A widely applied method of supported lead estimation in sediments using gamma spectrometric 226Ra determination via 222Rn short lived daughter products relies on radioactive equilibrium between 226Ra and 222Rn being established after sealing the samples. Advantages and disadvantages of methods of 226Ra estimation in sediments, using either 226Ra daughter products or direct estimation by the 186.2 keV gamma-emissions are discussed. An equilibrium experiment was performed using test samples and in one case radioactive equilibrium was not reached. On theoretical sediment profiles it is shown how systematic errors in supported 210Pb estimation can lead to wrong interpretations of 210Pbxs profiles and therefore affect 210Pb derived chronologies. © 2011 EDP Sciences.