Synthetic DNA tracers provide a promising
approach for tracking
water because they are unique, environmentally safe, and versatile
and have low detection limits. This study aimed to develop and quantify
synthetic double-stranded DNA tracers using a droplet digital PCR
(ddPCR) platform and compared their performance with that of uranine
dye, a widely used conventional tracer for hydrological investigations.
The DNA tracers were stable in distilled water at 4 °C; however,
their concentrations decreased at 25 and 40 °C. The DNA tracers
degraded considerably in river water following a one-phase decay pattern
at different temperatures (k = 0.125–0.071
h–1). In column experiments with sand and limestone
media, the DNA tracers traveled at a greater speed (RV = 0.19) and
showed less dispersion (RS = 0.05) and lower mass recovery (RB = 0.26)
than uranine. To demonstrate concurrent tracing, two unique DNA tracers
were injected simultaneously in the column, could be detected in the
same sample, and exhibited similar peak concentration times. Finally,
in a field experiment, DNA tracers were deployed, could be detected
in a surface stream, and exhibited earlier breakthrough in comparison
to uranine. The results of this study demonstrate the feasibility
of using synthetic DNA tracers for tracking water and the effectiveness
of ddPCR in quantifying the tracers.
Human mitochondrial DNA (mtDNA) genetic markers are abundant in sewage and highly human-specific, suggesting a great potential for the environmental application as human fecal pollution indicators. Limited data are available on the occurrence and co-occurrence of human mtDNA with fecal bacterial markers in surface waters, and how the abundance of these markers is influenced by rain events. A 1-year sampling study was conducted in a suburban watershed impacted by human sewage contamination to evaluate the performance of a human mtDNA-based marker along with the bacterial genetic markers for human-associated Bacteroidales (BacHum and HF183) and Escherichia coli. Additionally, the human mtDNA-based assay was correlated with rain events and other markers. The mtDNA marker was detected in 92% of samples (n = 140) with a mean concentration of 2.96 log10 copies/100 ml throughout the study period. Human mtDNA was detected with greater abundance than human-associated Bacteroidales that could be attributed to differences in the decay of these markers in the environment. The abundance of all markers was positively correlated with rain events, and human mtDNA abundance was significantly correlated with various bacterial markers. In general, these results should support future risk assessment for impacted watersheds, particularly those affected by human fecal pollution, by evaluating the performance of these markers during rain events.
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