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: DISCUSSION : Epigenetic reprogramming that imparts functional changes in gene expression , the development of cancer stem cells , and immunomodulation are plausible underlying mechanisms by which early - life iAs exposure elicits latent carcinogenic effects .
### Output Text:
DISCUSSION : Epigenetic reprogramming that imparts functional changes in gene expression , the development of cancer stem cells , and immunomodulation are plausible underlying mechanisms by which early - life <span class="chemical">iAs</span> exposure elicits latent carcinogenic effects . 