Further studies of respiratory health of wool textile workers. Final report of a Health and Safety Executive funded project

We have previously reported the relationships between respiratory symptoms and the concentration of inspirable wool mill dust in wool textile mills in West Yorkshire,where inspirable dust is that fraction of the airborne dust passing into the nose or mouth. In the present study we have calculated the estimated relative risks of these symptoms in relation to dust concentrations in current job for different sections of the workforce. We have also carried out studies of the influence of exposure to dust in wool textile mills on chest radiographic appearances, and on lung function. Laboratory studies have also been performed to assess the inflammatory and immunological potential of wool mill dusts in rodent models and, finally, further analysis of existing data has enabled us to characterise some of the temporal relationships of the symptoms reported by the workTo estimate risks of symptoms in relation to exposure to dust in wool textile mills we have analysed further the data from the earlier study of 2151 wool textile workers. Persistent cough and phlegm, rhinitis, conjunctivitis, and breathlessness were related to inspirable dust concentration in current job.Different relationships for estimated relative risks of these symptoms were found for the three main groups in the industry; European men, European women and Asian men. Overall, the risk of having each symptom increases most rapidly over the dust concentration range 0-5 mg m-3. Slower increases in risk occur over subsequent increments in dust concentration.To study the influence of wool dust on chest radiographic appearances and lung function we examined 634 employees of five wool textile mills in which workers in selected jobs were examined. Four of these mills produced carpet yarns, and the other mill produced worsted tops. Opening, blending, worsted carding and carpet yarn backwinding were the particularly dusty processes to be found at these mills and the workforce on average was similar in terms of age, sex, ethnic group and other characteristics to the original, larger study population. Full-size chest radiographs were taken, and FEV,, FVC and single breath gas transfer factor (TLco) measured. Skin prick tests to grass pollen, house dust, Dermatophagoides pteronyssinus and two extracts of wool were performed. The radiographs were read by a panel of doctors experienced in the use of the ILO Classification.We found very few radiographic abnormalities in these workers (prevalence of category 1/1 or greater small rounded opacities 1.1% to 3.0%, depending on the reader) and none that could be shown to be associated with exposure to high dust concentrations in the wool textile industry. Smokers had more opacities than non-smokers. On the other hand lung function was shown to be rather inconstantly related to dust exposure in some groups of workers. In European women the FEV^FVC ratio decreased significantly (P<0.05) with increasing dust concentration in the current job; FVC demonstrated a similar but statistically insignificant relationship in Asian men.This indicates that exposure to dust in wool textile mills may adversely affect lung function. The reasons for demonstrating this effect only in some groups may be either that the effect of these exposures on lung function is slight, or that the estimates of past exposure to wool dust we were able to make were inadequate. We did not demonstrate that wool dust can cause a clinically important loss of lung function, but some additional work reconstructing exposure histories might enable a more accurate estimate of the functional effects to be made.were more likely than others to suffer respiratory symptoms but were not more susceptible than others to the effects of exposure to wool mill dust. Allergy to wool was detected by skin testing in very few individuals.We conclude from this that exposure to dust in wool textile mills is associated with a non-specific type of illness affecting eyes, nose and lower respiratory tract. Asthma-like variation in breathlessness was rare, though in a small number of individuals appeared to be related to exposure to dust. Byssinosis-like tightness in the chest which is worse on first day back at work after days off was also rare (15 individuals), and we conclude that the illness related to wool dust in these factories is in the majority of cases not like byssinosis. Some men working in the dyeing and scouring sections had symptoms of asthma and poor lung function, more likely related to the chemicals used for scouring than to wool dust. A few other workers had symptoms suggestive of humidifier fever (chills worse on first day back at work), often accompanied by rhinitis, cough and wheeze. Their illness did not appear to be related to wool dust, and some local investigations of the workplace including the humidifier systems would be appropriate.In the laboratory we found that intratracheal injection of inspirable wool mill dusts into the lungs of laboratory rats caused an acute proliferation of neutrophils and lymphocytes, which declined rapidly to near normal values after 1-3 days. This inflammatory response to some constituent of the dusts, also present in dust leachates, varied from one mill to another and this variation may have been partly associated with the degree of processing and the aerodynamic size of the dust particles. Clumps of predominantly mononuclear cells (lymphocytes and macrophages) also appeared between 3 and 14 days post-exposure, indicating a possible immunological component to this response. This was investigated further by injecting mice with wool dust and measuring the proliferation of spleen cells from treated and untreated mice following incubation with dusts, dust extracts and lipopolysaccharide (LPS), the principal constituent of bacterial endotoxin. There was a marked proliferation to dusts from early processes (opening) and combing, but much less response to dust from back winding. However, there was a non-specific response by control spleen cells from untreated mice to dusts and their extracts, due possibly to B cells responding to endotoxin. In practice we were only able to detect small quantities of endotoxin, probably because of an inhibitory substance in the dusts. The high non-specific response of normal spleen cells to dusts and leachates also suggests that more endotoxin could be present than was detectable by the Limulus assay. We also detected a diffusible agent in wool dust, which was able to cause cell detachment and lysis in alveolar epithelial cells. If bronchial cells respond similarly, this might help explain the presence of respiratory symptoms in wool textile workers.The findings indicate a need for an occupational exposure limit for dust in wooltextile mills lower than the nuisance dust limit (10 mg/m3).Evidence is presented, on which it should be possible to base an occupational exposure limit for the wool textile industry.Possible lines of investigation to answer remaining questions include the reconstruction of exposure histories to enable a more reliable estimate of the lung functional effects of dust to be made and further laboratory studies of the dust in wool textile mills to determine the role of endotoxin and other components in the inflammatory and allergic response. ""