Follow-up study of respiratory function in hemp workers.

A 3-year follow-up study was performed on 38 women and 28 men from the originally studied textile workers employed in a soft hemp processing mill. Acute and chronic respiratory symptoms and ventilatory capacity were recorded during the cross-sectional and the follow-up studies. Maximum expiratory flow-volume (MEFV) curves were obtained on these workers, and forced vital capacity (FVC), 1-second forced expiratory volume (FEV1) and flow rates at 50% and at 25% of the VC (FEF50, FEF25) were measured. High prevalences of acute and chronic respiratory symptoms persisted at the follow-up study. In particular, high prevalences of byssinosis were documented at both studies (women: 47.4% and 47.4%; men: 64.3% and 67.9%, respectively). Statistically significant mean across-shift reductions were recorded for all ventilatory capacity tests at the initial study. A large mean annual decline was calculated for FEV1 in women and for all ventilatory capacity parameters in men; these declines were greater for workers with symptoms of byssinosis than for those without. The accelerated decline in FEV1 noted in the women workers, who were predominantly nonsmokers, suggests an independent hemp effect. Exposures in the work environment were measured with Hexhlet filters and revealed very high dust concentrations (mean total: 21.4 mg/m3, 22.4 mg/m3; respirable: 8.4 mg/m3, 9.9 mg/m3) at both initial and follow-up studies. These levels are much higher than those found in mills processing organic materials in North America. Our data demonstrate that work in the hemp industry, particularly in small poorly regulated mills, continues to have deleterious effects on respiratory function.