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: Recent findings in a bipolar patient receiving maintenance lithium therapy who developed hypercalcemia and severe bradyarrhythmia prompted the authors to conduct a retrospective study of bipolar patients with lithium - associated hypercalcemia .
### Output Text:
Recent findings in a bipolar patient receiving maintenance <span class="chemical">lithium</span> therapy who developed hypercalcemia and severe bradyarrhythmia prompted the authors to conduct a retrospective study of bipolar patients with <span class="chemical">lithium</span> - associated hypercalcemia . 