Polymeric Drift Control Adjuvants for Agricultural Spraying

Adjuvant use for the management of pesticide drift, leaching and runoff

Adjuvants are included in many pesticide spray mixtures to enhance the performance of the applied chemical. Many adjuvants which modify the emulsion or extensional viscosity of the tank-mixture have been found to offer benefits in drift management, primarily by eliminating or reducing the 'Fine' droplets included in the spray with diameters <100-200 μm that can move off-target in unfavorable conditions during ground, airblast and aerial pesticide applications. Among wind tunnel and field studies conducted around the world, there is consensus that while some adjuvants are effective for drift management, the performance varies on a case-by-case basis, requiring verification for each adjuvant which could be achieved through a programme such as certification based on showing a reduction in Fine droplets and/or a reduction in airborne drift. These can be measured in wind tunnel studies according to international standards. This article provides a review of the current science in this subject area, from the approaches to data collection to a review of existing data and regulatory application for encouraging and rewarding the use of appropriate adjuvants that have been demonstrated to reduce airborne spray drift potential and therefore the size of no-spray buffer zones appropriate to protect nontarget sensitive areas from drift exposure. Some adjuvants can offer the same reduction in drift as offered by hooded sprayer retrofits. A drift reduction programme based on adjuvant use could include testing candidate adjuvants for their effect on droplet size and reduction in Fine droplets when sprayed through reference nozzles and compared against sprays without the adjuvant. Testing could also be based alternatively on measurements of drift potential on collectors such as monofilament line in wind tunnel or field studies. Once shown to be effective in reducing 'Fines' or spray drift, adjuvants could be certified and then referenced on pesticide labels and/or regulatory or best management practice schemes to encourage their use and offer reductions in use restrictions or no-spray buffer zone sizes based on drift management. Studies have shown that some adjuvants can reduce pesticide leaching into soils and contamination of groundwater, as well as runoff of active ingredients from plants into the environment. Performance depends on the adjuvant type, the pesticide with which it is used, the soil or plant type, the timing and mass of water input from rainfall and climatic factors. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Droplet spatial distribution of oil-based emulsion spray

Introduction

Oil-based emulsion solution is a common pesticide formulation in agricultural spraying, and its spray characteristics are different from that of water spraying. The well understanding of its spray characteristics is the theoretical basis to improve the pesticide spraying technology. The objective of the present study is to deepen the understanding of the spray characteristics of oil-based emulsion.

Method

In this paper, the spatial distribution characteristics of spray droplets of oil-based emulsion were captured visually using the high-speed photomicrography. On the basis of image processing method, the droplet size and distribution density of spray droplets at different spatial locations were analyzed quantitatively. The effects of nozzle configuration and emulsion concentration on spray structures and droplet spatial distribution were discussed.

Results

Oil-based emulsion produced a special perforation atomization mechanism compared with water spray, which led to the increase of spray droplet size and distribution density. Nozzle configuration had a significant effect on oil-based emulsion spray, with the nozzle changed from ST110-01 to ST110-03 and ST110-05; the sheet lengths increased to 18 and 28 mm, respectively, whereas the volumetric median diameters increased to 51.19% and 76.00%, respectively. With emulsion concentration increased from 0.02% to 0.1% and 0.5%, the volumetric median diameters increased to 5.17% and 14.56%, respectively.

Discussion

The spray droplet size of oil-based emulsion spray can be scaled by the equivalent diameter of discharge orifice of nozzles. The products of volumetric median diameters and corresponding surface tensions were nearly constant for the oil-based emulsion spray of different emulsion concentrations. It is expected that this research could provide theoretical support for improving the spraying technology of oil-based emulsion and increasing the utilization of pesticide.

Can We Structure Biomaterials to Spray Well Whilst Maintaining Functionality?

Structured fluid biomaterials, including gels, creams, emulsions and particle suspensions, are used extensively across many industries, including great interest within the medical field as controlled release vehicles to improve the therapeutic benefit of delivered drugs and cells. Colloidal forces within these materials create multiscale cohesive interactions, giving rise to intricate microstructures and physical properties, exemplified by increasingly complex mathematical descriptions. Yield stresses and viscoelasticity, typically arising through the material microstructure, vastly improve site-specific retention, and protect valuable therapeutics during application. One powerful application route is spraying, a convenient delivery method capable of applying a thin layer of material over geometrically uneven surfaces and hard-to-reach anatomical locations. The process of spraying is inherently disruptive, breaking a bulk fluid in successive steps into smaller elements, applying multiple forces over several length scales. Historically, spray research has focused on simple, inviscid solutions and dispersions, far from the complex microstructures and highly viscoelastic properties of concentrated colloidal biomaterials. The cohesive forces in colloidal biomaterials appear to conflict with the disruptive forces that occur during spraying. This review explores the physical bass and mathematical models of both the multifarious material properties engineered into structured fluid biomaterials and the disruptive forces imparted during the spray process, in order to elucidate the challenges and identify opportunities for rational design of sprayable, structured fluid biomaterials.

