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Biomedical subjects

N A Esmen

Publications and source records attributed to N A Esmen.

At least 19 recordsLinked to original sources
PubMed1998

Exposure estimation in four major epidemiologic studies in the acrylonitrile industry.

The reconstruction of worker exposures has been the mainstay of modem industrial epidemiologic studies. In most cases, the researchers are faced with the difficult dilemma created by the scarcity of the exposure measurement data vis-à-vis the demands for refined quantification. The 4 industrial epidemiologic studies of workers exposed to acrylonitrile share many similarities to illustrate strengths and weaknesses of the current exposure reconstruction methodologies. The analysis of the reported exposure reconstruction methods and comparative analysis of some of the results suggest that there is a certain degree of conformity in the results of the exposure reconstruction processes in these 4 studies. At the same time, the same analysis invokes some questions with respect to the interpretation of the exposure reconstruction results.

Acrylonitrile↗
PubMed1997

A case-control study of lung cancer mortality in six Gila Basin, Arizona smelter towns.

To investigate factors related to lung cancer mortality in six Arizona copper smelter towns, we identified 185 lung cancer cases and two matched controls per case from decedent residents during 1979-1990. Detailed information on lifetime residential, occupational, and smoking history was obtained by structured telephone interviews with knowledgeable informants. Interviews were completed for 82% of 183 eligible cases and 88% of the targeted number (366) of controls. Estimated historical environmental exposures to smelter emissions, based on atmospheric diffusion modeling of measured SO2 concentrations, were linked with residential histories to derive individual profiles of residential exposure. Occupational histories were characterized by potential exposure to smelter emissions, asbestos, and ionizing radiation. Conditional logistic regression was used to compare study factors in cases and controls with adjustment for potential confounding factors: gender, Hispanic ethnicity, and smoking. In overall and gender-specific analyses, no statistically significant associations were observed between lung cancer risk and any of the measures of residential exposure to smelter emissions considered (town of residence at time of death, highest level of exposure, and duration or cumulative exposure above background levels), or any of the estimated occupational exposures (definite or potential asbestos, potential ionizing radiation, definite or potential smelter). Among male residents of some, but not all, towns, there was some evidence of a positive association between lung cancer risk and reported copper smelter-related employment (reported as definite), with the highest risk observed for Miami, Arizona. This study provided little evidence of a positive association between lung cancer mortality and residential exposure to smelter emissions. Specific factors associated with the apparent heterogeneity in lung cancer risk across study towns cannot be identified in this community-based study.

Arizona↗
PubMed1997

An updated meta-analysis of formaldehyde exposure and upper respiratory tract cancers.

In this study, we summarize 47 epidemiologic studies related to formaldehyde exposure and use meta-analytic techniques to assess findings for cancers of the lung, nose/nasal sinuses, and nasopharynx. Our analyses indicate that workers with formaldehyde exposure have essentially null findings for lung cancer and a slight deficit of sinonasal cancer. Nasopharyngeal cancer rates were elevated moderately in a minority of studies. Most studies, however, did not find any nasopharyngeal cancers, and many failed to report their findings. After correcting for underreporting, we found a meta relative risk of 1.0 for cohort studies. Case-control studies had a meta relative risk of 1.3. Our review of the exposure literature indicated that the nasopharyngeal cancer case-control studies represented much lower and less certain exposures than the cohort studies. We conclude that the available studies do not support a causal relation between formaldehyde exposure and nasopharyngeal cancer. This conclusion conflicts with conclusions from two previous meta-analyses, primarily because of our consideration of unreported data.

Carcinogens, Environmental↗
PubMed1996

Mortality among chemical workers in a factory where formaldehyde was used.

OBJECTIVES: An independent and updated historical cohort mortality study was conducted among chemical plant workers to investigate further an association between exposures to formaldehyde and particulates and cancers of the nasopharynx and lung reported in an earlier National Cancer Institute study of the same plant. METHODS: Subjects were 7359 workers who were first employed between 1941 and 1984 in a factory in Wallingford, Connecticut where formaldehyde was used. Vital status was determined on 31 December 1984 for 96% of the cohort and death certificates were obtained for 93% of 1531 known deaths. Exposures of individual workers were estimated quantitatively for formaldehyde, product particulates, and non-product particulates, and qualitatively for pigment. Statistical analyses focused on 6039 white men in 1945-84. Cohort data that could not have been included in the National Cancer Institute study were also analysed separately. RESULTS: Mortality among long term workers (employed > or = 1 y) was generally similar to or more favourable than that of the general population, and there was little evidence of a relation between either rates of lung cancer or standardised mortality ratios (SMRs) and several measures of exposure to formaldehyde, particulates, and pigment. For several causes including lung cancer, death rates among short term workers (employed < 1 y) were significantly increased. Short term workers did not seem to differ from long term workers for the exposures considered. Among all white men, a significant SMR of 550 (local comparison) for nasopharyngeal cancer (NPC) was based on the same four index cases identified in the earlier study of this plant. Only one case of nasopharyngeal cancer had any appreciable exposure to formaldehyde. No new cases of nasopharyngeal cancers were found among the cohort data that could not have been included in the National Cancer Institute study--that is, extended observation time and additional study members. CONCLUSIONS: Among workers employed for at least one year, this study provides little evidence that the risk of lung cancer is associated with exposure to formaldehyde alone or in combination with particulates or pigment. The significant increases in both the rates and SMRs for lung cancer seem to be primarily a phenomenon of short term workers, but the possibility remains that unmeasured occupational or non-occupational factors may have played a part.

