Validity of surrogates for determination of 30-1000 Hz magnetic field exposure for video display terminal users in office settings.

In studies investigating adverse reproductive outcomes associated with video display terminal (VDT) usage, amounts of time spent in front of a VDT or magnetic field (MF) levels in front of the VDT are used as surrogate measures of subject's MF exposure. However, the relevance of such surrogates to actual exposures has not been demonstrated, and the validity of the use of such measures as a surrogate for the actual MF exposure is only speculative. This study examines 1) measurements of MFs at frequencies of approximately 30-1000 Hz at a fixed distance from the VDTs, 2) reported hours of VDT use, and 3) reported distance between the VDT and the subject's waist as surrogate measures for the average MF exposure level of a VDT user during one 8 h workday. The results showed a weak correlation between the average exposure level of a VDT user and the MF 46 cm from a VDT (R = 0.52, n = 67, P < 0.001). This study showed no association between self-reported hours of VDT usage, or self-reported distance between waist and VDT, and the average MF exposures. Moreover, individuals' average MF exposures did not seem to be affected by other variables, such as position of a VDT on the desk, hours of desk use, and the VDT type (color vs. monochrome). These findings indicate that VDT exposures within office settings are complex and cannot be easily predicted by surrogates.