Spectacular Behavior of a Viscoelastic Droplet Impinging on a Superhydrophobic Mesh

Spray formation using the droplet impact on superhydrophobic mesh surfaces is particularly important because of its application in different industries. The present study revealed that adding a trivial amount of the poly(ethylene oxide) (PEO) polymer to a water droplet can considerably change the impact phenomena on the superhydrophobic mesh surfaces and suppress the spray formation. Droplet rebound is observed only in a narrow range of impact velocities of PEO aqueous droplets when the tiny filaments still connect the surface and droplet. Rebound suppression and deposition of the PEO aqueous droplet is attributed to the higher interaction between the polymer chains and the superhydrophobic mesh surface. After a critical impact velocity and We number which is independent of the PEO concentration, the liquid penetrates the mesh pores. The penetrated liquid formed the ligaments that grow until they reach the maximum length and surprisingly retract back to the mesh surface and the mother droplet. The ligaments destabilized at low PEO concentrations (c = 0.5 and 1 g/L) and a mesh opening size of H = 357 μm to the crest swell droplets when the droplet size is reduced by increasing the impact velocity. The ligament fragmentation and droplet detachment are observed only at high impact velocities when c = 0.5 and 1 g/L and H = 357 μm. The result shows that the PEO additive does not significantly affect the maximum spreading diameter. An empirical model to calculate the maximum spreading factor is developed.

Visualization of the evolution of bubbles in the spray sheet discharged from the air-induction nozzle

BACKGROUND

The air-induction nozzle greatly reduces drift potential by increasing spray droplet size compared with a standard flat-fan nozzle. The current study aims to reveal the mechanism behind the formation of large droplets through the air-induction nozzle from the aspect of bubble evolution in the spray sheet.

RESULTS

Bubble break-up leads directly to the formation of perforations because large bubbles reach both sides of the spray sheet. The surface disturbance induced by bubble break-up modulates spray sheet thickness, which indirectly leads to the generation of perforations. Compared with the spray pressure, nozzle configuration has a more significant effect on both the volumetric flow rate of intake air and the thickness of the spray sheet. As the nozzle is changed from ID-120-01 to ID-120-05, the volumetric flow rate of intake air increases by 801.30% at a spray pressure of 0.3 MPa, whereas spray sheet thickness increases by 412.50% at a radial distance of 10 mm.

CONCLUSION

Bubble break-up is the main reason for the generation of perforations within an air-induction nozzle, leading to early break-up of the spray sheet and the production of large spray droplets. Bubble break-up can be effectively controlled by modifying the nozzle configuration.

Toward a Framework for Environmental Fate and Exposure Assessment of Polymers

Development of risk-assessment methodologies for polymers is an emerging regulatory priority to prevent negative environmental impacts; however, the diversity and complexity of polymers require adaptation of existing environmental risk-assessment approaches. The present review discusses the challenges and opportunities for the fate and exposure assessment of polymers in the context of regulatory environmental risk assessment of chemicals. The review discusses the applicability and adequacy for polymers of existing fate parameters used for nonpolymeric compounds and proposes additional parameters that could inform the fate of polymers. The significance of these parameters in various stages of an exposure-assessment framework is highlighted, with classification of polymers as solid or dissolved being key for identification of those parameters most relevant to environmental fate. Considerations to address the key limitations and knowledge gaps are then identified and discussed, specifically the complexity of polymer identification, with the need for characterization of the most significant parameters for polymer grouping and prioritization; the complexity of polymer degradation in the environment, with the need to incorporate the fate and hazards of degradation products into risk assessment; the requirement for development and standardization of analytical methods for characterization of polymer fate properties and degradation products; and the need to develop exposure modeling approaches for polymers. Environ Toxicol Chem 2022;41:515-540. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Water-soluble polymers in agriculture: xanthan gum as eco-friendly alternative to synthetics

