32 
Table 2: 
Extreme activity values of 
artificial radionuclides in fish, in 
Bq kg ' wet weight (1999-2006) 
Table 3: 
Extreme activity values of 
artificial radionuclides in Fucus 
vesiculosus, in Bq kq ' dry 
weight (1999-2006) 
Table 4: 
Activity values of the naturally 
occurring alpha emitting 
radionuclide 2 '°Po in Baltic 
Sea fish, in Bq kg ' wet weight 
(1990-2006) 
Species 
137 Cs 
90 Sr | 239.240p u 
241 Am 
(flesh) 
min. 
max. 
min. 
max. 
min. 
max. 
min. 
max. 
Herring 
0.5 
21 
0.0028 
0.0049 
0.000019 
0.0000912 
0.0000137 
0.000143 
Cod 
0.61 
41 
0.0015 
0.0067 
0.000021 
0.000021 
0.0000186 
0.0000186 
Whiting 
6.5 
11 
0.0013 
0.0020 
Mackerel 
4.5 
4.5 
Flounder 
1.9 
11 
0.01 
0.047 
0.000044 
0.000045 
0.000157 
0.000157 
Plaice 
0.15 
14 
0.016 
0.016 
0.0000201 
0.000026 
0.0000218 
0.000196 
Pike 
9.2 
73 
0.0098 
0.33 
Perch 
0.35 
12 
0.016 
0.05 
Herring, (edible 
parts) 
4.6 
19 
0.011 
0.103 
137 Cs 
1 
“Sr 
239,240p u 
“'Am 
“Tc 
min. 
max. 
min. 
max. 
min. 
max. 
min. 
max. 
min. 
max. 
1.3 
66 
4 
10 
0.023 
0.12 
0.0020 
0.0069 
8.2 
168 
Species 
2'opo 
(flesh) 
min. 
max. 
Mean 
Herring 
0.19 
8.5 
1.3 
Cod 
0.043 
1.5 
0.41 
Flounder 
0.26 
3.4 
1.1 
species (herring, cod, whiting and mackerel), 
because the analysed samples of the former 
may contain more small parts of bones which 
have accumulated bone-seeking 90 Sr much 
more than fish muscle. The 90 Sr values of 
herring analysed as “edible parts” (fish without 
head and entrails, i.e. containing larger 
fractions of bones) are significantly larger than 
those of herring flesh alone. Samples of the 
flesh of flat fish also suffer from increased 
bone fractions leading to slightly larger 90 Sr 
activities. 
The radionuclides 239 24 °Pu and 241 Am exhibit 
maximum activity values which are even one 
to two orders of magnitude lower than those 
of 90 Sr; so, they do not have any significance 
with respect to the doses caused by fish 
consumption. 
Table 3 shows the corresponding ranges of 
radionuclide activity concentrations in bladder 
wrack of the species Fucus vesiculosus. 
Practically all of the radionuclides shown 
are significantly accumulated from seawater. 
Besides 137 Cs and "Sr, the alpha-emitting 
radionuclides Pu and Am can also be safely 
detected. The dominant sources of Pu 
and Am isotopes are global fallout as well 
as discharges from nuclear reprocessing 
facilities; additionally, 241 Am is slowly in 
growing from the radioactive decay of the 
beta-emitter 241 Pu, which has originated from 
the same sources. The very long-lived beta- 
emitter "Tc, which originates from nuclear 
reprocessing discharges and has been 
measured in samples from Danish waters, is 
also accumulated significantly. 
The radionuclide which is the most important 
with respect to doses caused by fish con 
sumption is the alpha-emitting 210 Po, which 
belongs to the naturally-occurring radionu 
clides. The activity values of 104 samples of 
fish flesh collected in the Kattegat and the 
Bornholm Sea since 1990 have been summa 
rised in Table 4. Maximum values, between 
1.5 and 8.5 Bq kg 1 wet weight, were slightly 
different between the three species consid 
ered in these measurements. The average of 
the three mean values is about 0.94 Bq kg 1 
wet. In a former evaluation of 210 Po in fish from 
Danish waters including the North Sea (Dahl- 
gaard 1996) average values of 0.35, 0.65 and 
0. 96 Bq kg -1 wet weight were observed for 
cod, herring and plaice fillets, respectively. 
3C.4.3 Activity ratios 
Some of the biota species serve as good 
biological indicators of activity concentration 
ratios of alpha emitting radionuclides, 
1. e. the ratios ^Pu/ 239 ' 24 ^ anc | 24i^ m / 
239,24op u Measured results of these ratios 
may be compared with values known to 
be characteristic for their sources, such as 
global fallout or discharges from nuclear 
reprocessing. Activity ratios have been 
measured within the MORS-PRO monitoring 
project in samples of bladder wrack (Fucus 
vesiculosus), blue mussel (Mytilus edulis) 
and small sprat (Clupea harengus ).These 
organisms were analysed as whole body 
samples, so the blue mussel samples (small 
organisms) mainly consisted of shells. Some 
of the measured 238 Pu activity values were 
not significant, i.e. their uncertainties were 
too large and thereby reported as “less-than” 
values, which leads to “less-than” values