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: These are nephrotoxic , but SRL seems to act differently displaying only minor nephrotoxic effects , although this question is still open .
### Output Text:
These are nephrotoxic , but <span class="chemical">SRL</span> seems to act differently displaying only minor nephrotoxic effects , although this question is still open . 