Epidemiological studies put in advance the possibility of a doubling of the risk of childhood leukaemia for children exposed to magnetic flux density in average higher than 0.4 µT.
The origin of childhood leukeamia is expected to be multifactorial and many unknown factors are remaining. Magnetic fields, if involved, should be one factor and could not explain all the cases.
In the Flemish part of Belgium, if the relationship was confirmed, according to the global exposure of the children from powerlines and the prevalence of childhood leukaemia, between one and two additional case(s) per two years (see Decat et al, 2007) could find its origin in magnetic fields from powerlines. The risk is very low. However, according to the importance of the subject, studies are on their way around the world to go further. For example, within the BBEMG, Maurice Hinsenkamp & Jean-François Collard are currently working on the research of a potential mechanism of action through in vitrostudies.
In 2002, with the epidemiological data in mind and without demonstration of any mechanism of action in laboratory studies (in animals exposed all their life long or in cells), the International Agency for Research on Cancer classified EM field in the 2B class which means possibly carcinogenic to humans.
What is the meaning of the IARC classification in 2B?
For 30 years, several well-conducted epidemiological studies and meta-analyses established a statistical link between exposure to extremely low frequencies (ELF) magnetic fields and an increased risk of acute childhood leukaemia. This happens from an exposure being in average higher than 0.4 µT.
Years after years, epidemiolgists have been looking for bias or confounders, but they do not reach any firm conclusion in this matter.
In the same time, other researchers were working in their lab on animals or in cells to find mechanisms of action... but without success. Even in animals exposed all their life long, the link between ELF magnetic fields and acute leukaemia was not proved through well done studies. For all known human carcinogens there is at least one animal for which the agent is also a carcinogen. Up to now, no mechanism of action could explain the potential link.
In 2002, after analysing the data, the International Agency for Research on Cancer decided to classified ELF magnetic fields in 2B class (meaning possibly carcinogenic).
The 2B class is currently (May 2015) composed by 287 agents, as ELF magnetic fields, coffee, lead, pickled vegetables (traditional in Asia), chloroform, nickel, gazoline.
Data on children exposure
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 %).
|Line voltages||Load of the line in % and 1/2 width of the corridor "0,4 µT"|
|70 kV||25% - 9 m
50% - 18 m
75% - 27 m
100% - 36 m
(on average 15m)
|150 kV||25% - 15 m
50% - 30 m
75% - 43 m
100% - 58 m
(on average 40m)
|380 kV||25% - 33 m
50% - 66 m
75% - 98 m
100% - 130 m
(on average 90m)
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
|Load of the line||High voltage |
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 100 000 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, 2011). 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.
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.
Documents & Links
- MIRA (2011) Milieurapport Vlaanderen, Achtergronddocument 2011, Niet-ioniserende straling Verschaeve L., Brits E., Bossuyt M., Adang D., Decat G., Martens L., Joseph W., Vlaamse Milieumaatschappij, www.milieurapport.be
Available on-line at :
- Decat, G. Meynen, G., Peeters, E. Van Esch, L. Deckx, L. & Maris, U. (2007). Modellering en GIS-toepassing voor het bepalen van de blootstelling en het epidemiologisch risico van het 50 Hz magnetisch veld gegenereerd door de ondergrondse hoogspanningskabels in Vlaanderen Studie uitgevoerd in opdracht van de Vlaamse Milieumaatschappij (VMM) - MIRA-rapport 2007/IMS/R/426.
Available on-line at :
http://www.milieurapport.be/Upload/main/miradata/MIRA-T/02_themas/02_19/2007-07-ondergrondse%20hoogspanningskabels%20-%20eindrapport.pdf (in Dutch)
- Maslanyj et al. (2007). Investigation of the sources of residential power frequency magnetic field exposure in the UK Childhood Cancer Study. Journal of Radiological Protection, 27:41-58.
- Schüz et al. (2000). Extremely low frequency magnetic fields in residences in Germany. Radiat Environ Biophys, 39:233-240.
- Classification of IARC: Characteristics of the classification is available in the IARC website