Environmental tracing is a direct way to characterize aquifers, evaluate the solute transfer parameter in underground reservoirs, and track contamination. By performing multitracer tests, and translating the tracer breakthrough times into tomographic maps, key parameters such as a reservoir's effective porosity and permeability field may be obtained. DNA, with its modular design, allows the generation of a virtually unlimited number of distinguishable tracers. To overcome the insufficient DNA stability due to microbial activity, heat, and chemical stress, we present a method to encapsulated DNA into silica with control over the particle size. The reliability of DNA quantification is improved by the sample preservation with NaN 3 and particle redispersion strategies. In both sand column and unconsolidated aquifer experiments, DNA-based particle tracers exhibited slightly earlier and sharper breakthrough than the traditional solute tracer uranine. The reason behind this observation is the size exclusion effect, whereby larger tracer particles are excluded from small pores, and are therefore transported with higher average velocity, which is pore size-dependent. Identical surface properties, and thus flow behavior, makes the new material an attractive tracer to characterize sandy groundwater reservoirs or to track multiple sources of contaminants with high spatial resolution.
DNA is often used as a tracer in both environmental fluid flow characterization and in material tracking to avoid counterfeiting and ensure transparency in product value chains. The main drawback of DNA as a tracer is its limited stability, making quantitative analysis difficult. Here, we study length-dependent DNA decay at elevated temperatures and under sunlight by quantitative PCR and show that the stability of randomly generated DNA sequences is inversely proportional to the sequence length. By quantifying the remaining DNA length distribution, we present a method to determine the extent of decay and to account for it. We propose a correction factor based on the ratio of measured concentrations of two different length sequences. Multiplying the measured DNA concentration by this length-dependent correction factor enables precise DNA tracer quantification, even if DNA molecules have undergone more than 100-fold degradation.
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