Sentence:  It is not clear whether this system bears any resemblance to the in vivo iodinating mechanism , and a system generating <WSD>peroxide</WSD> has not been identified in thyroid tissue . 
Meaning of the word marked with <WSD> tags:  a viscous liquid with strong oxidizing properties; a powerful bleaching agent; also used (in aqueous solutions) as a mild disinfectant and (in strong concentrations) as an oxidant in rocket fuels