Shape characterization of dust from seed treatments by X-ray Microtomography

The emission of abraded seed treatment particles by pneumatic seed drills into the environment has been linked with honey bee poisoning incidents in several countries in recent years (Nuyttens et al., 2013). The problem of dust drift has since received significant scientific interest (Nikolakis et al., 2009). In an effort to better understand this problem and to propose dust drift mitigation measures, a computational fluid dynamics model is developed.
If a Lagrangian particle tracking approach is adopted, the physical properties of the dust particles need to be measured accurately in order to predict the particle trajectories. Specifically, the size distribution, the density and the shape of the particles need to be determined. Indeed, a particle’s drag coefficient in an air flow is highly dependent on its shape (Hölzer and Sommerfeld, 2008). The shape was characterized by means of X-ray microtomography. Five micropipette tips were filled with dust samples of different size fractions from treated maize seeds and scanned in a Skyscan 1172 device. Also, dust samples of all sizes from various treated crops (maize, wheat, barley, rye, rapeseed) were scanned. The image resolution was 1,92 µm for all but the largest dust sample (4,87 µ). Image processing was performed using Avizo software (Fire edition 8.0.0). The data processing protocol was optimized in terms of image filtering, histogram equalization, image binarization and noise removal. To guarantee accuracy, object segmentation was carried out manually. After segmentation, all relevant shape parameters (including equivalent diameter, surface area, volume, sphericity, length and width) were calculated. The shape parameters were implemented in the CFD model by means of correlation formula to account for particle non-sphericity.
Results showed a high variability of particle size, shape, density and porosity for the different crops and for the different size fractions within a single dust sample. Indeed, particle shape ranged from mostly spherical (rapeseed) to rod-shaped (wheat) and disk-shaped (maize, rye). Porosity was very high in some samples (barley) and intermediate or low in others (rapeseed, wheat). In general, particle sphericity decreased with size.

Hölzer A., Sommerfeld M. (2008). New simple correlation formula for the drag coefficient of non-spherical particles. Powder Technology, 184(3), 361–365.
Nikolakis A., Chapple A., Friessleben R. Neumann P. Schad T. Schmuck R. Schnier H. et al. (2009). An effective risk management approach to prevent bee damage due to the emission of abraded seed treatment particles during sowing of seeds treated with bee toxic insecticides. Julius-Kühn-Archiv 423, 132–148.
Nuyttens D., Devarrewaere W., Verboven P. Foqué D. (2013). Pesticide-laden dust emission and drift from treated seeds during seed drilling: a review. Pest management science, 69(5), 564–75.