This study investigates the environmental quality, of water, treatments by evaluating the effectiveness of advanced oxidation technologies, such as H2O2/Fe(II) and H2O2/UV, in treating phenol-contaminated effluents, Toxicity measurements complement the chemical analyses used to evaluate the environmental quality of a treated effluent and are an additional method for interpreting the effects of chemicals not directly measured; This study proposes an estimation model for toxicity based on the Microtox test that is adaptable to the contaminant concentration of each case. The model allows for analysis of the contribution of the different components of the treated effluent: hydrogen peroxide, phenolics, colored compounds, and others. In the second part of this work, a study was conducted of the toxicity of samples treated with the aforementioned oxidative systems. In the Fenton system, the sample after oxidation was analyzed, and it was observed that the toxicity was due to intermediate oxidation compounds, such as carboxylic acids, which rejects the influence of compounds of color and other phenolics. The H2O2/UV system tracks the progress of toxicity. This parameter quickly reaches minimum values (within about 15 min) from the start of the reaction and is a representation of the final values of primary degradation. Therefore, it is not recommended to extend the oxidation beyond this point to minimize the toxicity.