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: It has been shown that exposure to diazinon may interfere with lipid metabolism .
### Output Text:
It has been shown that exposure to <span class="chemical">diazinon</span> may interfere with lipid metabolism . 