Fluorescent properties and bifenthrin binding behavior of maize (Zea mays L.) seedling root exudates

The binding parameters of root exudates for organic pollutants are important for understanding the mechanisms involved in phytoavailability and phytoremediation. However, quantitative information about organic pollutant binding to root exudates is lacking. Fluorescent properties and bifenthrin (insecticide) binding behavior of root exudates from maize (Zea mays L.) seedlings were investigated using excitation emission matrix fluorescence spectroscopy. The protein-like fluorophores in root exudates from (Z. mays L.) are strong complexing ligands for bifenthrin, with logK(a) in the range of 3.6 -5.7. Two protein-like fluorescence peaks were identified in the EEM spectrum of root exudates and fluorescence of both peaks could be quenched by bifenthrin. The protein-like substances in root exudates had larger binding capacity for bifenthrin under acidic condition than under neutral and basic condition. The conditional stability constants were also higher in acidic solution than in the neutral or basic solution. Similarly, more fluorescence is accessible for bifenthrin at acidic pHs. More than one binding sites are needed in root exudates for binding one bifenthrin molecule. Enough attention should be paid to the effects of root exudates on adsorption, transport and fate of pesticides in environments. (C) 2012 Elsevier Masson SAS. All rights reserved.