Promises and limitations in the use of sulfonates colourless tracers in hydrogeology

Colourless fluorescent UV tracers are increasingly used in hydrogeological studies in drinking water catchments, in which classical dyes (uranine, sulforhodamines) can sometimes be of significant concern if unexpectedly exceeding the limit of visibility. Among these colourless tracers, optical brighteners and sulfonates (presently naphthionate and amino G acid) are widely used despite lower fluorescence yields, strong interferences with natural organic matter, as well as oxy- or photo-degradation. As a result, higher amounts of tracer are sometimes used, yielding higher concentrations in drinking water and giving rise to the question of their toxicity and the occurrence of their by-products in waterworks. In this paper, several years of practice and improvement of the detection's performance using combined laboratory spectrofluorometric and field fluorometric techniques are summarized and illustrated with several case studies in different aquifers. The developments of UV LEDs optical systems, as well as the increase of time resolution and controllability using telemetric dataloggers, are here considered as main catalysts of this knowledge.