Octylphenol polyethoxylate (OPEOn) surfactants are used in numerous commercial and industrial products. Large amounts of such surfactants and their various residual biodegradation by-products are ultimately released into the environment. OPEOn biodegradation was performed in this study using pure cultures of Pseudomonas species and strains under different environmental conditions. Environmental factors including the pH, nitrogen sources, and growth kinetics of the cells were investigated. The intermediates of Triton X-100 biotransformation were detected by high performance liquid chromatography-mass spectrophoto-graph (HPLC-MS). We found the highest specific growth rate (mu) was 0.56 h(-1) and this was achieved by strain E with an initial concentration of Triton X-100 of 5000 mg L-1. A pH level of 7 was most favorable for cell growth for all five strains. The highest specific growth rate was achieved using (NH4)(2)SO4 as the sole nitrogen source for strain E. Strain A showed an enhancement of growth when between 0.2 and 1.4 mg L-1 of H2O2 was added. Detection of intermediates was possible after four days of transformation and the octylphenol triethoxylate (OPEO3) peak was predominant, while the high molecular weight peaks had all disappeared. The kinetic analysis demonstrated that the greatest maximum specific growth rate (mu(max)) and the greatest saturation constant (K-s) of 0.83 h(-1) and 5.24 mgL(-1), respectively, were obtained for strain E in 5000 mgL(-1) Triton X-100. The higher K-i revealed that strain A was resistant to higher Triton X-100 concentrations. (c) 2005 Elsevier Ltd. All rights reserved.