Lawrence C. Mohr

Mortality among US commercial pilots and navigators

The airline industry may be an occupational setting with specific health risks. Two environmental agents to which flight crews are known to be exposed are cosmic radiation and magnetic fields generated by the aircrafts electrical system. Other factors to be considered are circadian disruption and conditions specific to air travel, such as noise, vibration, mild hypoxia, reduced atmospheric pressure, low humidity, and air quality. This study investigated mortality among US commercial pilots and navigators, using proportional mortality ratios for cancer and noncancer end points. Proportional cancer mortality ratios and mortality odds ratios were also calculated for comparison to the proportional mortality ratios for cancer causes of death. Results indicated that US pilots and navigators have experienced significantly increased mortality due to cancer of the kidney and renal pelvis, motor neuron disease, and external causes. In addition, increased mortality due to prostate cancer, brain cancer, colon cancer, and cancer of the lip, buccal cavity, and pharynx was suggested. Mortality was significantly decreased for 11 causes. To determine if these health outcomes are related to occupational exposures, it will be necessary to quantify each exposure separately, to study the potential synergy of effects, and to couple this information with disease data on an individual basis.

Hypoxia during air travel in adults with pulmonary disease.

At the present time, commercial aircraft cabins are required to be pressurized to the equivalent of 8,000 feet or less. Although in-flight medical emergencies are infrequent, some adults with pulmonary disease may experience significant physiological stress, exacerbation of their underlying illness, and severe hypoxemia during air travel. A careful preflight medical evaluation is essential to determine which patients with pulmonary disease can fly safely, which patients require supplemental oxygen, and which patients should not fly at all. All adults with pulmonary disease who have a preflight arterial oxygen tension of less than 70 mm Hg or a preflight pulse oximetry saturation of less than 92% should receive supplemental oxygen during air travel. The hypoxia altitude simulation test and the 6-minute walk test are useful when additional evaluation for supplemental in-flight oxygen is needed. Patients with an unstable condition, an acute exacerbation of their pulmonary disease, severe pulmonary hypertension (Class III and Class IV), or an active pneumothorax should not fly.

Trichloroethylene risk assessment: A review and commentary

Trichloroethylene (TCE) is a widespread environmental contaminant that is carcinogenic when given in high, chronic doses to certain strains of mice and rats. The capacity of TCE to cause cancer in humans is less clear. The current maximum contaminant level (MCL) of 5 ppb (μg/L) is based on an US Environment Protection Agency (USEPA) policy decision rather than the underlying science. In view of major advances in understanding the etiology and mechanisms of chemically induced cancer, USEPA began in the late 1990s to revise its guidelines for cancer risk assessment. TCE was chosen as the pilot chemical. The final guidelines emphasized a “weight-of-evidence” approach with consideration of dose-response relationships, modes of action, and metabolic/toxicokinetic processes. Where adequate data are available to support reversible binding of the carcinogenic moiety to biological receptors as the initiating event (i.e., a threshold exists), a nonlinear approach is to be used. Otherwise, the default assumption of a linear (i.e., nonthreshold) dose-response is utilized. When validated physiologically based pharmacokinetic (PBPK) models are available, they are to be used to predict internal dosimetry as the basis for species and dose extrapolations. The present article reviews pertinent literature and discusses areas where research may resolve some outstanding issues and facilitate the reassessment process. Key research needs are proposed, including role of dichloroacetic acid (DCA) in TCE-induced liver tumorigenesis in humans; extension of current PBPK models to predict target organ deposition of trichloroacetic acid (TCA) and DCA in humans ingesting TCE in drinking water; use of human hepatocytes to ascertain metabolic rate constants for use in PBPK models that incorporate variability in metabolism of TCE by potentially sensitive subpopulations; measurement of the efficiency of first-pass elimination of trace levels of TCE in drinking water; and assessment of exogenous factors’ (e.g., alcohol, drugs) ability to alter metabolic activation and risks at such low-level exposure.

