Photosensitizing properties of protein hydrolysates-based fertilizers.

The use of protein hydrolysates-based fertilizers (PHF) as adjuvant for pesticides or herbicides has been proposed, however, the behavior of mixtures PHFs and pesticides under solar light are not known and various photochemical reactions may occur. The photosensitizing properties of PHFs were investigated in water solutions (0.8 g TOC L-1) within the wavelength range 300 - 450 nm, using furfuryl alcohol (FA) as a probe to test the involvement of singlet oxygen and Irgarol 1051 as an example of organic pollutant. Two commercial PHFs and one standard PHF were studied, all the products being of animal origin. PHFs photosensitize the transformation of FA (10-4 M), and the kinetics of FA disappearance follows an apparent first-order rate law. Using sodium azide (1⋅10-3 M) as singlet oxygen scavenger and deuterium oxide (D2O) for increasing the singlet oxygen lifetime we show that singlet oxygen contributes largely to the phototransformation of FA. The replacement of water by D2O increases the apparent first-order rate constant of 6 times, while the addition of sodium azide reduces it by approximately 90 %. These results are confirmed using Irgarol 1051 (10-5 M). The photosensitizing properties of PHFs might be due to pigments naturally present in tissues from which they are extracted, or to compounds generated during the production processes.