Microalgal bioassays as a test of pesticide photodegradation efficiency in water.

Photodegradation is one of the processes that pesticides may undergo once dispersed in the environment. It requires an adequate overlapping between the emission spectrum of the light source and the absorption spectrum of the compound to be degraded. When such condition is fulfilled, molecules undergo light absorption, being promoted to an excited electronic state, from where they can relax via different pholophysical and/or photochemical processes. Considering the typical absorption spectra shown by common pesticides, the small portion of UVA and the UVB components of sunlight reaching the Earth’s surface (Murov et al. 1993) are adequate to initiate such photodegradation processes. UVA light is widely used nowadays as basis of advanced water-disinfection methods (Sommer et al. 1997), with the subsequent photo-initiated reactions of the organic pollutants present in water (Moctczuma ct al. 1999).