Sorption and Mobility of Charged Organic Compounds: How to Confront and Overcome Limitations in Their Assessment

Permanently charged and ionizable organic com-pounds (IOC) are a large and diverse group of compoundsbelonging to many contaminant classes, including pharmaceuticals,pesticides, industrial chemicals, and natural toxins. Sorption andmobility of IOCs are distinctively different from those of neutralcompounds. Due to electrostatic interactions with natural sorbents,existing concepts for describing neutral organic contaminantsorption, and by extension mobility, are inadequate for IOC.Predictive models developed for neutral compounds are based onoctanol-water partitioning of compounds (Kow) and organic-carbon content of soil/sediment, which is used to normalizesorption measurements (KOC). We revisit those concepts and theirtranslation to IOC (DowandDOC) and discuss compound and soilproperties determining sorption of IOC under water saturatedconditions. Highlighting possible complementary and/or alternative approaches to better assess IOC mobility, we discussimplications on their regulation and risk assessment. The development of better models for IOC mobility needs consistent andreliable sorption measurements at well-defined chemical conditions in natural porewater, better IOC-, as well as sorbentcharacterization. Such models should be complemented by monitoring data from the natural environment. The state of knowledgepresented here may guide urgently needed future investigations in thisfield for researchers, engineers, and regulators.

Automated summary

Permanently charged and ionizable organic compounds (IOC) are a diverse group of contaminants. Existing models for neutral compounds are inadequate for describing the sorption and mobility of IOC. Better models and monitoring data are needed to assess the mobility of IOC and guide further research.