American Journal of Epidemiology Vol. 154, No. 3 : 288
Copyright © 2001 by The Johns Hopkins University School of Hygiene and Public Health
LETTERS TO THE EDITOR |
RE: "LUNG CANCER AMONG INDUSTRIAL SAND WORKERS EXPOSED TO CRYSTALLINE SILICA"
Department of Biology and Program in Medical Sciences Indiana University Bloomington, IN 47405
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INTRODUCTION |
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 TOP INTRODUCTION REFERENCES |
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In a 22-year study in 18 plants of 4,027 domestic industrial sand workers exposed to crystalline silica, Steenland and Sanderson (1
) observed a 60 percent excess of lung cancer mortality in the exposed cohort compared with the US male population. This finding supports the 1997 judgment by the International Agency for Research on Cancer that inhaled crystalline silica from occupational sources is a carcinogen (2). Indeed, as early as 1940, inhaled silica was shown to induce lung cancers in mice (3).
However, the International Agency for Research on Cancer noted that the epidemiologic evidence was not entirely consistent and that different forms of silica might vary in carcinogenic efficacy. A possible cause of fluctuation in potency might be variable contamination of silica with a known carcinogen such as iron (4). In addition, inconsistency could reflect different levels of tissue iron in persons who inhale silica. Evidence is available to support each of these possibilities.
Ghio et al. (5) observed that the ability of silica to stimulate production of reactive oxygen radicals and induce lung inflammation was suppressed by the iron chelator desferrioxamine. Furthermore, in rats exposed to silica, exogenous iron contamination of the inhaled sand markedly enhanced such lung responses as leukocyte recruitment, macrophage synthesis of oxygen radicals and nitric oxide, and lipid peroxidation (6).
Moreover, after introduction of silica into the lower respiratory tract, surface complexation of iron has been observed to occur on the phagocytosed particles (5). Subsequently, silica was instilled intratracheally in rats maintained on low- or high-iron diets. Compared with animals fed high-iron diets, rats on the low amount of iron had diminished fibrotic injury (7).
Iron loading of humans can occur via alimentary or respiratory routes. Ingestion of excessive amounts of red meat or of alcohol as well as several genetic disorders can enhance intestinal absorption of iron. Sources of inhaled iron include mainstream cigarette smoke, asbestos, and urban air particulates (4). Thus, both the use of protective masks and measures to reduce alimentary iron loading might be useful in minimizing the carcinogenic danger of silica for industrial sand workers.
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NOTES |
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Editor's note: In accordance with Journal policy, Drs. Steenland and Sanderson were asked whether they wished to respond to this letter but chose not to do so.
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REFERENCES |
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TOPINTRODUCTIONREFERENCES |
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Steenland K, Sanderson W. Lung cancer among industrial sand workers exposed to crystalline silica. Am J Epidemiol 2001;153:695–703.
[Abstract/Free Full Text] - International Agency for Research on Cancer. Silica, some silicates, coal dust, and para-aramid fibrils. Monograph 68. Evaluation of carcinogenic risks to humans. Lyon, France: International Agency for Research on Cancer, 1997.
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Campbell JA. Effects of precipitated silica and of iron oxide on the incidence of primary lung tumours in mice. Br Med J 1940;2:275–80.
[Free Full Text] - Weinberg ED. The development of awareness of the carcinogenic hazard of inhaled iron. Oncol Res 1999;11:109–13.[Web of Science][Medline]
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Ghio AJ, Kennedy TP, Wharton AR et al. Role of surface complexed iron in oxidant generation and lung inflammation induced by silicates. Am J Physiol 1992;263:L511–18.
[Abstract/Free Full Text] - Castranova V, Vallyathan V, Ramsay DM, et al. Augmentation of pulmonary reactions to quartz inhalation by trace amounts of iron-containing particles. Environ Health Perspect 1997;105(suppl 5):1319–24.
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Ghio AJ, Jaskot RH, Hatch GE. Lung injury after silica instillation is associated with an accumulation of iron in rats. Am J Physiol 1994;267:L686–92.
[Abstract/Free Full Text]
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