaching in soil columns, and maintained herbicidal activity, as compared with the currently available commercial hexazinone formulation (wettable powder). Loosely bound hexazinone-HDTMASA formulations, which led to the slowest breakthrough of hexazinone in soil columns along with the greatest amounts of herbicide released from the clay particles, displayed the most interesting characteristics for their use as slow release formulations and to prevent ground water contamination.  相似文献   

9.
采用定点试验的方法,在哈尔滨市呼兰区选择典型农田生态系统进行试验,研究施用不同浓度乙草胺对农田中小型土壤动物群落组成、多样性及垂直分布的影响。本调查共获中小型土壤动物4 648只,隶属于2门4纲10目15个类群,其中甲螨亚目和中气门亚目为优势类群。研究结果表明,施用不同浓度的乙草胺对农田中小型土壤动物群落组成、多样性及垂直分布均产生一定影响。Sorenson相似性系数和Morisita-Hron相似性系数均表现为高浓度与中浓度差异高浓度与低浓度差异高浓度与对照差异,表明随乙草胺浓度的增加土壤动物的群落结构差异逐渐显著;除优势度指数外,其余多样性指数均表现为中浓度和低浓度样地与对照样地存在显著差异(P0.05),高浓度样地与对照样地间存在极显著差异(P0.001)。5月、7月和9月土壤动物的密度在0~5 cm土层中均表现为对照样地低浓度样地中浓度样地高浓度样地,而在其下部的各土层中土壤动物密度变化与乙草胺浓度变化无明显相关性。中小型土壤动物可以作为揭示施用乙草胺过程中土壤质量变化的生物学指标。其群落组成、多样性和垂直分布的变化表明,中小型土壤群落对乙草胺的不同施用浓度产生了响应,过高浓度乙草胺会对土壤生态系统产生干扰,对土壤环境造成威胁。  相似文献   

10.
The design and tests of slow-release formulations of sulfometuron (SFM), an anionic sulfonylurea herbicide, are described. The formulations are based on incorporation of the herbicide in octadecyltrimethylammonium (ODTMA) micelles, which adsorb on a clay mineral, montmorillonite. An optimization of herbicide/micelle clay ratios yielded high adsorption of SFM (95%), and at a 1% (w/w) water suspension only 0.5% of the adsorbed SFM was released at times varying from hours to 9 days. An analytical test in Seville soil showed that under excessive irrigation (400 mm) 100% of the commercial formulation leached, whereas the micelle-clay formulations showed only 50-65% elution. A plant bioassay in Rehovot soil showed that the commercial dispersible granule formulation (Oust, 75% ai sulfometuron methyl) yielded only 23% root elongation inhibition at the top 5 cm of the soil, whereas complete inhibition was achieved with the micelle-clay formulation. The detected concentration of SFM for the micelle-clay formulation at a depth of 15-20 cm was half of that detected for the commercial one, indicating a reduction in leaching when applying the micelle-clay formulation. A 10-fold reduction in the applied dose of SFM in the micelle-clay formulations resulted in good herbicidal activity of 60-87% inhibition. These characteristics make the new formulation promising from the environmental and economic points of view.  相似文献   

11.
Natural or synthetic sorbents for pesticides can be used to reduce contamination of soils and natural waters. The sorption of simazine and 2,4-D on montmorillonite minerals has been studied and their potential use to retard pesticide leaching in soil evaluated. Simazine and 2,4-D did not sorb on high-layer charge montmorillonite, whereas sorption on the lower layer charge montmorillonite SWy varied depending on the saturating cation. Simazine sorption increased in the order Ca(2+)SWy < K(+)SWy < Fe(3+)SWy. Simazine molecules sorb on hydrophobic microsites of the montmorillonite. Once protonated, further sorption through cation exchange takes place in the interlamellar space of the montmorillonite, as corroborated by X-ray diffraction and FT-IR studies. 2,4-D does not sorb on K(+)SWy or Ca(2+)SWy, but does sorb on Fe(3+)SWy, because the acidic character of this sorbent allows the molecular form of 2, 4-D to sorb by hydrogen bonding and/or by hydrophobic interactions. Leaching experiments in hand-packed soil columns indicate that simazine and 2,4-D application as a complex with FeSWy renders later breakthrough and lower maximum concentration peaks, and the total herbicide leached is lower than when applied as the pure analytical grade compound. These results suggest the possible use of natural soil colloids as sorbents for herbicides such as simazine and 2,4-D to retard pesticide leaching in soil, thus reducing their ground water contamination potential.  相似文献   

