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: When this conversion is impaired with ethinyl estradiol treatment , sulfation may be an important alternate pathway for excretion of this potentially harmful bile acid .
### Output Text:
When this conversion is impaired with <span class="chemical">ethinyl estradiol</span> treatment , sulfation may be an important alternate pathway for excretion of this potentially harmful <span class="chemical">bile acid</span> . 