Chromosome aberrations induced in the lymphocytes of pilots and stewardesses

Increased frequency of chromosome translocations in airline pilots with long-term flying experience

BACKGROUND

Chromosome translocations are an established biomarker of cumulative exposure to external ionising radiation. Airline pilots are exposed to cosmic ionising radiation, but few flight crew studies have examined translocations in relation to flight experience.

METHODS

We determined the frequency of translocations in the peripheral blood lymphocytes of 83 airline pilots and 50 comparison subjects (mean age 47 and 46 years, respectively). Translocations were scored in an average of 1039 cell equivalents (CE) per subject using fluorescence in situ hybridisation (FISH) whole chromosome painting and expressed per 100 CE. Negative binomial regression models were used to assess the relationship between translocation frequency and exposure status and flight years, adjusting for age, diagnostic x ray procedures, and military flying.

RESULTS

There was no significant difference in the adjusted mean translocation frequency of pilots and comparison subjects (0.37 (SE 0.04) vs 0.38 (SE 0.06) translocations/100 CE, respectively). However, among pilots, the adjusted translocation frequency was significantly associated with flight years (p = 0.01) with rate ratios of 1.06 (95% CI 1.01 to 1.11) and 1.81 (95% CI 1.16 to 2.82) for a 1- and 10-year incremental increase in flight years, respectively. The adjusted rate ratio for pilots in the highest compared to the lowest quartile of flight years was 2.59 (95% CI 1.26 to 5.33).

CONCLUSIONS

Our data suggests that pilots with long-term flying experience may be exposed to biologically significant doses of ionising radiation. Epidemiological studies with longer follow-up of larger cohorts of pilots with a wide range of radiation exposure levels are needed to clarify the relationship between cosmic radiation exposure and cancer risk.

Analysis of spontaneous and bleomycin-induced chromosome damage in peripheral lymphocytes of long-haul aircrew members from Argentina

Spontaneous and bleomycin (BLM)-induced chromosomal aberrations in G0 and G2 stages of the cell cycle have been analyzed in peripheral lymphocytes of 21 long-haul aircrew members from Argentina in order to assess BLM-induced clastogenesis as a first approach to determine the DNA repair capacity and thereby the susceptibility to environmental cancers in aircrew. The possibility that occupational exposure of flight personnel to cosmic radiation can induce an adaptive response in their peripheral lymphocytes that can be detected by a subsequent in vitro treatment with BLM was also investigated. For comparison, aberrations were also scored in the lymphocytes of 15 healthy volunteers matched by age, health, sex, drinking and smoking habits to the flight personnel group. Aircrew exhibited a higher frequency of spontaneous dicentrics and ring chromosomes than the control population (p<0.05). BLM sensitivity test showed that aircrew and controls are equally sensitive to BLM G2 clastogenic effects, since both groups exhibited a similar frequency of chromatid breaks per cell (p>0.05). However, the aircrew sampled population was almost two times more sensitive to BLM G0 clastogenic effects than controls (p<0.05). Therefore, our data suggest that chronic exposure of aircrew to cosmic radiation increases the in vitro chromosomal sensitivity of their peripheral lymphocytes to BLM (at least in the G0 stage of the cell cycle), and that occupational exposure of flight personnel to cosmic radiation does not induce an adaptive response to this radiomimetic compound. Our results justify further studies aimed at determine if those aircrew members hypersensitive to BLM are more prone to develop environmental cancer than BLM-insensitive individuals.

Risk factors, health risks, and risk management for aircraft personnel and frequent flyers

Health risks associated with long periods of time in flight are of concern to astronauts, crew members, and passengers. Many epidemiological studies showed that occupational and frequent flyers may be susceptible to ocular, cardiovascular, neurological, pulmonary, gastrointestinal, sensory, immunological, physiological, and even developmental disorders. In addition, the incidences of cancer and food poisoning are expected to be higher in such individuals. This article reviews health risks and risk factors associated with air travel, and discusses risk management strategies. To reduce adverse health risks, risk factors such as radiation, infection, stress, temperature, pressure, and circadian rhythm need to be avoided or reduced to levels that are as low as technologically achievable to protect flight personnel and passengers.

Cosmic radiation exposure and cancer risk among flight crew

Nearly 20 epidemiologic or related studies of cancer incidence and mortality have been published during or since 2000, with several reporting increased risks of female breast cancer among flight attendants and melanoma among both pilots and cabin crew. Occasionally, excesses of other cancers have been observed, but not consistently. Although the real causes of these excess cancer risks are not known, there is concern that they may be related to occupational exposures to ionizing radiation of cosmic origin. It is possible that confounding risk factors may partially or totally explain the observed relationships, but several investigations are beginning to address lack of past adjustment for reproductive factors and sun exposure with improved study designs. With progress in aviation technology, planes will fly longer and at higher altitudes, and presumably the number of flights and passengers will increase. To respond responsibly to the real and perceived risks associated with flying, more extensive data are needed, but special efforts should be considered to ensure new projects can genuinely add to our current knowledge.

