Cesium-137, cerium-144 and ruthenium-106 discharged into the nearshore environment of the Bombay harbour, have been found to be readily sorbed by the sedimentary particles. On reaching peak sorption levels, however, the levels of all the three radionuclides in the sediment were found to drop exponentially with time (1971–1976) under environmental conditions, despite the continued discharges at low levels. From the distribution patterns of radioactivity in the harbour, the rate of decline of 137Cs (the sedimentary half-life) was found to be 1.86 years, significantly lower than its radioactive decay time (30 years). In contrast, those of 144Ce (0.59 year) and 106Ru (0.87 year) were found to bepractically the same as their radiological half-lives. The difference between the sedimentary and radiological half-lives of both cerium and ruthenium suggests about 20% influx of fresh sediment following monsoon runoff. The effective sedimentary half-life (1.86 years) of 137Cs was found to be significantly affected by other environmental parameters, in addition to that caused by the influx of fresh material. Of the various environmental factors, salinity (i.e. Co-ion, Na +, K +, Mg ++, concentrations) was found to affect the desorption of cesium significantly. The possible sorption-desorption mechanism of cesium, cerium, ruthenium and cobalt radionuclides both under laboratory and field conditions are discussed.