Water-soluble polymers (WSPs) are a versatile group of chemicals used across industries for different purposes such as thickening, stabilizing, adhesion and gelation. Synthetic polymers have tailored characteristics and are chemically homogeneous, whereas plant-derived biopolymers vary more widely in their specifications and are chemically heterogeneous. Between both sources, microbial polysaccharides are an advantageous compromise. They combine naturalness with defined material properties, precisely controlled by optimizing strain selection, fermentation operational parameters and downstream processes. The relevance of such bio-based and biodegradable materials is rising due to increasing environmental awareness of consumers and a tightening regulatory framework, causing both solid and water-soluble synthetic polymers, also termed 'microplastics', to have come under scrutiny. Xanthan gum is the most important microbial polysaccharide in terms of production volume and diversity of applications, and available as different grades with specific properties. In this review, we will focus on the applicability of xanthan gum in agriculture (drift control, encapsulation and soil improvement), considering its potential to replace traditionally used synthetic WSPs. As a spray adjuvant, xanthan gum prevents the formation of driftable fine droplets and shows particular resistance to mechanical shear. Xanthan gum as a component in encapsulated formulations modifies release properties or provides additional protection to encapsulated agents. In geotechnical engineering, soil amended with xanthan gum has proven to increase water retention, reduce water evaporation, percolation and soil erosion - topics of high relevance in the agriculture of the 21st century. Finally, hands-on formulation tips are provided to facilitate exploiting the full potential of xanthan gum in diverse agricultural applications and thus providing sustainable solutions.

Does polyacrylamide-based adjuvant actually reduce primary drift of airborne pesticides?

Atmospheric drift of pesticides sprayed outside treated fields may pose serious environmental and health concerns. Chemical adjuvants, among other techniques, reduce drift by modifying the physicochemical properties of the pesticide solution, which presumably produces larger droplets upon spraying that are less prone to drift. Previous studies, that have addressed the effect of adjuvants on drift reduction, mainly rely on measurements of droplet sedimentation while ignoring the presence of pesticides in the forms of small aerosols and vapor. Such forms are expected to be highly susceptible to atmospheric drift that may pose human health risk via inhalation exposure. The present study examines the effect of a polymer-based adjuvant on airborne-pesticide drift using active air sampling in two field campaigns. Surprisingly, these measurements indicate higher primary drift (PD) of airborne pesticides in the presence of adjuvant in the spraying solution. The results are further supported by comparing measured drifts to those calculated using a modified Gaussian puff dispersion model, which enabled to evaluate the impact of varying meteorological conditions during the field experiments. In addition, the adjuvant effect on droplet size distribution generated by common nozzles, was tested in a wind tunnel. The resulting size-distributions demonstrated that while the addition of adjuvant resulted in a desired shift of the volumetric distribution towards larger droplets, it also led to a significant increase in the number concentration of fine droplets. Such trends can explain how the addition of polymeric adjuvant can yield both, a reduction in sedimenting drift outside treated areas and an increase in airborne PD intensity, as observed in the present study. This study demonstrates the complex effect of chemical adjuvants and the urgent need to further explore and understand their environmental impact.

Ultra-high molecular weight linear coordination polymers with terpyridine ligands

This first report of ultra-high molecular weight (>1000 kDa) linear coordination polymers demonstrates their use in agricultural spray drift control.

Ultra-high molecular weight (UHMW, M_n > 1000 kDa) polymeric drift control adjuvants (DCAs) for agricultural spraying are prone to mechanical degradation and rapidly lose performance. To overcome this, we have designed linear coordination polymers (LCPs) composed of 400 kDa telechelic bis-terpyridine end-functionalised polyacrylamide units, which ‘self-heal’ upon shearing through reformation of coordination bonds. After addition of Fe(ii) to dilute aqueous solutions of the terpyridine telechelics, UHMW LCPs were obtained as demonstrated by UV-vis spectroscopy, MALS GPC and intrinsic viscosity measurements. Importantly, these UHMW LCPs were shown to function as effective DCAs, reducing the formation of fine ‘driftable’ droplets during spray testing at concentrations as low as 100 ppm. Following mechanically-induced coordination bond-scission, the UHMW LCPs were found to recover up to 90% of their performance compared to un-sheared samples, at a rate dependent on the transition metal ion used to form the complex.

Effect of adhesion force on the height pesticide droplets bounce on impaction with cabbage leaf surfaces

The relationship between adhesion force and the height drops containing difenoconazole-loaded mesoporous silica nanoparticles (DF-MSNs)/Tween 80 bounce on cabbage leaf surfaces was investigated as a function of Tween 80 concentration. The adhesion force of a pesticide droplet on cabbage leaf surfaces was assessed using a high-sensitivity microelectromechanical balance system and the impact behavior was recorded with a high-speed camera. The height droplets bounced decreased with increasing adhesion force, with a negative correlation between the height of the bouncing drops and adhesion force. Although droplets containing ≥0.06% Tween 80 adhered to the cabbage leaves, the retraction height was still observed to decrease as the adhesion force increased. The experimental results indicate that for cabbage leaf surfaces, the adhesion force has a significant effect on the height drops bounce. The results provide new insights into how researchers can screen for formulations for hydrophobic target crops and how to increase spray adhesion to difficult-to-wet crop leaf surfaces.