Use of bentonite and humic acid as modifying agents in alginate-based controlled-release formulations of imidacloprid

In order to prepare a formulation to be used for controlled release, imidacloprid was incorporated into alginate granules by using calcium chloride as gellant. The formulation prepared (alginate–imidacloprid–water) was modified by the addition of different sorbents. The effects on release rate of the addition of natural bentonite desiccated at 105 °C, untreated, acid-treated with sulfuric acid solutions over a concentration range between 0.5 mol dm⁻³ and 2.5 mol dm⁻³, and a commercial humic acid, were studied by immersion of the granules in water under static conditions. The time taken for 50% of the active ingredient to be released into water, (T₅₀), was calculated from the data obtained. On the other hand, the sorption–desorption processes of imidacloprid from a 0.01 M aqueous calcium chloride solution at 25 °C, by natural, acid-treated bentonite samples, and humic acid, have been studied by using batch experiments in order to evaluate the potential of these materials for their application in controlled-release formulations of pesticides. The experimental data have been fitted to the Freundlich equation in order to calculate the adsorption capacities (K_f). K_f values ranged from 1.76 mg kg⁻¹ for the untreated bentonite up to 126.9 mg kg⁻¹ for the humic acid. A correlation study was performed with T₅₀, the surface area (S) and the Freundlich parameter (K_f) of the bentonite samples in order to know the factors that affect release rate of imidacloprid from bentonite granules. A linear correlation of the T₅₀ values and both S and K_f parameters was observed. © 1999 Society of Chemical Industry     

Mobility of imidacloprid from alginate-bentonite controlled-release formulations in greenhouse soils

The mobility of imidacloprid [1-(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine] from alginate-based controlled-release (CR) formulations was investigated in two different soil profiles. In one, a layered bed system simulating the typical arrangement under a plastic greenhouse, which is composed of sand, peat, amended soil and native soil, was used. In the other, the layer containing amended soil was used in order to determine the mobility of the insecticide in a soil system with a low content of organic matter and a high content of clay. Two CR formulations based on sodium alginate (1.87% wt/wt), imidacloprid (1.21%), natural or acid-treated bentonite (3.28%), and water (93.64%) were compared to technical grade imidacloprid. The use of alginate CR formulations produced less vertical mobility of the active ingredient as compared to the technical product. With the technical grade product treatment, the total amount of imidacloprid leached from columns packed with amended soil was 82.3% of that applied, whereas for the alginate-based CR formulations containing natural or acid-treated bentonite, the leached percentages were 44.7% and 37.1%, respectively. In the column experiments simulating the layered bed system, no insecticide was found in the leachate when the alginate-based CR formulations containing natural bentonite were used. However, 3% of the applied imidacloprid appeared when the treatment was carried out with technical grade material. Sorption-desorption capacities of the various soil layers for imidacloprid molecules were also calculated using batch experiments. © 1999 Society of Chemical Industry     

控制释放制剂的组成对异丙甲草胺释放速率的影响

将海藻酸盐与膨润土复合作为载体制备除草剂异丙甲草胺的控制释放制剂,研究了载药量、载体原料配比、膨润土类型等制剂组成因素对异丙甲草胺释放速率的影响。采用Ritger和Peppas方程分析释放动力学过程,计算50%的异丙甲草胺被释放所需时间(t50),并以此表征释放速率。结果表明,采用海藻酸盐/膨润土复合载体时, t50随载药量和载体原料配比不同介于29.4~68.0 h 之间,控制释放效果明显优于单纯以有机改性膨润土作载体(t50=5.9 h)。将有机改性膨润土与海藻酸盐复合作载体时,t50可达110 h。释放动力学方程的n值(0.436~0.496)接近Fickian扩散模型,说明该控制释放制剂中异丙甲草胺的释放过程主要受到扩散控制。     

Release of atrazine and alachlor from clay-oxamide controlled-release formulations

