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: There is considerable interest in identifying the molecular mechanisms that relate early - life iAs exposure to the development of these latent diseases , particularly in relationship to cancer .
### Output Text:
There is considerable interest in identifying the molecular mechanisms that relate early - life <span class="chemical">iAs</span> exposure to the development of these latent diseases , particularly in relationship to cancer . 