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: Neurotoxic esterase activities 24 hr after TOTP or DFP were less than 20 % of values measured in chickens not given organophosphorous compounds .
### Output Text:
Neurotoxic esterase activities 24 hr after <span class="chemical">TOTP</span> or <span class="chemical">DFP</span> were less than 20 % of values measured in chickens not given <span class="chemical">organophosphorous</span> compounds . 