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: By contrast , we were unable to substantiate an increased risk from paracetamol consumption for renal papillary necrosis or any of these cancers although there was a suggestion of an association with cancer of the ureter .
### Output Text:
By contrast , we were unable to substantiate an increased risk from <span class="chemical">paracetamol</span> consumption for renal papillary necrosis or any of these cancers although there was a suggestion of an association with cancer of the ureter . 