The pathologist Walter Bauer was best known for his leadership of the “baby tooth” study. Bauer, with the biologist and environmentalist Barry Commoner, was a founding member of a committee of scientists, doctors and citizens concerned about the consequences of nuclear-weapon testing in the 1950s. The committee grew out of daily lunch meetings of scientists at Washington University, St Louis.

The committee, called the Greater St Louis Citizens Committee for Nuclear Information, led the St Louis Baby Tooth Survey from 1958 until 1970, which collected and studied almost 300,000 baby teeth looking for evidence that human beings were ingesting radioactivity in the fallout from atomic and hydrogen bombs exploded in the atmosphere. Other baby tooth surveys, patterned after the St Louis survey, were undertaken in America and in other countries.

The St Louis study showed that the radioactive isotope strontium-90 was accumulating in the teeth of babies. The strontium was produced as a fission product when nuclear weapons were tested in the atmosphere.

The fission products were widely spread by the winds. Some radioactivity was brought down to Earth, particularly by the rain, and cows ate some of the contaminated grass. Human beings then drank the cows' milk and absorbed the radioactive strontium, which behaves like calcium in the body, into their bones and teeth. To speak out about the serious adverse health effects of nuclear testing during the Cold War in the 1950s took considerable courage.

Mothers, worried about damage to the health of their babies, joined the campaign to end nuclear testing in the atmosphere. This public pressure was a big contribution to the negotiation in 1963 of a ban on the testing of nuclear weapons in the atmosphere and under water, known as the Partial Test Ban Treaty (PTBT), which was eventually ratified by 125 countries.

The first nuclear test took place at Alamogordo in the New Mexico desert on July 16, 1945. Between then and October 10, 1963, when the PTBT came into force, about 518 nuclear tests were conducted in the atmosphere, by China, France, the Soviet Union, Britain and the US.

The total yield of these nuclear tests was about 40,000 times that of the Hiroshima atomic bomb. The radioactivity from them spread all around the Earth resulting in the pervasive pollution of the Earth, damaging the health of people well into the future.

Today, caesium, strontium and plutonium radioactive isotopes from the atmospheric tests pollute our food and water. The pollution would be much worse if the PTBT had not been negotiated. It is estimated that more than two million people will die of cancer because of their exposure to radiation from fallout from atmospheric nuclear tests; many have already died.

Walter Bauer was born in 1925 in Columbus, Ohio, of German parents who migrated to America after the First World War. He took his BSc in chemistry from Ohio State University.

In 1954 he went to the Washington University School of Medicine and after completing a fellowship in surgical pathology he joined the staff at the medical school. In 1973 he was appointed head of the surgical pathology department at the Barnes-Jewish Hospital, St Louis, a post he held until 1987.

He retired from Barnes-Jewish in 1989 and took a part-time appointment at St Louis University School of Medicine as a teacher of surgical pathology. He continued teaching until shortly before he died.

Bauer was an enthusiastic and accomplished runner of marathons, running 17 of them, and a keen mountain climber and fisherman. He died of acute respiratory distress.

His wife, three daughters and a son survive him.

Walter Bauer, pathologist, was born on September 25, 1925. He died on February 2, 2008, aged 82