Respiratory Health Program: Occupational Risks
Input: Occupational Risks
Risk of Airway Diseases
Asthma is an inflammatory airways disease causing episodic, reversible airways obstruction. “Work-related asthma” refers to both new-onset asthma caused by work and pre-existing asthma exacerbated by work. New-onset asthma associated with work can be occupational asthma caused by immunological sensitization to agents in the workplace; or irritant-induced asthma caused by irritant exposures in the workplace. Work-exacerbated asthma refers to exacerbation of pre-existing asthma by workplace exposures. Work-related asthma was recognized by Hippocrates (460 – 370 B.C.) and it was associated with occupations involving work with metals, textiles, and animals including fish. Today work-related asthma is commonly encountered in isocyanate production, in healthcare workers who use natural rubber latex gloves (although this is becoming less of a problem due to the substitution of other materials), and among office workers due to poor indoor environmental quality. It is estimated that between 15 and 30 percent of asthmatics have new-onset adult asthma or work-exacerbated asthma. Thus, over two million workers in the United States suffer from work-related asthma.
Chronic obstructive pulmonary disease (COPD)
Chronic obstructive pulmonary disease refers to chronic bronchitis, emphysema, and combined presentations of these two diseases. Chronic obstructive pulmonary disease is a leading cause of morbidity and mortality in the United States and world-wide. In 2003, 10.7 million United States adults were estimated to have COPD. However, close to 24 million adults were estimated to have impaired lung function, suggesting under-diagnosis of COPD. Although often thought of as a disease caused by cigarette smoking, it is well-recognized that COPD is also caused by occupational exposures. It has been estimated that 15% of COPD is attributable to occupation. Coal mine dust and crystalline silica encountered in industries such as mining and construction are known risks. A study of participants in the Third National Health and Nutrition Examination Survey found increased risk for COPD in a number of industries including rubber, plastics, and leather manufacturing; utilities; building services; textile manufacturing; and construction.
Risk of Interstitial Lung Diseases
Coal mine dust
As already noted, coal mine dust exposure can cause COPD. However, it is best known for causing coal workers’ pneumoconiosis (CWP), a type of lung disease affecting the tissues and gas-exchange surface of the lung (interstitial lung disease). CWP usually develops slowly, taking 10 years or more from initial exposure to onset of disease. It causes changes in the chest radiograph and, in more serious cases, can cause shortness of breath, loss of pulmonary function, and even death. In the United States, the Coal Mine Health and Safety Act of 1969 (42 CFR Part 37) mandated a comprehensive set of measures to prevent CWP. Enactment was followed by a marked reduction in the prevalence of CWP in long-term coal miners. In the period 1970-1974, about 32% of miners with 25 or more years of tenure in coal mining who participated in a national x-ray surveillance program had evidence of CWP. By the period 1995-1999, prevalence in this group had dropped to about 4%. Unfortunately, in the recent period 2005-2006, prevalence increased to 9%. In addition, advanced cases have recently been detected in miners in their 30s and 40s. Especially in view of the increasing use of coal as an energy source and the predicted growth of coal mining, protecting coal miners from respiratory disease continues to be an important and ongoing priority.
Silica, also known as silicon dioxide, is the most common mineral on earth. Inhaling dusts that contain crystalline forms of silica can cause a fibrosing interstitial lung disease called silicosis. Silicosis usually takes at least 10 years after exposure to develop. However, it can develop more quickly, especially after large exposures. Quartz is a common type of crystalline silica and is a large component of many types of rock. Inhalation exposure can occur in many kinds of work, including tunneling, quarrying, mining, construction, roadway repair and demolition, sandblasting or any type of work that breaks up quartz-containing rock. Cristobalite exposure can occur in foundry work as a result of heating amorphous silica. In addition to causing silicosis, crystalline silica exposure has been associated with pulmonary function impairment and COPD. Silica has also been classified by the International Agency for Research on Cancer (IARC) as a known human carcinogen. Crystalline silica is thought to damage lung tissue in large part as a result of oxidant mechanisms, with freshly fractured crystalline silica is being more potent than aged materials. Silica-induced diseases can be prevented by reducing exposures. It is encouraging that deaths from silicosis have fallen from more than 1060 in 1968 to less than 170 in 2005.
