The riceblast is produced by Pyricularia orizae fungus, is an important disease of this cereal that, in the years in which appears, causes serious economic losses. For it, nowadays, they are in use systematicly fungicidal to anticipate his possible appearance, treatments that in most of the cases are unjustified, due to the fact that they do not give themselves the conditions necessary for the development of pathogenic this one. The pesticide treatments, they carry the periodic or punctual emission of xenobitics that, as residues proceeding from these tasks, come to the aquatic ecosystems across irrigation ditches, channels of outlet and enclosedly airway, causing with it important effects on the biota. These substances can be bioaccumulated for different links of the trophic chains and manage to reach levels highly harmful to the ecosystem. Although, the environemntal levels of pesticides are very low to induce the direct and sudden death of the aquatic organisms. It is necessary to know the capacity of the aquatic species to resist and therefore to live in these contaminated environment. To establish the risk derived from the use of pesticides it is necessary to perform many studies directed to evaluating the potential risk for the environment, for the above mentioned evaluation of the risk the following studies have been carried out: 1. To determine the guidelines of evolution of the considered fungicides, in aquatic systems, studying experimentally his degradation kinetics and, biodegradation process. 2. To determine the toxicity, sublethal effects and bioaccumulation of the pesticides used to control the riceblast in the Lake of Albufera Natural Park (ANP) in Valencia in different present representative organisms in the aquatic ecosystem. 3. To determine the levels of pollution and the temporary evolution of the residues of fungicides in the treated plots and in the irrigation channels. As well as to realize a follow-up of the pollution in the ANP analyzing the values of unmission of the selected fungicides. 4. To evaluate the environmental risks of the use of fungicides in the mediterranean paddy fields To carry out these studies there have been realized chromatographic analyses of water samples taken in different points of the Albufera Lake of Valencia, determining the PEC (Predicted Environmental Concentrations) for every compound. Alter that, there were established the PNEC values (Predicted Non Effect Concentrations) by means of ecotoxicological tests in two types of aquatic microorganisms from estuarine and fresh water. The ERA is established by means of the PEC/PNEC ratio. Finally, tebuconazole was selected as model to establish the Bioconcentration Factor in zebra (Danio rerio) finally with the theoretical BCF obteined in laboratory was designed a mathematical model based on the Mackay Fugacity Model for the rest of azolic pesticides.