Evaluation of DNA damage in flight personnel by Comet assay

There have been some suggestions that air-crew are at a higher-than-normal risk of developing cancer, since they are exposed to potential genotoxic factors. These include cosmic radiations, airborne pollutants such as the combustion products of jet propulsion, ozone, and electromagnetic fields. We used the Comet assay to investigate DNA damage in flight personnel with the aim of assessing potential health hazards in this occupational category. We studied 40 civil air-crew members who had been flying long-haul routes for at least 5 years, and compared them with a homogeneous control group of 40 healthy male ground staff. The Comet assay, or single-cell gel electrophoresis (SCGE), detects DNA single- and double-strand breaks (DSBs) and alkali-labile lesions in individual cells, and is a powerful and sensitive technique for detecting genetic damage induced by different genotoxic agents. Taking into consideration occupational risk and possible confounding factors, this assay showed a small increase, that did not reach statistical significance, of DNA damage in long-haul crew members compared to controls, indicating a lack of evident genotoxic effects. An association, although again not statistically significant, was found between reduced DNA damage and use of protective drugs (antioxidants).

Chromosomal aberrations in long-haul air crew members

The increasing use of air travel suggests the need for risk assessment and cytogenetic analysis of flight personnel, to check for the risk of developing cancer. Taking into consideration occupational risk and possible confounding factors, we used traditional cytogenetics, the micronucleus test and fluorescent in situ hybridization (FISH) analysis to study 48 male crew members working on long-haul flights and a control group of 48 ground staff. Compared to controls, we detected a significant increase in the relative risk of gaps and breaks (adjusted odds ratio (OR(adj))--7.8; 95% confidence interval (CI) - 2.4-24.9) and of translocations (OR(adj)--5.1; 95% CI 1.5-17.3) in crew members, with a non-significant difference in the other chromosomal aberrations. The possibility of a correlation between translocations and cancer risk highlights the need for preventive measures for aircraft personnel.

Chromosomal damage in air crew members of international flights: A preliminary report

Air crew members of international flights are exposed to ionizing radiations originated from the collision of cosmic particles with atoms of the atmosphere. The degree of exposure varies according to the altitude, latitude, and solar activity. The cytogenetical analysis showed a significant increase of dicentric chromosomes (14.5 ± 0.76 per 1,000 cells) in active air crew members as well as in retired air crew members (7.5 ± 0.59 per 1,000 cells) in relation to controls (0.5 ± 0.05 per 1,000 cells). In active members the frequency of ring chromosomes was also increased (2.0 ± 0.31 per 1,000 cells) but not found in retired crew members. These observations suggest a high degree of exposure to ionizing radiations of air crew personnel. Consequently, the cytogenetic follow-up of air crews chronically exposed to low radiation doses is an open field for further investigations.

Chromosome aberration analysis in Concorde pilots

Chromosomal aberrations, micronuclei, and sister chromatid exchanges have been analysed in human peripheral lymphocytes of 18 Concorde pilots and 10 controls. There was an eightfold significant increase of dicentric chromosomes in the Concorde group. The yield of micronuclei was also significantly elevated. Sister chromatid exchanges in the Concorde group did not differ from the control. Comparing the results to flight personnel from subsonic routes, the dicentric yield was higher in personnel from supersonic crews but the difference was not statistically significant. The overdispersion of dicentric chromosomes showed the influence of high LET cosmic radiation. The estimated mean dose per year ranged from 11 to 37 mSv depending on the radiation weighting factor for neutrons. It is recommended that actual and future high-speed transport should consider not only physical measurements, but also biological data like the frequencies of chromosomal aberrations because the latter reflect sensitively the high biological effectiveness of cosmic radiation.

Increased levels of sister chromatid exchanges in military aircraft pilots

Sister chromatid exchanges (SCEs) were scored in lymphocytes of nine high-performance pilots of alphajet aircrafts and of ten control individuals from the same air base. Statistical analysis of the mean SCE count per cell in the total number of cells analyzed as well as in those having 12 or more SCEs (high-frequency cells, HFCs) revealed a significant difference between pilots and controls, after adjusting for the effect of smoking. Analysis of the cell cycle kinetic data (replication and mitotic indices) revealed no significant differences either between pilots and controls or between smokers and nonsmokers. Previously, we reported an increase in the SCE levels in workers of the aeronautical industry exposed to noise and whole-body vibration. The present results corroborate those findings and indicate that noise and whole-body vibration may cause genotoxic effects in man.