Naturally occurring radionuclides of terrestrial origin exist ubiquitously in the environment and contribute significantly to external and internal doses to the population.Among them,of particular importance are the solid radionuclides belonging to the 238U and 232Th series which are present in soil and rocks.The aim of this work is to study the transfer of 238U and 232Th during the treatment of waste water by infiltration percolation through a phosphate bed.To assess radiation dose due to the treated water which is used in agriculture and for the irrigation of gardens in urban areas,these radionuclides have been measured in waste water,phosphate samples and treated water by using solid state nuclear track detectors.