Controlled-release herbicide formulations have been shown to decrease the leaching potential of several herbicides under laboratory and field conditions. The utility and efficacy of these formulations may be improved by combining several herbicides and a fertilizer source in a single formulation. The objective of these studies was to develop granular alginate formulations that were composed of a combination of the herbicides atrazine and alachlor with the slow-release nitrogen source oxamide (ethanediamide). Controlled release of the herbicides was obtained by addition of selected minerals, including calcium bentonite, fine-grind bentonite, montmorillonite K10, kaolinite and iron (III) oxide. A formulation without clay was used as a comparison. The formulations tested had herbicide active ingredient contents ranging from ∽0·02 to 0·54% and a nitrogen content of 21%. Release of the herbicides was studied by equilibrating the formulations with deionized water on a rotary shaker at 200 rev min^-1 and sampling at regular time intervals up to 104 hours. The minerals used in the different formulations influenced the herbicide active ingredient composition, as well as the release properties of the individual formulations. The atrazine content of the formulations decreased in the order calcium bentonite>fine-grind bentonite>kaolinite>montmorillonite=iron oxide>no clay. For alachlor the content decreased in the order of calcium bentonite>fine-grind bentonite>montmorillonite>iron oxide>kaolinite>no clay. Controlled release of atrazine (i.e. reduction in release rate) varied in the order calcium bentonite>iron oxide>montmorillonite>fine-grind bentonite= kaolinite>no clay, and for alachlor fine-grind bentonite>calcium bentonite>montmorillonite>no clay=kaolinite=iron oxide. A certain percentage of the applied active ingredient of both alachlor and atrazine was not recovered. From 5 to 27% of the active ingredient was not released, with the greatest retention by the bentonite formulations. Release of nitrogen was not strongly influenced by mineral type, although a trend indicated greater release with formulations containing kaolinite. © 1998 SCI     

Leaching of Alachlor from Alginate-Encapsulated Controlled-Release Formulations

The mobility of alachlor from alginate-encapsulated controlled-release (CR) formulations was investigated in two contrasting soil profiles. Two CR formulations of alachlor were prepared with the following components (1) base—sodium alginate+kaolin+‘Tween’ 20 (1+10+0·5 by mass) and (2) base+40 g kg⁻¹ linseed oil. These were compared to technical grade alachlor and to a commercial alachlor EC formulation (‘Lasso’ 4EC). All herbicide treatments were labeled with [¹⁴C]alachlor and were applied to duplicate soil columns that were composed of a surface and a subsoil horizon. Each horizon was packed to a depth of 12·5 cm, giving a total column length of 25 cm. The columns were leached with 21 cm (420 ml) to 30 cm (600 ml) of 0·01M calcium chloride for a period of 7 to 10 days. Alachlor leaching from the EC formulations was the same as that from the technical material in both soils: 33% in the Evesboro and 10% in the Conover soil. The CR-Oil formulation leached 4 and 2% of the applied [¹⁴C]alachlor, compared to 12 and 3% for the CR-N formulation for the Evesboro and Conover soils, respectively. The CR-Oil formulation also increased the amount of [¹⁴C]alachlor retained in the soil surface horizon (105–114%), compared to CR-N (39–45%), technical material (14–23%) and EC (12–17%).     

羧甲基壳聚糖/改性膨润土复合载体对莠去津释放和淋溶的影响

首次尝试将羧甲基壳聚糖与改性膨润土复合用作除草剂莠去津的载体,制备得到控释型颗粒剂,以延缓莠去津的释放,减少淋溶损失,提高药效及控制其污染。通过水中释放实验研究了制剂配方对莠去津释放速率的影响,并借助半经验方程探讨了其释放机理,采用土壤薄层实验考察了复合载体对降低莠去津淋溶的效果。 结果表明,采用复合载体时莠去津的半数释放时间(t 50)可达700 h 以上,比对照采用单一羧甲基壳聚糖作载体时延长了1倍以上。莠去津由颗粒剂向水相释放的过程主要受费克扩散(Fickian diffusion)控制,且经9次淋洗后莠去津的累计淋出率仅为6.0%,表明该复合载体控释制剂可显著减少莠去津对地下水的污染。     

