Car cabin filters as sampling devices to study bioaerosols using eDNA and microbiological methods

The aim of this study was to examine whether bioaerosols could be isolated and quantified from used car cabin filters. Car cabin filters are widely available and can provide a vast untapped resource for sampling of bioaerosols in areas with enhanced air pollution. We developed a test system where we exposed car cabin filters to birch pollen under compressed air to represent airflow onto the filter. The flow of pollen within the test system was confirmed by microscopy and real-time PCR. Testing of extraction methods was performed on the most prevalent types of filters in UK cars and confirmed it was possible to extract and quantify viable fungi, birch pollen or proteins from car filters. The main challenge of their use is envisaged to be the lack of temporal resolution as car cabin filters are not routinely changed at intervals greater than 1 year; however, the systematic recording of the different routes driven during the sampling interval has been enabled through the common use of GPS, smartphones or similar technologies. Car filters therefore provide substantial possibilities to monitor exposure of harmful bioaerosols in the polluted traffic regions defined by the road network. This method could also be applied to studying allergen exposure associated with bioaerosols and their delivery into the human respiratory system. These findings demonstrate that car cabin filters have the potential to be used to isolate and quantify a range of bioaerosols including pollen and fungi, as well as fractions of bioaerosols, such as proteins.