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 possibility that habitual use of acetaminophen alone increases the risk of ESRD has not been clearly demonstrated , but cannot be dismissed .
### Output Text:
The possibility that habitual use of <span class="chemical">acetaminophen</span> alone increases the risk of ESRD has not been clearly demonstrated , but cannot be dismissed . 