Volatile Herbicides Research Articles

Controlled release and mitigation of the volatility of 2,4-dichlorophenoxyacetic acid herbicide using biopolymer microparticles as carriers

Herbicides play a crucial role in sustaining crop productivity. However, growing concerns about their impact on both the environment and human health necessitate strategies to improve their effectiveness and suitability. Of particular concern are volatile herbicides like 2,4-dichlorophenoxyacetic acid (2,4-D), which not only pose risks to the environment but also impact neighboring crops. To deal with this, we developed a microparticle system comprising chitosan ionotropically crosslinked with tripolyphosphate anions to encapsulate 2,4-D. Optimization of the biopolymer/herbicide ratio yielded remarkable encapsulation efficiencies (> 95 %) and loading capacities (> 32 %). Characterization analyses revealed interactions between 2,4-D and chitosan, resulting in microparticles (1.7 ± 0.4 µm) with distinct thermal, morphological, and surface charge properties compared to pristine microparticles. In vitro experiments demonstrated pH-dependent release kinetics, with optimal release observed under neutral conditions. A 94 % release was achieved at pH 7 after 37 days, driven by sustainable diffusional processes. This ability to control the release of 2,4-D was pivotal in controlling its volatilization. As demonstrated, the volatilization rate for 2,4-D encapsulated within the chitosan microparticles was found to be 64 times lower compared to the commercial herbicide. This encapsulation approach presents an innovative strategy for regulating the presence of 2,4-D in agricultural settings, effectively tackling its significant volatility concerns.

Enhanced Trifluralin Metabolism Can Confer Resistance in Lolium rigidum.

Resistance to the pre-emergence herbicide trifluralin is increasing in Australian annual ryegrass ( Lolium rigidum) populations. Three L. rigidum populations (R1, R2, and R3) collected from Australian grain fields were identified with trifluralin resistance. Both target-site and nontarget-site resistance mechanisms were investigated. No target-site α-tubulin mutations were detected in populations R1 and R3, while an Arg-243-Lys mutation was found in R2. Compared with the three trifluralin-susceptible populations, enhanced [14C]-trifluralin metabolism, quantified by measuring the amount of [14C] label partitioning into the polar phase of a hexane:methanol system, was identified in all the three resistant populations. This is the first report of metabolic resistance to trifluralin. Coevolution of target-site and nontarget-site resistance to trifluralin is occurring, and metabolic resistance is not rare in L. rigidum populations in Australia. A method was established for trifluralin metabolic resistance detection, overcoming the difficulties of quantifying this highly volatile herbicide by chromatographic methods.

Simultaneous Determination and Quantitation of Paraquat, Diquat, Glufosinate and Glyphosate in Postmortem Blood and Urine by LC-MS-MS.

A simple method, incorporating protein-precipitation/organic backwashing and liquid chromatography-tandem mass spectrometry (LC-MS-MS), has been successfully developed for the simultaneous analysis of four highly water-soluble and less volatile herbicides (paraquat, diquat, glufosinate and glyphosate) in ante- and postmortem blood, urine and gastric content samples. Respective isotopically labeled analogs of these analytes were adopted as internal standards. Acetonitrile and dichloromethane were used for protein precipitation and organic solvent backwashing, respectively, followed by injecting the upper aqueous phase into the LC-MS-MS system. Chromatographic separation was achieved using an Agilent Zorbax SB-Aq analytical column, with gradient elution of 15 mM heptafluorobutyric acid and acetonitrile. Mass spectrometric analysis was performed under electrospray ionization in positive-ion multiple reaction monitoringmode. The precursor ions and the two transition ions (m/z) adopted for each of these four analytes were paraquat (185; 169 and 115), diquat (183; 157 and 78), glufosinate (182; 136 and 119) and glyphosate (170; 88 and 60), respectively. Analyte-free blood and urine samples, fortified with the analytes of interest, were used for method development/validation and yielded acceptable recoveries of the analytes; interday and intraday precision and accuracy data; calibration linearity and limits of detection and quantitation. This method was successfully incorporated into an overall analytical scheme, designed for the analysis of a broad range of compounds present in postmortem samples, helpful to medical examiners' efforts to determine victims' causes of death.

Air concentrations of currently used herbicides and legacy compounds in the Canadian prairies, subarctic, and arctic

