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: Nephrotoxicity was assessed by measuring the concentrations of creatinine and urea in the plasma and reduced glutathione ( GSH ) in the kidney cortex , and by light microscopic examination of kidney sections .
### Output Text:
Nephrotoxicity was assessed by measuring the concentrations of <span class="chemical">creatinine</span> and <span class="chemical">urea</span> in the plasma and reduced <span class="chemical">glutathione</span> ( <span class="chemical">GSH</span> ) in the kidney cortex , and by light microscopic examination of kidney sections . 