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: There are many strategies to prevent this toxicity , including the use of mannitol as a nephroprotectant in combination with hydration .
### Output Text:
There are many strategies to prevent this toxicity , including the use of <span class="chemical">mannitol</span> as a nephroprotectant in combination with hydration . 