The distribution of natural radioactive elements like Uranium, Thorium, Radium isotopes and also some stable element distributions were measured in sea water, biological samples and sediment leaches from the samples collected off Tarapur coast during 1966, post-monsoon period. Studies were also made to obtain the seasonal fluctuations for all these elements in all the three matrices. Copper and Phosphatephosphorus values were significantly lower in post-monsoon period than in the pre monsoon period and this was attributed to uptake of these elements by phytoplankton blooms during this period High values of Ra²²⁸ relative to its parent nuclide Th²³² have been observed (factor of 13 to 20) in sea water and this may be due to the easy migration of Radium from sediments or from land run off. An attempt has been made to explain the Ra²²⁸'Th²³² activity ratio observed in biological species and sediment leaches. Some of the commonly available fishes have been analysed for major and trace element distribution and it was found that enriching capacity for various nuclides varies from species to species and also from season to season and this observation will have to be taken into account while computing the discharge levels of these radioisotopes.