Surface-active potential of biosurfactants produced cost-effectively in curd whey by Pseudomonas aeruginosa strain-PP2 and Kocuria turfanesis strain-J were tested using parameters viz, surface tension (ST) reduction, F-CMC (highest dilution factor to reach critical micelle concentration) and emulsification index (EI-24) of pesticides; monocrotophos and imidacloprid at extreme environmental conditions. Results have shown that ST reduction of biosurfactants was stable at pH 2-11. High F-CMC of the biosurfactant in the fermented whey at low pH improved emulsification of pesticides. ST marginally increased at 5% and 15% NaCl, resulting in high EI-24 and F-CMC. Over a range of temperatures 30-121 degrees C, ST remained low with a higher F-CMC and EI-24 at 60 degrees C than at 121 and 30 degrees C. The biosurfactants have shown differences in their surface-active property and have marked specificity to emulsify pesticides in extreme environmental conditions. (C) 2012 Elsevier Ltd. All rights reserved.