Pattern of Detections Across Multiple Environmental Messenger <scp>RNAs</scp> (e‐ <scp>mRNAs</scp> ) in Stressor‐Exposed Zebrafish ( <i>Danio rerio</i> )

Environmental RNA (eRNA) is gaining ground as an environmental monitoring tool. Whereas eDNA is mainly utilized for species detection, eRNA may provide additional classes of inference. The comparatively more rapid signal decay rates of eRNA provide narrower temporal windows for species presence, while detection of environmental messenger RNAs (e-mRNAs) could provide evidence of genomic responses to environmental stressors. We explored e-mRNA as an environmental tracer for stress imposed on animal populations by investigating the decay dynamics of e-mRNA gene detections from target organism presence to recent presence. We tested seven select e-mRNAs of known molecular targets of perfluorooctanesulfonic acid (PFOS) toxicity in tanks containing zebrafish (<i>Danio rerio</i>) exposed to an environmentally relevant concentration of PFOS. eRNA samples were collected just prior to fish removal following a 21-day exposure and continued over nine timepoints across 3 days. The quantity and quality of total eRNA declined over time for both treatments, but were still detectable at 72 h post fish removal. The PFOS exposure failed to elicit observable shifts in e-mRNA target concentrations compared to control tanks, perhaps because the selected gene targets are primarily responsive to PFOS in liver and kidney, which may not contribute strong eRNA signatures. Detection rates for all e-mRNAs dropped significantly beyond 3 h post fish removal, with most being undetectable by 72 h. The signal lifespan of e-mRNAs in this study implies that the detection of such traces will be a strong indicator of target organism presence (or recent presence), and that given the right combination of stressor concentrations, impacted tissues or organs, and gene targets, contaminant impacts on organism health should be detectable in environmental samples. Future studies targeting toxicologically effective stressor doses for well-established gene targets will be an important advancement in establishing the utility of e-mRNA as a noninvasive environmental stressor monitoring tool.