After the U.S. tested a new generation of nuclear bombs at Bikini Atoll in 1954, Saruhashi - using a method she had developed herself - tracked the spread of radioactivity through the Pacific Ocean. The fallout reached Japan's shores within a year and a half, and it had dispersed through the entire Pacific ocean within 15 years. Those results helped encourage the U.S., the UK, and the Soviet Union to sign the Limited Nuclear Test Ban Treaty in 1963. The treaty prohibited underwater nuclear tests along with tests in space or in the atmosphere.
Saruhashi continued to study peaceful nuclear applications for the rest of her career. She was also a tireless advocate for the status of female scientists, and in 1958, she established the Society of Japanese Women Scientists. In 1981, she established the Saruhashi Prize for female scientists who serve as role models to their younger colleagues.
Before her work with radioactive fallout, Saruhashi had developed the first method for accurately measuring the amount of carbonic acid in water. Although few recognized the importance of her discovery at the time, today scientists know that the amont of carbonic acid in seawater has a significant impact on its habitability for marine life, which is why many are alarmed about changes in ocean acidity due to CO2 emissions.
By 1979, Saruhashi had become the executive director of the Geochemical Laboratory, where she had done her groundbreaking work on radioactive fallout. She won several awards for her work, including the Miyake Prize for geochemistry and the Tanaka Prize from the .Society of Sea Water Sciences. Saruhashi passed away in 2007 at the age of 87.