Chemical Industry↗
PubMed1990

Human occupational and nonoccupational exposure to fibers.

Human exposure to fibers in occupational and nonoccupational environments has been a health concern for nearly a century. In this review, selected results from the literature are presented to highlight the availability, limitations, and interpretive difficulties associated with the past and current human fiber exposure data sets. In the traditionally defined asbestos fibers, large amounts of the data available suffer from the diversity of sample collection and analysis methods. Two simple generalizations suggest that occupational exposures are several orders of magnitude higher than that of environmental exposures; and currently extant data and the current routine measurement practices present significant difficulties in the consistent interpretation of the data with respect to health effects. The data on the human exposures to man-made vitreous fibers are much more complete than the data on asbestos exposure, while exposure data on other man-made fibrous materials are lacking. The human exposure data to many minerals which, at times, exist in fibrous habit, are very scanty, and in view of the biological activity of some of these fibers, this lack may be of significant concern.

Air Pollutants↗
PubMed1987

Some effects of cigarette smoking, arsenic, and SO2 on mortality among US copper smelter workers.

Previous studies of the relationship between arsenic levels and respiratory cancer among copper smelter workers have not directly accounted for possible effects of SO2 exposure and cigarette smoking. This is a report on the 1949-1980 mortality experience of 6,078 white male workers who worked at least 3 years between 1 January 1946 and 31 December 1976 at one or more of eight US copper smelters. The completeness of the cohort was verified statistically, and worker exposures to arsenic, SO2, dust, nickel, cadmium, and lead were estimated from retrospective industrial hygiene surveys reported elsewhere. By using internal controls, a dose-response relationship for lung cancer was observed with exposure to arsenic and SO2. When cigarette smoking data were included with arsenic and SO2 exposure data in a nested case-control analysis, only smoking and arsenic were statistically significant factors. The arsenic-lung cancer relationship was confined to a single smelter associated with high content feed. In the remaining smelters mortality for all causes of death and for all cancer was not high based on comparisons with national, state, and local rates.

Air Pollutants, Occupational↗
PubMed1986

Design and calibration of a low flow parallel stage impactor.

A low flow, compact Parallel Stage Impactor was designed, constructed and calibrated. This instrument has six stages: one for total collection of air particulates, and the other five with cut-off sizes of 0.34 micrograms, 0.75 micrograms, 1.90 micrograms, 3.12 micrograms and 7.43 micrograms aerodynamic equivalent diameter. Flow through the individual stages is controlled by adjustable needle valves, which act as critical orifices. Flow was 700 mL/min per stage, resulting in a total flow of 4.2 L/min. The instrument was calibrated using uranine test aerosols, photofluorescence and optical microscopy techniques. There was excellent agreement between theoretical calculations and observed performance. The instrument design details and performance suggest a rugged and reliable field instrument for particle size analysis.

Aerosols↗
PubMed1985

The status of indoor air pollution.

Indoor air pollution, specifically restricted in its meaning to chemicals in home indoor air environment, presents a new and probably an important challenge to the researchers of the air pollution field. The general overview of this topic suggests that the voluminous data generated in the past ten or so years have only defined the rudiments of the problem, and significant areas of research still exist. Among the important areas where information is lacking, the exposures to contaminants generated by the use of consumer products and through hobbies and crafts represent perhaps the most urgent need for substantial research.

Air Pollution↗
PubMed1983

Respiratory disease among workers exposed to man-made mineral fibers.

