Rapid Responses to:
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Rapid Responses: Rapid Responses published:
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Danger of Power Lines
- John E Burgess (3 June 2005)
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Associated with pregnancy?
- Wen Bin Liang (3 June 2005)
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Childhood cancer in relation to distance from high voltage power lines: Some important considerations
- Sarah J. Hepworth, Richard G. Feltbower, Roger C. Parslow, Patricia A. McKinney (3 June 2005)
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Finding effect far from lines
- Volker Koenigsbuescher (3 June 2005)
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Re: Childhood cancer in relation to distance from high voltage power lines: Some important considerations
- David R. Whitlock (3 June 2005)
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Proximity of power lines to motorways and railways
- Thomas Netter (4 June 2005)
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Nitrogen oxides and ozone near power lines
- Robin N Poston (6 June 2005)
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Omissions from the Draper et al. study
- Roger W Coghill (6 June 2005)
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The need for accurate measurements on electromagnetic fields.
- W John Lincoln (6 June 2005)
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What Are The Chances?
- Adrian P Gaylard (7 June 2005)
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Draper et al's findings may have a causal origin
- Denis L Henshaw (7 June 2005)
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Childhood cancer and power lines
- tony fogarty, NR2 2AH (8 June 2005)
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Mechanisms of leukaemogenisis by powerlines
- Alan W Preece, Mary G. Wright (8 June 2005)
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Other incidental carcinogens near power lines
- Wayne A. Hunter (9 June 2005)
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Levels of Exposure
- Bonnie M McKinnon (11 June 2005)
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Electrical occupations and leukaemia
- Marie B Mc Devitt (13 June 2005)
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Not so plausible causal origin
- Les A Coulton (14 June 2005)
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High voltage magnetic fieldsand childhood malignancies
- Dr JK Anand (15 June 2005)
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Both Draper and UKCCS data support Henshaw hypothesis
- Alasdair M Philips (16 June 2005)
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Missing dose - effect relation
- Gerhard Juli (17 June 2005)
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Comments on Draper et al BMJ 1290 4June 2005
- Michael J O'Carroll (21 June 2005)
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Re: Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study.
- Leeka Kheifets, Maria Feychting , Joachim Schuz (22 June 2005)
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Control Selection in the study of Childhood cancer in relation to distance from high voltage power lines in England and Wales
- Leeka Kheifets, Maria Feychting , Joachim Schuz (22 June 2005)
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Control selection in the Study of Childhood cancer in relation to distance from high voltage power lines in England and Wales
- Leeka Kheifets, Maria Feychting, Joachim Schuz (28 June 2005)
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Fields from Transit System
- Donald S Amstrong (29 June 2005)
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Authors' reply
- Gerald Draper, Tim Vincent, Mary E. Kroll, and John Swanson (4 July 2005)
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Childhood Cancer and distance from high-voltage power lines – what do the data mean?
- Eve Roman, Nick Day, Tim Eden, Patricia McKinney, Jill Simpson (5 July 2005)
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reply to authors' reply
- Michael J O'Carroll (20 July 2005)
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Re: Childhood Cancer and distance from high-voltage power lines – what do the data mean?
- David E Jeffers (21 July 2005)
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Proximity and exposure metric deficiencies.
- Michael J O'Carroll (25 July 2005)
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Authors’ reply to Roman et al
- Gerald Draper, Tim Vincent, Mary Kroll, John Swanson (25 July 2005)
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Induced electric field
- Katarina Vestin (10 August 2005)
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Completeness of birth address data
- Richard G. Feltbower, Sarah J. Hepworth, Roger C. Parslow, Patricia A. McKinney (11 December 2006)
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Childhood cancer and powerlines : distinguishing between `magnetic field` and `airborne electroactivity` unterpretations.
