Tracking Water with Synthetic DNA Tracers Using Droplet Digital PCR

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.