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 rats treated with DFP - atropine showed severe typical OP - induced toxicity signs .
### Output Text:
The rats treated with <span class="chemical">DFP</span> - <span class="chemical">atropine</span> showed severe typical <span class="chemical">OP</span> - induced toxicity signs . 