Industry or sector-oriented studies
Studies that examine an industry or sector have the advantage that the exposure is often described and categorised. The disadvantage is that the participants may differ from the normal population (selection bias), which can result in an underestimation of risk.
Exposure to quartz occurs in several industries, such as building and construction, the steel industry, mining, and during tunnelling and sandblasting. A German study of miners exposed to quartz (n = 1 421) confirms that exposure to quartz (1 mg/m³ over the course of 220 eight-hour shifts per year) may increase the risk of stage I COPD (OR 1.8, 95 % CI 1.3 – 2.6), and it is estimated that exposure to 0.1 mg/m³ (Norwegian threshold value) over a 40 year period will result in reduced pulmonary function (15). The study shows an elevated risk of COPD at current levels of exposure, where new rock-drilling technology (higher rate of revolutions per minute) may conceivably produce a greater number of finer particles. Increased prevalence of COPD has previously been shown in a Norwegian study of tunnel workers from 2001 (10) and in a large-scale Swedish study of construction workers from 2004 (24).
The extent to which textile workers have an elevated risk of COPD is a matter of debate, as the findings from previous studies have been at variance. In a study from 2010, 447 textile workers were followed up for 25 years and it was found that previous exposure to endotoxin (median 2 086 – 1289 EU/m³ for 1981 – 92) was associated with reduced forced expiratory volume after one second (FEV₁), while recent exposure (median 98 EU/m³) was associated with chronic shortness of breath and cough (16). Although the data on smoking were incomplete, the researchers have measured exposure and adjusted for other possible causal factors. There is still a need for further studies, but the results give grounds to suspect an increased risk of COPD in textile workers.
Firefighters are periodically exposed to high-grade exposure, but this has been insufficiently studied. An increased risk of COPD was found in firefighters who were involved in the rescue and recovery work following the terror attacks on the World Trade Center (17). In a later study no such correlation was found for New York firefighters who were exposed for five years, but recruited after 2003 (18). The 9/11 exposure was typically extremely high-grade, complex and consisted of pulverised cement, glass, lead, polycyclic aromatic hydrocarbons, metals and polychlorinated biphenyls, and had a pH of around 12. While it is still unclear whether firefighters in general have an elevated risk of COPD, the 9/11 studies may be relevant for the assessment of exposure to high-grade, complex, alkaline dust.
The effects of another type of alkaline dust have been investigated in a large-scale prospective study of cement production workers from eight European countries (19). In the Norwegian-led study, 4 998 employees were followed up for 4.6 years and a dose-response relationship was found between level of dust and reduced FEV₁/standing height² per mg/m³ and year, with 9.7 (95 % CI 7.6 – 12) for the lowest category of exposure (0.6 – 1.6 mg/m³) and 19 (15) – (22) ml for the highest (5.4 – 14 mg/m³). Job-exposure matrices were used to categorise exposure, and asthmatics were excluded from the analyses. A study of 171 cement workers from 2014 found that a reduction in dust levels (from 10.6 mg/m³ to 5.8 mg/m³ total dust) resulted in a reduced prevalence of COPD (from 22.6 % to 1.9 %) after two years (20), thereby indicating an effect from dust-reducing measures. The results provide sound evidence for an elevated risk of COPD in the cement production industry, and are also considered relevant for employees in the building and construction industry.
A three-year follow-up of Norwegian employees (N = 383) working with nitrate fertiliser production showed reductions in FEV₁ of 18 ml/year (95 % KI 10 – 27) with an exposure of 1.1 mg/m³ and 0.2 mg/m³ for inhalable and thoracic aerosols (21). There was no correlation between reduced pulmonary function and exposure, which indicates that factors other than the measured aerosol fraction are of significance. There is a need for further studies, but the results may give rise to the suspicion that work at the fertiliser factory entails an increased risk of COPD.
In a study from 2010 which followed up 2 620 workers at Norwegian metallurgical smelters for five years and used job-exposure matrices to characterise exposure, FEV₁/standing height² fell with rising dust level (22). Annual reduction in FEV₁/standing height² for a worker (1.80 cm tall) was 5.7 ml/year in smelters that produced silicomanganese, ferromanganese and ferrochrome, whereas it was 6.4 ml/year for a non-smoking worker in a smelter that produced ferrosilicon and silicon metal. FEV₁ was lower for women than for men. In a review article the authors have concluded that there is sound evidence of an increased prevalence of COPD also in non-smokers in the metallurgical smelting industry (25).