Investigation of the sources of residential power frequency magnetic field exposure in the UK Childhood Cancer Study.

There is an unexplained association between exposure to the magnetic fields arising from the supply and use of electricity, and increase in risk of childhood leukaemia. The UK Childhood Cancer Study (UKCCS) provides a large and unique source of information on residential magnetic field exposure in the UK. The purpose of this supplementary study was to investigate a sample of UKCCS homes in order to identify the particular sources that contribute to elevated time-averaged exposure. In all, 196 homes have been investigated, 102 with exposures estimated on the basis of the original study to be above 0.2 microT, and 21 higher than 0.4 microT, a threshold above which a raised risk has been observed. First, surveys were carried out outside the property boundaries of all 196 study homes, and then, where informed consent had been obtained, assessments were conducted inside the properties of 19 homes. The study found that low-voltage (LV) sources associated with the final electricity supply accounted together for 77% of exposures above 0.2 microT, and 57% of those above 0.4 microT. Most of these exposures were linked to net currents in circuits inside and/or around the home. High-voltage (HV) sources, including the HV overhead power lines that are the focus of public concern, accounted for 23% of the exposures above 0.2 microT, and 43% of those above 0.4 microT. Public health interest has focused on the consideration of precautionary measures that would reduce exposure to power frequency magnetic fields. Our study provides a basis for considering the options for exposure mitigation in the UK. For instance, in elevated-exposure homes where net currents are higher than usual, if it is possible to reduce the net currents, then the exposure could be reduced for a sizeable proportion of these homes. Further investigations would be necessary to determine whether this is feasible.

Exposure to power frequency electric fields and the risk of childhood cancer in the UK.

The United Kingdom Childhood Cancer Study, a population-based case-control study covering the whole of Great Britain, incorporated a pilot study measuring electric fields. Measurements were made in the homes of 473 children who were diagnosed with a malignant neoplasm between 1992 and 1996 and who were aged 0-14 at diagnosis, together with 453 controls matched on age, sex and geographical location. Exposure assessments comprised resultant spot measurements in the child's bedroom and the family living-room. Temporal stability of bedroom fields was investigated through continuous logging of the 48-h vertical component at the child's bedside supported by repeat spot measurements. The principal exposure metric used was the mean of the pillow and bed centre measurements. For the 273 cases and 276 controls with fully validated measures, comparing those with a measured electric field exposure >/=20 V m(-1) to those in a reference category of exposure <10 V m(-1), odds ratios of 1.31 (95% confidence interval 0.68-2.54) for acute lymphoblastic leukaemia, 1.32 (95% confidence interval 0.73-2.39) for total leukaemia, 2.12 (95% confidence interval 0.78-5.78) for central nervous system cancers and 1.26 (95% confidence interval 0.77-2.07) for all malignancies were obtained. When considering the 426 cases and 419 controls with no invalid measures, the corresponding odds ratios were 0.86 (95% confidence interval 0.49-1.51) for acute lymphoblastic leukaemia, 0.93 (95% confidence interval 0.56-1.54) for total leukaemia, 1.43 (95% confidence interval 0.68-3.02) for central nervous system cancers and 0.90 (95% confidence interval 0.59-1.35) for all malignancies. With exposure modelled as a continuous variable, odds ratios for an increase in the principal metric of 10 V m(-1) were close to unity for all disease categories, never differing significantly from one.