Cosmic radiation and magnetic field exposure to airline flight crews

BACKGROUND Flight crews are exposed to elevated levels of cosmic radiation and to magnetic fields generated by the aircrafts electrical system. The purpose of this study was to quantify these two occupational exposures. METHODS Magnetic fields were measured during 37 flights (23 in the cockpit and 14 in the cabin) using an Emdex Lite personal dosimeter. All cockpit measurements were taken on the B737/200. Cabin measurements were taken in several aircraft types, including the B737, B757, DC9, and L1011. Cosmic radiation was computer estimated for 206 flights using the Federal Aviation Administrations program CARI-3C. RESULTS Magnetic field levels in the cockpit had a mean value of approximately 17 milliGauss (mG), while cabin measurements were lower (mean values of approximately 3 or less in economy, 6 in first class, 8 in front serving areas). Cosmic radiation equivalent dose rates to bone marrow and skeletal tissue ranged from 0.3 to 5.7 microsieverts per hour. CONCLUSIONS Elevated magnetic field levels in front serving areas and the cockpit suggest the need for further study to evaluate long-term exposure to flight crew members who work in these areas. Cosmic radiation levels are well below occupational limits for adults, but may require some pregnant flight crew members to adjust their flying time or routes.

137Cesium Exposure and Spirometry Measures in Ukrainian Children Affected by the Chernobyl Nuclear Incident

Background After the Chernobyl accident in 1986, children of the contaminated Narodichesky region of Ukraine were obliged to participate in a yearly medical screening. They have been exposed to 137cesium (137Cs; half-life = 30 years) in contaminated soils, air, and food. Objective Using a “natural experiment” approach and a longitudinal prospective cohort study design, we investigated the association of soil 137Cs and spirometry measures for 415 children using 1,888 repeated measurements from 1993 to 1998. Methods Mean baseline village soil 137Cs measurements, which varied from 29.0 to 879 kBq/m2, were used as exposure indicators. A standardized spirometry protocol and prediction equations specific to Ukrainian children were used by the same pulmonologist in all screenings. Results Children living in villages with the highest quintile of soil 137Cs were 2.60 times more likely to have forced vital capacity (FVC) < 80% of predicted [95% confidence interval (CI), 1.07–6.34] and 5.08 times more likely to have a ratio of forced expiratory volume in 1 sec (FEV1) to FVC% < 80% (95% CI, 1.02–25.19). We found statistically significant evidence of both airway obstruction (FEV1/FVC%, peak expiratory flow, and maximum expiratory flow at 25%, 50%, and 75% of FVC) and restriction (FVC) with increasing soil 137Cs. Conclusions These findings are unique and suggest significant airway obstruction and restriction consequences for children chronically exposed to low-dose radioactive contaminants such as those found downwind of the Chernobyl Nuclear Power Plant.

Racial, age, and rural/urban disparity in cervical cancer incidence.

PURPOSE: High mortality rates of cervical cancer among black women have been observed for several decades in the Southeast. The purpose of this study is to assess the factors associated with this geographic and racial enigma, and to see if incidence is consistent with mortality.METHODS: Using the Savannah River Regional Health Information System (SRRHIS), a 5-year cancer registry from 1991-1995, incidence rates were calculated and compared to rates from Surveillance, Epidemiology, and End Results (SEER). The rates per 100,000/year were analyzed by race, rural/nonrural, and age (<45 and >/=45).Rates are similar between SRRHIS and SEER except in the case of black women over the age of 45. These women in rural SRRHIS have 1.66 times the incidence rate compared to those in nonrural SRRHIS and 1.97 times the rate of rural SEER.RESULTS:Table 1CONCLUSIONS: The results of the study suggest that the incidence of cervical cancer in the region is consistent with the mortality rates. The age-group with the highest rates are black women over 45 in rural areas, suggesting the need to target this group to reduce the racial disparity in cervical cancer.

Application of cryopreserved human hepatocytes in trichloroethylene risk assessment : Relative disposition of chloral hydrate to trichloroacetate and trichloroethanol

Background Trichloroethylene (TCE) is a suspected human carcinogen and a common ground-water contaminant. Chloral hydrate (CH) is the major metabolite of TCE formed in the liver by cytochrome P450 2E1. CH is metabolized to the hepatocarcinogen trichloroacetate (TCA) by aldehyde dehydrogenase (ALDH) and to the noncarcinogenic metabolite trichloroethanol (TCOH) by alcohol dehydrogenase (ADH). ALDH and ADH are polymorphic in humans, and these polymorphisms are known to affect the elimination of ethanol. It is therefore possible that polymorphisms in CH metabolism will yield subpopulations with greater than expected TCA formation with associated enhanced risk of liver tumors after TCE exposure. Methods The present studies were undertaken to determine the feasibility of using commercially available, cryogenically preserved human hepatocytes to determine simultaneously the kinetics of CH metabolism and ALDH/ADH genotype. Thirteen human hepatocyte samples were examined. Linear reciprocal plots were obtained for 11 ADH and 12 ALDH determinations. Results There was large interindividual variation in the Vmax values for both TCOH and TCA formation. Within this limited sample size, no correlation with ADH/ALDH genotype was apparent. Despite the large variation in Vmax values among individuals, disposition of CH into the two competing pathways was relatively constant. Conclusions These data support the use of cryopreserved human hepatocytes as an experimental system to generate metabolic and genomic information for incorporation into TCE cancer risk assessment models. The data are discussed with regard to cellular factors, other than genotype, that may contribute to the observed variability in metabolism of CH in human liver.

