Relating environmental concentrations of pharmaceuticals to consumption: A mass balance approach for the river Rhine

In this study, pharmaceuticals were frequently monitored in the Rhine delta between the year 2002 and 2008. Average concentrations of several X-ray contrast mediums were above 0.1 µg/L, the average concentration of carbamazepine was about 0.1 µg/L, while average concentrations of the other pharmaceuticals generally fell between 0.1 and 0.01 µg/L. Concentrations were used to calculate annual loads transported by the Rhine at Lobith. These loads were compared to the annual sales upstream of Lobith. This mass balance approach shows that substantial fractions (1.1% to 70.4%) of the 20 most frequently observed pharmaceuticals sold in the Rhine catchment area are recovered in the Rhine at Lobith. The observed annual loads were compared to loads predicted from annual sales in the catchment area, excreted fractions by humans and removal by waste water treatment. Observed and predicted annual loads were rather similar. The difference of the loads obtained from monitoring data and estimated from consumption was smaller than a factor of seven and did not exceed a factor of two for 15 out of the 20 pharmaceuticals. This illustrates the potential of using sales data for the prediction of concentrations in the aqueous environment.