Preparation of controlled-release formulations of 14C-labelled thiobencarb herbicide and study of their environmental behaviour

Controlled-release formulations of ¹⁴C-labelled thiobencarb herbicide were prepared in calcium alginate using kaolin as an inexpensive filler. The rates of release of the herbicide from these and from a commercial granular formulation were studied in static distilled water contained in open and closed vessels. The rate of release of the herbicide was much higher from the commercial formulation than from the controlled-release formulations. Increasing the proportion of kaolin to calcium alginate in controlled-release formulations reduced the rate of release of the herbicide. There was a significant loss of thiobencarb-related radioactivity from the water solution when the vessels containing the solutions were left uncovered and exposed to light. The loss of the herbicide seemed to be due to degradation and evaporation.     

Optimisation of a semiochemical slow-release alginate formulation attractive towards Aphidius ervi Haliday parasitoids

BACKGROUND: Optimisation of alginate formulations is described in order to develop semiochemical (E-β-farnesene and E-β-caryophyllene) slow-release devices in biological control approaches by attracting predators and parasitoids of aphids. Various formulation criteria were optimised with respect to semiochemical encapsulation capacity. Moreover, the optimised formulation was characterised by texturometry and confocal microscopy. The slow-release rates of semiochemicals were calculated in laboratory controlled conditions. The attractiveness of semiochemical formulations towards Aphidius ervi was demonstrated by olfactometry. RESULTS: Two major parameters were highlighted in encapsulation optimisation: the type of alginate (Sigma L) and the type of crosslinker ion (Ca²⁺). Other formulation parameters were optimised: ionic strength (0.5 M), Ca²⁺ (0.2 M) and alginate (1.5%) concentrations and the maturation time of beads in CaCl₂ solution (48 h). After physical characterisation of beads, semiochemical slow-release measurements showed that alginate formulations were efficient sesquiterpene releasers, with 503 µg of E-β-farnesene and 1791 µg of E-β-caryophyllene totally released in 35 days. The efficiency of semiochemical alginate beads as attractants for female parasitoids was demonstrated, with high percentages of attraction for semiochemical odours (88 and 90% for E-β-farnesene and E-β-caryophyllene respectively) and significant statistical results. CONCLUSION: Semiochemical alginate beads can be considered as efficient slow-release systems in biological control. These formulations could be very useful to attract aphid parasitoids on crop fields. Copyright © 2011 Society of Chemical Industry     

Permeation of urea through various polyurethane membranes

BACKGROUND: Controlled‐release systems using polymer membranes are very important in agriculture for labour‐saving and effective delivery of pesticides and other agents. Polymer‐coated granules are one of the most useful formulations, and a study of the factors for polymer design is necessary to achieve various release patterns. A permeation study using plain membranes was carried out in order to clarify parameters, and the results were compared with the release from polymer‐coated granules. RESULTS: The permeation coefficient of urea through a plain polyurethane membrane decreased significantly as the urethane and alkyl side chain content increased. The glass transition temperature and crosslink density of the polyurethanes hardly influenced its permeability. The release rate from polyurethane‐coated granules was also reduced by alkyl side chains. However, it was faster than that through a plain membrane because of capsule expansion by continuous water penetration and structural changes in the membrane. CONCLUSION: The release rate of urea through a polyurethane plain membrane and from polyurethane‐coated granules can be controlled by changing the chemical properties of the membrane. In addition, physical properties such as the glass transition temperature T_g or crosslink density should be considered to assess the release profile from polyurethane‐coated granules. Copyright © 2009 Society of Chemical Industry     

Slow release pirimicarb granular formulations: Measurements of release rate under field conditions

Various granular formulations based on a non-disintegrating granular carrier of the aphicide, pirimicarb, were tested for release rate under natural conditions by placing the granules in small bags made of a non-woven fabric in various soils and analysing the contents at monthly periods. There was complete release from the control formulation within 1 month. The other formulations contained slow release additives. These slowed down the release rate but half of the active ingredient was still released in the first month from the formulation with the slowest release rate. It appears that if very slow rates of release are required than a different type of granule is needed. Laboratory release rates bear some relationship to field results justifying the use of laboratory tests as a method for selecting a short list of formulations for testing in the field.     

