Radioactivity - The Changing Arctic Environment: The Arctic Messenger - page 50

Fallout From Atmospheric Testing of Nuclear
Weapons, Peaceful Nuclear Explosions and the
Chernobyl Accident
The main overall source of anthropogenic radiation in the circumpolar Arctic has been fal-
loutfromatmosphericnuclearweaponstesting.Between1945and1980,520suchtestswere
carried out. Arctic fallout was in particular dominated by Northern Hemisphere tests, in-
cluding the 88 tests that took place on the Arctic island of Novaya Zemlya. The radionuc-
lides most commonly used to study this fallout are the fission products caesium-137 ( 137 Cs),
strontium-90 ( 90 Sr) and iodine-131 ( 131 I).
Apart from distance from test locations, the actual geographical distribution of fallout
depends mainly on patterns in air movement (which roughly translates to increasing fallout
with increasing latitude) and the degree of wet deposition (that is, with rain). The latter es-
sentiallymeansthatrainandsnowtendtowashoutpollutants,includingradionuclides,from
the atmosphere. Therefore, when the 1998 AMAP assessment team estimated the circumpo-
lar ground distribution of nuclear fallout in the Northern Hemisphere from 50 to 90 degrees
latitude, they found relatively low deposition in High Arctic areas that receive low levels
of precipitation, such as northern Greenland (less than 250 137 Cs Bq per square metre), and
high levels in very wet regions, such as western North America (including southern Alaska)
and the Atlantic coastal margins of Europe, including Ireland and southern Iceland (above
2,500 137 Cs Bq per square metre). Much of the remaining western Eurasian Arctic received
deposition in the range of 1,000 to 2,500 137 Cs Bq per square metre.
AMAP has also reported a consistent time trend of decreasing deposition of nuclear
fallout that is independent of geographic location. It directly reflects the falling frequency of
Northern Hemisphere nuclear testing in the atmosphere from the 1960s to the global curtail-
ment of testing in 1980. Therefore, in 1963, there was a combined wet and dry deposition
rate of more than 500 Bq per square metre for 137 Cs and 90 Sr in Finland and Greenland, but
by 1985, rates had fallen to well below 10 Bq per square metre. In 1986, the accident at