Fibrous glass and mineral wool workers exposed to airborne man-made mineral fibers prior to 1964 were identified and followed for deaths caused by respiratory disease. Fiber exposure levels were estimated for each worker. Average fiber concentrations were very low in relation to a National Institute of Occupational Safety and Health recommendation that exposure to man-made mineral fibers less than 3.5 microns in diameter be limited to 3 fibers per cubic centimeter of air. Fibrous glass workers were exposed to about one hundredth and mineral wool workers to about one tenth of that amount. Respiratory cancer death rates were not excessive for the fibrous glass workers, but they were significantly elevated for the mineral wool workers. When respiratory cancer deaths were compared with fiber exposure levels, however, there was in no instance a strong positive correlation. There was a significant excess in nonmalignant respiratory disease deaths (excluding influenza and pneumonia) for fibrous glass workers and for the total cohort. When these nonmalignant respiratory disease deaths were compared with fiber exposure levels, however, there was in no instance a strong positive association. A special study was made of workers exposed to small diameter fibers. Respiratory cancer deaths were not in excess; however, there was an excess in nonmalignant respiratory disease deaths. This study provided no consistent evidence of a respiratory disease hazard related to exposure to man-made mineral fibers among the workers who produce these fibers. Results must be interpreted in relation to the relatively low exposure levels for these workers.

Adult↗
PubMed1981

Limitations on dose estimation.

The process of estimation of dose at a target organ from the measurements of environmental concentration of potentially hazardous agents is theoretically examined. The analysis of the estimation process suggests that the design of any study which aims to find the health effects of an agent or to construct a dose-response relationship from environmental measurements must be fully scrutinized to see whether a representative dose is tractable from such measurements made on the agent or extrapolation from a set of known effects at high dose levels is feasible and desirable.

Air Pollutants↗
PubMed1980

Generation of monodisperse fibrous glass aerosols.

Investigations of the aerodynamic behavior of fibers, lung deposition studies which involve fibers and investigations which are concerned with the biological effects of fibers create the need for fibrous aerosols monodisperse with respect to both fiber length and diameter. The method of preparation presented in this paper is primarily based on embedding the bulk quantity of fibers in a plastic histological preparation medium and subsequently cutting the fibers to the desired lengths. The slices which are obtained by the microtoming process are purified of the plastic medium by burning and ashing and the fibrous dust obtained in this manner is then cleared of any debris by liquid elutriation. The results show that gram quantities of nearly monodisperse glass fiber dust with lengths of up to 50 micrometers can be obtained.

Aerosols↗
PubMed1980

Design, calibration and testing of a parallel stage impactor.

The fractionation of airborne particles according to aerodynamic size by a number of impactor stages operated in parallel offers significant advantages over the commonly employed cascade impaction technique when determining mass or chemical size distribution of an aerosol. A seven stage, round jet impactor based on the parallel stage concept was designed, manufactured, calibrated and tested. The stages operate at 25 liters per minute collecting fractions of zero to 0.35, 0.70, 2.0, 4.0 and 7.0 micrometers aerodynamic diameter. The last two stages have no impaction surface and collect aerosol over the entire size range. All stages are mounted on standard 47 mm filter holders. For each stage, particles larger than the cut-off size impact on a thick adhesive surface and are discarded while those smaller are collected on a filter. The ratio of the particle mass penetrating to the filter of a given stage to the mass of the entire aerosol represents the cumulative mass fraction associated with the cut-off diameter for that stage. Any losses associated with non-ideal behavior in the impactor become an inherent part of the calibration. Calibration of the impactor showed that stage cut-off sizes are close to the values predicted by impactor theory. A novel technique employing polydisperse aerosol was used in the calibration. Challenge of the impactor calibration with solid aerosols of known size distribution gave excellent results. Tests for particle bounce after four hours of operation in urban aerosol showed that accumulation of particles at the impaction surface does not increase bounce or blow-off. Microscopic examination of impaction surfaces immediately after sampling showed most of the particles to be embedded within the adhesive rather than on the surface.

Air Pollutants↗
PubMed1980

Distortion of cascade impactor measured size distribution due to bounce and blow-off.

Accurate measurement of particle size distribution by a cascade impactor requires that particles remain on the collection surfaces after impaction. Recent studies show that, when a solid aerosol is sampled, significant rebound and re-entrainment of particles occur in cascade impactors. A mathematical model of a cascade impactor including collection efficiency functions for solid aerosols on various impaction surfaces was developed and used to operate upon a series of log-normal size distributions. The impactor modeled was a six stage Andersen operated at 28.3 L/min. When bare metal or glass impaction surfaces are used, the impactor indicates non-log-normal distributions and the estimated distribution parameters are in error by as much as a factor of 7. When glass fiber impaction surfaces are used, although less serious errors are indicated, the deviation from log-normality is significant for aerosols with MMD larger than 3 micrometers. When oil covered impaction stages are used the indicated distributions parameters are acceptably close to the input parameters. The accuracy of the model was verified experimentally.

Aerosols↗