Differentiating between physical and chemical constraints on pesticide and water movement into and out of soil aggregates

A laboratory experiment comparing the movement of ³H₂O and [¹⁴C]isoproturon into and release from soil aggregates is described. Small aggregates (2.0–2.4 mm) were prepared from a clay topsoil and maintained at three different initial moisture conditions. A small volume of the radioisotope solution was introduced prior to bathing the aggregates in a 2 mM CaCl₂ solution to represent new rainwater. Whilst the ³H₂O was imbibed by the air-dry aggregates, the pesticide did not follow the water but remained on the surface of the aggregates. This may be related to its sorptive properties and an excess of sorption sites on the sorbent with respect to the sorbate. Increasing the length of exposure of the moist aggregates to [¹⁴C]isoproturon reduced the initial release of the compound into the bathing solution, probably due to diffusion (retarded by sorption) into the aggregates. The diffusion model described by Crank and a non-equilibrium desorption model were used to analyse the ³H₂O and [¹⁴C]isoproturon release curves. This showed that the release of ³H₂O from the dry aggregates was controlled by diffusion. The release of isoproturon was probably controlled by non-equilibrium sorption/desorption from air-dry aggregates and by a combination of non-equilibrium sorption/desorption and diffusion from wet aggregates. © 1999 Society of Chemical Industry     

Influence of formulation on triticonazole solubilisation and sorption in a soil–water system

The effect of agronomic doses of three suspension concentrate formulations and two anionic surfactant adjuvants on the solubilisation and sorption characteristics of triticonazole fungicide in a loamy clay soil was investigated. Soil sorption of [¹⁴C]triticonazole alone, in the formulations, and in the presence of increasing doses of formulation additives was measured using the classical batch equilibration technique. Triticonazole solubilisation in water‐formulation systems was also evaluated using a batch procedure, and sorption of the formulation aqueous phases on soil was examined. Solubilisation of triticonazole in the formulation systems occurred in excess of the solubility in water (S_w). This was attributed to triticonazole association with surfactant monomers. Sorption isotherms of triticonazole with diluted surfactants and other formulation additives were similar to that of triticonazole alone. We concluded that in soil‐formulation systems, triticonazole solubilisation in excess of the S_w may increase the amount available in soil solution for plant absorption. However, triticonazole molecules preferentially associated with the soil surfaces, and the presence of diluted amounts of the formulation adjuvants would not significantly affect the soil sorption process. © 2000 Society of Chemical Industry     

灭蚊幼球形芽孢杆菌漂浮颗粒剂研制与应用

根据蚊虫的生活习性和球形芽孢杆菌BS-10灭蚊特点,以玉米棒芯颗粒为载体、以球型芽胞杆菌BS-10为杀虫活性物质,加工制成生物灭蚊漂浮颗粒剂新剂型,经试验与示范应用,该颗粒剂具有高效,毒力效价达106.5 IU／mg,每平方米水面使用颗粒剂2 g,对蚊幼虫(孑孓)杀灭效果达95%以上;持效期长,药后12 d,灭蚊效果达96.8%;性质稳定,室内常温储存1 a,药效无变化;生产工艺简单,药剂使用方便,与环境相容性好。     

