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 evaluated cancer incidence through 2010 / 2011 ( NC / IA ) for 49 , 616 applicators , 53 % of whom reported ever using metolachlor .
### Output Text:
We evaluated cancer incidence through 2010 / 2011 ( NC / IA ) for 49 , 616 applicators , 53 % of whom reported ever using <span class="chemical">metolachlor</span> . 