Throughout the 2014 field season, we had over two dozen biologist throughout the western US collect over 300 samples for eDNA analysis with paired controls. Control samples were collected by filtering 0.5 L of distilled water. No samples had any evidence of field contamination. This method of sampling verifies the cleanliness of the field equipment, as well as the handling methods of the field collector. However, it cannot measure any contamination that may occur in the process of collecting a sample from a stream or lake. For example, standing upstream of the sampling area in waders that have brook trout DNA on them while a sample is being collected may result in a false positive detection of brook trout in that sample. Similarly sampling for lake trout from a boat that was previously in a waterbody containing the fish may also contaminate a sample, leading to a false positive detection of lake trout in a field sample. As a result, we believe that a better approach for detecting false positives is to consider the local expert opinion of the area and verify results with repeated sampling where necessary.
Related web site: Broad-scale genetic monitoring of aquatic species
For most current version of publication: http://www.fs.fed.us/research/genomics-center/docs/edna/edna-protocol.pdf