PARIS — On Friday, it will be five years to the day since an earthquake-triggered tsunami caused the explosion of three reactors at Japan's Fukushima Daiichi Nuclear Power Plant. Then next month, on April 26, the world will also mark the 30th anniversary of the catastrophic nuclear accident at the Chernobyl plant in Ukraine.

In hindsight, what can we say about the impact on health, society and the environment of these major nuclear accidents? Here's a review of the primary conclusions from a host of researchers.

Animal populations wiped out

Two short videos by Anders Moller, from Paris-Sud University's Systematic Ecology and Evolution laboratory, are gripping. Each shows a patch of countryside in the Fukushima region. In fact, the images are almost identical. Only the soundtracks differ: In the video shot in the non-contaminated region, you can hear birds singing. In the other video, there is a deafening, deadly silence.

In fact, a study of birds at Fukushima showed that the roughly 15 species present in one contaminated area had a survival rate of only 30% — far lower than the birds in an unaffected area. Even when radiation doesn't directly cause fatal illnesses, the populations of many different species of animals (birds and others) can diminish to the point of disappearing entirely after a nuclear disaster. For instance, a small rodent suffering from cataract problems, one of the afflictions noticed in Chernobyl, has fewer chances of finding a mate and reproducing.

That said, the impact of a nuclear accident on flora and fauna remains difficult to evaluate, and one issue in particular has been controversial. On-site studies at Chernobyl revealed five to 10 times greater sensitivity to radiation than what lab tests had indicated. Why the difference?

According to Jean-Christophe Gariel, director of the environment at France's Institute for Radiological Protection and Nuclear Safety (IRSN), the reason is probably that the on-site studies underestimate the dose actually absorbed. Typically, only external contamination, tied to exposure to ionizing rays, is taken into consideration, while internal contamination from inhalation or ingestion of contaminated substances is ignored.

Last year IRSN and Anders Moller's lab conducted a new Fukushima study to evaluate total radiation exposure (internal and external). Again focusing on birds, the tests showed that 90% of the 57 species analyzed had been exposed to enough radiation that their ability to reproduce was compromised.

An increase in thyroid cancer

Of all radiation-induced illnesses (endocrine cancer, leukemia, cardiovascular problems and cataracts, to name a few), thyroid cancer in children has been the focus of study for Elisabeth Cardis, from Barcelona's Center for Research in Environmental Epidemiology, and IRSN's Jean-René Jourdain. The thyroid, especially in the very young, is one of the most radiation-sensitive human organs.

Ghost town: the 22,000 residents of Namie near the Fukushima plant were permanently evacuated. — Photo: Steve Herman

In the case of Chernobyl, their conclusions left no room for doubt. Placing a map of the geographic distribution of radiation exposure over a map of individual cases of thyroid cancer demonstrates that the 1986 explosion caused a spike in the number of tumors. Between 1986 and 2005, more than 6,800 cases of thyroid cancer were reported in the three former Soviet republics (Belarus, Ukraine and Russia) that were most affected by the accident. Because thyroid cancer has a relatively good survival rate, the majority of these 6,800 cases were fortunately not fatal.

But Chernobyl's lasting impact on public health is still sobering. The situation certainly deteriorated under the dysfunctional, incompetent Soviet leadership of the time. No systematic screening was developed, and worse, no one went distributed iodine pills to young Belarusians and Ukrainians to saturate their thyroids and prevent poisoning. In fact, in many cases children developed cancer after consuming milk containing radioactive iodine.

Japan in 2011 was a far cry from the Soviet Union of the 1980s, and the long-term health consequences of Fukushima will no doubt be less serious. For starters, Japan took all the necessary precautions (trade restrictions, for instance) to eliminate as many sources of internal contamination as possible. It also installed a systematic screening process in the Fukushima prefecture, with 360,000 children — from newborns to age 18 — required to undergo regular check-up X-rays. Because thyroid cancer has a lengthy latency period (at least three years), it's too early to know whether the screening will reveal an increase in incidence.

Unequal treatment for the displaced

The "triple catastrophe" of March 11, 2011 — the earthquake, the tsunami and then the nuclear accident — displaced 340,000 people, including 160,000 from the nuclear accident alone. The spill contaminated nearly 1,800 square kilometers of land and took a far greater toll than the tsunami in terms of displacing people, according to Reiko Hasegawa, a researcher at the Sciences Po Medialab in Paris.

This imbalance is apparent in the number of indirect deaths (suicides, or illnesses exacerbated by a lack of care, for example) attributable to the tsunami or to the nuclear disaster: The figure is 1.5 times higher for the latter. Of the nearly 2,000 indirect deaths connected to Fukushima, 90% were people over age 65. These same people were among those who agreed to return to three cities that had been evacuated once the order was lifted. For the senior citizens who returned home, it is likely to be a short-lived stay, as they will soon need the care of a younger generation of doctors and nurses who did not want to go back.

Hasegawa believes that the Japanese government is responsible for this difference in impact. Whereas tsunami victims were able to choose between rebuilding their homes on the ruins of their former dwellings or making a new life elsewhere, those affected by the Fukushima nuclear accident were offered no choice but to go home once the area had been decontaminated.

The efficiency and degree of the decontamination process is the subject of heated controversy, which in turn has divided public opinion and compounded the breakdown of family and community relations that so often occurs in the wake of catastrophes.