The multiple states of environmental DNA and what is known about their persistence in aquatic environments

Increased use of environmental DNA (eDNA) analysis for indirect species detection has spurred the need to understand eDNA persistence in the environment. Understanding the persistence of eDNA is complex because it exists in a mixture of different states (e.g., dissolved, particle-adsorbed, intra-cellular and organellar), and each state is expected to have a specific decay rate that depends on environmental parameters. Thus, improving knowledge about eDNA conversion rates between states and the reactions that degrade eDNA in different states is needed. Here, we outline how water chemistry and suspended mineral particles likely affect conversion among each eDNA state and indicate how environmental parameters affect persistence of states in the water column. Based on deducing these controlling parameters, we conducted a meta-analysis of the eDNA literature to assess whether we could already derive a general understanding of eDNA states persisting in the environment. However, we found that these parameters are often not being measured or reported when measured, and in many cases very few experimental data exists from which to draw conclusions. Therefore, further study of how environmental parameters affect eDNA state conversion and eDNA decay in aquatic environments is needed. We recommend analytic controls that can be used during the processing of water to assess potential losses of different eDNA states if all were present in a water sample and outline future experimental work that would help determine the dominant eDNA states in water.