the present invention relates to a device for detecting traces of hydrocarbon - containing pollutants present in an aqueous medium , comprising an electric circuit including at least one sensitive element reacting through degradation to the presence of said pollutants , electric means co - operating with said sensitive element and a means for checking the condition of said circuit . according to the invention , said electric means include at least two contactors holding said sensitive element in compression . fig . 1 to be published .