Response to comment of Sierra Rayne on “Targeting aquatic microcontaminants for monitoring: exposure categorization and application to the Swiss situation [Götz et al., Environ Sci Pollut Res (2010) 17:341–354]”

In the comment of S. Rayne on the article “Targeting aquatic microcontaminants for monitoring,” two concerns are raised: (1) The article lacked pKa data. The author of the comment claims that the pKa values are missing for 26 of the approximately 250 substances investigated. (2) The model that was applied for the calculation of water–organic phase partitioning is too simplistic to correctly describe sorption to solid phases. Essentially, both questions target the applicability of the presented method for assessing the aquatic fate of ionizable substances. The method presented clearly has its shortcomings with respect to these substances. However, since the method presented in our article was intended as a screening tool to select substances for monitoring, it was developed to cover the broadest range of chemicals possible, and therefore false positive and negative answers have to be accepted to a certain extent, as in every screening tool. The main objective was to develop an easily applicable method that had a lower data demand than other existing models and allowed the identification of new substances that might warrant more intense investigation. Response to query 1: “lack of pKa data”