Occupational asthma due to zinc

We describe a subject who developed asthma symptoms 2 yrs after being employed at a plant where metals were galvanized in heated zinc. The subject was not atopic. Baseline spirometry was normal three months after he left work but there was mild bronchial hyperresponsiveness to methacholine. Monitoring of forced expiratory volume in one second (FEV1) during a day at work showed a maximum fall in FEV1 of 24% at the end of the day and an increase in bronchial responsiveness on the following day. Environmental monitoring revealed that zinc and iron were present in the working environment at concentrations that were lower than the "threshold limit value-short term exposure level" (TLV-STEL) standards. Positive immediate skin tests to zinc sulphate at concentrations of 1 and 10 mg.ml-1 were obtained, although no specific immunoglobulin E (IgE) antibodies to zinc could be found. Skin tests with copper, chromium and cobalt were negative. Specific inhalation challenges were performed, having the subject inhale a solution of zinc sulphate at a 10 mg.ml-1 concentration for 6 min. An immediate reaction was elicited (maximum fall in FEV1 of 23%). We conclude that zinc can cause occupational asthma.