Finnish studies on radioactivity in the Baltic Sea in 1987

Monitoring of radioactive substances in the Baltic Sea was continued within the framework of the Finnish national monitoring programme. The only regularly detected gamma nuclides in sea water were 40K, 134Cs and 137Cs. The ratio 134Cs/137Cs in surface water samples was 0.36+-0.01. The activity concentrations of 137Cs have became more evenly distributed during the last year, so that in the surface water of the Baltic Proper the values were 100-200 Bq m-3, in the Gulf of Finland 200-300 Bq m-3, in the Bothnian Sea 300-400 Bq m-3 and in the Bothnian Bay about 100 Bq m-3 in 1987. The sedimentation of the Chernobyl fallout into the bottom sediments of the open sea basins only began to increase in 1987. The addition of 137Cs and other fallout nuclides was strongest at the XV 1 station in the eastern part of the Gulf of Finland, where the total deposition of 137Cs was about 18 kBq m-3 during the last year. No areal differences were found in the fish samples caught from the coastal waters of Finland in 1987. In pike and cod the 137Cs values have slightly increased since 1986, being now about five times (15-30 Bq kg-1 fresh weight) the values before the Chernobyl accident. The activity concentrations of 90Sr (0.030-0.11 Bq kg-1 fresh weight) were at the same level as in 1985 and the preceding years