The influence of two non-ionic surfactant additives (Triton X-100 and Brij 35) on polycyclic aromatic hydrocarbon (PAH) biodegradation was evaluated using the chemical molecular interaction method, which is based on the theory Of cohesive energy density (CED). The results indicated that PAHs have relatively higher CED values because aromatic compounds with labile pi are more polarized and this encourages molecular attractions involving induced dipole force. Under different PAH-surfactant compositions, similar CED values, which facilitated their intermolecular attractions through pi-pi electron interactions, gave rise to a similar biodegradation pattern. For example, when induced enzymes were able to target the same molecular bonding on the PAH and Triton X-100, rapid degradation rates were observed in both systems. The distribution of the PAH in the monomer or micelle surfactant bulk affected the rate of PAH biodegradation. Quantification of the bacterial activity by applying specific oxygen uptake requirements (SOUR) identified an effect involving chemical molecular interaction. Changes in the physiological characteristics as measured by BioLog GN microplate measurements were identifiable and also could be related to the chemical structure of the dual substrates. Community-level physiological profiling (CLPP) changed when PAH biodegradation took place in the presence of the different surfactants. Cluster analysis using matching coefficient and carbon degradation potential values also varied with the different PAH-surfactant compositions. (c) 2007 Society of Chemical Industry.