Metazachlor traces in the main drinking water reservoir in Luxembourg: a scientific and political discussion.

This discussion is centralized around an incident that took place in the Belgian village Witry the 17th of September 2014. A tractor accident led to the discharge of an aqueous solution of the herbicide metazachlor into the creek that further merges into the river . About 20 km downstream, these waters supply the lake of the Upper-Sûre in Luxembourg, the biggest artificial lake and the main drinking water reservoir in the country. The evolution of the concentration of metazachlor and its metabolite 479M08 was partially tracked down from the river to the dam situated in the east. At this location, the SEBES drinking water treatment plant has its raw water intake from the lake. After this incident, substantial pollution by the metazachlor breakdown product 479M08 of the lake and of some other groundwater sources in the Grand Duchy was revealed due to a strong monitoring program that was started by the national water authority (AGE). This was for example the case in the SEBES groundwater resource . There is also the reason to assume that contamination by 479M08 existed already in the lake before the incident in Witry, certainly due to agricultural activity. In the second part of this discussion, these perceptions are placed in their appropriate political context. Indeed, the quality of groundwater and drinking water is strongly regulated in the European Union and in Luxembourg. Compound 479M08, for instance, is submitted to a maximum parametric value of 0.1 µg/L in Luxembourg. Several short- and longtime political measures had to be taken to guarantee the wholesomeness of the water from a legal point of view.