Exposure to biogenic silica fibers and respiratory health in Hawaii sugarcane workers

Our plain-English summary of Exposure to biogenic silica fibers and respiratory health in Hawaii sugarcane workers, by T. Sinks, R. Hartle, M. Boeniger, et al (Journal of Occupational Medicine., 1994).

The study

• Authors: T. Sinks, R. Hartle, M. Boeniger, D. Mannino, J.E. Boyd, J. Fernback, M. Hawkins, G. Grimes, K.L. Watkins, P. Dill
• Journal: Journal of Occupational Medicine.
• Published: 1994;36(12):1329-34
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We conducted a cross-sectional environmental and medical survey of 355 male sugarcane workers in Hawaii to determine whether exposure to biogenic silica fibers (BSF) affected their respiratory health. Exposures to BSF ranged from nondetectable to more than 0.700 BSF/mL and varied by job and department. Respiratory symptoms, chest radiograph findings, and pulmonary function were not associated with BSF exposures. Cigarette smoking was associated with respiratory symptoms and pulmonary obstruction. Fifteen workers had pleural thickening or pleural plaques and 3 of these workers were exposed to BSF for more than 10 years. BSF exposure does not appear to influence the respiratory health of sugarcane workers; however, further study is warranted.

In plain English

Researchers carried out a cross-sectional survey at two Hawaii sugar plantations in August 1989. They studied whether biogenic silica fibers (BSF), natural fibers in sugarcane, affected workers' respiratory health. Of 486 male workers selected, 355 took part; most were current or retired workers. Air samples ranged from nondetectable to 0.712 BSF/mL. Only harvest rake operators averaged above 0.050 BSF/mL (mean 0.089). Respiratory symptoms, abnormal breathing-test patterns and percent predicted FVC were not associated with years in BSF- or asbestos-exposed jobs. Smoking was linked to symptoms and obstruction. Workers with 10 or more years in BSF-exposed jobs had a lower FEV1/FVC ratio. However, the authors saw no dose-response pattern, and adjusting for age altered this association (F = 1.77, P less than .17). Fifteen workers had pleural plaques or thickening; 3 of them had held BSF-exposed jobs for 10 or more years. The authors could not attribute these findings to any single factor. Two workers had X-ray signs consistent with pneumoconiosis; neither held a heavily BSF-exposed job. The authors concluded that BSF exposure did not appear to influence respiratory health, but further study was warranted.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional environmental and medical survey (air sampling, questionnaire, spirometry, chest radiographs)
• Who was studied: Male sugarcane workers at two plantations, one on Maui and one on the island of Hawaii, surveyed in August 1989. Of 486 selected, 355 took part: 213 current workers, 130 retired workers and 12 on disability leave or with unknown work status. The average participant was 54 years old and had worked 30 years in the industry.
• Exposure: Biogenic silica fibers (amorphous opaline silica fibers from sugarcane) were measured in 147 personal breathing zone samples by transmission electron microscopy. Asbestos was also measured (fiber type not specified). Only harvest rake operators were counted as BSF-exposed (mean above 0.050 fibers/mL). Jobs were classed as probably or probably not exposed to asbestos.
• Main results:
  • The harvest rake operator category was the only one with mean BSF above 0.050 BSF/mL (35 samples, mean 0.089 BSF/mL). All other field workers had a mean of .016 BSF/mL (57 samples).
  • Ten air samples contained asbestos, at .001 to .774 fibers/mL. The highest was a single sample from a bagasse tractor driver; two further samples on the same worker that day found no detectable asbestos.
  • Among all workers, 24% had shortness of breath grade 1 or higher, 7% had wheezing and 5% had chronic cough. Symptoms were associated with cigarette smoking but not with years in BSF-exposed or asbestos-exposed jobs.
  • Of 353 workers who attempted spirometry, 66 had an obstructive pattern and 18 a restrictive pattern. Neither pattern was associated with duration of BSF or asbestos exposure. Workers with obstruction averaged 31.6 pack-years of smoking, compared with 18.4 for those without.
  • A decrease in FEV1/FVC ratio was associated with pack-years of smoking and with BSF exposure. Mean ratios were 75.4 for 0 years (N = 243), 77.3 for 1-9 years (N = 59) and 72.4 for 10 or more years (N = 37) in BSF-exposed jobs. The authors reported that no dose-response relationship appears to exist.
  • Adjusting for age altered the association between BSF exposure and FEV1/FVC ratio (F = 1.77, P less than .17) but did not alter the association with smoking (F = 6.91, P less than .01).
  • Percent of predicted FVC was not statistically associated with smoking, BSF exposure or asbestos exposure.
  • Of 344 workers with chest radiographs, two had bilateral irregular opacities consistent with pneumoconiosis. Neither had worked in a heavily BSF-exposed job.
  • Twelve workers had circumscribed pleural plaques (11 bilateral, 1 unilateral) and 3 had bilateral diffuse pleural thickening. Among workers with pleural abnormalities, 3 had held BSF-exposed jobs for 10 or more years, 5 had worked 10 or more years in jobs with potential asbestos exposure, and 2 reported asbestos exposure outside the sugarcane industry. The authors could not attribute the pleural abnormalities to any single factor.
  • Pleural plaques were associated with a lower mean percent predicted FEV1: 81.0% plus or minus 29.7%, compared with 101.9% plus or minus 19.6%.
• The authors' conclusion: The authors concluded that BSF exposure does not appear to influence the respiratory health of sugarcane workers. They wrote that a moderate association between BSF exposure and both a decreased FEV1/FVC ratio and pleural plaques meant further study is warranted.
• Limitations the authors state:
  • Assumptions about BSF and asbestos exposures may have caused some misclassification.
  • Air samples were collected over a 2-week period and may not represent exposures in other seasons, weather or plantations.
  • Asbestos exposure was classified only from job titles and an industrial hygiene walk-through survey.
  • The cross-sectional design prevented the authors from examining the risk of illness over time.
  • Workers who left before retirement or who had died could not be studied. Participation also varied by job, which may have caused selection bias.
  • BSF concentrations may have been too low to cause illness in this population.

Topics

Medical terms in this study, explained in our Lexicon: Chest X-Ray, Pleural Thickening, Pleural Plaques.

Related studies

• A case-control study of mesothelioma and employment in the Hawaii sugarcane industry — T. Sinks, M.T. Goodman, et al. (1994)
• Respiratory impairments due to dust exposure: a comparative study among workers exposed to silica, asbestos, and coalmine dust — X. Wang, E. Yano, et al. (1997)
• Fine biogenic silica fibres in sugar cane: a possible hazard — R.H. Newman (1986)
• Association of biogenic silica with disease — R. Newman (1986)
• An epidemiological study of the respiratory health of workers in the European refractory ceramic fibre industry — H.A. Cowie, P. Wild, et al. (2001)
• Mortality from lung cancer and respiratory disease among pottery workers exposed to silica and talc — T.L. Thomas, P.A. Stewart (1987)

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