Recently, a new procedure was developed to estimate total body residues (TBRs) in biota after exposure to complex mixtures of organic chemicals in water. The procedure is based on a simulation of bioconcentration using a hydrophobic phase and on the measurement of total molar concentrations on this hydrophobic phase via vapor pressure osmometry and gas chromatography–mass spectrometry. In this paper, the results of the application of this procedure to effluents and surface water are presented. Estimated TBRs (TBRests) give information on the potential total bioaccumulation of complex mixtures. Moreover, using these estimated total body burdens, baseline toxicity effects can be predicted, including the contributions of chemicals with specific modes of action to the overall baseline toxicity. The advantage of the parameter TBRest is that it determines total molar concentrations of organic chemicals, including those chemicals that are usually not measured because they cannot be identified or because their concentrations are below the detection limits of individual compounds.