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: Several reports have linked the abuse of PPA with myocardial injury , especially when overdose is involved .
### Output Text:
Several reports have linked the abuse of <span class="chemical">PPA</span> with myocardial injury , especially when overdose is involved . 