Enver Tohti remembers the week that it rained dust. That summer of 1973 he was in elementary school in Xinjiang Province, China’s westernmost region, which is inhabited mostly by Uygurs, one of the country’s minority ethnic groups. “There were three days that earth fell from the sky, without wind or any sort of storm. The sky was deadly silent—no sun, no moon,” he recalls. When the kids asked what was happening, the teacher told them that there was a storm on Saturn (its Chinese name translates into “soil planet”). Tohti believed her. It was only years later that he realized it was radioactive dust raised by the test detonation of a nuclear bomb within the province.

Three decades on, Tohti, now a medical doctor, is launching an investigation into the toll still being taken—and one that the Chinese government steadfastly refuses to acknowledge. A few hundred thousand people may have died as a result of radiation from at least 40 nuclear explosions carried out between 1964 and 1996 at the Lop Nur site in Xinjiang, which lies on the Silk Road. Almost 20 million people reside in Xinjiang, and Tohti believes that they offer unique insight into the long-term impact of radiation, including the relatively little studied genetic effects that may be handed down over generations. He is establishing the Lop Nur project at Sapporo Medical University in Japan with physicist Jun Takada to evaluate these consequences.

“It is a sad opportunity, but it is an opportunity nonetheless to both learn something new and replicate what we think we are seeing elsewhere,” observes Anders Møller, who co-directs the Chernobyl Research Initiative (CRI) and is based at the National Center for Scientific Research in Paris.

Takada has calculated that the peak radiation dose in Xinjiang exceeded that measured on the roof of the Chernobyl nuclear reactor after it melted down in 1986. Most damage to Xinjiang locals came from detonations during the 1960s and 1970s, which rained down a mixture of radioactive material and sand from the surrounding desert. Some were three-megaton explosions, 200 times larger than the bomb dropped on Hiroshima, says Takada, who published his findings in a book, Chinese Nuclear Tests (Iryo­ka­gakusha, 2009).

In the early 1990s Takada, who studied radiation effects from tests conducted by the U.S., the former Soviet Union and France, was invited by scientists in Kazakhstan, which borders Xinjiang, to evaluate the hazard from Chinese tests. He devised a computer model to estimate fallout patterns using Soviet rec­ords of detonation size and wind velocity as well as radiation levels measured in Kazakhstan from 1995 to 2002. Takada was not allowed into China, so he extrapolated his model and used infor­mation about the population density in Xinjiang to estimate that 194,000 people would have died as a result of acute radiation exposure. Around 1.2 million received doses high enough to induce leukemia, solid cancers and fetal damage. “My estimate is a conservative minimum,” Takada says.

The figures came as little surprise to Tohti. Ironically, as a teenager, he was proud that his province was chosen for tests marking China’s technological and military progress. His view changed when he became a physician and saw a disproportionate number of malignant lymphomas, lung cancers, leukemia cases, degenerative disorders and babies born with deformities. “Many doctors suspected this was connected to the tests, but we couldn’t say anything,” Tohti recalls. “We were warned away from researching by our superiors.”

Tohti was only able to speak out in 1998, when he moved to Turkey, ostensibly as part of his medical training. There he joined forces with a team of British documentary filmmakers whom he smuggled back into Xinjiang as tourists. Together they uncovered medical records showing that cancer rates were 30 to 35 percent higher in the province than the national average.

Tohti and Tanaka’s Lop Nur project could fill in many gaps left open by analyses of other mass radiation poisonings. In studying the Chernobyl aftermath, Møller and his colleagues found that animal populations in the area still show a significant decline in numbers and an increase in genetic mutations, in contrast to earlier reports of recovering wildlife.

But pinning down generational effects in humans has proved difficult, because relatively little time has passed since the disaster and a small number of people were affected, explains Timothy Mousseau, a CRI co-director based at the University of South Carolina. Still, accumulating data suggest “that there is serious genetic damage in people living in these contaminated areas,” he says. For this reason, Mousseau is optimistic that the Lop Nur project will build up a dossier of genetic evidence. The difficulty, Møller and Tanaka agree, will be deciphering whether effects on second and third generations are inherited genetic mutations or are caused by exposure to contaminated water and soil.

For Tohti, the priority is helping the sick. In March the French government announced that it would compensate civilian victims of its nuclear tests, which were conducted in Polynesia. In 2008 the Chinese state news service Xinhua reported that its government is paying undisclosed subsidies to military personnel involved in the tests. Tohti wants aid extended to affected civilians, adding that 80 percent do not have health care. “Right now, they can’t afford treatment,” he says. “So all they can do is wait to die.”

The Lop Nur project is just the tip of an international iceberg, remarks Abel Gonzalez of the Argentine Nuclear Regulatory Authority in Buenos Aires. Radiation researchers have had easy access to only three sites where nuclear blasts occurred—the U.S.’s site Bikini Atoll, the Soviet Union’s Semipalatinsk site in Kazakhstan and France’s site in Polynesia—and these areas represent just a small fraction of the approximately 500 atmospheric tests the world has seen. “We have a moral responsibility to investigate all nuclear test sites,” Gonzalez says. Certainly for the Xinjiang people affected by the Lop Nur tests, truer words have never been spoken.

When Population Bombs Go Nuclear

Does repeated exposure to radiation affect germ-line cells such that the same mutations get passed on, generation after generation? That is one question the Lop Nur project hopes to answer. The other two major instances of a large population exposure to radiation—the atomic bombs dropped over Hiroshima and Nagasaki—have produced no generational effects in survivors, points out Roy Shore, chief of research at the Radiation Effects Research Foundation in Hiroshima. But he adds that the exposure patterns vary. “The atomic bomb was an almost instantaneous exposure,” Shore explains. “We still need good data on radiation that has been delivered time and time again, over a long period—there may be different effects.”

Note: This article was originally printed with the title, "Blasts from the Past."