My attention was caught this week by a headline on the BBC website: Fukushima fish still contaminated from nuclear accident. This is interesting on two levels; first that it is the flooding of the Fukushima nuclear generating plants which is remembered, rather than the hugely destructive tsunami resulting from the Tohoku earthquake, and second that there remains such a fear of rather low levels of residual radiation.
First, the March 2011 earthquake which led to the disaster. At just over 9.0 on the Richter scale, this was the biggest earthquake ever known to have hit Japan, and one of the most powerful recorded over the last century. The tsunami was over 40 metres high in places and reached up to ten kilometres inland in the Sendai area. Aerial video footage of the catastrophe was shocking.
Recently, the official death toll stood at 15,870, with a further 2,814 people missing; the number missing alone was almost as high as the death toll in the 9/11 attacks on the World Trade Centre and Pentagon. While being an order of magnitude smaller than the loss of life during the 2004 Indian Ocean tsunami (itself caused by an even more massive undersea earthquake), the casualties and devastation were particularly shocking as they occurred in Japan, a rich country seemingly well prepared for natural disasters.
One of the effects of the tsunami was to flood backup diesel generators needed to provide cooling for reactors in the Fukushima Daiichi complex; the reactors themselves had automatically shut down when the earthquake struck. Prior to this catastrophic loss of cooling, the reactors and containment vessels had sustained relatively minor damage. Because there was not an additional level of backup, and because the power supply for the cooling system was inadequately protected by the sea wall, a relatively small incident at a time of major disaster became the major part of the story.
Eighty thousand people were evacuated from a 20 km exclusion zone centred on the complex, doubtless a sensible precaution in the early stages when the extent of the problem was not properly appreciated. In March this year, about 16,000 were allowed to return to some areas, but it is unclear how many have actually done so. The abstract fear of radiation seems to be rather worse than the practical reality.
Three nuclear reactors suffered meltdowns, and there seems to have been ongoing minor leakage of radioactivity from these. The BBC story reports the official position that 40% of fish caught near Fukushima are ‘regarded as unfit for humans under Japanese regulations’ (a study published in the journal Science: Fishing for answers off Fukushima). The last three words in the quote are particularly important.
Radioactive caesium isotopes (Cs-134 and Cs-137) in fish caught in the area were measured, and found to be relatively elevated. Normally, these isotopes are eliminated from fish tissues quite quickly, so the continued higher levels indicates either that bottom-feeders are accumulating more caesium via sediments, or that more radioactive Cs is leaking into the seawater itself (sediments seem to be the major source, judging by the fish species mainly affected).
However the headline, although not inaccurate, is a little deceptive. Later on in the story we learn ‘And while the 40% figure for unsafe catch in the Fukushima prefecture may sound alarming, the bald number is slightly misleading. Last April, the Japanese authorities tried to instil greater market confidence by lowering the maximum permitted concentration of radioactivity in fish and fish products from 500 becquerels per kilogram of wet weight to 100 Bq/kg wet. This tightening of the threshold immediately re-classified fish previously deemed fit as unfit, even though their actual contamination count had not changed.’
So, although 500 Bq/kg was deemed safe prior to the accident (and it was already low by international standards), the Japanese authorities seem to have taken the same superficially-attractive but misguided path as policymakers have done in similar situations elsewhere. Seeking to reassure consumers by introducing arbitrarily stringent safety standards actually has the opposite effect: the apparent need for higher standards simply reinforces the perceived risk.
It is recognised by many experts that radiation exposure standards are already set unnecessarily low, based on the mistaken assumption that there is no minimum safe dose. In fact, there is evidence that very small doses can actually be beneficial (in the same way as highly toxic compounds can also improve health at low enough levels). Knowledge of hormesis, as this phenomenon is known, should have resulted in higher limits for acceptable radiation exposure than are currently in place and, in the case of the Fukushima incident, would have meant a much smaller exclusion zone being declared.
Instead, disruption has been greater than needed, and it will be difficult for the authorities to justify a return to the previous acceptable limit for radioactivity in fish. No lives have been saved, health has not been improved, and indeed it is likely that the psychological impact of the forced evacuation and fear of the risk will have caused considerable harm. Knock-on effects have also been significant, in particular the knee-jerk reaction of the German government to abandon nuclear generation, which will have large implications for carbon dioxide emissions.
Unfortunately, governments behave no more rationally than most voters. It is tempting to hope that policies aimed at safeguarding public health would be based on hard evidence, but there seems little chance of this happening. In misguided attempts to do what they think public opinion demands, politicians too often make things worse.
The Scientific Alliance
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