Evaluation of Occupational and Environmental Exposure to Extremely Low Frequency-Magnetic Fields in Workers: Results of Two Days Personal Monitoring in 543 Workers

Introduction
ELF-MF exposure at work and during non-working time, both at home and outside, should be considered in studies on possible effects. Another problem in exposure evaluation is the variability of ELF-MF levels among different days. We measured exposure at work and during non-working time for 2 consecutive days in a large group of workers, and repeated the measure after some months in 10% of the sample

Methods
ELF-MF exposure was measured in 543 workers using Emdex Lite personal meters. Participants worn the meter during 2 complete work-shifts, to take into account potential within-days variability, and during non-working period. In 53 workers the monitoring was repeated after 6-9 months using the same procedure

Results
The median of TWA during work was 0.14 µT (5° - 95° percentiles: 0.04 - 2.50 µT). The occupational exposure was below 0.4 µT in 79%. The correlation between the TWA measured in the first and in the second monitoring in the 53 workers was 0.80 (p < 0.001). The median TWA exposure at home was 0.03 µT (5° - 95° percentiles 0.01-0.24 µT). About 94% of the subjects at home presented an exposure below 0.2 µT. The median environmental TWA not at home was 0.05 µT.

Discussion
In the whole sample exposure proved to be low, and relatively higher levels were observed for a small fraction of workers.
The individual exposure at home was lower than the occupational one, and in the large majority of subjects lower than the thresholds suggested for suspected long term effects: 97% of subjects had exposure below 0.4 µT.
In the whole group, exposure during occupational activities gives the largest contribution to the overall 24 hours exposure.