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Abstract
An optical method based on fluorescence spectroscopy was developed for in-situ non-destructive, real time, organic pollutant detection and quantification in soil. Optical fiber-based light-induced fluorescence probes allowing in-situ specific chemical detection were constructed. Pyranine was chosen as a model fluorescent Polycyclic Aromatic Hydrocarbon (PAH). The effect of sand particles on fluorescence measurements was established: the fluorescence intensity in water-saturated sand was eight times lower than in aqueous solutions, due to light scattering by the sand particles. To adapt the method to dynamic pollutant concentration measurements in soil, two different designs of light diffusers were constructed and compared. A light distributor with a quartz window was chosen for its higher sensitivity and reproducibility. The probes were introduced into two different columns: short ones used to study the effect of the measurement location in the column and longer ones to study pyranine transport. It was shown that, in columns, the measurement location plays an important role; measurements near the walls, in particular, were different from those performed more towards the center of the column in a given section. As a consequence, one should avoid measurements near the circumference. Preliminary results were successfully compared to a chemical transport model and revealed that the methodology is a powerful tool to measure in-situ concentration changes; on the other hand, fluorescent measurements can be used efficiently to determine transport parameters and give results comparable with those obtained with classical breakthrough curve fittings.