Environmental Nucleic Acid Pollution: Characterization of Wastewater Generating False Positives in Molecular Ecological Surveys

Environmental nucleic acids (eDNA and eRNA) metabarcoding
analyses
have attracted considerable research attention as they non-invasively
and cost-effectively monitor ecosystems. For heretofore unknown reasons,
however, they often detect false positives. Here, we focused on domestic
wastewater as a possible source of false positives and characterized
fish nucleic acids in the influent and effluent of a wastewater treatment
plant (WWTP). The metabarcoding analysis revealed that DNA and RNA
detected in the influent wastewater originated from over 120 fish
species, and most of these were consumed fish. The nucleic acid content
was significantly higher in the influent than in the effluent, and
the copy numbers of DNA in the influent were significantly higher
than those of RNA. These findings were corroborated by the current
literature and indicated that eRNA could effectively mitigate false
positives. The present study demonstrated that rivers may be extensively
contaminated by fish nucleic acids, and WWTPs substantially alter
the quantities and ratios of fish DNA and RNA. Therefore, analyses
of the wastewater near sampling points and coverage of the sewage
system enable us to select and use the appropriate nucleic acid type
(DNA or RNA) for metabarcoding analysis and improve the accuracy of
fish species detection and identification.