Two soils were used in this study: a creosote-polluted clay soil and an agricultural soil. The polluted soil (Calcaric Fluvisol) constituted the source of aged contaminants as well as PAH- degrading microorganisms for our greenhouse and laboratory experiments. This soil was provided by EMGRISA (Madrid, Spain) from a wood-treating facility in southern Spain that had a record of creosote pollution exceeding 100 years. The agricultural, non- polluted soil was a loamy sand soil from Coria del Río, Seville, Spain (Typic Xerochrepts). A PAH-containing soil mixture was obtained from these soils in two steps. First, the agricultural soil was mixed (67:33 w/w) with washed sand (Aquarama), and subsequently autoclaved. Next, 6 kg of this mixture (referred to as uncontaminated soil) was homogenized with polluted soil (1:1 w/w) in a cement mixer for seven days (9 h per day), with regular changes in the direction of rotation. This homogenization