- G Hugh Sidaway (11 February 2008)
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geography and Controls
- David E Jeffers (19 March 2008)
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John E Burgess, Consultant Occupational Physician East Anglia
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3 June 2005 Sirs I was interested to hear, on the early morning news today, of a definitive study about childhood leukaemia and its incidence related to living in proximity to overhead power lines. My colleagues in the power industries have laboured long over similar articles and hypotheses. Naturally, I was soon reading the actual article in the BMJ. I must assume that the statistical methodology is suitable but there was one more obvious correlation which sppears to have been completely disregarded. The relative risks for disease groups at varying distance from the power lines are itemised. I concur that there may be a higher relative risk for childhood leukaemia. More obvious to me were the relative risks of CNS/Brain tumours which appear to have considerably lower relative risks the nearer one lives to the transmission cables. Does this imply that there is a positively beneficial effect for the prevention of these illnesses or is this also a result of "chance" or "confounding"? Whilst the estimated figure of 5 extra deaths from leukaemia is of concern and sufficient to undertake further study and action is it not also important to mention to the many thousands of worried parents who live in these areas that there may be a reduction in the incidence of other childhood cancers. Perhaps a figure of the number of deaths prevented by this apparent advantageous effect, and in line with the statistical methods applied for leukaemia, should also be calculated and if it is more than 5 then maybe we should take more care before worrying a generally uninformed public with "horror" headlines. Sincerely Dr John Burgess Competing interests: None declared |
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Wen Bin Liang, taking master of public health Curtin University of Technology
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The ‘home address at birth’ may be related to the address of accommodation of the mothers during the pregnancy. While the research shows that there seems to be relationship between leukaemia and the ‘exposure’ during the earliest period of the babies or even during the time of the pregnancy, there might be difference in the age of the disease onset between the cases which were ‘exposed’ and the cases which were ‘unexposed’. Competing interests: None declared |
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Sarah J. Hepworth, Medical statistician Paediatric Epidemiology Group, University of Leeds, Leeds, LS2 9LN, Richard G. Feltbower, Roger C. Parslow, Patricia A. McKinney
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The paper from Draper and colleagues [1] on the relation between childhood cancer and the distance of birth residence close to high voltage power lines presents some notable findings. The study has distinct advantages of size, in terms of the number of case children, and the unbiased selection of the control sample. However, the findings are inconsistent with another large UK study where estimates of dose to extremely low frequency magnetic fields from power lines were used [2]. If this investigation was established primarily to examine risk in relation to exposure to magnetic fields it is not clear why the categories used as a measure of exposure were extended beyond 200m distance to high voltage power lines, a point at which their contribution to exposure can be considered equivalent to 'background' levels compared to the contribution from other sources [3]. The strength of the findings are based on trend statistics with the reference group comprising birth residences over 600m distance from power lines, an analysis that can have no basis for inferring associations with extremely low frequency magnetic fields. No plausible biological evidence yet exists linking magnetic field exposure to cancer per se or to childhood leukaemia. Despite this, the paper quantifies the possible number of cases of childhood leukaemia 'associated' with high voltage lines for which the main exposure will be to magnetic fields. The statistically significant associations revealed in this geographical analysis lack any adjustment for population characteristics other than social class, estimated by the Carstairs index (it is unclear how this measure was calculated for the period prior to the 1981 census). Crucially, it is known that the areal distribution of childhood leukaemia varies with other factors, also measurable using census data, such as population density and population mixing [4], neither of which have been adjusted for in the analysis as potential confounders for the excess risk. The authors indicate that the mobility of cases did not differ with respect to power line proximity as assessed by different postcodes recorded between birth and diagnosis. Apart from mobility of the individual, characteristics of the area in which they live may also influence the risk of disease and these need to be considered in the analysis. It is of interest that the level of risk was diluted by the use of all controls as the comparison group, although the authors fail to clarify this. Matched analyses may be preferred in a matched study design but findings can be considered to be less robust if the estimates are noticeably different when the matching is broken. All controls, irrespective of the case diagnosis, were selected to represent the entire population and the reasons why differences were observed merit more detailed investigation. The findings of this study are of interest in that they point towards geographical correlates of risk for childhood leukaemia but do not support the hypothesis that electromagnetic fields have a causal role. 1. Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study. BMJ 2005;330:1290-2. 2. UKCCS Study Investigators (Writing committee: J Skinner, MP Maslanyj, TJ Mee, SG Allen, J Simpson, E Roman, NE Day). Childhood cancer and residential proximity to power lines. Br J Cancer 2000; 83(11): 1573- 1580. 3. Vistnes AI, Ramberg GB, Bjørnevik LR, Tynes T, Haldorsen T. Exposure of children to residential magnetic fields in Norway: is proximity to power lines an adequate predictor of exposure? Bioelectromagnetics 1997; 18: 47-57. 4. Parslow RC, Law GR, Feltbower R, Kinsey SE, McKinney PA. Population mixing, childhood leukaemia, CNS tumours and other childhood cancers in Yorkshire. Eur J Cancer 2002; 38: 2033-2040 Competing interests: None declared |
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Volker Koenigsbuescher, IT Manager, former nonmedical practitioner CH - 4002 Basel
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Sirs, In your conclusion you wrote: "but it is nevertheless surprising to find the effect extending so far from the lines." But is it surprising? If the effect exists at all and if children live near the lines, it will happen that they play or walk under or close to them or visit neighbor houses closer to under the the lines. So one might expect an partial effect related somehow to the partial time they spend in the "effected" zone. Volker Koenigsbuescher Competing interests: None declared |
