Lessons learned from water/sediment-testing of pharmaceuticals.

Previous studies revealed large differences in the transformation of pharmaceuticals in rivers with similar characteristics. The present work aimed at answering the question whether these differences are related to the transformation capacity of the specific river sediments. More generally, we also aimed at evaluating the overall diagnostic power of water/sediment tests. Incubation experiments with 9 pharmaceuticals were carried out with sediments sampled from three rivers. All compounds expect carbamazepine were removed at dissipation half-lives between 2.5 and 56 days; biotransformation was identified as the major removal process. Interestingly, sediment from river Roter Main was more efficient in removing pharmaceuticals than sediment from river Gründlach, while the opposite pattern was observed in previous field studies. Obviously, the physical boundary conditions are governing the actual elimination of pharmaceuticals and not the transformation potential of the specific sediments. In a separate experiment, an immediate onset of transformation was observed after introducing oxygen to an anoxic water/sediment system. Transformation rates in sediments sampled from several sites within one river varied up to a factor of 2.5. This considerable in-stream variability is a critical factor for environmental risk assessment where single cutoff values are being used for evaluating a compound's persistence.