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 saw no association between metolachlor use and incidence of all cancers combined ( n = 5 , 701 with a 5 - year lag ) or most site - specific cancers .
### Output Text:
We saw no association between <span class="chemical">metolachlor</span> use and incidence of all cancers combined ( n = 5 , 701 with a 5 - year lag ) or most site - specific cancers . 