1) To measure the strength of the magnetic field produced by power transformer stations.
2) To use these magnetic field data and additional data collected on the patterns of exposure to estimate subjects' exposure in power transformer stations.
3) To determine whether the exposure levels exhibited dose-response patterns that might influence the ECG.
A total of 59 subjects (transformer substation workers), divided into three independent magnetic field strength groups, were compared. ECGs were recorded in the resting position at the Occupational Health Centre (not at workplace).
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
daily exposure of 12 h for at least 5 years
location 1
|
|
|
Exposure 2:
50 Hz
Exposure duration:
daily exposure of 12 h for at least 5 years
location 2
|
|
|
Exposure 3:
50 Hz
Exposure duration:
daily exposure of 12 h for at least 5 years
location 3
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | daily exposure of 12 h for at least 5 years |
| Additional info | location 1 |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0.067 µT | average over time | estimated | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | daily exposure of 12 h for at least 5 years |
| Additional info | location 2 |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1.18 µT | average over time | estimated | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | daily exposure of 12 h for at least 5 years |
| Additional info | location 3 |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 5.2 µT | average over time | estimated | - | - |
The data suggest that the relationship between field strength and response is non-linear. The adjusted mean QTc values are similar between the "low" exposure and the "high" exposure, but significantly lower in the "medium" group.
The authors' interpretation of the results is that a specific exposure pattern might be responsible for the non-linear effects, so that generally, characterizing exposure to electric and magnetic fields using simple metrics such as time-weighted average (TWA) may be insufficient.
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