By Quirin Schiermeier of Nature magazine
Radiation released by the tsunami-struck Fukushima Daiichi nuclear power plant could have long-lasting consequences for the natural environment in the vicinity of the damaged plant.
estimate that in the first 30 days after the accident on 11 March,
trees, birds and forest-dwelling mammals were exposed to daily doses up
to 100 times greater-and fish and marine algae to doses several thousand
times greater - than are generally considered safe.
with the French Institute of Radioprotection and Nuclear Safety (ISRN)
in Cadarache converted concentrations of radioisotopes measured in the
soil and seawater into the actual doses that various groups of wildlife
were likely to have received. Their results are published this week in Environmental Science & Technology.
soil samples used for the analysis came from a contaminated forest area
25-45 kilometers northwest of Fukushima. The seawater samples were
taken from a region close to the reactor site. Both were measured in
French team reckons that about 50 radioisotopes have been released,
with iodine-131 and caesium-137 being the most abundant (see 'Radiation release will hit marine life').
At the end of March, concentrations of caesium-137, which has a half
life of 30 years, reached 47,000 becquerel per liter in seawater, and
72,900 becquerels per kilogram in soils. A becquerel is defined as one
radioactive decay per second.
team then plugged those concentrations into a piece of software called
ERICA (Environmental Risk from Ionizing Contaminants) to calculate the
radiation dose that various groups of wildlife would have received.
ERICA accounts for factors that are known to affect the rate at which
organisms absorb radioisotopes, such as a species' cellular
characteristics and metabolism. The dose rate (measured in milligrays
per day) specifies how much radiation is absorbed per kilogram of
organic tissue per day, a more biologically meaningful indication of how
organisms are affected by exposure to radioactivity.
so, it's just a rough assessment," says Thomas Hinton, a co-author of
the study. "We need many more samples before we can try to determine the
full extent of Fukushima's ecological effects."
team found that flatfish, mollusks, crustaceans and brown seaweed
offshore of Fukushima received radiation doses that, according to known
dose-effect relationships, are likely to markedly increase mortality.
organisms are somewhat better off. However, the dose rates were still
high enough to reduce the reproductive success of birds, rodents and
trees-in particular pine and spruce.
reported values are not written in stone but they're definitely
plausible," says Nick Beresford, a radioecologist at the Centre for
Ecology & Hydrology in Lancaster, UK. "But even though it's
preliminary, this is a very useful ecological assessment."
land species, says Hinton, may get off relatively lightly because the
accident happened early in the flowering season. Had it occurred in
mid-spring, the harm would probably have been much more severe,
especially for plants.
Radiation effects on egg hatching and the survival of newborn mammals still need to be surveyed, he cautions.
all the desolation it has caused, the Fukushima event could help
scientists to gain a better understanding of the effects of nuclear
radiation on wildlife and the environment.
is wild disagreement, for example, over how radiation affects the
fitness of birds and invertebrates. A recent study that reports reduced
survival in barn swallows (Hirundo rustica) in the Chernobyl exclusion zone, where dose rates are now barely above natural values, has met with sharp criticism.
researchers are reporting-possibly biased--results downright contrary
to established paradigms of radioecology," says Hinton. "So what's going
on? Long-term surveys in the Fukushima forest zone will hopefully help
us find out."
regret that the few ecological studies done after the Chernobyl reactor
meltdown 25 years ago missed out on many research opportunities and
hope that the Fukushima area will become the natural observatory site
that Chernobyl has not, owing mainly to political circumstances. The
contaminated zone should ideally be thoroughly surveyed at least twice a
year, says Hinton.
more pressing priorities, the Japanese government is preparing an
environmental monitoring program that involves around 300 experts from
across the country.
"They have all the expertise, no doubt," says Beresford, "and the sooner the work starts the more useful it will be."
This article is reproduced with permission from the magazine Nature. The article was first published on May 27, 2011.
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