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Toxicité et écotoxicité des principaux traceurs fluorescents employés en hydrogéologie et de leurs produits de dégradation

Abstract : Chemicals used for tracing water in karst aquifers often don't resurface at the monitored water points (springs, wells, boreholes). For example, in the karstified chalk, which is the main French aquifer (70,000 km2 of outcrop), only half of the tracing tests had a successful breakthrough : the tracers reached the drinking water supply. They were then submitted to the water treatment, generally a chlorine disinfection. The other part of the injected tracers was probably adsorbed in the subsurface (on clays) or came out at unmonitored points, including springs or diffuse emergences. In this cave, the tracers join the rivers where they can be degraded by light (photolysis) or by the action of atmospheric oxygen. This paper presents the laboratory-scale degradation of three widely used fluorescent tracers in Norman chalk (and more generally in French karst), i.e. uranine, ti nopal and sodium naphtionate. Theses tracers have been diluted in water to obtain an initial tracer solution concentrated at 1 g/l : this concentration is intermediate between the concentrations poured in injection points (>100 g/l) and found at breakthrough points (< 7 mg/l). First, each tracer solution has been submitted to strong and fast laboratory breakdown by contact with gaseous chlorine : this is to simulate the tracer transit through the drinking water supply. Another set of the same tracers is then submitted to natural degradation substances, with UV and sunlight irradiations as well as a mixing with air. Because of their molecular structure (long carbon chains or aromatic cycles), the fluorescent tracers undergo significant changes and keep on degrading into sub-products (metabolites). These degradations have been highlighted by H PLC and the metabolites obtained have been analyzed by LC-MS : unfortunately, they were not able to be identified except one for tinopal. A bibliographic synthesis has then been realized to summarize the human and environmental impact of all tracers. Toxicity and ecotoxicity of degradation products of each tracer have been tested. Toxicity tests have been conducted by oral path on rats, and ecotoxicity tests by two complementary methods : one method with a small aquatic crustacean (Daphnia magna) to test their impact on aquatic fauna, the other method on micro-algae (Pseudokirchneriella subcapitata) to test their impact on aquatic flora. These laboratory tests show that at high concentration (10s higher than in breakthrough curve peaks), the degraded tracers have none acute toxicity and only a moderate ecotoxicity, except for sodium naphtionate. In conclusion, the fluorescent tracers studied do not exhibit significant toxicity to humans and aquatic environment, at levels generally observed at breakthrough points, both as tracers as their major metabolites.
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Submitted on : Friday, March 21, 2014 - 2:23:12 PM
Last modification on : Tuesday, April 28, 2020 - 9:47:35 PM

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  • HAL Id : ineris-00963331, version 1
  • INERIS : EN-2013-162

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Philippe Gombert, Jean Carré. Toxicité et écotoxicité des principaux traceurs fluorescents employés en hydrogéologie et de leurs produits de dégradation. KARSTOLOGIA, Fédération Française de Spéléologie et Association Française de Karstologie, 2011, pp.41-53. ⟨ineris-00963331⟩

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