Zinc cadmium sulfide is a mixture of zinc sulfide (ZnS) and cadmium sulfide (CdS). It is used for its fluorescent properties.
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Use
Operation LAC (Large Area Coverage), was a Chemical Corps operation in 1957 and 1958 which dispersed microscopic zinc cadmium sulfide (ZnCdS) particles over much of the United States. The purpose was to determine the dispersion and geographic range of biological or chemical agents. Zinc cadmium sulfide was used as it could be easily detected. It was not thought at the time to pose any particular health risk.
It was also used in an experiment against unwilling civilians in the UK
Health effects
Anecdotal evidence exists of ZnCdS having adverse health effects as a result of LAC. However, a 1997 U.S. government study, done by the U.S. National Research Council stated, in part, "After an exhaustive, independent review requested by Congress, we have found no evidence that exposure to zinc cadmium sulfide at these levels could cause people to become sick." It said that the material was dispersed at very low levels, and people were exposed to higher levels in typical urban environments. Such testing of ZnCdS remains controversial, and one critic accused the Army of "literally using the country as an experimental laboratory".