For use in estimating or predicting bioaccumulation of a chemical analyte, even a surfactant, log P.sub.ow values for the analyte may be determined by calculating the log of the ratio of the concentrations of the analyte in n-octanol and in water, equilibrated using a slow-stir method. In this method, samples of the analyte are prepared and stirred in n-octanol and water (or other largely immiscible solvents) at a rate sufficiently low to avoid emulsions over time at a constant temperature. After stirring, the n-octanol layer and the water layer are sampled and the quantity of analyte in each measured.