Entity

Time filter

Source Type

Nebraska City, NE, United States

Craig I.P.,University of Southern Queensland | Hewitt A.,University of Queensland | Hewitt A.,The University of Nebraska | Terry H.,Terry Spray Consulting
Crop Protection | Year: 2014

Pesticide application efficiency from aircraft could be increased substantially, and required downwind buffer distances to avoid drift damage reduced significantly, if sharp issuing points or pins were added to existing rotary cage atomizer designs. This would enable existing rotary cage units, already successfully deployed for Ultra Low Volume (ULV) applications of insecticides, to be also used for Large Droplet Placement (LDP) application of herbicides. Studies at Cranfield University using high speed photography and laser droplet sizing instrumentation demonstrated that the addition of fine pins to the final atomizing surface of the rotating cage would increase uniformity of droplet production, by promoting fluid atomization in the ligament mode. This would lead to a substantially increased percentage of droplets in the spray falling between 100 μm and 300 μm in size, suggested here as a biological/environmental droplet size optimum. Development of a 'spinning pins' rotary atomizer for aircraft would therefore be highly desirable for agricultural and other purposes. Investment in this technology has the potential to significantly reduce pollution of atmosphere, soil, fresh water and oceans with pesticides. © 2014 Elsevier Ltd. Source


Wang R.,University of Queensland | Dorr G.,University of Queensland | Hewitt A.,University of Queensland | Hewitt A.,The University of Nebraska | And 2 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2016

Polymers and surfactants are commonly used as adjuvants in agrochemical spray solutions. In this study, we probe the effects of changes in steady state polymer chain conformation (as a result of surfactant addition) on the physical properties of dilute polymer solutions and the resulting spray performance when such solutions are processed through a commercial spray nozzle. To create a panel of model adjuvant formulations for spraying, we added either an associative (sodium dodecyl sulfate (SDS)) or non-associative (Tween20 (polysorbate20)) surfactant, over a range of concentrations, to a base dilute Poly(ethylene oxide) (PEO) solution. The addition of the associative SDS to the PEO solution decreased the dynamic surface tension, slightly increased the zero shear viscosity and substantially increased the extensional properties of the solutions, with a strong dependency on SDS concentration. Under the high deformation processes experienced in a spray nozzle, the addition of SDS shifted the droplet size distribution to larger droplet sizes, and substantially reduced the spray drift. No such changes were seen for the non-associative PEO/Tween20 system. The changes in the dynamics of extension of the PEO chains induced through the association of a surfactant were found to be the dominant effector dictating spray performance. © 2016 Elsevier B.V. Source


Zhang H.,University of Queensland | Zhang H.,Nanjing Forestry University | Dorr G.J.,University of Queensland | Hewitt A.J.,University of Queensland | Hewitt A.J.,The University of Nebraska
Environmental Science and Pollution Research | Year: 2015

To combat mosquitoes and the public health hazards they present, spraying chemical adulticides is an efficient and timely control method for immediate reduction of adult populations. With the growing consciousness of environmental and public health concerns, effective mosquito control means not only maximizing the effectiveness (in terms of mosquito mortality rates) of the pesticide application, but also minimizing the unintended effects (health hazard and environmental pollution). A series of experiments was carried out to assess the efficacy and deposition of ultra-low volume (ULV) sprays on adult mosquitoes which included the influence of chemical type, spray volume, spray concentration, droplet size, and deposit location (where the droplets land on the mosquito). A modified Potter Tower was used to apply an extremely fine spray (volume median diameter ∼20 μm) on caged adult mosquitoes (Culex quinquefasciatus). Reslin® (50 g/L bioresmethrin) was diluted in either water or D-C-Tron® plus spray oil (782 g/L paraffinic petroleum oil), Twilight® (89 g/L phenothrin) was diluted in D-C-Tron®, and the mosquito mortality was assessed 24 h after spraying. A fluorescent tracer was added to the spray mixture to determine the amount of spray on mosquitoes. A fluorescent microscope was also used to view the deposit of droplets on mosquitoes. It was found that droplet retention and mortality were reduced with the larger droplet sizes. Large water-based droplets tend to bounce off adult mosquitoes. There is a tendency for droplets approximately 20 μm in size to be retained on the fine hairs on the mosquito. The largest spray deposit was found on the adult mosquito wings and the lowest deposit on the head. Mortality was higher for formulations diluted with oil compared to those diluted with water. ULV applications with ultra-fine sprays (VMD 20 μm) and oil-based products resulted in maximum target efficacy under laboratory conditions, at minimum cost, and with the minimum amount of chemical adulticides. © 2015, Springer-Verlag Berlin Heidelberg. Source


Ross J.H.,150 Fair Oaks Blvd. and 101 370 LLC | Hewitt A.,University of Queensland | Hewitt A.,Lincoln University at Christchurch | Hewitt A.,The University of Nebraska | And 4 more authors.
Science of the Total Environment | Year: 2015

Using recognized methods routinely employed by pesticide regulatory agencies, the exposures of military personnel that were mixer/loader/applicators (M/L/A) of Agent Orange (AO) for perimeter foliage at bases during the Vietnam War were estimated. From the fraction of TCDD in AO, absorbed dosage of the manufacturing contaminant was estimated. Dermal exposure estimated from spray drift to residents of the bases was calculated using internationally recognized software that accounted for proximity, foliar density of application site, droplet size and wind speed among other factors, and produced estimates of deposition. Those that directly handled AO generally had much higher exposures than those further from the areas of use. The differences in exposure potential varied by M/L/A activity, but were typically orders of magnitude greater than bystanders. However, even the most-exposed M/L/A involved in perimeter application had lifetime exposures comparable to persons living in the U.S. at the time, i.e., ~. 1.3 to 5. pg TCDD/kg bodyweight. © 2014 Elsevier B.V. Source


Armitage J.M.,University of Toronto | Ginevan M.E.,M.E. Ginevan and Associates | Hewitt A.,University of Queensland | Hewitt A.,Lincoln University at Christchurch | And 4 more authors.
Science of the Total Environment | Year: 2015

The fate and transport of 2,3,7,8-tetrachloro-p-dibenzodioxin (TCDD) released into the environment of South Vietnam (SVN) as a consequence of the aerial application of the herbicidal defoliant Agent Orange (AO) were simulated for a generic upland forest scenario and followed over a 50-year period (1965, 1968 and 1970 onwards). Modeled concentrations of TCDD in the environment were then used as inputs to a human exposure model, which focused on long-term exposures via the food chain. Intake rates and body burdens of TCDD were estimated for adult males over the course of the simulation period and compared to available biomonitoring data. One of the most important factors determining the magnitude of the simulated human exposure to TCDD was the fraction of the chemical deposited directly to soil (where it was assumed to have a degradation half-life of 10 or 15. years) relative to the fraction assumed to remain on/in the forest canopy following the spray application (where it was assumed to have a degradation half-life of ≤. 48. h). The simulated body burdens under the various scenarios considered were broadly consistent with the biomonitoring data from SVN collected in the mid-1980s to late 1990s. Taken together, the modeling results and empirical data suggest that highly elevated exposures to TCDD (i.e., body burdens in the several 100s of pg/g lipid range and greater) were not common among people inhabiting upland forest locations in SVN sprayed with AO and that peak and average body burdens were broadly similar to those of the general population of the U.S. in the 1970s and early 1980s. The model-based assessment is consistent with the 'hot spot' hypothesis i.e., potential exposures to TCDD linked to activities conducted on or near former bases where AO was stored are greater than potential exposures in areas subjected to aerial spraying. © 2014 Elsevier B.V. Source

Discover hidden collaborations