Robert J. Roscoe

NEW DEVELOPMENTS IN THE LIFE TABLE ANALYSIS SYSTEM OF THE NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH

In the 1970s, the National Institute for Occupational Safety and Health developed a Life Table Analysis System to analyze occupational cohort studies. We have updated the original system by adding two new features: direct standardization with a test for linear trend, and analyses by lagged exposure (either duration of exposure or cumulative exposure). We have also updated US reference rates through 1989. The updated systems and documentation (version F) are available upon request. In collaboration with the National Cancer Institute, we have also developed multiple cause-of-death rate files, which consider contributory as well as underlying cause. These files (also available upon request) will enable investigators to derive the expected prevalence of diseases at death, which can then be compared with the observed prevalence in an exposed cohort. Work is currently underway to produce a personal computer version of the Life Table Analysis System.

Mortality among Navajo uranium miners.

OBJECTIVES To update mortality risks for Navajo uranium miners, a retrospective cohort mortality study was conducted of 757 Navajos from the cohort of Colorado Plateau uranium miners. METHODS Vital status was followed from 1960 to 1990. Standardized mortality ratios were estimated, with combined New Mexico and Arizona non-White mortality rates used for comparison. Cox regression models were used to evaluate exposure-response relationships. RESULTS Elevated standardized mortality ratios were found for lung cancer (3.3), tuberculosis (2.6), and pneumoconioses and other respiratory diseases (2.6). Lowered ratios were found for heart disease (0.6), circulatory disease (0.4), and liver cirrhosis (0.5). The estimated relative risk for a 5-year duration of exposure vs none was 3.7 for lung cancer, 2.1 for pneumoconioses and other respiratory diseases, and 2.0 for tuberculosis. The relative risk for lung cancer was 6.9 for the midrange of cumulative exposure to radon progeny compared with the least exposed. CONCLUSIONS Findings were consistent with those from previous studies. Twenty-three years after their last exposure to radon progeny, these light-smoking Navajo miners continue to face excess mortality risks from lung cancer and pneumoconioses and other respiratory diseases.

Modifiers of Lung Cancer Risk in Uranium Miners from the Colorado Plateau

Given the scientific consensus that exposure to radon decay products causes lung cancer, most recent studies have focused on the nature of the exposure-response relationship. Since residential radon exposure is now a primary public health issue, a better understanding of the effects of low levels of radon as well as factors modifying risk estimates has become very important. Several factors are shown to affect risk estimates in the latest update of the vital status follow-up (through 1990) and smoking history for the cohort of underground uranium miners in the Colorado Plateau. This analysis confirms earlier results indicating a strong dependence of relative risk estimates upon attained age. Quantitative estimates of relative risk as a function of cumulative exposure to radon decay products (WLM) are provided for three age strata. The non-linearity often reported in the Colorado Plateau data is shown to be at least partially due to an inverse exposure-rate effect, i.e., low exposure rates for long periods are more hazardous than equivalent cumulative exposure received at higher rates for shorter periods of time. However, this effect is shown to diminish at lower exposure rates and cumulative exposures. In addition, use of the new smoking data indicates that the radon/smoking interaction is submultiplicative and may depend upon attained age.

An update of mortality from all causes among white uranium miners from the Colorado plateau study group

