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: We compared age - specific mortality rates from 1 year post - discharge through 2008 between those in whom the liver injury led to an acute liver failure and those in whom it did not .
### Output Text:
We compared age - specific mortality rates from 1 year post - discharge through 2008 between those in whom the liver injury led to an acute liver failure and those in whom it did not . 