Asbestos is a commercial term that refers to six types of fibrous minerals, including one serpentine (chrysotile) and five amphiboles [crocidolite (riebeckite asbestos), amosite (cummingtonite-grunerite asbestos), anthophyllite asbestos, tremolite asbestos, and actinolite asbestos]. Asbestos mineral fibers are flame and heat resistant, pliable, strong, refractory to corrosive chemicals, and provide insulation. Because of its ability to insulate from heat and protect against fire, asbestos has been widely used as a building material. It has been especially important in the shipbuilding industry. It has also been woven into fabric to make fireproof, protective textile products, such as fireproof blankets and suits, It has been used as a brake liner (e.g., in automobiles and railroad rolling stock) and for engine gaskets and has been used to make filters (e.g., in the chemical industry). Although known and used for its fire resistant properties as early as 3000 B.C., asbestos, use of the material grew markedly in the U.S. during the 20th century, peaking from the 1950s through the 1980s. Although its use in the US has largely disappeared, exposure continues to occur due to renovation or demolition of existing building stock or through exposure to asbestos-containing products such as brake linings or asbestos-containing cement products that continue to be imported. Inhalation of asbestos fibers can have many adverse health effects. Because these develop slowly, usually presenting a decade or more after exposure, asbestos-caused diseases remain an important problem. Asbestos fibers can cause asbestosis, a fibrosing interstitial lung disease. They can also penetrate through the lung tissue to the pleura, which are the tissues lining the lungs and chest cavity. In the pleura, they can cause conditions including pleural effusions (fluid collections), pleural plaques, and diffuse pleural fibrosis. Asbestos fibers are also a cause of lung cancer. Risk increases multiplicatively if an exposed person also smokes. Another much-feared type of cancer caused by asbestos is mesothelioma, which arises in the pleura or peritoneum (lining of the abdominal cavity). Mesothelioma usually cannot be cured and thus has a high fatality rate. NIOSH has recently developed a “Roadmap” for research in the area of asbestos fibers and other elongated mineral particles.
Flock consists of short fibers that are cut from long filaments and glued to backing material such as cloth to provide a fuzzy, carpet-like surface texture. They are usually prepared from synthetic materials such as nylon, rayon, or polypropylene. The cutting process results in formation of airborne particles or fibers in the respirable range. Inhalation of flock dust has been associated with an interstitial lung disease called flock workers’ lung. NIOSH has made recommendations to companies that manufacture flock and make flock containing products that aim to reduce workers’ exposure to flock dust. These include: engineering controls and alternative methods to cleaning the workplace with compressed air, which re-aerosolizes settled dust.
Beryllium (Be): It has been estimated that more than 134,000 workers in the United States are involved in the manufacture, machining or manipulation of beryllium or beryllium-containing materials. Downstream from manufacture and primary machining jobs are a wide variety of occupations that include: dental technicians, jewelers, precious metal reclamation workers, welders, plumbers, electricians, and others. Beryllium exposure can result in immune sensitization; it is thought that continuing exposure in the face of sensitization can cause chronic beryllium disease (CBD). In CBD, immune responses to inhaled beryllium lead to lung damage. In addition to inhalation exposure, skin exposure is also suspected of being an important route for beryllium sensitization. Beryllium has also been classified by IARC as a known human carcinogen.
Risk of Infectious Lung Diseases
Tuberculosis is a massive worldwide problem. It is estimated that more than one third of the world’s population is infected and that about 1.8 million people die of the disease each year. Fortunately, the U.S. has a much lower prevalence of infection. It was estimated in 2002 that between 9.6 and 14.9 million people in the U.S. had latent TB infection and that there are 25,000 new infections annually, of which ~10,000 occur among immigrants from countries where the disease is endemic. Occupations at highest risk are healthcare professionals who treat TB patients and prison guards and other who provide service to populations with high rates of TB.
