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: CONCLUSION : Primary hyperparathyroidism is a rare but potentially life - threatening side effect of long - term lithium therapy .
### Output Text:
CONCLUSION : Primary hyperparathyroidism is a rare but potentially life - threatening side effect of long - term <span class="chemical">lithium</span> therapy . 