Carl M. Shy

Snuff Dipping and Oral Cancer among Women in the Southern United States

A case-control study in North Carolina involving 255 women with oral and pharyngeal cancer and 502 controls revealed that the exceptionally high mortality from this cancer among white women in the South is primarily related to chronic use of snuff. The relative risk associated with snuff dipping among white nonsmokers was 4.2 (95 per cent confidence limits, 2.6 to 6.7), and among chronic users the risk approached 50-fold for cancers of the gum and buccal mucosa--tissues that come in direct contact with the tobacco powder. In the absence of snuff dipping, oral and pharyngeal cancer resulted mainly from the combined effects of cigarette smoking and alcohol consumption. The carcinogenic hazard of oral snuff is of special concern in view of the recent upswing in consumption of smokeless tobacco in the United States.

Micronuclei and other nuclear anomalies in buccal smears: methods development

Laboratory work aimed at improving the epidemiologic utility of an innovative genotoxicity assay is described. The exfoliated cell micronucleus assay involves microscopic analysis of epithelial smears to determine the prevalence of micronucleation, an indicator of structural or numerical chromosome aberrations. While the assay holds promise for the study of epithelial carcinogens, it is hampered by the fact that exfoliated cells are moribund and undergo degenerative phenomena that can produce extranuclear objects difficult to distinguish from classical micronuclei. Modifications in the protocol were assessed in sample buccal smears from several study populations: radiotherapy patients, nonusers of tobacco, and snuff users. Refinements in micronucleus scoring criteria and the inclusion of other nuclear anomalies in the scoring system are proposed. We demonstrate that our criteria are successful in detecting excess micronucleation in positive controls. We also provide evidence that other nuclear anomalies are at least as common as micronucleation and that therefore there is the potential for extensive misclassification. Reliability was assessed in duplicate readings.

Reduced fertility among women employed as dental assistants exposed to high levels of nitrous oxide

BACKGROUND Fertility is reduced in female rats exposed to levels of nitrous oxide similar to those found in some dental offices. Epidemiologic studies have suggested an association between exposure to mixed anesthetic gases and impaired fertility. We investigated the effects of occupational exposure to nitrous oxide on the fertility of female dental assistants. METHODS Screening questionnaires were mailed to 7000 female dental assistants, ages 18 to 39, registered by the California Department of Consumer Affairs. Sixty-nine percent responded. Four hundred fifty-nine women were determined to be eligible, having become pregnant during the previous four years for reasons unrelated to the failure of birth control, and 91 percent of these women completed telephone interviews. Detailed information was collected on exposure to nitrous oxide and fertility (measured by the number of menstrual cycles without contraception that the women required to become pregnant). RESULTS After controlling for covariates, we found that women exposed to high levels of nitrous oxide were significantly less fertile than women who were unexposed or exposed to lower levels of nitrous oxide. The effect was evident only in the 19 women with five or more hours of exposure per week. These women were only 41 percent (95 percent confidence interval, 23 to 74 percent; P less than 0.003) as likely as unexposed women to conceive during each menstrual cycle. CONCLUSIONS Occupational exposure to high levels of nitrous oxide may adversely affect womens ability to become pregnant.

Review of occupational lung carcinogens.

Lung cancer is the most common malignancy in the United States and is ranked second only to bladder cancer in the proportion of cases thought to be due to occupational exposures. We review the epidemiology of occupational lung cancer, focusing on agents identified as pulmonary carcinogens by the International Agency for Research on Cancer. We derive estimates of overall relative risks from the major studies of these lung carcinogens, and we also provide estimates of the number of exposed workers. Using our data as well as estimates from other authors, we estimate that approximately 9,000-10,000 men and 900-1,900 women develop lung cancer annually in the United States due to past exposure to occupational carcinogens. More than half of these lung cancers are due to asbestos. This estimate is likely conservative, in that we have restricted our analysis to confirmed lung carcinogens and have ignored occupations with documented excess risk but for which the specific agents are unknown. Also, our estimate of the proportion of workers exposed in the past is probably too low. Our estimate should be viewed only as broad approximation. Nevertheless, it is in line with other estimates by authors using different methods. The current number of cases estimated to be due to occupational exposure reflects past high exposures and is likely to drop in the future, unless other occupational lung carcinogens are confirmed or new carcinogens are introduced into the workplace.

Particulate matter and heart rate variability among elderly retirees: the Baltimore 1998 PM study.

This study investigates the relationship between ambient fine particle pollution and impaired cardiac autonomic control in the elderly. Heart rate variability (HRV) among 56 elderly (mean age 82) nonsmoking residents of a retirement center in Baltimore County, Maryland, was monitored for 4 weeks, from July 27 through August 22, 1998. The weather was seasonally mild (63–84°F mean daily temperature) with low to moderate levels of fine particles (PM2.5 <50 μg/m3). Two groups of approximately 30 subjects were examined on alternate days. A spline mixed-effects model revealed a negative relationship between outdoor 24-h average fine particulate matter (PM2.5) and high-frequency (HF) HRV that was consistent with our earlier Baltimore study for all but 2 days. These 2 days were the only days with significant precipitation in combination with elevated PM2.5. They were also unusual in that back-trajectoryof their air masses was distinctly different from those on the other study days, emanating from the direction of rural Pennsylvania. Mixed-effects analysis for all 24 study days showed a small negative association of outdoor PM2.5 with HF HRV (−0.03 change in log[HF HRV] for a 10 μg/m3 increment in PM2.5) after adjustment for age, sex, cardiovascular status, trend, maximum temperature, average dew point temperature, random subject intercepts, and autocorrelated residuals. After excluding study days 4 and 5, this association was strengthened (−0.07 change in log[HF HRV] for 10 μg/m3 PM2.5, 95% CI −0.13 to −0.02) and was similar to that obtained in an earlier study (−0.12 change in log[HF HRV] for a 10 μg/m3 increment in outdoor PM2.5, 95% CI −0.24 to −0.00) [Liao D., Cai J., Rosamond W.D., Barnes R.W., Hutchinson R.G., Whitsel E.A., Rautaharju P., and Heiss G. Cardiac autonomic function and incident coronary heart disease: a population-based case-cohort study. The ARIC Study. Atherosclerosis Risk in Communities Study. Am J Epidemiol 1997: 145 (8): 696–706]. Acute (1 to 4 h) previous PM2.5 exposure did not have a stronger impact than the 24-h measure. A distributed lag model incorporating the six preceding 4-h means also did not indicate any effect greater than that observed in the 24-h measure. This study is consistent with earlier findings that exposures to PM2.5 are associated with decreased HRV in the elderly.

