An international agency set up to monitor for nuclear tests is collecting extensive data on the levels of radionuclides in the air in and around Japan and the Asia-Pacific and transmitting this daily to its member states. The data would be of enormous public interest as it would provide a far fuller picture of the extent and spread of any current or future radioactive release from the major Japanese nuclear accident now under way. But none of these data are being released to the public, Nature has learned.

The worldwide network of radionuclide particulate monitoring stations is operated by the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), a Vienna-based body setup to build a verification regime for a global ban on the testing of nuclear weapons, so that this is operational when enough of the organization’s member states have ratified the treaty for it to enter force. The organization monitors radionuclide, seismic, hydroacoustic, and infrasound characteristics at stations across the globe to check for the tell-tale signals of a nuclear bomb test.

The CTBTO has 60 radionuclide particulate monitoring stations currently in operation, and two of these are in Japan, near Tokyo, while there are dozens of others, often on islands, throughout the Asia-Pacific region (see map). These stations monitor the air continuously, and so will have extensive data on any radionuclides detected during the ongoing nuclear disaster that followed the 9.0-magnitude earthquake, and destructive tsunami, that hit Japan on 11 March.

Radionuclide monitoring stations of the CTBTO International Monitoring System in the Asia-Pacific region (Map credit: CTBTO)

The CTBTO does make available its hydroacoustic and seismic data – among the most reliable and rapid around – for the purposes of tsunami warnings, and indeed these data helped contribute to the rapid alerts issued by tsunami warning systems following the 9.0-magnitude earthquake – the agency’s member states agreed to this following the 2004 Indian Ocean tsunami. But the CTBTO has no mandate for making radionuclide data publicly available for the purposes of monitoring nuclear accidents, because its member states have not yet agreed for it to have this role — it does, however, have a mandate to release radionuclide data within its mandate for detecting nuclear tests (see for example, “North Korea’s ignoble blast“).

Yet it’s radionuclide network is also well-adapted to monitoring levels of radiation in the fallout from nuclear accidents – it is still picking up background levels of radioactive Caesium-137 (which has a 30-year half-life) from the 1986 Chernobyl reactor explosion in the Ukraine, for example – and its website lists such work as one of the civilian benefits of its network of monitoring stations. Each particulate monitoring station sends one gamma ray spectrum per day, a two-dimensional plot showing which radionuclides, and how much of each, occur in its sampling – as radionuclides decay they emit specific energies of gamma radiation which act as signatures allowing radionuclides to be identified.

The CTBTO’s data processing is geared towards detecting the tiny quantities of radioactivity – micro to tens of Becquerels, relevant to its mandate for detecting nuclear tests. The levels from nuclear accidents relevant to public health radiation protection are many orders of magnitude higher, but its sensor network nonetheless does detect and quantify them, explains Lassina Zerbo director of the CTBTO Preparatory Commission’s International Data Centre Division in Vienna.

Although the Vienna centre doesn’t process the nuclear accident relevant data itself, it does transmit the raw data to member states. Nuclear accidents produce a spectrum of radioactive fission products – including various radioisotopes of iodine, caesium, zirconium – and the network can pick up all of them, says Zerbo.

“The data is being sent continuously [to member states], and we are monitoring the situation, our people were here specifically for this over the weekend,” says Annika Thunborg, chief spokesperson for the CTBTO’s Preparatory Commission. The CTBTO is monitoring carefully the nuclear disaster, she adds, and has offered the Japanese government its assistance in it’s areas of expertise, which also include modelling of radiation plumes under different weather patterns.

But the agency, which like all intergovernmental organizations, answers to its member states, is not allowed to make data about nuclear accidents public. “We have a mandate from our 182 member states to communicate seismic data to the outside world,” she says, “When it comes to this radionuclide data [for monitoring nuclear accidents], we don’t have such a mandate, so I can’t tell you, for example, what it is that we are finding.” Even for seismic and hydroacoustic data for the purposes of tsunami warning systems, which saves lives, there were some countries that in the past resisted the idea of making it public. There has been some discussion among member states about disseminating radionuclide data more widely.

Zerbo says that the CTBTO’s radionuclide monitoring service would be well-placed to take on any international role in monitoring nuclear accidents for radiation protection purposes. “Japan and other countries have their own national radiation protection services, but where we could be useful is the worldwide nature of our monitoring network, because countries lack monitoring capabilities outside their own countries.,” he says, “We are the only truly worldwide radionuclide monitoring network.”

For full coverage of the Fukushima disaster, go to Nature’s news special.