Variable KOC and Poor-Quality Data Sources Cause High Discrepancy in Current Mobility Assessment of Organic Substances

The widespread distribution of persistent, mobile, and toxic organic chemicals (PMT) in aquatic environments poses a threat to water resources. Current mobility assessments rely on the organic carbon normalized adsorption coefficient (K_OC), but it is sometimes highly variable with sorptive phase (soil/sediment) properties. There is a common oversight that this variability causes assessment discrepancies. Herein, this variability was quantitatively evaluated based on compiled experimental K_OC data sets, which were obtained under OECD guidelines. The results show that both the average discrepancy rate and relative difference rate are nearly half of those of the substances among recent reports. The underlying reasons are high K_OC variability and poor-quality assessment data sources which fail to capture this variability. The variation in K_OC values for one-third of the charged organic compounds is more than 1 order of magnitude, around twice higher than that of neutral organic compounds. The K_OC values from common integrated databases or available quantitative structure–property relationships all have almost orders of magnitude differences compared with data sets, especially for charged compounds. The insights presented here have significant value in the future development of a proper mobility assessment.