Avian and Pandemic Influenza
Avian influenza (H5N1, for type-5 hyaluronidase/type-1 neuraminidase) is an influenza A virus subtype that occurs mainly in birds. Influenza A virus H5N1 does not usually infect people, but human cases of H5N1 infection have occurred. Most of these cases have resulted from direct or close contact with infected poultry or contaminated surfaces. A few rare cases of human-to-human spread of H5N1 virus have occurred, but transmission has never continued beyond one person. The mortality rate of avian flu in affected humans exceeds 50 percent. Pandemic influenza can occur when a strain of influenza A undergoes antigenic shift, potentially creating a virulent new strain for which human populations have little or no immunity. Pandemic influenza can spread easily from person to person, causing a global outbreak, or pandemic. Some pandemic strains have caused very severe illness, such as during the outbreak of 1918. Given the severity of disease caused by H5N1 avian influenza, there is concern that it could transform into a pandemic strain capable of causing severe disease. During a pandemic, transmission can be anticipated in the workplace, not only from patient to workers in healthcare settings, but also among co-workers in general work settings. A pandemic would cause high levels of illness, death, social disruption, and economic loss. Everyday life would be disrupted because so many people in so many places become seriously ill at the same time. Impacts could range from school and business closings to the interruption of basic services such as public transportation and food delivery.
The use of naturally occurring infectious agents to inflict deliberate harm has become a major concern following the anthrax attacks of 2001. Anthraxexternal icon is a potentially deadly disease caused by Bacillus anthracis, a bacterium that forms spores. Inhalational anthrax can result from spore inhalation. Cutaneous (skin) anthrax can result from skin contact. Inhalational anthrax causes severe illness with a mortality rate exceeding 50 percent. In 2001, seven anthrax-contaminated letters were sent through the U.S. Postal Service (USPS) (investigators recovered four and presumed three others). These letters killed five people and infected at least 17 others with inhalational or cutaneous anthrax. In part due to lack of information about the most cost effective approaches to decontamination, the anthrax attacks also led to huge expenditures for decontamination. It is estimated that $42 million was spent decontaminating the Hart Senate Office Building and other Capitol Hill offices. Decontaminating the Brentwood postal facilities in Washington, D.C. and Hamilton Township, New Jersey, cost in excess of another $100 million. Implementation of additional preventive strategies to protect USPS workers, the general population, and decontamination workers continue to add substantially to these costs. Significant questions remain about exposure assessment and disease prevention in the face of an attack.
Severe Acute Respiratory Syndrome (SARS)
SARS was first reported in Asia in February 2003. The disease is a viral respiratory infection caused by SARS-associated coronavirus. It can cause fatal pneumonia associated with acute respiratory distress syndrome. Over a period of months, the illness spread to more than two dozen countries across the globe. According to the WHO, a total of 8,098 people worldwide became sick with SARS during the 2003 outbreak. Of these, 774 died. In the U.S., only eight people had laboratory evidence of SARS. Health workers contracted SARS from occupational exposure. Although there have been very few cases of occupationally acquired SARS in the U.S., there is potential for spread of the disease within the workplace, especially for healthcare workers and workers who experience daily contact with the general public.
Risk of Malignant Lung Diseases
A number of agents have been associated with work-related lung cancer. Examples include: asbestos, bischloromethyl ether (BCME), diesel exhaust, various metals (As, Be, Cd, Cr, Ni), polycyclic aromatic hydrocarbons (PAHs), secondhand or environmental tobacco smoke (ETS) and silica.external icon
Asbestos has already been discussed in the section on interstitial lung diseases. It causes lung cancer and mesothelioma, a type of cancer arising from the mesothelial lining of the chest cavity (pleura) and abdominal cavity (peritoneum).
