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: Lindane is also widely used as an agricultural and industrial pesticide , and as a result the toxic profile of this insecticide is well understood .
### Output Text:
<span class="chemical">Lindane</span> is also widely used as an agricultural and industrial pesticide , and as a result the toxic profile of this insecticide is well understood . 