To place previously recognized mortality risks into the context of the total mortality from all causes, an updated retrospective cohort mortality study was conducted on 3,238 white males from the US Public Health Service cohort of Colorado Plateau uranium miners. Vital status was followed from 1960 through 1990. Life-table analyses used combined New Mexico, Arizona, Utah, and Colorado mortality rates for external comparison and mortality risks within the lowest radon-exposure or duration-employed category for internal comparison. Significantly elevated SMRs were found for pneumoconioses (SMR = 24.1, 95% CI 16.0-33.7), lung cancer (SMR = 5.8, 95% CI 5.2-6.4), tuberculosis (SMR = 3.7, 95% CI 1.9-6.2), chronic obstructive respiratory diseases (SMR = 2.8, 95% CI 2.2-3.5), emphysema (SMR = 2.5, 95% CI 1.9-3.2), benign and unspecified tumors (SMR = 2.4, 95% CI 1.0-4.6), and diseases of the blood and blood-forming organs (SMR = 2.4, 95% CI 1.0-5.0). No significantly lowered SMRs were found for any disease. For lung cancer and pneumoconioses standardized rate ratios increased with increasing exposure to radon progeny or duration of employment. Most findings from this update are consistent with previous studies. Not observed were previously elevated SMRs for chronic nephritis and for acute alcoholism. New findings observed were elevated SMRs for benign and unspecified tumors and for diseases of the blood and blood-forming organs. The most important long-term mortality risks for the white uranium-miners continue to be lung cancer and pneumoconioses, for which SMRs remain significantly elevated after a mean period of 22.4 years since last uranium mining.

Modifiers of exposure--response estimates for lung cancer among miners exposed to radon progeny

The association between lung cancer and exposure to radon decay products has been well established. Despite agreement on this point, there is still some degree of uncertainty regarding characteristics of the exposure-response relationship. The use of studies of underground miners to estimate lung cancer risks due to residential radon exposure depends upon a better understanding of factors potentially modifying the exposure-response relationship. Given the diversity in study populations regarding smoking status, mining conditions, risk analysis methodology, and referent populations, the risk estimates across studies are quite similar. However, several factors partially contributing to differences in risk estimates are modified by attained age, time since last exposure, exposure rate, and cigarette smoking patterns. There is growing agreement across studies that relative risk decreases with attained age and time since last exposure. Several studies have also found an inverse exposure-rate effect, i.e., low exposure rates for protracted duration of exposure are more hazardous than equivalent cumulative exposures received at higher rates for shorter periods of time. Additionally, the interaction between radon exposure and cigarette smoking appears to be intermediate between additive and multiplicative in a growing number of studies. Quantitative estimates of these modifying factors are given using a new analysis of data from the latest update of the Colorado Plateau uranium miners cohort.

Industrial hygiene characterization of automotive wood model shops

A suspicion of an excess cancer risk in automotive model shops prompted the Industrywide Studies Branch, NIOSH, to conduct a proportionate mortality study and an industrial hygiene characterization of operations in these shops. The mortality study showed a statistically significant excess proportion of deaths due to colon cancer and leukemia (for woodshops only). The materials used in the model shops include various natural woods, laminated woods, plastics, resins, varnishes, putties and paints. Personal breathing zone samples were collected for total and respirable dust, amines, various hydrocarbons (including styrene, and toluene), formaldehyde, and nitrosamines. Particle size distribution studies were conducted on the wood dust and bulk airborne samples of dusts were subjected to various mutagenicity test systems. Work practices, ventilation and general housekeeping were checked. Total wood dust samples ranged from 0.03 to 25 mg/m3 with an average around 1.0 mg/m3. The percent respirable dust ranged from 19 to 38% as measured with Andersen impactors. Solvent exposure samples ranged from non-detectable to about 10% of the OSHA Permissible Exposure Levels. Relevant recommendations for improvement of contaminant control were made.

Colon and stomach cancer mortality among automotive wood model makers.

Automotive wood model makers have been reported to be at excess risk for colon and other cancers in recent epidemiologic studies. To further explore these risks, we conducted a retrospective cohort mortality study, with follow-up from 1940 through 1984, of 2294 white male wood model makers employed at any time until 1980 by three US auto makers. Using US mortality rates for comparison, we found elevated standardized mortality ratios of 1.2 (95% CI, 0.8-1.9) for colon cancer and 1.6 (95% CI, 0.9-2.6) for stomach cancer. We also conducted nested case-control studies for 20 colon and 17 stomach cancer cases and 543 age-matched controls. We found no trend of increased risk for colon or stomach cancer mortality with increased exposure to wood dust or to duration employed in wood model making.