EFFECT OF SOME UV-LIGHT ABSORBERS ON THE PHOTOSTABILIZATION OF AZADIRACHTIN, A NEEM-BASED BIOPESTICIDE

Photostabilization of neem-based azadirachtin insecticide (AZ-A) appli ed onto glass surfaces was studied in the presence of three UV absorbe rs, 2,4-dihydroxybenzophenone (Uvinul M-400, UM), 4-aminobenzoic acid (PABA) and Fluorescent brightener-28 (FB-28), a stilbene disulfonic ac id derivative. The UV absorber, UM, provided excellent protection, inc reasing the dissipation half-life (DT50) of pure AZ-A from 3.87 to 22. 54 d. Photostabilization due to PABA was marginal. The UV absorber, FB -28 acted as an effective photosensitizer. reducing the DT50 of AZ-A f rom 3.87 to 0.31 d. Similar trends in DT50, were observed when the thr ee UV absorbers were added to four formulations containing AZ-A. It wa s found that for effective photostabilization. both AZ-A and the UV ab sorber must have matching UV spectra. with simile lambda(max). The mec hanism of photostabilization was likely due to either energy transfer: from AZ-A to the UV absorber and/or competitive absorption of UV phot ons by the absorber. Photoinstability of AZ-A in the presence of FB-28 was due to energy transfer from the activated FB-28 to AZ-A molecules . Based on the UV spectral data, UV protectants due be selected and ma tched to stabilize UV-labile pesticides.