12 
Figure 1: 
Location of nuclear facilities in 
the Baltic Sea region. 
venly distributed in the drainage area of the 
Baltic Sea; the most contaminated areas were 
situated in the land areas surrounding the 
Bothnian Sea and the eastern Gulf of Finland. 
River discharges 
The amount of Chernobyl-derived 137 Cs car 
ried into the Baltic Sea by river runoff has 
been evaluated in Finland for all Finnish rivers 
discharging into the Baltic Sea, in Russia for 
five rivers discharging from the former Soviet 
Union, and in Poland for the River Vistula. 
Thorough calculations showed that a total of 
65 TBq of 137 Cs was discharged by Finnish riv 
ers into the Baltic Sea during the period 1986- 
1996 (Saxen & llus 2000). Corresponding 
calculations performed in Russia showed that 
14 TBq were discharged by five large rivers 
from the territory of the former Soviet Union 
during the years 1986-1988 (Gavrilov et al. 
1990). A Polish estimate made for the River 
Vistula showed that a total of 18 TBq of 137 Cs 
were discharged during the period 1986-1996 
(llus & llus 2000). The total river input of 137 Cs 
was estimated at 300 TBq during the decade 
1986-1996 (llus & llus 2000). 
2.3.3 Atmospheric nuclear 
weapons tests 
The impact of global fallout caused by the 
nuclear weapons tests in the 1950s and 
1960s as a source of radioactivity in the 
Baltic Sea was thoroughly considered in the 
first Joint Evaluation Report of the HELCOM/ 
MORS Group (Nies et al. 1995). According 
to recent calculations (Nielsen, pers. comm.),