Système d'exposition d'échantillonneurs passifs de type POCIS en rivière (2017).
© BRGM - Anne Togola
The EU Framework Water Directive, which aims to achieve a favourable ecological status of EU waters by 2015, requires regular monitoring of the chemical status of water bodies.
The usual practice in monitoring networks relies on point sampling coupled with laboratory analyses, but this is a costly and difficult way of producing relevant results.
Passive samplers for more representative measurements of the chemical quality of water
For several years, BRGM has been investigating a different approach involving the use of passive samplers. This technique, based on the accumulation of pollutants on a submerged sampler, provides a more representative picture of the chemical quality of water by estimating average pollutant concentrations throughout the duration of exposure.
Although the principle is widely used for surface waters, it had not been investigated for groundwaters. One of the Metro programme's objectives is to test the potential of different types of passive samplers designed for specific pollutant families (metals, pesticides, PAH, etc.).
The Masques project: alternative methods for groundwater quality monitoring
Masques, an acronym for “Méthodes alternatives pour le suivi de la qualité des eaux souterraines”, is a project commissioned by the Loiret Conseil général that involves BRGM and the ISTO laboratory (CNRS- University of Orléans), with support from the DREAM water and environments cluster.
The aim is to conduct in situ tests of Pocis-type passive samplers (sensors capable of adsorbing and accumulating a wide spectrum of molecules, especially certain pesticides) together with the rapid and economical Elisa method for analytical testing.
Two drinking water supply sites were studied, the Val d’Orléans karst system (source of the Loiret river) and the Trois Fontaines springs (east of the Loiret).
Pocis integrating sensors to monitor pollutants at very low concentrations
The work conducted confirmed the relevance of combining the two methods. The Pocis sensors demonstrated their effectiveness for monitoring pollutants even at very low concentrations, by accumulating them in infinitesimal quantities throughout the monitoring period.
They have proved to be an effective tool for qualitative and semi-quantitative monitoring (evolution of a contaminant, identification of an emerging pollutant) in karstic environments - where water quality can change very rapidly - provided they are regularly replaced.
Rapid analytical tests (Elisa method) to monitor a very large number of samples
The Elisa tests, based on a biochemical immuno-enzymatic recognition technique, can only recognize one molecule (or group of molecules) at a time, but they have the advantage of being able to test a very large number of samples at once, cheaply and easily.
The possibility of making multiple tests compensates for the margin of error when testing a given molecule in very small quantities.