The term ‘wood industry’ is used to describe those industrial processes that use trees as their raw material. One branch of the industry includes forestry, sawmills, building and construction (including pre-fabrication of detached and semi-detached houses, as well as on-site construction work), furniture manufacture and board production. Woodwork teachers are an often overlooked group subject to the exposures common to these sectors. Another important branch includes those industries that extract cellulose from wood pulp; that is, pulp and paper mills. The final products of these mills are a wide variety of paper products including different kinds of paper boards.

The majority of the trees harvested throughout the world are used for sawn lumber, while most of the rest are used by the pulp and paper industry. However, a minor fraction is used for fuel, a fraction that will increase in the future. Similarly, the production of ethanol from wood – for use as fuel – is likely to be increasingly important.

The largest forested areas in the world are in Russia, Brazil, Canada, the USA and China, while the largest exporters of forest products are Canada, the USA, Finland and Sweden. The major forest export products from Canada, Finland and Sweden are pulp and paper.

The wide spectrum of industries and production technologies implies a number of different occupational exposures, the most obvious being wood dust. In Sweden in the late 1990s 6.4% of men and 0.5% of women of working age reported occupational exposure to wood dust.

Occupational asthma

Occupational asthma due to sensitization to different varieties of wood is well described. The best-known type is asthma due to western red cedar (Thuja plicata), although many other common tree species such as eastern white cedar (Thuja occidentalis), ash, cedar of Lebanon, mahogany, birch and teak have also been reported to induce occupational asthma. Sensitization properties have been found to vary by species, and so it is thought that the sensitization is due to naturally occurring substances that vary between the species. For example, the causative agent in western red cedar and eastern white cedar asthma has been identified as plicatic acid.

It is not clear whether exposures to softwood from coniferous species such as pines, spruces and firs increases the risk of asthma. Several studies of workers exposed to these kinds of dust have shown an increased prevalence of respiratory symptoms, but no clearly increased risk for asthma.

The clinical investigation of a wood-working patient with suspected occupational asthma is similar to other occupational asthma investigations. However, the clinican should be aware that such a patient may be exposed to other agents that can cause respiratory disease. Some of these occupations require frequent handling of paints, glues and varnishes containing reactive chemicals such as diisocyanates and acrylates. The standard adhesive used by carpenters and other woodworkers is based on urea-formaldehyde, and formaldehyde is released during heating. Exposure to formaldehyde may exacerbate asthma.

Extrinsic allergic alveolitis (hypersensitivity pneumonitis)

Extrinsic allergic alveolitis (hypersensitivity pneumonitis) has been described among sawmill workers and wood trimmers in Northern Europe, the USA and Canada. The antigens responsible for these diseases are molds growing in the wood dust or in the bark of the logs. The main species are Cryptostroma corticale in maple strippers’ disease, Alternaria spp. in sawmills and Aspergillus spp. and Thermoactinomyces vulgaris in moldy wood chips. In Sweden in the 1970s, there was an outbreak of allergic alveolitis among wood trimmers due to the fact that unsawn wood was stored under warm and damp conditions, promoting the growth of Rhizopus spp. and Penicillium spp. Outbreaks of maple bark disease occurred among workers peeling off moldy bark from maple logs.

Patients with allergic alveolitis often present with febrile influenza-like reactions with cough, chest tightness, malaise and chills. These symptoms start 4-8 hours after the beginning of the exposure, and disappear during the following night. If the exposure continues the symptoms will recur. In the typical case there will be bilateral crackles on chest auscultation. In addition to this acute form of allergic alveolitis, there may also be a subacute form characterized by progressively increasing dyspnea and dry cough. A chronic form is mainly characterized by the development of pulmonary fibrosis. The two latter forms result from long-standing, chronic exposure to the causative agents.

When faced with a patient of working age presenting with a febrile illness as described above, it is wise to consider the possibility of allergic alveolitis. Key questions that should be asked are the patient’s occupation and whether he or she has handled moldy material; note that the latter may have occurred in nonoccupational settings, for instance while burning woodchips in a domestic boiler.

