Automated Microscopy Techniques on Passively Collected Samples Provide Reliable Quantitative Data on Airborne Pollen

Abstract

Data on airborne particles are of great importance for human health. Anthropogenic (e.g. soot, tire and brake wear) as well as biogenic (e.g. pollen, spores) particles are usually monitored by active samplers located in urban environments; thus, very few data are available for remote, mountainous areas. In addition, bioaerosol analysis is time-consuming and skill-demanding. This study was carried out to explore if passive sampling combined with automated analysis methods for pollen detection could be an option to overcome the constraints of active sampling (i.e. costs, electricity need) and to simplify data analysis. For this purpose, two Sigma-2 passive samplers were exposed during twelve one-week periods in 2018 in San Michele a/A (Italy), where airborne pollen has been monitored since 1990 by a volumetric Hirst-type sampler. Samples were analyzed by (i) automated optical microscopy (OM) followed by image analysis based on particle size and grey values, and (ii) automated scanning electron microscopy coupled to energy dispersive x-ray spectroscopy (SEM/EDX), delivering morpho-chemical information of single particles. By the automated OM, bright particles (i.e. from natural source) in the size range of 20-80 µm well represented the total pollen amount. By filtering the particles for size, shape and chemical composition, the SEM/EDX allowed to select the pollen-like fraction. In conclusion, automated analytical approaches can simultaneously provide data on anthropogenic, geogenic and biogenic airborne particles, including pollen. In addition, passive sampling is a reliable option for aerobiological studies, especially suitable in remote areas, where the maintenance of active samplers is challenging.

The Current Status of Atmospheric Micro/Nanoplastics Research: Characterization, Analytical Methods, Fate, and Human Health Risk

“…However, for smaller-size nanoplastics, the resolution of optical microscopes is limited by diffraction (Schwaferts et al, 2019). Optical microscopes are used to visually sort and count plastic particles, a process which is very labor intensive and still prone to human error (Gottardini et al, 2021). In addition, the technique is inadequate to distinguish plastic particles from similar-looking inorganic and organic materials.…”