PARENT SESSION
MP2 Chemical, biological and combined methods for the detection of pollutants
3:00 PM to 6:30 PM, Monday, 07 May 2001
Session Chair: D. Santiago Laguna
Room 2

(084) Photostabilization of the herbicide norflurazon by using organoclays.

Undabeytia, Tomas¹, Nir, Shlomo², Tel-Or, Elisha², Rubin, Baruch², ^{1 2}

ABSTRACT- Photo-stable formulations of the herbicide norflurazon [4-chloro-5-methylamino-2-(,,-trifluoro-m-tolyl)pyridazin-3-(2H)- one] were achieved by adsorbing it on pillared clay, or on montmorillonite preadsorbed with the organic cation thioflavin-T (TFT). A bioassay based on the response of the aquatic plant Lemna showed a photo-stabilization of norflurazon up to 50% for formulations prepared from montmorillonite and up to 70% for that from pillared clay, under irradiation which completely inactivated the commercial formulation. These data demonstrate the potential of organo-clays in the development of photo-stable formulations of norflurazon, and perhaps other herbicides. Diffuse Reflectance Fourier Transform Infrared (DRIFT) spectra showed the existence of strong interactions between the aromatic moieties of preadsorbed TFT and the herbicide, particularly after irradiation. The photo-stabilization of norflurazon obtained with TFT-clay was mainly due to energy transfer from the herbicide to the organic cation via -* interactions. Additional mechanism is the lower production of radicals from the clay when the clay mineral surface is covered with the organic cation. These radicals are responsible for the enhanced photo-degradation observed when norflurazon was irradiated in the presence of untreated montmorillonite.

Key words: norflurazon, photostabilization, montmorillonite, pillared clay