Examining Standard Environmental DNA Sample Extraction and Archival Methods

Environmental DNA (eDNA) analysis is a novel method for species detection and biological monitoring, but empirical testing of methods is still needed. A common practice for extracting DNA from filters used in eDNA analysis is to first split the filter into equal halves whereby one half is processed and the other half is archived by drying in 200-proof molecular grade ethanol and freezing at -20°C or -80°C. Our objectives were: (1) to evaluate the assumption that both filter halves have evenly distributed eDNA; and (2) to assess the effect on DNA yield from archiving filters over years. We used samples collected annually in the Okanogan Basin as part of another study dating back to 2012. Preliminary results suggest that eDNA is not always evenly distributed across both halves of a cellulose nitrate filter with a 0.45 micron pore size, although on average, the amount of DNA on each half was not significantly different. DNA on archived filters does degrade annually at a rate of about 10% every 20 months. Results of this study could help improve eDNA laboratory methods and provide insight into proper sample archival procedures, helping to safeguard eDNA archives for future use