阿维菌素B2海藻酸钠-壳聚糖包埋颗粒剂的制备及性能研究

为了提高阿维菌素B2的农药利用率,以海藻酸钠与壳聚糖为复合载体,采用复凝聚法制备了阿维菌素B2海藻酸钠-壳聚糖包埋颗粒剂,并研究了其理化性质及其在土壤中的释放性能。通过单因素试验筛选出对包埋颗粒剂包埋率影响较大的因素,并进行正交试验,以获得优化制备配方;用红外光谱表征包埋颗粒剂的化学结构,用扫描电子显微镜（SEM）观察其物理形态。采用土壤包埋法研究了其模拟释放性能。结果显示:制备阿维菌素B2海藻酸钠-壳聚糖包埋颗粒剂的优选配方为海藻酸钠质量分数1.5%,壳聚糖质量分数1%,Tween-20质量分数0.75%,投药量m（阿维菌素B2）: m（海藻酸钠）= 1 : 2,油水比[m（油相）: m（水相）] = 1 : 20;所制备的包埋颗粒剂的载药量为22.38% ± 0.25%,包埋率为95.26% ± 0.61%。SEM图像显示,包埋颗粒剂形状不规则;红外光谱数据显示,阿维菌素B2被成功包埋于载体中。土壤中的释放性能试验结果表明:包埋颗粒剂在土壤中突释明显,在前30 d,阿维菌素B2的释放量占80 d总释放量的60%以上;小粒径颗粒剂具有更快的释放速率。粒径150~300 μm和 > 300 μm的包埋颗粒剂释放符合一级动力学方程,粒径150~300 μm和 < 150 μm的包埋颗粒剂亦符合Higuchi方程。     

乙草胺碳酸钙微球的制备方法及其缓释性能研究

为增加乙草胺的持效性,将乙草胺与氯化钙-十二烷基硫酸钠溶液混合后与碳酸钠反应制得乙草胺碳酸钙微球。通过扫描电镜、粒径分布仪及高效液相色谱等对该微球进行了表征,并对制备工艺、载药率及缓释性能等进行了探讨。结果表明:碳酸钙载体晶型主要为方解石结构;常温条件下,当n(CaCl2):n (Na2CO3):n(SDS)=1:2:2、搅拌速率为500 r/min、搅拌时间为10 min时,损耗率为0.2%,载药率接近20%;所得碳酸钙微球呈球形,粒径分布窄,且呈正态分布;微球中乙草胺的释放速率随温度和pH值的升高而增加。该微球制备工艺的优化及缓释性能研究结果可为田间定时、定量的释药研究及应用提供参考。     

Growth of Coniothyrium minitans,Gliocladium roseum,Trichoderma harzianum and T. viride from alginate pellets and interaction with water availability1

Conidia, chlamydospores and mycelia of Coniothyrium minitans, Gliocladium roseum, Trichoderma harzianum and T. viride were obtained from liquid or solid culture and formulated within alginate pellets. Quantitative assessment of these pellets over a 12-week period showed a decrease in the number of colony-forming units (cfu) from about 10⁷ to 10³-10⁴ g^-1 air-dried pellets. Qualitatively, growth was assessed by direct plating the alginate pellets on rich (potato dextrose agar, PDA) and poor (water agar, WA) substrates. Rate of growth (mm day^-1) from individual pellets was decreased by water potential in the range -0.25 to-2.8 MPa, with growth significantly less on WA than PDA for all species except G. roseum. All species grew from 95 to 100% of direct-plated pellets on PDA over the water-potential range tested. However, on WA, interaction between water stress (-2.8 MPa) and lack of nutrients resulted in a reduction, with less than 30% of pellets of some formulations showing growth. In contrast to the quantitative results, there was little change in the growth rate of test species from pellets over a 12-week period, particularly on PDA. Growth from pellets could not be conclusively demonstrated in unsterile soil. The shelf-life and viability of alginate pellets in soil is assessed.     

Some studies on the use of alginates for the placement and controlled release of diquat on submerged aquatic plants

Viscous solutions of sodium alginate can be extruded under water in the form of a string which will stick to weeds. The sodium alginate reacts with calcium ions to form an insoluble gel of calcium alginate so that the strings become more firmly attached to the weeds. Diquat dibromide can be incorporated into the alginate and this is slowly released into the water close to the plants. Two experiments are described in which this technique is tested in a fast-flowing river and for localised control in a lake. Diquat dihromide was found to be effective, when formulated with alginate, on Ranunculus spp. in the river and Groenlandia densa in the lake.     

