[en] In order to know factors which influence ⁶⁰Co contamination sargassoes in Urazoko Bay, where a nuclear power plant is located, correlations between the contamination of the algae and of the marine environment were examined, based on field data observed since January 1971. It was found that; [1] correlation between the ⁶⁰Co concentration in sargassoes (Y sub(algae) pCi/kg raw weight) and discharge outlet of the nuclear power plant to the sampling points (d km) was expressed by a function, (Y sub(algae) = C.exp(-kd), where C and k are constants, and k increased successively from 0.388 in Nov. 1971 to 1.200 in Nov. 1974, whereas C decreased from 120 to 27 during the same period. [2] ⁶⁰Co content in the sargassoes seemed to be contributed dominantly by the dislodged ⁶⁰Co from heavily contaminated sediment rather than freshly discharged ⁶⁰Co from the power plant. The amount of dislodged ⁶⁰Co was estimated from both the ⁶⁰Co distribution in marine sediment in Urazoko Bay and results of a tracer experiment concerning the dislodgement of ⁶⁰Co from marine sediment. On the other hand, contents of ⁹⁰Sr, ¹³⁷Cs and ⁶⁰Co in surface sediments were investigated. The main source of ⁹⁰Sr and ¹³⁷Cs was recognized to be radioactive fallout, whereas ⁶⁰Co was considered to originate from the nuclear power plant. Using the ¹³⁷Cs concentration as an indicator of sorption capacity of the sediment, the behaviour of ⁶⁰Co was investigated. No seasonal variation was observed in the distribution pattern of ⁶⁰Co/¹³⁷Cs ratio and the retention of the heavy initial discharge in 1969 was considered to dominate the radionuclide level in the sediment. Correlation of ⁶⁰Co/¹³⁷Cs ratio in the sediment and the distance from the discharge outlet was expressed by a simple exponential function of the distance. (author)