The Limited Test Ban Treaty, restricting nuclear tests to underground, was signed with scientific support from Saruhashi's research on Pacific radioactive fallout.
On August 5, 1963, the United States, United Kingdom, and Soviet Union signed the Limited Test Ban Treaty, an international agreement restricting nuclear weapons tests to underground detonations and banning atmospheric, underwater, and outer space testing.
Katsuko Saruhashi's meticulous scientific research in the years prior played a crucial supporting role in the case for this treaty. Following the 1954 Castle Bravo nuclear test at Bikini Atoll, Saruhashi was tasked with tracing the distribution of radioactive isotopes, particularly cesium-137, through the Pacific Ocean. Her 1958 findings demonstrated that fallout had spread from Bikini Atoll to Japanese waters in under two years, contradicting the prevailing assumption that radioactive contamination would remain localized.
Her data provided concrete, peer-reviewed evidence of the global environmental danger posed by atmospheric nuclear testing, strengthening the international scientific and diplomatic case for restricting such tests. Saruhashi was also known for her willingness to publicly challenge findings from U.S. government scientists that she believed understated the risks of fallout, further amplifying the credibility of independent Japanese oceanographic research.
While Saruhashi was not a signatory or direct negotiator of the treaty, her scientific contributions are widely credited by historians of science as part of the broader body of evidence that made the political case for nuclear test restrictions more urgent and difficult to ignore.