BACKGROUND: Four silicone oils (PolyDiMethylSiloxane, PDMS) of different viscosities, namely 5, 20, 50, and 100 mPa s were characterized to select the most suitable polymer for the biological treatment of toluene. The PDMS volatilities and the partition coefficients of toluene between air and PDMS were investigated. Toluene biodegradation tests were also carried out to assess the absence of toxicity of the considered PDMS vis-a-vis the microorganisms. RESULTS: PDMS 20, 50 and 100 had negligible volatilities at 25 degrees C and 35 degrees C, whereas PDMS 5 was volatile even at 25 degrees C. The results indicate that the amount of VOCs emitted by PDMS increased with the temperature according to a logarithmic law. The partition coefficient of toluene between air and the four PDMS were similar (H=2.9 Pa m(3) mol(-1)) indicating that the affinity between toluene and PDMS was identical whatever their viscosity. Moreover, biodegradation tests allowed the conclusion that the four PDMS tested are not toxic for microorganisms. CONCLUSION: PDMS 20, 50 and 100 were suitable at 25 degrees C for the biological treatment of toluene. Since all these PDMS were satisfactory at 25 degrees C, it could make sense to select the least viscous oil for use in the process, i.e. PDMS 20. (C) 2015 Society of Chemical Industry