Passive environmental DNA sampling: A review of current practices, limitations and future directions for biodiversity monitoring

Passive environmental DNA (eDNA) sampling is rapidly emerging as a powerful alternative to active sampling methods (e.g. direct water sampling), with a rapidly growing diversity of tested approaches but little methodological convergence. Comparative studies show that passive samplers can match or surpass the performance of traditional filtration, particularly in challenging field conditions. Several key factors emerge as critical to their success: the choice of substrate, deployment duration and the environmental matrix in which the sampler is placed. Based on recent literature, this review identified these substrates as the best choices for the following conditions: (1) nylon membranes and synthetic sponges show strong potential in marine environments; (2) glass fibre and granular activated carbon are promising for freshwater; while (3) dust cloths and plant swabs stand out for airborne DNA. Although passive approaches have also been tested in groundwater, runoff and rainwater, the limited number of studies in these contexts prevents solid analysis. Comparative evidence further suggests that deployment times of only a few hours may already suffice for reliable detection, while material pore size and sampler shape appear to exert minor influences. Together, these findings demonstrate the strong promise of passive sampling and provide practical guidance for its application in future biodiversity monitoring.