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: Defects in superoxide and hydrogen peroxide production may be implicated in the high incidence of bacterial infections in patients with acute liver failure ( ALF ) .
### Output Text:
Defects in <span class="chemical">superoxide</span> and <span class="chemical">hydrogen peroxide</span> production may be implicated in the high incidence of bacterial infections in patients with acute liver failure ( ALF ) . 