An association between exposure to magnetic fields from power lines and the incidence of childhood leukemia is suspected, based on epidemiological studies. The most cited epidemiological threshold is 0.4µT.
Around the world, most study results estimated that less than 1% of the population is exposed to magnetic field levels on average equal or higher than 0.4 microT.
In Flanders, researchers from VITO (Vlaamse Instelling voor Technologisch Onderzoek) established an analytical model based on parameters of high voltage powerlines and calculated a line corridor where fields levels are on average equal or higher than 0.4 microT.
The figure below presents the distance in meter from the axis of the line (or the half width of the corridor) according to the load of the line (in %).
Source : MIRA report (2011)
These researchers also evaluated the number of children (< 15-year-old) exposed to magnetic field higher than 0.4µT from powerlines and underground cables. Results are summarized in table below:
Percentage of children (< 15-year-old) exposure at home ≥ 0.4µT
from powerlines and underground cables
Source : MIRA reports (2007 & 2011)
In the worst-case scenario (maximal load of lines and cables), 1.8% of young people in Flanders would lived in an area with an average magnetic field strength greater than 0.4 μT. In the best-case (25% of the loads), percentages would dropped to less than half percent.
The epidemiological assumption of a causal link between exposure to a magnetic field in the neighborhood (greater than 0.4 μT) and childhood leukemia was in Flanders a case of childhood leukemia every two years from the powerlines and 1/3 of case from underground cables network. This means that if the link is causal, 1.3 additional cases could occur every 2 years. This takes into account all types of leukaemia.
As a basis for comparison, the incidence (number of new cases per 1 000 000 children under 15 year-old per year) of lymphocytic leukaemia (the most common form of childhood leukemia) in Flanders is around 40 children (source: Belgian cancer registry, 2019). On average about 1 in 2000 children gets leukaemia. This is the background risk for all children. In the group of children with a relative risk = 2, about 1 child in 1000 gets leukaemia.
It is worth noting that high voltage powerlines are not our only source of magnetic field exposure. To take into account general exposure, a campaign of 50 Hz magnetic field exposure measurement has been performed in chidren from 0 to 15-year-old by researchers from VITO.
Children carried all day long a recorder (gaussmeter : a magnetic field measurement device) that continuously measured their actual exposure, at home, at school, during transport, during their sleep … Data have been collected for around 650 children. Results showed that:
- The median exposure to the ELF magnetic field is very weak at school (0.01µT) and at home (0.02 µT).
- The percentage of children exposed to cut-off point (0.2, 0.3 and 0.4µT) is less during school time than during all phases of home time.
- 1% of children at school, 1.5% in average at home and 2% during sleep are exposed to intensities higher than 0,4 microT.
- (See the BBEMG project of Gilbert Decat)
In the UK Childhood Cancer Study (Maslanyj et al., 2007) , which studied the association between exposure to the magnetic fields from the supply and use of electricity and the increase risk of childhood leukaemia, only 43 % of the exposures above 0.4 µT were associated with high voltage lines. 57 % of those above 0.4 µT were caused by low-voltage sources associated with the final electricity supply in the house and the use of electrical appliances. For the exposure above 0.2 µT only 20 % were caused by high voltage lines. The German epidemiological study (Schüz et al., 2000) on the association between magnetic fields and childhood leukaemia came to a similar result: high voltage overhead lines were linked with exposure above 0.2 µT in 29 % of the children.
Recent studies showed that the presence of indoor transformer stations in apartment buildings generated a high exposure in the neighboring apartments. That is why the international epidemiological TransExpo Study is now studying the risk for childhood leukaemia in children living in these apartments.