Permanently charged
and ionizable organic compounds (IOC) are a
large and diverse group of compounds belonging to many contaminant
classes, including pharmaceuticals, pesticides, industrial chemicals,
and natural toxins. Sorption and mobility of IOCs are distinctively
different from those of neutral compounds. Due to electrostatic interactions
with natural sorbents, existing concepts for describing neutral organic
contaminant sorption, and by extension mobility, are inadequate for
IOC. Predictive models developed for neutral compounds are based on
octanol–water partitioning of compounds (
K
ow
) and organic-carbon content of soil/sediment, which
is used to normalize sorption measurements (
K
OC
). We revisit those concepts and their translation to IOC
(
D
ow
and
D
OC
) and discuss compound and soil properties determining sorption of
IOC under water saturated conditions. Highlighting possible complementary
and/or alternative approaches to better assess IOC mobility, we discuss
implications on their regulation and risk assessment. The development
of better models for IOC mobility needs consistent and reliable sorption
measurements at well-defined chemical conditions in natural porewater,
better IOC-, as well as sorbent characterization. Such models should
be complemented by monitoring data from the natural environment. The
state of knowledge presented here may guide urgently needed future
investigations in this field for researchers, engineers, and regulators.