Norfolk, Suffolk, England. A military plane carrying 70kg of a special cadmium zinc sulfide pigment released it 150m downwind of the city. On the ground, chemical defense officials from Porton Down in Whitstable stationed themselves at 40 locations and collected samples. Decades later, the documents were declassified: it was an exercise to test the effectiveness of certain biological warfare methods; the pigments were merely a convenient tracer. The exercise was repeated four more times in early 1964. An independent report in 2002 revealed that the dose to which people in Norfolk were exposed was equivalent to that which could be inhaled in any city over several weeks of exposure.
