Greater influence of sediment clay particles in partitioning of PAHs over other factors. High molecular weight PAHs were more sensitive to the OC changes than low molecular weight PAHs. Variability in specific interactions and unequal partition efficiencies with sediment organic matter under natural condition. Partition effect of PAHs with SOM increases more rapidly with increasing molecular weight. Natural organic matter is an important sedimentary hydrophobic domain in PAH assessment.