Cohort mortality study of North American industrial sand workers. I. Mortality from lung cancer, silicosis and other causes

Background: In 1997 a Working Group of the International Agency for Researc h on Cancer changed an earlier classification of crystalline silica as a hu man carcinogen from Group 2A to Group 1, though commenting that the carcino genicity might vary dth industrial circumstances and depend on additional f actors affecting biological activity, including the distribution of its pol ymorphs, Objective: We aimed to determine whether pure quartz exposure uncomplicated by the presence of other contaminating carcinogens, as experienced by work ers in the production of high-grade industrial sand, was causally related t o an increased risk of lung cancer. Methods: A cohort of 2670 men employed before 1980 for 3 years or more in o ne of nine North American sand-producing plants and a large associated offi ce complex was selected for study, Of the cohort, 2644 (99%) were traced th rough 1994, and certificated cause of death ascertained for 1025 (99%) of t he 1039 men known to have died. Standardised mortality ratios (SMRs) were c alculated for the main causes of death, using both US and state or provinci al male mortality rates for reference, Findings: The main analyses of deaths, 20 or more years after first employm ent against regional rates, gave the following SMRs: all causes 109, lung c ancer 139, other malignancies 98, non-malignant respiratory disease 161, an d nephritis/nephrosis 244, There were, in total, 37 deaths from silicosis o r silico-tuberculosis, with one or more death at least in all nine producti on plants, Analyses failed to show any relation between lung cancer risk an d duration of employment, The increased SMR for lung cancer was wholly due to high rates in four plants in two states, whereas no increase was found i n the remainder of the cohort. Conclusion: In the absence of information on smoking histories and risk in relation to estimated exposure, the increased SMR for lung cancer (139), al though statistically significant, cannot be attributed confidently to cryst alline silica. An answer to the question of attributability must await the findings of the nested case-control study, in which level of exposure and s moking habits were ascertained for cases and matched controls. The strong i ndication in this cohort of excess mortality from non-malignant renal disea se deserves further investigation. (C) 2001 British Occupational Hygiene So ciety. Published by Elsevier Science Ltd. All rights reserved.