le travail à l'écran de visualisation work with display units

Il 70VDT WORK RELATED FACTORS AND PREGNANCY OUTCOMES - RESEARCHHYPOTHESESUlf Bergqvist, Department of Neuromedicine, National Institute of Occupational Health, Solna,Sweden.The question whether work with visual display terminals during pregnancy affects thepregnancy outcome has been given increased scientific attention during the last decade. Anumber of possible causal factors for such an interaction have been proposed, and will bereviewed here. Evaluating the proposed factors by current scientific knowledge, two criteriacan be put forward; first, whether the factor exist in VDT work situations, and second, whetherdata suggest a potency for interaction in general with pregnancy processes. Using both thesecriteria, a number of the suggested factors can be eliminated.Remaining contenders for an interaction are two for which some suggestive data are available;viz low frequency pulsed magnetic fields and excessive stress or worry. Some other suggestedfactors exist in VDT work situations, but the suggestion for interaction potency is by and largeunsupported.The suggestion that stress and/or worry can influence the risk of miscarriage has beenrepeatedly made - and is supported by effects on animals and some human observations, thelatter primarily from situations of habitual abortions. Counterarguments have e g centered onspecies differences (concerning animal data) and the possibility of individual factors(concerning interpretation of habitual abortion experiences). In summary, a number ofindications but no conclusive evidence appear to support the stress/worry hypothesis. Inaddition, the relationship between stress/worry and VDT work is not clear-cut.The second contender, low frequency magnetic fields is more distinctly associated with VDTsbased on CRTs. The current inability to propose an acceptable model for interaction withbiologic materia makes it, however, extremely difficult to evaluate fields of different temporalappearances - thus, VDT-specific issues are reviewed based on studies with magnetic fields ofthe same temporal appearance ("saw-tooth" form). Five studies have so far been made onvarious animal and in vitro systems, with varying and partly conflicting results. In summary,while some studies do indicate the possibility of an interaction, other studies have not been ableto confirm this.A final reflexion on the outcome of epidemiological studies in light of these two hypotheses canbe made: Both of these two factors exist in VDT work situations, but the degree of variabilityacross different VDT work situations may be of interest. The major factor for variability of themagnetic field exposure is probably posture - something basically unpredictable and pro primonot predicted by work types. This appears to be in sharp contrast with the situation concerningstress situations. Thus, it is possible to argue that the outcome of the Kaiser Permanente study -in which different risk ratios for miscarriages were observed in different job categories - didlend some increased credibility to the stress/worry hypothesis, but none to the magnetic fieldhypothesis.EFFECTS ON NON-IONIZING RADIATIONKjell Hansson Mild, Natl Inst Occup Health, Umeâ, Sweden.I'l - 71The electric and magnetic fields around VDTs have been surveyed byseveral investigators. There are five different types of fields present in thevicinty of the cathode ray tube based VDT: an electrostatic field, ELF electricand magnetic fields with the refresh rate frequency, VLF electric andmagnetic field with line frequency. Measurement show that the equivalentelectrostatic surface potential on the screen can reach up to 20 kV for someVDTs, and the ELF electric field in front of the VDT at a distance of 0.5 mrange from some up to tens of volts per meter but most of the time it is notdistinguishable from the office background 50 Hz electric field. The ELFmagnetic field can reach a few tenths of a jiT, and close to the tube thevalues are up to some (iT. The VLF electric fields range from some up to tensof volts per meter and the corresponding magnetic field is of the order of afew tenths of a JIT at 0.5 m in front of the VDT.The question have been raised about possible health effects from exposureto these weak electromagnetic fields in connection with work with thedisplay terminal. It has been known for some time that weak alternatingelectromagnetic fields can give rise to biological effects on many organizationlevels, from subcellular level to effects on humans. Several reports showeffects on such fundamental cellular processes as DNA synthesis, changes incell membrane properties, chromosome aberrations, changes in transcriptionpatterns. Experiments have shown that the early embryonic development inchicks and mice may be affected by weak magnetic field exposure. In somestudies an altered behaviour response of the experimental animals is seenafter exposure. Weak magnetic field exposure of human volunteers havebeen shown to give a reduction in heart rate with up to 5-10 beats perminut. There are also recent epidemiological studies that suggests thatmagnetic field exposure in excess of 0.2-0.3 |iT may act as a cancerpromotor, and that fetal development may be affected.It is difficult to understand how such weak field can cause these effectssince the energy associated with the fields are orders of magnitude belowthe thermal energy of random motion. At present there is not sufficentinformation available as to which factor, electric or magnetic field, is themore important. Furthermore the role of the geomagnetic field, the roles offield strength, frequency, duration of exposure, intermittent versuscontinous exposure are also unknown. It is not until the question on theinteraction mechanism(s) is solved that we can answer the question onpossible health effects from exposure to weak alternating electromagneticfields. The definition of safe and unsafe field levels must await furtherresearch that will elucidate the interaction mechanism.KEYWORDS: electric and magnetic field, non-ionizing radiation, biologicaleffects.Keywords: Stress, magnetic fields, pregnancy outcomes.TEV 1989 — DEUXIÈME CONFÉRENCE SCIENTIFIQUE INTERNATIONALE • MONTRÉAL • SECOND INTERNATIONAL SCIENTIFIC CONFERENCE — WWDU 1989TEV 1989 — DEUXIÈME CONFÉRENCE SCIENTIFIQUE INTERNATIONALE • MONTRÉAL • SECOND INTERNATIONAL SCIENTIFIC CONFERENCE — WWDU 198912586