In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The participation of reactive oxygen species in aminoglycoside - induced ototoxicity has been deduced from observations that aminoglycoside - iron complexes catalyze the formation of superoxide radicals in vitro and that antioxidants attenuate ototoxicity in vivo .
### Output Text:
The participation of reactive <span class="chemical">oxygen</span> species in <span class="chemical">aminoglycoside</span> - induced ototoxicity has been deduced from observations that <span class="chemical">aminoglycoside</span> - <span class="chemical">iron</span> complexes catalyze the formation of <span class="chemical">superoxide</span> radicals in vitro and that antioxidants attenuate ototoxicity in vivo . 