12.
Abstract

The activity of residual herbicides employed for weed control varies with adsorption, lixiviation, degradation, and biological transformation of these compounds in the soil. The purpose of this study was to evaluate the activity of the herbicide acetochlor (2‐chloro‐N‐ethoxymethyl‐6′‐ethylacet‐o‐toluidine) in Typic Paleodult under no tillage and conventional tillage. Field and laboratory experiments were carried out at the Universidade Federal do Rio Grande do Sul. Weed control with and without straw coverage, and adsorption and lixiviation of acetochlor, in soil with both tillage systems were evaluated. Adsorption and lixiviation processes were determined by high‐performance liquid chromatography (HPLC) with UV detector. The coefficients K d and K oc were higher in no‐tillage soil, indicating a more effective acetochlor adsorption. The maximum concentration of acetochlor was found in a depth of 15–20 cm, indicating a higher lixiviation in this soil. The acetochlor was more effective in weed control using conventional tillage when compared to no tillage. The straw coverage reduced the control efficiency of the herbicide.  相似文献   

13.
Atrazine and alachlor formulations were designed by encapsulating the herbicide molecules into phosphatidylcholine (PC) vesicles, which subsequently were adsorbed on montmorillonite. PC and montmorillonite are classified as substances of minimal toxicological risk by the U.S. EPA. PC enhanced alachlor and atrazine solubilities by 15- and 18-fold, respectively. A 6 mM PC:5 g/L clay ratio was found as optimal for PC adsorption on the clay. Active ingredient contents of the PC-clay formulations ranged up to 8.6% for atrazine and 39.5% for alachlor. Infrared spectroscopy showed hydrophobic interactions of herbicide molecules with the alkyl chains of PC, in addition to hydrophilic interactions with the PC headgroup. Release experiments in a sandy soil showed a slower rate from the PC-clay formulations than the commercial ones. Soil column experiments under moderate irrigation and bioactivity experiments indicate that a reduction in the recommended dose of alachlor and atrazine can be accomplished by using PC-clay formulations.  相似文献   

14.
Sulfentrazone and metolachlor have been detected in groundwater due to extensive leaching. To reduce herbicide leaching and increase weed control, we have developed, designed, and tested controlled release formulations (CRFs) for both herbicides based on their solubilizion in cationic micelles and adsorption of the mixed micelles (surfactant and herbicide) on a clay mineral, montmorillonite. A better understanding of solubilizing anionic (sulfentrazone) and nonionic (metolachlor) organic molecules in cationic micelles was reached. The percent of active ingredient in the formulations was much higher than previously designed CRFs due to the enhanced solubilization of the herbicides in the micelles and due to their adsorption on the clay. Both CRFs demonstrated controlled release (compared to the commercial formulations) when applied to a thin soil layer. A bioassay in soil columns determined that the new sulfentrazone and metolachlor CRFs significantly improve weed control and reduce leaching (for the latter) in comparison with the commercial formulations.  相似文献   

15.
Abstract

A pot culture experiment with four levels of soil moisture (40, 55, 70, and 85% of field capacity) and five levels of sodium chloride (NaCl) concentration (0, 50, 100, 150, and 200 mM) in soil was conducted to examine the interactive effect of soil moisture and NaCl on the growth of halophyte Suaeda salsa. Results showed that growth was largest at 55% of field capacity, in the range of 50–100 mM NaCl. However, at 85% of field capacity, it can grow better at higher salinity levels; and at 40% of field capacity, the growth of S. salsa was increased greatly by moderate salinity. Contents of sodium (Na) and chloride (Cl) in plant tissues increased with the decrease of moisture levels of soil. Potassium (K) concentrations were also increased at low soil moisture. Drought tolerance was increased by moderate NaCl concentrations. It is thus considered that some amounts of Na and Cl are required to absorb water in this plant.  相似文献   

16.
The development of controlled-release formulations of alachlor to diminish its leaching in sandy soils, avoiding groundwater contamination and maintaining its efficacy, was studied. For this purpose, ethylcellulose (EC) microencapsulated formulations (MEFs) of alachlor were prepared under different conditions and applied to soil columns to study their mobility. The results show that in all cases the release into water of alachlor from MEFs was retarded when compared with commercial formulation. Total leaching losses in soil columns were reduced to 59% from 98%. The mobility of alachlor from EC microspheres into soil columns has been greatly diminished in comparison with its current commercial formulation (CF), above all with increasing EC/herbicide ratios. Distribution of alachlor applied as MEFs at different depths in the soil was higher in the soil surface (66.3-81.3% of herbicide applied at the first 12 cm). In contrast, the residues from CF along the complete soil column were only 20.4%. From the results of bioassays, MEFs showed a higher efficacy than CF at 30 days after the treatment. The use of ME formulations could provide an advantage in minimizing the risk of groundwater contamination by alachlor and reducing the application rates, as a result of maintaining the desired concentration of the herbicide in the top soil layer, obtaining longer periods of weed control.  相似文献   

