In order to follow the long term evolution of the pollutant discharge pattern, and to detect changes in the situation, information about the discharge mass flow is necessary. First, the paper deals with the behaviour of the fluoride concentration in the river Meuse. Data are presented for the stretch Remilly (France) to Keizersveer (Netherlands), and the evolution over the period 1970–1984 is described. Data from waste waters and tributaries are discussed, and a dominating fluoride source is identified. In the second part, a linear first order equation is proposed for fitting the C-Q data at Liège (Belgium). Five methods for estimating the mean fluoride mass flow of the discharge are compared and discussed. The weighted least squares method is proposed for further use. It makes use of data from a routine measuring station, and gives the possibility to estimate a natural concentration which is constant over the studied period 1970–1984. The thus obtained value of 0.19 mg/l is equal to the mean fluoride concentration upstream of the discharge point. The estimated discharge mass flow is about 6 t/d, and this value remained constant since 1979.

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