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: CONCLUSIONS : Evidence is mounting that relates early - life iAs exposure and cancer development later in life .
### Output Text:
CONCLUSIONS : Evidence is mounting that relates early - life <span class="chemical">iAs</span> exposure and cancer development later in life . 