Scanning Electron Microscope Study of Iron-Containing Particles on Foxtail

Samples of Setaria viridis (wild foxtail) were collected from the side of a heavily traveled road near a steel manufacturing region in Pittsburgh. SEM-EDS techniques were used to locate and size 127 iron-containing particles deposited on awns near the tops of the plants. The particles were nearly perfect spheres of somewhat uniform diameter: 3.7 ± 2.2 pm (mean ± standard deviation). Application of deposition theories from the literature suggests that inertial impaction in low Reynolds number flow is responsible for transport of these particles onto the vegetation.