Fig. 8

Sphericity-Elongation plots with the solid line representing the maximum elongation for a given sphericity [106]. A For this example, the values of all shape descriptors were in the theoretical range and, thus, the particle shape measurement was considered to be valid. B Contrary to the former example, here, the shape descriptors of many microplastics had values outside the theoretical range. Consequently, the particle shape measurement was invalid. To overcome this issue, a more robust computer algorithm should be applied for the determination of shape descriptors. If this does not solve the issue, the image acquisition has to be optimized