[THS] Fallout at Fukushima

[The Harder Stuff in news and commentary]

http://www.the-scientist.com/news/display/58085/

By The Scientist Staff
Fallout at Fukushima
What risks does Japan face as a result of radiation leakage from the nuclear power
plant hit by the recent earthquake and tsunami?

[Published 22nd March 2011 03:31 PM GMT]

Nuclear power plant in Cattenom, France
Image: Wikimedia Commons, Stefan Kuhn

Technicians in Japan struggle to contain breeches in cooling and containment
apparatuses at the Fukushima Daiichi nuclear reactor in eastern Japan, which was hit
by the massive earthquake and subsequent tsunami on March 11th. Though
considerable uncertainty remains concerning the exact amount of radioactive material
that has leaked from the facility thus far, low level radiation has turned up in crops
grown in the vicinity of the plant, and the danger of a widespread catastrophe
lingers. This week, The Scientist examines the latest research on the effects of
radiation and explores some of the worst-case-scenario health and environmental
effects of a nuclear disaster in Japan.

The acute effects of radiation

Late last week, a skeleton crew of about 50 workers at the Fukushima Daiichi plant
was urgently attempting to cool the reactor core, as specially-fitted helicopters tried
(and failed) to drop tons of seawater on the failing facility. Early this week, reports
from Japan indicated that the last workers trying to save the facility from catastrophe
evacuated as smoke billowed from two of the reactor units. Radiation levels currently
being reported by Japanese officials are still quite low, and the early public
evacuation reduced the concern for community health risks, said William Schull,
emeritus professor at the University of Texas Health Science Center in Houston and
an expert on the health effects of the atomic bombs dropped on Hiroshima and
Nagasaki in the 1940s. But the workers at the nuclear plants still risked acute
radiation exposure and serious health problems as a result, he added.

Upon direct exposure to ionizing radiation, anemia -- the loss of red blood cells -- and
leucopenia -- the loss of white blood cells such as those important in fighting off
infection -- can result, increasing susceptibility to disease. In addition, someone
directly exposed to radiation may display other symptoms of acute radiation
syndrome (ARS), such as vomiting, diarrhea, excessive bleeding brought on from the
death of hematopoietic stem cells in bone marrow, and hair loss. Such symptoms,
however, are caused by exposure of 1-10 grays (Gy), a unit of absorbed radiation
dose. The doses of radiation leaking from the Japanese reactor are far below this: On
Saturday, Japanese news outlet NHK News reported that the plant's operator, Tokyo
Electric Power Company, detected radioisotope iodine 131 at about 5.9 milibecquerels
per cubic centimeter, or about 0.0003 Gy/hour. (Click here for an infographic
comparing the radiation dose absorbed by humans engaged in various activities.)

But "things could quickly worsen," Schull said. If radiation continues to seep from the
reactor, officials could use a recently devised classification system to assess the health
of those exposed. The Radiation Injury Severity Classification (RISC) system estimates
three sets of clinical and haematological parameters to calculate "a combined score
[that] gives you a pretty accurate estimate of what's going to happen to this person,"
said University of Pittsburgh biostatistician Richard Day, who collaborated in the
creation of RISC. Applying the system to 59 workers in a Russian nuclear fuel
production facility, Day, Niel Wald of the University of Pittsburgh, and coauthors
estimated threshold values for some ARS symptoms, including vomiting (~1.5 Gy),
severely low white blood cell count (~3.5 Gy), and mortality (~6-7 Gy).

"In the roughly 115 years since Roentgen discovered X-rays we have learned a lot
about the values and hazards of exposure to ionizing radiation," Schull said. "But we
still have a hell of a lot to learn."

-- Bob Grant


Radiation and the immune system

Although most cells in the body can withstand considerable doses of radiation before
dying, immune cells begin to react at even small doses of radiation. While recent
reports suggest that the workers at the Fukushima Daiichi plant have so far only been
exposed to relatively low levels of radiation, their exposure could trigger
immunological reactions -- though depending on the dose, not all of them may be
harmful.

According to several reports, workers at the Fukushima plant have been exposed to
radiation levels ranging from 200-400 millisieverts (mSv, a measure of radiation
absorbed by a person) per hour -- levels that the human body can withstand with
minimal damage, said Richard Wakeford, visiting epidemiology professor at the
Dalton Nuclear Institute of the University of Manchester. Once doses reach levels of
500 mSv or more, however, the number of lymphocytes, white blood cells involved in
immune response, is cut by half within a few days, and there is considerable damage
to stem cells in the bone marrow, said Yoichiro Kusunoki, chief of the department of
radiobiology and molecular epidemiology at the Radiation Effects Research
Foundation in Hiroshima, Japan, in an email.

At high doses, these effects can be long lasting. According to studies of atomic bomb
survivors, T-cells never fully recover, neither in number nor effectiveness, although
stem cells and other immune cells bounce back to normal levels in about two months.
The body compensates for these shortfalls by increasing levels of inflammatory
cytokines -- a pattern that resembles the immune systems of the elderly, suggesting
that the immune system may age more rapidly after radiation exposure.

But the production of inflammatory cytokines can be seen even at "a relatively low
dose (several mSv) that does not trigger apoptosis of any types of cells," added
Kusunoki. This short term inflammation could initially be protective by helping clear
cells damaged by the radiation. However, researchers studying radiation exposure
during cancer radiation therapy suggest that low doses of radiation that trigger
inflammation could also initiate the kind of chronic inflammation that leads to cancer.

-- Edyta Zielinska