Optimizing exposure duration and material selection for Passive Samplers for an improved wastewater surveillance of faecal pollution

The efficacy of Passive Samplers in providing near real-time data on the public health status during the SARS-CoV-2 pandemic has been demonstrated. Though they are not fully developed or tested for the detection of bacteria and resistant genes. Our main objective was to analyse the applicability of different Passive Sampler (Polythene Stripe, Steel Wool Sponge, Glass Beads, Torpedo, Pensive, Q-Tip, Filter Membranes) for selected microbial parameters (Total Bacteria, Enterococci, Tetracycline A, and Class-1 Integron) and the identification of their optimal exposure duration (2 h to 48 h). DNA gene copies were analysed using a ddPCR. A new normalization approach is presented, allowing the direct comparison of sediment and biofilm Passive Samples to Wastewater Samples. With all Passive Samplers we were able to detect bacteria and resistant genes at all exposure durations. The results indicate: (1) Passive Samples yield reasonable normalized ratios of microbial parameters compared to composite Wastewater Samples; (2) Different Passive Sampler types (biofilm, sediment, material) have different optimal exposure durations; (3) The handling effort and reproducibility of the sediment extraction is best for Glass Beads. With our study we have demonstrated, that Passive Samplers can be an important tool in WBE applications.