logKow

LogKow, commonly written as log Kow, is the common logarithm (base 10) of the octanol–water partition coefficient Kow for a chemical. Kow is the equilibrium ratio of a compound’s concentration in the octanol phase to its concentration in the aqueous phase, Kow = Coctanol / Cwater. Because octanol approximates a biological lipid, log Kow serves as a widely used indicator of a compound’s lipophilicity and hydrophobicity.

Log Kow is a key descriptor in environmental fate and risk assessment. Higher log Kow values indicate a greater tendency to partition into organic matter, sediments, and lipid tissues, and they generally correlate with higher bioaccumulation potential, stronger sorption to soils and sediments, and longer environmental persistence. It is used in regulatory models, QSARs, and screening assessments to compare chemicals and to prioritize substances for more detailed study. For ionizable compounds, log Kow refers to the neutral form; the observed distribution at a given pH is described by Dow, which accounts for ionized species.

Measurement and estimation: log Kow can be determined experimentally via shake-flask methods (and related standard procedures) or inferred from chromatographic or spectroscopic methods. It can also be estimated by computational approaches, including fragment constants, empirical QSPR models, and structure-based predictions.

Interpretation and limitations: A broad range of values exists, typically from below 0 for very hydrophilic substances to above 5–7 for highly lipophilic hydrocarbons. While a high log Kow suggests greater sorption and potential bioaccumulation, it is not a definitive predictor of environmental risk. Metabolism, ionization, degradation, exposure route, and biological factors also influence fate and effects, so log Kow should be used alongside complementary data.