By Jack El-Hai (Regular Contributor)
In 1953, students at Clinton Elementary School in Minneapolis began taking part in a strange ritual. As they stood in a line outside the music room, a man passed a fluoroscope tube over their clothing and shoes. He was testing for traces of a chemical called zinc cadmium sulfide.
Preparations and Chemical Mimesis
For several weeks that year, the U.S. Army sprayed this chemical into the air around the school in an attempt to mimic the effects of a biological warfare attack. Simple to track with air filtering devices and easy to spread by wind currents, zinc cadmium sulfide was a “tracer” that the Army used to simulate how living microbes would spread as biological invaders in cities.
From 1952 through 1969, the Army dropped thousands of pounds of zinc cadmium sulfide in nearly 300 secret experiments conducted in such places as Fort Wayne, Indiana (1964-66); St. Louis (1953, 1963-65); San Francisco (1964-68); Corpus Christi (1962); and Oceanside, California (1967). Remote areas were also targeted: During 1964 the Army dropped zinc cadmium sulfide on Minnesota’s Chippewa National Forest.
Millions of Americans who escaped these experiments received exposure to zinc cadmium sulfide in 1957-58 during the Army’s high-altitude scattering of the chemical from a cargo plane that flew from the Rocky Mountains to the Atlantic and from the Gulf of Mexico to the Canadian border. In all of these tests, the military kept secret the purpose of the studies.
In Minneapolis, the Army’s tests took place over 195 square blocks of the city’s south side. Brigadier General William M. Creasey had earlier told the mayor, Eric Hoyer, that the purpose of the testing would be “to conduct certain meteorological studies regarding the smoke screening of cities from aerial operations.” This explanation was itself a smoke screen for the Army’s real intent to investigate how fake germs could scatter in a northern city whose climate and geography resembled that of many cities in the Soviet Union. These were, after all, some of the darkest days of the Cold War.
A few months later, unknown to Clinton Elementary students, teachers, and their families, machines mounted in trucks and on rooftops began systematically spraying zinc cadmium sulfide into the air of the school’s neighborhood, and about 80 collection boxes on the school’s grounds recorded residue levels.
In the volumes of paperwork from the testing that has surfaced in declassified documents since the 1990s, the Army’s experimenters raise no concerns over the wisdom of exposing countless people to zinc cadmium sulfide. Even so, Army staff conducting the tests in Minneapolis wore protective garb. One resident who lived in the test area in 1953 recalled workers scattering the chemical outside late at night. “They were wearing masks and operating what looked like a big fog machine,” he said. “I asked them what they were doing, and they said they were spraying for bugs…. It was blowing all over, and there was a residue left on the cars.”
In St. Louis, Army researchers mounted apparatus to spray zinc cadmium sulfide from atop the Pruitt-Igoe housing project, a residence for thousands of low-income people. In 2012, researcher Lisa Martino-Taylor presented evidence suggesting that the Army may have mixed radioactive particles with the zinc cadmium sulfide.
Government Assertions v. Scientific Studies
The Army has long maintained that zinc cadmium sulfide is an inert substance, harmless to humans in the concentrations sprayed in the air in Minneapolis, St. Louis, and the other test sites. But at least fifteen studies published before or during the Army’s testing established the danger to human health of one prominent ingredient, cadmium. One, published in the Journal of Industrial Hygiene in 1932, concluded that “cadmium, no matter how small the amount taken into the lungs, causes pathologic changes…. There is, therefore, no permissible amount of cadmium” safe for human exposure. Cadmium is now a suspected human carcinogen that causes kidney damage, and it also can contribute to liver disorders, nervous system problems, and perhaps reproductive health problems.
In 1995 a Toxicology Committee of the National Academy of Sciences, in a Congressionally ordered review of the Army’s testing, observed that research on potential dangers was scanty and based only on animal studies. It concluded, however, that the Army did not endanger the public through exposure to the zinc cadmium sulfide. Critics of that review, however, pointed out that the chemical can persist in the soil and in homes for a long time and that its resuspension by people’s activities and the wind may have lengthened exposure times long beyond what the Army expected.
More than 60 years after the experimentation began, the U.S. Army has not acknowledged the possibility of harm from the testing and has commissioned no follow-up studies.
Cole, Leonard. The Eleventh Plague: The Politics of Biological and Chemical Warfare. Holt, 1996.
LeBaron, Wayne. America’s Nuclear Legacy. Nova Science Publishers, 2013.
Subcommittee on Zinc Cadmium Sulfide, National Research Council, et. al. Toxicologic Assessment of the Army’s Zinc Cadmium Sulfide Dispersion Tests. National Academies Press, 1997.