Pesticide contamination of waters presents a serious environmental problem because of their potential toxicity and widespread use. Therefore, information about their possible degradation mechanisms in the environment is important in order to estimate the persistence of these compounds and to identify the factors that influence their behavior. Among the different transformation processes (biotic and abiotic), photodegradation is an important factor influencing the fate of organic micropollutants in the field.
Competitive sunlight absorption by water and soil chromophores, variable sorption of pesticides on organic water and soil colloids, and competing biotic and abiotic transformation processes complicate the photodegradation process in natural conditions.
Photodegradation occur by direct and indirect absorption of light. In direct photolysis, the substances absorbs UV-visible light energy and undergoes transformation whereas during indirect photolysis light energy is absorbed by other constituents of the media (water, soil). The excited species can then either transfer the energy to the substance (sensetization) undergo an electron transfer with the substance or lead to the formation of reactive species, such as singlet oxygen or hydroxy radical, which enter into a series of reactions .
Dissolved organic matter have an optical filter effect or a sensitisation effect depending on their structure and the pollutant.
4. V.A. Sakkas, D.A. Lambropoulou and T.A. Albanis, “Kinetics of chlorothalonil photodegradation in natural and humic water”. Chemosphere, 48, 939-945, (2002). PDF