This study first investigated the degradation performance of BDE209 using ferrous activated persulfate-based advanced oxidation process. The results indicated that a lower pH would result in a greater increase in the BDE209 removal efficiency, and the maximum removal efficiency was obtained at pH = 3.0. The effects of sodium persulfate (PS) dosage and molar ratio of PS/Fe(II) were also determined, and 0.2 mol L-1 and 2:1 were the best conditions, where the removal of BDE209 in soil could reach to about 53% after 6 h. Additionally, hydroxylamine (HA) was firstly introduced to a PS/Fe(II) system, and resulted in a large enhancement of BDE209 removal efficiency. Compared to the controls, the degradation rate increased by 13% with the ratio of HA/Fe(II) 4/1, which might be because HA accelerated the transformation from Fe(III) to Fe(lI). Additionally, 9 intermediate products during iron-activated persulfate oxidation process were identified, and a possible reaction mechanism was further proposed. (C) 2016 Elsevier B.V. All rights reserved.