A patient with suspected allergic alveolitis should be investigated with pulmonary function tests, chest X-ray or CT and sometimes also bronchoscopy. An occupational hygiene investigation is often helpful. IgG antibodies may appear after repeated exposures to airborne fungal spores. Specific IgG antibodies to Saccharopolyspora, Aspergillus, Penicillium and Rhizopus have been used as markers of exposure in studies of farmers and workers from sawmills. Clinically, such analyses can be useful for establishing that an exposure has occurred; however, the presence of specific IgG is only a marker of exposure and is not a sign of the disease.

Chronic bronchitis

Wood dust and volatile chemicals have irritant properties which may cause inflammation in the upper airway, as well as increasing the risk for chronic bronchitis. Exposure to wood dust is associated with acute effects on lung function, as well perhaps as longterm effects, such as development of chronic airways obstruction. An increased risk for rhinitis has been described among woodwork teachers.

Cancer

The International Agency for Cancer Research has classified wood dust as a group I human carcinogen. There are several studies showing a very high risk for sino-nasal adenocarcinoma among workers exposed to dust from hardwoods, such as oak, mahogany and beech. There is probably also an increased risk for sino-nasal cancer after exposure to softwood, but studies are less conclusive.

The production of paper from fiber originates from China, where paper from rags and grass was produced as early as 100 AD. Rags were the main source of fiber for paper production until middle of 1800s. In the early years of the Industrial Revolution there was an increasing demand for paper; however, paper production was greatly hampered by the lack of raw material, as rags were the only existing fiber source. In the middle of the 1850s, the fiber supply shifted as several different methods were developed to extract pulp from wood. This was a major breakthrough of great importance for further scientific and industrial development. The main methods were mechanical (abrasion), acidic (sulfite) or alkaline (sulfate or Kraft). Today the use of recycled paper has increased. In some parts of the word bagass (the remains of sugar cane after the extraction of raw sugar) is used for pulp production. The main producers of pulp are the USA, Canada, China and Sweden.

The fibers used to make paper are often bleached; this was originally achieved by a combination of sunlight and acid. The use of chlorine became widespread during the 1800s, and chlorine was later replaced with chlorine dioxide. Many nonchlorine bleaching methods have since been developed, including bleaching based on peroxides, oxygen, ozone and peracetic acid. Pulp originating from the sulfite process is lighter and generally easier to bleach; hence, for environmental reasons, the use of sulfite fibers for paper production has increased.

The textile industry includes a wide range of different processes, such as spinning, weaving, knitting and the production of yarn. It includes also the dyeing of yarn and fabrics. Originally the textile industry was based on natural fibers from silk, cotton and wool, but the use of synthetic fibers is increasing: in 2004, more than 50% of the worldwide fiber supply to the textile industry was synthetic.

Byssinosis

Respiratory diseases have always been one of the most important ailments among textile industry workers. The most common is byssinosis, an acute or chronic lung disease among workers exposed to organic dust, usually derived from cotton, hemp or flax. Byssinosis-like syndromes have also been demonstrated among workers exposed to other kinds of organic dust, for instance agricultural workers.

The most important exposure today is cotton dust: about 300,000 workers in the USA are exposed to cotton dust, but in recent years there has been a steep decline in cotton dust-induced lung disease in the USA. The prevalence of byssinosis in cotton workers in industrially developed countries is now just a few percent. This is in sharp contrast to the conditions in low- and middle-income countries where the prevalence is much higher. In countries like Indonesia, India and Sudan, byssinosis has been reported to affect 30-50% of the workforce. The prevalence of byssinosis in Turkish cotton processing workers was reported to be 14% [1].

