The aging effects of sorption-desorption of two polycyclic aromatic hydrocarbons (PAHs), that is, phenanthrene and chrysene on different natural organic matters (NOMs), that is, humic acid, fulvic acid, and humins of different sources were studied. Both organic carbon-normalized distribution coefficients (K-oc) and the reversible desorption fractions (f(rd)) were evaluated. Results showed that aging effects were both sorbent and sorbate specific. With increasing aging duration, K(oc)s of phenanthrene on humins increased, whereas K(oc)s of chrysene did not change significantly. Significant f(rd) declinations over aging times were observed for all the NOMs, which demonstrated the effects of aging on availability of PAHs. Furthermore, the f(rd) was not only positively correlated with the atomic O/C ratio of NOMs, which represent the geological maturity of NOMs, but also varied with the property of sorbates. We conclude that aging effects of HOCs on NOMs should be a case-specific process and the desorption reversibility depends on the structure and characteristics of both NOMs and sorbates. (C) 2012 Elsevier Inc. All rights reserved.