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: Acute nephrotoxicity , which occurs in the early period after transplantation , leads to a higher rate of dialysis , and chronic nephrotoxicity may eventually result in graft loss .
### Output Text:
Acute nephrotoxicity , which occurs in the early period after transplantation , leads to a higher rate of dialysis , and chronic nephrotoxicity may eventually result in graft loss . 