The effect of occupational exposure to mercury vapour on the fertility of female dental assistants.

Exposure to mercury vapour or inorganic mercury compounds can impair fertility in laboratory animals. To study the effects of mercury vapour on fertility in women, eligibility questionnaires were sent to 7000 registered dental assistants in California. The final eligible sample of 418 women, who had become pregnant during the previous four years, were interviewed by telephone. Detailed information was collected on mercury handling practices and the number of menstrual cycles without contraception it had taken them to become pregnant. Dental assistants not working with amalgam served as unexposed controls. Women with high occupational exposure to mercury were less fertile than unexposed controls. The fecundability (probability of conception each menstrual cycle) of women who prepared 30 or more amalgams per week and who had five or more poor mercury hygiene factors was only 63% of that for unexposed women (95% CI 42%-96%) after controlling for covariates. Women with low exposure were more fertile, however, than unexposed controls. Possible explanations for the U shaped dose response and limitations of the exposure measure are discussed. Further investigation is needed that uses biological measures of mercury exposure.

Plasma selenium and skin neoplasms: A case‐control study

Although experimental studies in animals show that selenium may prevent cancer, case-control studies of internal human cancers have been difficult to interpret because neoplastic tissue sequesters selenium. We therefore conducted a case-control study to examine the association between plasma selenium level and skin cancer, a neoplasm with minimal tumor mass at the time of diagnosis. The mean selenium level among patients with either basal cell epithelioma (N = 142), squamous cell carcinoma (N = 48), or both (N = 50), was 0.141 micrograms/g. This was significantly lower than the mean plasma selenium level of the 103 control subjects, which was 0.155 micrograms/g. The noncancer control groups were drawn from current clinic patients and past clinic patients. The logistic estimate of the odds ratio for the lowest versus the highest decile of selenium for all cases combined versus the group of current patient controls was 4.39; for all cases combined versus the past patient controls, the logistic estimate of the odds ratio was 5.81.

Chronic respiratory disease. In military inductees and parents of schoolchildren.

Several surveys, relating air pollution exposure to the prevalence of chronic respiratory disease, have recently been conducted by the Community Health and Environmental Surveillance program of the Environmental Protection Agency. The effects of sulfur oxides were studied in the Salt Lake Basin, Rocky Mountain smelter communities, New York City, and Chicago. In all four areas, chronic bronchitis prevalence was higher in polluted neighborhoods than in clean ones. In large urban areas, the effect of air pollution was comparable to the effect of moderate cigarette smoking. In all four areas, the effects of air pollution and of cigarette smoking were roughly additive. In Chattanooga, Tenn, no significant correlation was found between chronic bronchitis prevalence and exposure to moderate urban levels of nitrogen oxides.

Air Pollution Effects on Ventilatory Function of US Schoolchildren

The ventilatory performance of elementary schoolchildren living in neighborhoods of high and low air pollution in Cincinnati, Chattanooga, and New York was evaluated by in-school measurements of three-quar- ter second forced expiratory volume (FEV0.75). A consistent relationship between impaired ventilatory function in children 5 to 13 years of age and exposure to particulates plus sulfur oxide was demonstrated. In the Cincinnati study, performance of children in polluted neighborhoods improved during seasons of low pollution but not to the level of their counterparts in low exposure neighborhoods. In New York, results in children age 9 to 13 years indicate that early exposure for five to ten years to elevated air pollution levels was accompanied by a prolonged decrement in ventilatory function. Inconsistent and barely significant effects on lung function were found in Chattanooga where high exposures to nitrogen dioxide had occurred for only two to three years prior to the study.

Health effects of waste incineration: a review of epidemiologic studies.

ABSTRACT There is an increasing trend toward using incineration to solve the problem of waste management; thus, there are concerns about the potential health impact of waste incineration. A critical review of epidemiologic studies will enhance understanding of the potential health effects of waste incineration and will provide important information regarding what needs to be investigated further. This study reviews the epidemiologic research on the potential health impact of waste incineration. Previous studies are discussed and presented according to their study population, incinerator workers or community residents, and health end points. Several studies showed significant associations between waste incineration and lower male-to-female ratio, twinning, lung cancer, laryngeal cancer, ischemic heart disease, urinary mutagens and pro-mutagens, or blood levels of certain organic compounds and heavy metals. Other studies found no significant effects on respiratory symptoms, pulmonary function,twinning, cleft lip and palate, lung cancer, laryngeal cancer,or esophageal cancer. In conclusion, these epidemiologic studies consistently observed higher body levels of some organic chemicals and heavy metals, and no effects on respiratory symptoms or pulmonary function. The findings for cancer and reproductive outcomes were inconsistent. More hypothesis-testing epidemiologic studies are needed to investigate the potential health effects of waste incineration on incinerator workers and community residents.