Passive air samplers were installed in the summers of 2005 and 2007 for 90 days at four locations in the agricultural region of the Canadian Prairies and at five locations in the Canadian Subarctic and Arctic. The presence and masses of ten currently used herbicides and three legacy compounds in the polyurethane foam disks were quantified. Herbicides 2,4-D, bromoxynil and MCPA were detected at all locations in the Canadian Prairies and in both years because these herbicides are widely applied to control broadleaf weeds in cereal crops that are an integral part of Prairie agricultural production systems. MCPA was also detected at one location in the Arctic in 2007. The detection of the other seven herbicides in the 2 years combined ranged from no detections (atrazine only) to five detections for the relatively volatile herbicides trifluralin and triallate. Triallate was the only other herbicide detected in the Arctic (2005). Legacy compounds were either not detected (alachlor) or at levels near their detection level (γ-HCH and α-HCH). γ-HCH and α-HCH were more frequently detected in 2005 than in 2007 indicating that their concentrations in Canadian air have decreased over time. γ-HCH, widely used as an insecticide in Prairie oilseed production until 2002, was detected at larger concentrations in the Canadian Prairies than in the Subarctic and Arctic. α-HCH, a manufacturing by-product in technical HCH prior to 1971 in Canada, was not detected in the Canadian Prairies but was at detectable levels in the Subarctic and Arctic as the Arctic Ocean is reported to be a major source of α-HCH to the atmosphere. We conclude that some of the most widely used herbicides in Canadian agriculture today are commonly present in the air in regions where they are applied and that a portion of these herbicides may be traveling as parent molecules to the Canadian Arctic. To the authors’ knowledge, this is the first evidence of the presence of MCPA and triallate in Arctic air samples, perhaps because previous research has seldomly monitored for currently used herbicides in this region.

Vapor Movement of Aminocyclopyrachlor, Aminopyralid, and Dicamba in the Field

Vapor movement of synthetic auxin herbicides can injure desirable plants outside the treatment zone. Vapor movement of the synthetic auxin herbicides aminocyclopyrachlor and aminocyclopyrachlor methyl was compared with that of the relatively volatile herbicide dicamba and the low volatile herbicide aminopyralid with a soybean bioassay under greenhouse and field conditions. Soybean is very sensitive to these active ingredients. Under greenhouse conditions, 82 (61 to 104) mg ae ha−1of aminocyclopyrachlor, 26 (18 to 33) mg ae ha−1of aminocyclopyrachlor methyl, 82 (69 to 95) mg ae ha−1of aminopyralid, and 61 (47 to 75) mg ae ha−1of dicamba produced an estimated 25% visual soybean phytotoxicity response when soybean was treated POST at the V3 growth stage (GR25[95% confidence interval]). In field studies, aminocyclopyrachlor, aminocyclopyrachlor methyl, and aminopyralid were applied at 70 g ae ha−1and dicamba was applied at 560 g ae ha−1(labeled application rates) to soybean at the V3 growth stage. All herbicides were applied within an enclosed chamber (3 m by 3 m by 1 m) to mitigate movement of spray droplets. The enclosures were removed shortly after spray application and soybean response immediately surrounding the treated area was recorded in each of eight directions approximately 10 d after treatment. On the basis of bioassay responses, relative amount of vapor movement was dicamba > aminocyclopyrachlor methyl > aminopyralid ≈ aminocyclopyrachlor. Vapor movement of aminocyclopyrachlor was very low indicating that the risk of phytotoxic response of sensitive plants due to volatility of aminocyclopyrachlor is negligible.

Herbicide dissipation and dynamics modelling in three different tillage systems

The half-lives (t 50) of the herbicides metolachlor, terbuthylazine and isoproturon and the occurrence of desethyl-terbuthylazine and monomethyl-isoproturon were measured in soils managed with three different tillage systems (conventional tillage, ridge tillage and no tillage). The first-order dissipation model was well adapted to the field data. Under the trial conditions, characterised by silty soil, scarce permeability, and reduced rainfall, the tillage system did not substantially influence the dynamics of the herbicides; the t 50 was reduced in no tillage only with metolachlor, the more volatile herbicide. The measured concentrations were then compared with those calculated with SoilFug, a fugacity-based mathematical model; the calculated values approximate the kinetics of both herbicides and metabolites with good precision.

Volatilization of EPTC: Simulation and Measurement

AbstractMany of the organic chemicals used in agricultural production are susceptible to loss from the soil surface to the atmosphere by volatilization. Adequate prediction of the impact of these chemicals on the environment thus requires consideration of both downward movement through the soil to groundwater and upward movement in the gas phase to the atmosphere. We developed a method to mechanistically simulate volatilization within the framework of a conventionally formulated solute transport model and used it to simulate the gas‐phase losses of EPTC, a commonly used volatile herbicide. The model considers efflux of a trace gas at the soil surface to be a process of unsteady diffusion, interrupted intermittently by dispersive events that can be thought of as eddies at the innermost scale. Model results were compared to measurements of volatilization during the first 7 d following application of EPTC, conducted with a Bowen ratio system in a 17‐ha field at Rosemount, MN. The measurements indicated a relatively large initial flux (ca. 150 g ha−1 h−1) that rapidly decreased to negligible levels within a day following application. The model agreed reasonably well on the first day, if a measured value for Henry's constant was used rather than a value estimated from the saturation vapor pressure and the solubility. However, on subsequent days the model considerably overestimated volatilization, regardless of the Henry's constant that was used. It is likely that hysteresis in sorption/desorption, particularly as surface soil dries following herbicide incorporation, may be the primary reason why volatile losses are lower than might be predicted on the basis of equilibrium partitioning theory.

