Assessment and development of analytical methods regarding seawater quality (LOD, LOQ, accuracy, uncertainties…)

Supervisor: Philippe Cerdan, Flaence Crespy (HYDRECO-Laboratoire environnemental de Petit Saut, Guyane Française)
French Guiana is the only overseas department which is not an island. It is located on the north coast of South America and offers very different hydrodynamic and climatic characteristics compared to the European basins. The proximity of the Amazon River heavily influences the coastline and gives it very specific a dynamic morphology which suffers from several anthropogenic and natural pressures. The tropical climate of the region and the alternation of wet seasons and dry seasons impose a high pressure on the aquatic ecosystems. Moreover, the anthropogenic impact caused by the population living along the main rivers effects the environment due to waste water and run-off from the land where pesticides are used in agriculture. Gold-mining remains one of the main causes of pollution of the rivers in Guiana, due to high quantities of mercury released. The Water Framework Directive has been created to assess the ecological state of water masses regarding the biological, chemical and physio-chemical parameters. The framework allows us to assess the coastal and transitional water masses state of Guiana. The dosage methods used to conduct fresh water analysis of nitrites and ammonium had to be adapted for seawater. Salt water exhibits characteristics which make it difficult to measure ammonium as the salts and pH can heavily influence or even inhibit chemical reactions. It was therefore necessary to modify the methods used previously. Several attempts were made to adapt the freshwater analysis methods to validate them for seawater. After several attempts, statistical analysis determined that the analytical methods of dosage of nitrites and ammonium were validated. The laboratory is now able to use the adapted method to conduct an ongoing assessment for the WFD in Guiana. These adapted methods are both easy to perform and inexpensive. Because of this accessibility, they can be adapted in any laboratory for seawater analysis. Nevertheless, due to the average sensitivity of the methods (colorimetry by UV-Visible spectrophotometer) they cannot be used to measure ammonium or nitrites in trace quantities.

Key words: Analytical method validation, WFD, Nitrite, Ammonium