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: Exposure to appetite - suppressants was assessed on the basis of hospital records and standardized interview .
### Output Text:
Exposure to <span class="chemical">appetite - suppressants</span> was assessed on the basis of hospital records and standardized interview . 