02/08/2005 - Sources of magnetic fields in the home
Investigation and Identification of Sources of Residential Magnetic Field Exposures in the United Kingdom Childhood Cancer Study (HPA-RPD)
This new study went back to examine the details of the homes included in the UK Childhood Cancer Study (UKCCS) that had measured magnetic fields above 0.2 microtesla, in order to determine what caused the elevated magnetic field levels. There are less than 200 homes in this study, so the conclusions drawn can only be considered as very provisional.
The UKCCS published the results of exposure to power frequency magnetic fields in 1999 followed by a paper on residential proximity to power lines in 2000. They did find an association of child leukaemia with proximity to high voltage overhead powerlines, but did not have enough cases in high magnetic fields to determine if there was an association with elevated magnetic fields. However, when their magnetic field data was used in two large meta-analyses they showed that there was a doubling in the incidence of child leukaemia above 0.3 to 0.4 microtesla.
This new study went back to examine the details of the homes, of the cases and controls, that had measured magnetic fields above 0.1 to 0.2 microtesla, in order to determine what caused the elevated magnetic field levels. There are less than 200 homes in this study, so the conclusions drawn can only be considered as very provisional. This new research was funded by the Department of Trade and Industry and the Energy Networks Association.
The study claims that less than 2.5% of UK homes have background magnetic fields above 0.2 microtesla. This is slightly misleading as they use the "geometric mean of a time-weighted average" - this minimises the effect of short high peaks that may actually be the most biologically active components! The whole subject of what to measure and how to measure it ("metrics") is currently under debate by a small sub-group of SAGE, the UK Government's official consultation process on what precautionary advice to give as regards the health effects of power-frequency electric and magnetic field exposure.
This study found that the most common source of magnetic field exposure above 0.2 microtesla was found to be due to currents flowing in the supply to the home and possible wiring faults (32%) followed by nearby high voltage power lines of 132 kV (kilovolts) and above (20%). The effect of currents in low voltage distribution mains cables located near to homes was also identified as a source of exposure (16%). These residences were often characterised by little or no front garden and were therefore more likely to be closer to the cables.
Of 21 homes with exposures of 0.4 microtesla and above, the most common single source was high voltage overhead lines (43%), followed by currents in the supply to the home and possible internal wiring faults (33%).
Maslanyj, MP, Mee TJ and Allen SG, Investigation and Identification of Sources of Residential Magnetic Field Exposures in the United Kingdom Childhood Cancer Study (UKCCS). HPA-RPD-005. ISBN 0-85951-564-8.