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: Although much has been written about the management of the more common adverse effects of lithium , such as polyuria and tremor , more subtle lithium side effects such as cognitive deficits , loss of creativity , and functional impairments remain understudied .
### Output Text:
Although much has been written about the management of the more common adverse effects of <span class="chemical">lithium</span> , such as polyuria and tremor , more subtle <span class="chemical">lithium</span> side effects such as cognitive deficits , loss of creativity , and functional impairments remain understudied . 