The clinical manifestations are chest tightness, dyspnea and coughing. The symptoms begin on Monday and abate in the evening; this distinguishes byssinosis from occupational asthma, where the symptoms tend to increase over the working week. If the worker is away from exposure for a longer period, the symptoms tend to be more severe when re-exposure occurs. If exposure continues over the weekend, the Monday symptoms will not appear.

Pulmonary function is also affected in two different ways due to exposure to organic dust. The first effect is chronic and is characterized by reduced FEV₁ as well as reduced FEV₁:FVC. The reduction is dependent on the cumulative exposure to dust; that is, both dust concentration and duration of exposure. The second effect is an acute one, characterized by increasing obstruction over a work shift where there is exposure to cotton dust. The cross-shift decrement is more severe after an absence from exposure for more than 2 days.

Most of the diseases occurring among wood workers, pulp and paper mill workers and textile workers are preventable. Some specific respiratory diseases such as allergic alveolitis, inhalation fever and byssinosis are almost all (in close to 100% of cases) caused by occupational exposures. The burden of illness due to occupation is approximately 15-20% for asthma and chronic obstructive pulmonary disease. These figures imply that primary prevention action of choice is control of the occupational exposure by reducing or eliminating the levels at workplace. This can be accomplished by removal or substitution of hazardous substances, improved ventilation, the modification of production techniques or by automation of the process. If these efforts fail, personal protection could be used. Protective equipment may also be useful during very short tasks, such as maintenance tasks, where more general efforts are not feasible.

References

1. Altin, R., Ozkurt, S., FisekC¸ i, F., Cimrin, A.H., Zencir, M., Savinc, C. (2002) Prevalence of byssinosis and respiratory symptoms among cotton mill workers. Respiration 69: 52-56.

2. Sternbach, G. (2003) The history of anthrax. J. Emerg. Med. 24: 463-467.

3. Metcalfe, N. (2004) The history of woolsorter’s disease: A Yorkshire beginning with an international furure. Occup. Med. 54: 489-493.

4. Karahogacil, M.K., Akdeniz, N., Akdeniz, H., Çalka, Ö., Bilici, A., Bilgili, S.G., Evirgen, Ö. (2008) Cutaneous antrax in eastern Turkey: a review of 85 cases. Clin. Exp. Dermatol. 33: 406-411.

Further reading

Balmes, J., Becklake, M., Blanc, P., Henneberger, P., Kreiss, K., Mapp, C., Milton, D., Schwartz, D., Torén, K., Viegi, G. (2003) American Thoracic Society Statement: Occupational contribution to the burden of airway disease. Am. J. Respir. Crit. Care Med. 167: 787-797.

Blanc, P.D. (2007) How Everyday Products Make People Sick. Toxins at Home and in the Workplace. University of California Press: Berkeley, CA.

Camus, Ph., Nemery, B. (1998) A novel cause for bronchiolitis obliterans organizing pneumonia: exposure to paint aerosols in textile workshops. Eur. Respir. J. 11: 259-262.

Chan-Yeung, M., Malo, J.-L. (2006) Western red cedar (Thuja plicata) and other wood dusts. In Asthma in the Workplace, 3rd edn, Bernstein, I.L., Chan-Yeung, M., Malo, J.-L., Bernstein, D.I. (eds). Taylor&Francis: New York.

Cimrin, A., Sigsgaard, T., Nemery, B. (2006) Sandblasting jeans kills young people. Eur. Respir. J. 28: 885-886.

Eduard, W. (2006) The Nordic Expert Group for Criteria Documentation of Health Risk from Chemicals. 139. Fungal Spores. Arbete och Hälsa; 21.

Hendrick, D.J., Burge, P.S., Beckett, W.S., Churg, A. (2002) Occupational Disorders of the Lung. Recognition, Management and Prevention. Saunders: London.

Kern, D.G., Crausman, R.S., Durand, K.T.H., Nayer, A., Kuhn, C. (1998) Flock worker’s lung: Chronic interstitial lung disease in the nylon flocking industry. Ann. Intern. Med. 129: 261-272.