Slow Release of S-Ethyl Dipropylcarbamothioate from Clay Surfaces

The adsorption/desorption behavior of the volatile herbicide S-ethyl dipropylcarbamothioate (EPTC) to/from montmorillonite and sepiolite was studied. The clays were used as such or with their surface properties modified by adsorption of the cationic dye methyl green (MG). At 30 degrees C, the half-life time (T1/2) of the herbicide in its free form was 10 h, whereas when adsorbed to montmorillonite the T1/2 was more than 5 days. When EPTC was incorporated into the soil, the T1/2 values were 4 and 9 days for the free and adsorbed forms, respectively. The interactions between EPTC and clay surface were studied by Fourier-transform infrared spectroscopy. Vibrational spectra revealed two different populations of EPTC in the clay-organic complexes: one in which the molecules are adsorbed, interacting with the clay surface, and another in which they do not interact with the clay, their spectrum being almost identical to that of free EPTC. Coadsorbed MG impairs the EPTC-clay interactions, causing an increase in free EPTC, indicating that free EPTC is released from the organoclay at a rate higher than that of adsorbed EPTC. Oat bioassays showed that the herbicidal activity of clay-complexed EPTC was extended by more than 1 week. These data indicate that clay-EPTC interactions can be employed to improve herbicidal performance of EPTC and to control its release to the environment.

Atmospheric pollution by auxin-type herbicides in Tala Valley, Natal

The effectiveness of restrictions on the use of several auxin-type herbicides allegedly damaging vegetables in the Tala Valley, Natal was evaluated by monitoring atmospheric samples over the area for 7 months. No volatile herbicide esters were found in air samples. Out of 280 air samples, 11 contained 2,4- d (2,4-dichlorophenoxyacetic acid), one dicamba (3,6-dichloro- o-anisic acid), one MCPA (4-chloro- o-tolyloxyacetic acid), and one 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). The 2,4- d concentration ranged from 10 – 477 ng/m 3, depending on sample duration and volume. Of the 87 rain samples, 11 contained 2,4- d, two 2,4,5-T, and one dicamba. The levels were 1.4 – 430 μg/litre for 2,4- d. Out of 27 dew samples, three contained 0.1 – 0.8 ng 2,4- d/cm 2. Herbicide residues were therefore still found in the Tala Valley despite the restrictions.

Bioactivity of controlled release formulations of starch-encapsulated EPTC

Using a bioassay technique, the biological activities of starch-encapsulated formulations of EPTC (S-ethyl dipropylthiocarbamate) were determined in relationship to their controlled release characteristics. The bioactivity of the highly volatile herbicide EPTC was retained on a wet soil surface for 6 to 8 days by starch encapsulation utilizing several crosslinking processes (both chemical and non-chemical) and starches with different ratios of amylopectin to amylose. The rate of release, a measure of the integrity of the granule, depended on the nature of the starch and the crosslinking process. With the herbicide EPTC, encapsulation with a pearl or high amylose starch utilizing the jet-cooking process produced the best controlled release formulation even under the most adverse conditions.

Volatilization of Microencapsulated and Conventionally Applied Chlorpropham in the Field1

AbstractThe effectiveness of preemergence applications of herbicides to soil surfaces may be seriously reduced by losses due to volatilization to the air. Direct measurements of volatilization rates of two chlozopropham (isopropyl‐m‐chlorocarbanilate) formulations, a microencapsulated and a conventional emulsifiable concentrate, were made to establish the differences in volatilization rates in the field. During the first day after application to a bare silt loam soil, without cultivation, on 25 May, the volatilization from the encapsulated residues was about one.third that from the emulsified material. Volatilization decreased rapidly over the first 3 days, when 60% of the encapsulated and 30% of the emulsified chlorpropham remained in the target area. Volatilization was still measurable after 50 days, when 20% of the encapsulated and 2% of the emulsified remained. Over this whole period the emulsified residues volatilized about five times faster than the encapsulated. The results indicate the potential value of microencapsulaton techniques for controlling vapor losses and increasing the persistence of volatile herbicides in the field.

Controlled release of propham from plastic granules

Urea–formaldehyde granules containing propham, a volatile herbicide, have been tested in the laboratory as well as in the field as a suitable controlled release system. The advantages of such a system compared to the present commonly used formulas are being demonstrated.

An Injector-Planter for Subsurface Placement of Herbicides

We constructed an injector-planter which simultaneously plants seed and injects herbicides. It effectively placed volatile herbicides under the soil surface in precise spatial relationship to crop seed. Rolling coulters, placed in front of the herbicide delivery system, enabled the unit to cut through trash better than previously-described equipment and, therefore, perform effectively under a wider range of soil conditions.

An Environment System for Plant Studies with Controlled Temperature, Humidity, and Light

NTEED for reliable information concerning the effects of environN5 ment on the response of plants to herbicides motivated the construction of the controlled environment system described herein. A unit suitable for such studies should have these general specifications: 1. a useful range of control of light, temperature, and relative humidity; 2. no recirculation of air, to avoid overall contamination of the unit by volatile herbicides; 3. capability of maintaining several sets of conditions simultaneously; and 4. a design which may be modified easily. The system described was constructed with these points in mind. A schematic diagram illustrates the major structural components of the environment system (Figure 1). Outside air enters the cooling