Risk assessment demonstrated for the example of childhood leukaemia and exposure to power transmission lines

The possibility of a connection existing between electric or magnetic fields in the extremely low frequency range (50 Hz in Europe, 60 Hz in the USA) and cancer has been a topic of discussion for more than 20 years. The debate was first triggered by a case control study in Denver published in 1979, in which children living close to power transmission lines were found to be at a threefold higher risk of dying of leukaemia. Since then numerous studies have been carried out worldwide on this controversial topic. The scientific controversy lies in the fact that magnetic flux densities which epidemiologists classify as a burden in most cases above 0.2 microtesla (μ) are only a fraction of the 100 μT recommended as a limit value by the International Commission on Non-Ionising Radiation Protection (ICNIRP). This limit value in turn is many times lower than the magnetic flux densities at which biological effects such as oscillopsia or nerve irritation have been demonstrated. There is no known mechanism to explain how such very weak magnetic fields could have a cancerogenic effect. Two independent meta-analyses on EMF and the risk of childhood leukaemia, both based on the original data of all studies known at the time of publication, came to mutually consistent conclusions. Ahlboom et al., after pooling the results of the methodologically superior studies, found a twofold higher risk of leukaemia from 0.4 μT upward, but not below this exposure level. Greenland et al., after pooling the results of all available studies, reported a statistically significant odds ratio of 1.7 at magnetic flux densities greater than 0.3 μT. This led an expert committee commissioned by the ''International Agency for Research on Cancer (IARC)'', in the spring of 2001, to classify extremely low frequency magnetic fields as ''possibly carcinogenic to humans''. Static fields and extremely low frequency electric fields, by contrast, were considered ''not classifiable as to their carcinogenicity to humans''. The IARC justified its decision in favour of these classifications with the observation that especially the qualitatively more convincing epidemiological studies had yielded consistent results. This paper explains in detail the IARC's classification in the manner of a risk assessment