Toxicity and ecotoxicity of by-products degradation of fluorescent tracers in the karstic chalk of Normandy (France)
Résumé
The chalk is the most extensive French aquifer, and numerous tracer tests are executed here each year to delimit the protection zones of water supply wells. In the karstic chalk of Normandy, only 49 % of the tracer tests emerge at one of the monitoring points and subsequently pass into the water distribution network where they generally undergo chlorination. The majority of the tracers remains adsorbed in the subsurface or emerges at other points, notably untapped springs, in which case the tracers reach surface streams where they can be degraded by photolysis. Here, we study the degradation in the laboratory of three of the main fluorescent tracers, submitted to a chlorine flow or a strong luminosity. The tests were carried with concentrations greatly higher than the maximum ever recorded during tracer tests in chalk. In spite of an important degradation, the tests carried out on the by-products of degradation show an absence of acute toxicity and a moderate ecotoxicity, except for naphthionate (to relativize due to the high tested concentrations).