Byssinosis in Hemp Workers

Abstract

Severe byssinosis, chronic cough, and other chronic respiratory symptoms are highly prevalent among workers exposed to dust of raw, biologically retted, soft hemp (Cannabis sativa). Within this group non-reactors and reactors could be distinguished by the absence or presence of a decrease of forced expiratory volume (FEV1) during dust exposure on Mondays. The questionnaire interview underestimated the extent of the workers'' symptoms. Urinary excretion of a major histamine metabolite (1,4-methylimidazolacetic acid; MeIAA) was higher on Monday than on Wednesday in those reactors whose FEV1 decreased on Monday but not on Wednesday. Bronchoconstrictive response to hemp dust exposure on Monday is a result of the release of histamine in the lungs. A deleterious effect of long-term hemp dust exposure upon pulmonary function is highly probable: FEV1 (before dust exposure; adjusted for age and height) was significantly lower among the hemp workers than among a control group (farm workers), although the latter smoked more, and significantly lower among those with byssinosis grades 1 and 2 than among those without or with mild symptoms of disease; 9 out of 20 retired hemp workers had an FEV1 of 1/2 the expected value or less. Among the active workers, abnormally low values of FEV1 (before dust exposure) were only found in reactors and not in non-reactors. Irreversible pulmonary function changes develop primarily in those individuals who are sensitive to the acute bronchoconstrictive effect of hemp dust.