Cyanide intoxication among silver-reclaiming workers.

Thirty-six former workers in a silver-reclaiming facility who had been exposed over a long-term to excessive levels of cyanide were studied to determine acute and residual toxic reactions. The study involved physical examinations, laboratory studies, and a questionnaire to determine levels of exposure, symptoms during employment, and current symptoms. Questionnaire data showed that during the time of active employment there was a high prevalence of symptoms that are consistent with acute cyanide toxic reactions. A significant positive trend for prevalence of cyanide-related symptoms measured against levels of exposure was demonstrated, supporting a dose-response effect. Some symptoms occurring seven or more months after exposure had ceased also exhibited a dose-response trend. Mild abnormalities of vitamin B12, folate, and thyroid function were detected and suggest long-term cyanide effects.