EPA and German scientists examined air from cities with high rate of bronchitis, allergies and asthma and found that airborne particles induce the problem. People living near coal-burning plants and industry, which emit toxic metals such as zinc, copper, tin and copper were more affected by asthma and allergies than those living in nonindustrial, farming areas.
http://articles.latimes.com/print/2003/may/30/nation/na-asthma30
Also Peden DB. Pollutants and asthma: role of air toxics. Environ Health Perspect. 2002. http://www.ncbi.nlm.nih.gov/pubmed/12194888
Workers at risk are machinists, metal workers, solderers, platers and welder, grinders. First symptoms are coughing, shortness of breath, wheezing and chest tightness. Symptoms are worse at work and improve on off-work days.
Causes are metal dust and fumes from metals such as vanadium, cobalt, chromium, platinum, nickel, tungsten and zinc.
More information:
www.iapa.ca/pdf/fd_asthma_mf_sheet.pdf
Summary: In most developed countries 25% of adults with asthma are current cigarette smokers. Asthma and active cigarette smoking interact to cause more severe symptoms, accelerated decline in lung function, and impaired short-term therapeutic response to corticosteroids.
Rovina N, Gratziou Ch., Pneumon 2006, 19(3): 202-215.