Pleural Plaques and Their Effect on Lung Function in Libby Vermiculite Miners

BACKGROUND Multiple studies have investigated the relationship between asbestos-related pleural plaques (PPs) and lung function, with disparate and inconsistent results. Most use chest radiographs to identify PPs and simple spirometry to measure lung function. High-resolution CT (HRCT) scanning improves the accuracy of PP identification. Complete pulmonary function tests (PFTs), including spirometry, lung volumes, and diffusing capacity of the lung for carbon monoxide, provide a more definitive assessment of lung function. The goal of this study was to determine, using HRCT scanning and complete PFTs, the effect of PPs on lung function in Libby vermiculite miners. METHODS The results of HRCT scanning and complete PFTs performed between January 2000 and August 2012 were obtained from the medical records of 166 Libby vermiculite miners. Multivariate regression analyses with Tukey multivariate adjustment were used to assess statistical associations between the presence of PPs and lung function. Adjustments were made for age, BMI, smoking history, duration of employment, and years since last occupational asbestos exposure. RESULTS Nearly 90% of miners (n = 149) had evidence of PPs on HRCT scan. No significant differences in spirometry results, lung volumes, or diffusing capacity of the lung for carbon monoxide were found between miners with PPs alone and miners with normal HRCT scans. Miners with both interstitial fibrosis and the presence of PPs had a significantly decreased total lung capacity in comparison with miners with normal HRCT scans (P = .02). Age, cumulative smoking history, and BMI were significant covariates that contributed to abnormal lung function. CONCLUSIONS Asbestos-related PPs alone have no significant effect on lung function in Libby vermiculite miners.

Flight deck magnetic fields in commercial aircraft

BACKGROUND Airline pilots are exposed to magnetic fields generated by the aircrafts electrical system. The objectives of this study were (1) to directly measure flight deck magnetic fields in terms of personal exposure to the pilots when flying on different aircraft types over a 75-hour flight-duty month, and (2) to compare magnetic field exposures across flight deck types and job titles. METHODS Measurements were taken using personal dosimeters carried by either the Captain or the First Officer on Boeing 737/200, Boeing 747/400, Boeing 767/300ER, and Airbus 320 aircraft. RESULTS Approximately 1,008 block hours were recorded at a sampling frequency of 3 seconds. Total block time exposure to the pilots ranged from a harmonic geometric mean of 6.7 milliGauss (mG) for the Boeing 767/300ER to 12.7 mG for the Boeing 737/200. CONCLUSIONS Measured flight deck magnetic field levels were substantially above the 0.8-1 mG level typically found in the home or office and suggest the need for further study to evaluate potential health effects of long-term exposure.

Leukaemia in the vicinity of two tritium-releasing nuclear facilities: a comparison of the Kruemmel Site, Germany, and the Savannah River Site, South Carolina, USA.

In 1991, an increased rate of childhood leukaemia was reported from the small northern German community of Elbmarsch, which is located on the banks of the River Elbe opposite the Kruemmel nuclear power plant. Owing to the fact that the increase occurred six years after the start-up of the plant, radioactive discharges were suspected as being implicated in the development of the cases. Previous investigations have failed to identify any exposure which might be associated with the cluster. Nonetheless, concern regarding the increased tritium burden in the environment remains. To further assess the impact of tritium releases to the environment upon population cancer rates, the releases and leukaemia rates at the Savannah River site, USA, were compared with the Kruemmel site. Based on the data from 1991 to 1995, the incidence of childhood leukaemia in the vicinity of the Savannah River site was non-significantly less than expected compared with the significantly higher than expected rates close to the German plant. In contrast, tritium releases from the Savannah River site exceed those from the Kruemmel site by several orders of magnitude. The results of this observational study suggest that factors other than environmental tritium releases are associated with the increased number of leukaemia cases near the Kruemmel site.