BCMEexternal icon is used in the manufacture of other chemicals or it may be a byproduct of chemical manufacture. Epidemiologic studies suggest that lung cancer (primarily small cell) is related to BCME exposure with a 15-20 year latency period and that risk increases with duration of exposure and cumulative exposure.
Diesel exhaust is the product of incomplete combustion of diesel fuel and is a complex mixture that contains soot, PAHs, nitro-PAHs, oxides of carbon, sulfur and nitrogen. It is both gaseous and particulate. Many components of diesel exhaust are known to be carcinogenic in laboratory animals. Since 1988, NIOSH has recommended that whole diesel exhaust be regarded as a potential occupational carcinogen and that reductions in workplace exposure would reduce cancer risks.
Metals (As, Be, Cd, Cr, Ni): each of the metals listed has been classified as a Group I carcinogen by the International Agency for Research on Cancer.
View Overall Evaluations of Carcinogenicity to Humansexternal icon.
- Arsenicexternal icon has been associated with development of lung cancer in workers exposed to some pesticides and at copper smelters.
- Berylliumexternal icon has been identified as a lung carcinogen in the primary production industry in the United States. It has been estimated that as many as 134,000 workers in the United States may be exposed to beryllium.
- Cadmiumexternal icon is a byproduct of zinc-, copper- and lead-smelting, it is used in batteries, plastics, alloys and for electroplating – it is also encountered in welding. Cadmium exposure has been linked to lung and other cancers.
- Chromiumexternal icon exposure in welding, electroplating, steel manufacture and the production of pigments and dyes potentially affects 380,000 workers in the United States. These exposures have been linked to lung cancer. The current PEL, promulgated in 2006, of 5 μg (TWA) is still associated with a lung cancer risk of 45 per 1000 over a working lifetime.
- Nickelexternal icon exposure can occur in nickel extraction/production, electroplating, welding, machining and grinding. Reported standard mortality rates for lung cancer and nasal cancer among workers in these industries have ranged from 110-550 and 870-26,670, respectively.
Polycyclic aromatic hydrocarbonsexternal icon are formed in the incomplete combustion of vegetable materials and fossil fuels. They are essentially fused benzene ring structures that are chemically inert and require metabolic activation to exert their biological activity. They are metabolized by cytochrome P450 enzymes and epoxide hydrolases, which are polymorphic among the human population. Activated PAHs form highly reactive carbocations, which bind to biological molecules – like DNA. Covalent binding forms DNA adducts and can cause mutagenic events. Exposure to PAHs can occur in roofing, foundry work and in as a result of secondhand tobacco smoke exposure in indoor environments. (81KB, 18 pages)
Environmental tobacco smoke (ETS) or secondhand tobacco smoke is composed of side-stream tobacco smoke and exhaled main-stream tobacco smoke. This complex mixture contains hundreds of noxious chemical and carcinogens, which include: nitrosamines, PAHs, aromatic amines, metals (As, Cd, Cr, Se, Pb among others), formaldehyde, pyridine, phenol, benzene. ETS has been shown to have both chronic and acute affects in some workers who do not otherwise smoke themselves. Although the use of tobacco products in workplaces has been largely banned, it continues in some places. Exposure of employees in hospitality industry workplaces such as restaurants, bars, and casinos remains an important concern.
Nanoparticles in particular engineered nanoparticles, are an emerging occupational exposure. Their use in commercial products has grown markedly and is expected to continue to grow. A unique feature of nanoparticles is that they present a very large surface area to mass ratio. Thus, their toxic effects might be more related to surface area than mass. No epidemiological evidence from human studies has yet documented engineered nanomaterials as a human health hazard. However, early evidence from experimental toxicity studies provides cause for concern and continued vigilance. These studies suggest that engineered nanoparticles may, exhibit new or increased reactivity and increased toxic effects following inhalation exposure. Thus, workplace exposure to engineered nanoparticles is an important and emerging area of research.