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: Further work is warranted on the effect of the treatments on renal functional aspects in models of chronic renal failure , and on the mechanism ( s ) involved .
### Output Text:
Further work is warranted on the effect of the treatments on renal functional aspects in models of chronic renal failure , and on the mechanism ( s ) involved . 