17.
通过室内恒温(25℃)避光培养试验,研究了黑土环境中乙草胺的微生物降解特征。在适宜水分条件下,将土壤样品分别进行常规、灭菌、选择性抑菌剂加入等处理后培养并测定土壤乙草胺含量和土壤微生物量。结果显示:在灭菌土壤中乙草胺的残留量较未灭菌土壤显著增加,未灭菌土壤中乙草胺残留数量与微生物量变化密切相关,表明微生物活性是影响乙草胺降解的主要因素。适当的水分有益于土壤中微生物生长,从而促进了土壤中乙草胺的降解。加入青链霉素后乙草胺残留量远大于放线菌酮和常规培养,表明细菌比真菌具有更强的降解乙草胺的能力。随着乙草胺的施药量增加,初期微生物量显著降低,是导致乙草胺总降解率下降的主要原因。  相似文献   

18.
Using plate counting and ergosterol assay, single and joint effects of acetochlor and methamidophos on the dynamics of soil fungal population and total fungal biomass in the black soil zone of Northeast China were investigated. The results demonstrated that acetochlor at high concentration levels （150 and 250 mg kg^-1） had an acute and mostly chronic toxicity on both the soil fungal population and total fungal biomass, but at a low concentration （50 mg kg^-1） generally had a stimulating effect that was stronger with total fungal biomass than with the soil fungal population. Methamidophos at a high concentration level （250 mg kg^-1） alone and almost all of its combinations with various dosages of acetochlor increased the soil fungal population, whereas at most sampling dates with 250 mg methamidophos kg^-1 soil, total fungal biomass increased, but in combination with acetochlor it was decreased in the early period of incubation and then increased 28 days after incubation. Thus, through measuring the number of colony forming unit of the soil fungal population along with the total fungal biomass, a better understanding on effects of agrochemicals on soil fungi could be made.  相似文献   

19.
土壤微生物对除草剂乙草胺污染的响应和指示   总被引：1，自引：0，他引：1  
采用除草剂乙草胺作为土壤污染因子, 在人工可控制条件下, 研究乙草胺对土壤微生物细菌、真菌和放线菌数量及土壤微生物量碳的影响, 并探讨这些微生物学指标对土壤中乙草胺污染状况的指示.研究结果表明: 在整个试验过程中, 除草剂乙草胺在短时间内对微生物区系能产生明显抑制作用, 但随着时间增加和污染物的分解, 微生物数量逐渐得到恢复.在短时间抑制过程中, 细菌、放线菌数量以及微生物量碳与乙草胺浓度的对数之间有很好的剂量效应关系, 第7 d细菌数量与乙草胺浓度对数的拟合公式为y = -2.97x + 12.36, R2 = 0.999 3; 放线菌数量与乙草胺浓度对数的拟合公式为y = -2.13x + 6.67, R2 = 0.956 4; 微生物量碳在第14 d与乙草胺浓度对数的拟合公式为y = -89.25x + 348.90, R2 = 0.995 4; 其相关性都达到显著水平.而真菌在受到乙草胺污染后, 受抑制现象并不明显, 真菌对乙草胺有较强的抗性.总之在短期污染条件下, 土壤中的细菌、放线菌数量以及微生物量碳可以很好地指示土壤中乙草胺的污染状况.  相似文献   

20.
Research on organoclays as sorbents of pesticides has shown the usefulness of these materials as pesticide supports to prolong the efficacy of soil-applied pesticides and to reduce the large transport losses that usually affect pesticides applied in an immediately available form. Nevertheless, little information exists on the availability of organoclay-formulated pesticides for bacterial degradation. In this work, laboratory experiments were conducted to determine the adsorption-desorption behavior of two hexadecyltrimethylammonium-treated Arizona montmorillonites (SA-HDTMA50 and SA-HDTMA100) for the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), and to evaluate the ability of these organoclays to slow the release of the herbicide and to reduce herbicide leaching losses as compared to the free (technical) compound. The kinetics of mineralization of free and formulated 2,4-D by adapted bacteria was also determined. Organoclay-based formulations of 2,4-D displayed slow release properties in water and reduced herbicide leaching through soil columns, while maintained a herbicidal efficacy similar to that of the free (technical) 2,4-D. The total amount of 14C-2,4-D mineralized at the end of the biodegradation experiment (t=130 h) ranged between 30% and 46% of the formulated herbicide, which represented 53-81% of the amount of free 2,4-D mineralized in the same conditions. The release, leaching, and mineralization patterns of the formulated herbicide were found to depend both on the affinity of the organoclay for the herbicide and on the degree of interaction promoted during the preparation of the herbicide-organoclay complex. This suggests the possibility to select diverse preparations to achieve the desired release, leaching and biodegradation behavior.  相似文献   

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