The influence of formulation on Trichoderma biological activity and frosty pod rot management in Theobroma cacao

Frosty pod rot (FPR), caused by Moniliophthora roreri, is responsible for significant losses in Theobroma cacao. Due to limited options for FPR management, biological control methods using Trichoderma are being studied. Combinations of three formulations and two Trichoderma isolates were studied between May 2009 and April 2011. The formulations were 0·3 mL L^?1 of the surfactant BreakThru 100SL (BT), a mixture of 1% w/v Sure‐Jell (source of pectin) and 1% w/v potato dextrose broth (PDB) (PP), and an invert oil emulsion of 50% v/v corn oil/2·5% w/v lecithin/0·5% w/v PDB (COP). Water and fungicide, copper oxychloride, were included as controls. Humidity chamber studies indicated that Trichoderma conidia germinated in all formulations if free water was maintained, while only the COP formulation supported germination under drying conditions. In the field, Trichoderma ovalisporum DIS‐70a and Trichoderma harzianum DIS‐219f were applied monthly in each of the three formulations at a rate of 180 mL per tree, 2·46 × 10⁷ conidia per mL. The COP/DIS‐70a formulation provided the largest yield increase compared to all other treatments, including the fungicide control. Averaged over the 2 years, the COP formulation increased yield to 30·7% healthy pods compared to 9·7% healthy pods in the water control. Although the formulation/isolate combinations did not consistently increase endophytic colonization, the PP/DIS‐219f, COP/DIS‐219f and COP/DIS‐70a combinations increased total endophytic/epiphytic colonization by Trichoderma. The invert corn oil formulation of DIS‐70a significantly enhanced yield of healthy cacao pods over 2 years providing a promising model for optimizing Trichoderma‐based biocontrol strategies.     

Dégradation de l'isoproturon et disponibilité de ses résidus dans le sol

Degradation if isoproturon and availability of residues in soil The availability and degradation of ¹⁴C-ring-labelled isoproturon in soil was investigated over 140 days under controlled laboratory conditions. Degradation of the active ingredient followed and 65 days later only a minor fraction (0.6%) of the parent molecule remained extractable. A demethylated-isoproturon metabolite was detectable in soil from day 15 (2.6%). The amount of ¹⁴CO₂ derived from the ¹⁴C benzene ring label and liberated over time indicated that a total of 13.6% isoproturon was mineralized during the incubation period. In parallel, the amount of ¹⁴C residue extracted from the soil by water followed by methanol or remaining within the soil—analysed by combustion—was also determined at intervals. After 140 days, 72% of the radiolabel added remained in the soil as non-extractable residue. The degradation half-life of extractable isoproturon was an estimated 14 days.     

Pedotransfer functions for isoproturon sorption on soils and vadose zone materials

BACKGROUND: Sorption coefficients (the linear K_D or the non‐linear K_F and N_F) are critical parameters in models of pesticide transport to groundwater or surface water. In this work, a dataset of isoproturon sorption coefficients and corresponding soil properties (264 K_D and 55 K_F) was compiled, and pedotransfer functions were built for predicting isoproturon sorption in soils and vadose zone materials. These were benchmarked against various other prediction methods. RESULTS: The results show that the organic carbon content (OC) and pH are the two main soil properties influencing isoproturon K_D. The pedotransfer function is K_D = 1.7822 + 0.0162 OC^1.5 ? 0.1958 pH (K_D in L kg^?1 and OC in g kg^?1). For low‐OC soils (OC < 6.15 g kg^?1), clay and pH are most influential. The pedotransfer function is then K_D = 0.9980 + 0.0002 clay ? 0.0990 pH (clay in g kg^?1). Benchmarking K_D estimations showed that functions calibrated on more specific subsets of the data perform better on these subsets than functions calibrated on larger subsets. CONCLUSION: Predicting isoproturon sorption in soils in unsampled locations should rely, whenever possible, and by order of preference, on (a) site‐ or soil‐specific pedotransfer functions, (b) pedotransfer functions calibrated on a large dataset, (c) K_OC values calculated on a large dataset or (d) K_OC values taken from existing pesticide properties databases. Copyright © 2011 Society of Chemical Industry