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David R. Whitlock, engineer Separation Technologies
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There may be potential bias in the cases for which addresses could not be identified. Presumably, power lines are in more developed areas, where addresses might be more durable over time. Distances could not be calculated for some 12% of cases. A modest bias favoring inclusion of cases close to power lines and exclusion of cases far from power lines (because the address couldn't be identified) might produce the observed result. Presumably a stability of address effect due to proximity to power lines would extend beyond 600 meters. Examination of the data set for excess cases at large but fixed distances, for example 1,000 to 1,500 meters might show such an effect. Competing interests: None declared |
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Thomas Netter, Postdoc Zurich, Switzerland, 8050
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Sirs, The BMJ article on childhood cancer in relation to distances from high voltage power lines does not seem to take into account the fact that high voltage power lines are often built alongside motorways and railways. Not only are pollutants carried and generated by the vehicles but aerodynamic friction may charge the aerosols. Competing interests: None declared |
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Robin N Poston, Senior Lecturer Dept Histopathology, King's College London, London SE1 1UL
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The possibility that nitrogen oxides and ozone in the atmosphere around power lines may explain the increased risk of childhood leukaemia in their neighbourhood has lacked consideration. It is known that arcing and corona electrical discharges from power lines generate them. These compounds are mutagenic, and leukocytes and stem cells could be exposed during traffic through the pulmonary capillaries of children in the proximity. No studies have been reported on the mutagenicity of air near power lines, in contrast to the extensive work on similar pollutants produced by vehicles, and these would be of interest. Competing interests: None declared |
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Roger W Coghill, Research Director Coghill Research Laboratories, Lower Race, Pontypool NP4 5UH
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This study though large, omitted any cases near to 132kV powerlines. Whilst there are some 10,000 circuit kilometres (c/km) of 400 kV lines in the UK (but only around 6,000 c/km in 1970) and some 4000 c/km of 275kV lines(only 5,300 in 1970), there are over 20,000 c/km of 132kV lines in the UK and some 260,000 pole-mounted transformers (1) similar to those near homes in an early Denver US study first reporting the issue (2). Should the same effect be found near these lower voltage sources, the suggestion that only five cases per year would be added is therefore dramatically understated. Moreover, the principal exposure to electric and magnetic fields is not from powerlines at all, but from domestic electric appliances in the home, and these effects could also augment the likely number of cancer cases. In seeking an explanation why the elevated incidence is seen at distances where the magnetic field is down to background levels it should be remembered that at powerline frequencies (50 Hertz in the UK) there is no association between electric field strengths and magnetic field strengths, since the exposee is in the near field of the source. Magnetic fields from powerlines will attenuate at 1/the cube root whereas the electric field may only attenuate at the reciprocal of the distance, and may therefore still be at above average levels much further away, accelerated or diminished by metal objects or screening respectively, being least nearest the pylon structures themselves, and greatest along the perpendicular to the span midpoints. This study thus points strongly to the electric field as a candidate for investigation. The hypothesis put forward by Henshaw (3), however, cannot be anything like a complete answer since within homes corona discharges are not likely from domestic appliances or wiring within the home. Our 1996 study (4) found a near fivefold elevation of childhood leukaemia incidence (with good confidence intervals) when the electric component was on average 20 V/m., and we found that powerlines were only a minor source of exposure. The UKCCCR study (5) measured electric fields at leukaemic children's bedplaces and also found elevated incidences, but only reported spot and 48 hours measurements which were unrepresentative in the former case, and diluted to one third in the latter period the child's nocturnal exposure in arguably the most important residence locus, the bedplace. I speculate that if the UKCCCR data were re-analysed to reflect only the night-time bedplace exposure this study too would find similarly high incidence to ours. Should the electric component prove to be the bio-active parameter, (and most epidemiological research todate has been directed only to the magnetic component) then the issue of a biological mechanism becomes much easier to identify, since electric fields are superpositive (E = E1 + E2 ...+En), and several important life processes (heart beat rate, brain EEG, ATP synthesis) are known to be mediated via electric fields and the transport of electrons, all three being processes which powerline and other sources would inevitably perturb, and all with adverse effects linked to EMF exposure reported in the relevant epidemiological literature. Moreover there are many in vitro and animal studies reporting adverse electric field effects, particularly on lymphocytes and on the synthesis of melatonin, a primary oncostatic agent. Indeed, the supplementary use of melatonin is proving a useful adjuvant as a radioprotective agent, not only at power but also at radiofrequencies (6). 1. Statistics of Electricity Supply. Electricity Council, Millbank, London, 1987 2. Wertheimer N and Leeper, E. (1979) Electrical Wiring Configurations and Childhood Cancer. Am. J. Epidemiol. 109: 273-284 3. Henshaw DL Ross AN et al. (1996) Enhanced deposition of radon daughter nuclei in the vicinity of power frequency electromagnetic fields Intl. J. Radiat. Biol 69: 25-38 4. Coghill RW Steward J et al. (1996) ELF electric and magnetic fields measured in the bedplaces of children diagnosed with leukaemia: a case control study. Europ. J. Cancer Prev. 5: 153-158 5. Skinner J Mee TJ et al. (2002) Exposure to power frequency electric fields and the risk of childhood cancer in the UK Brit J Cancer 87: 1257-1266 (6) Vijayalaxmi Reiter RJ et al., (2004) Melatonin as a radioprotective agent: a review Intl. J Radiat. Oncol. Biol Phys 59(3): 639-653 Competing interests: None declared |
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W John Lincoln, Director of EMR Surveying company EMR Surveys P/L, 10 Annette Place, Belrose, NSW, 2085, Australia
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I am an electrical engineer with a small company involved in the measurement of electromagnetic fields in domestic and commercial locations. I am also a member of the ARPANSA, ELF WG. (ARPANSA is an Australian Government authority resposible for the health protection in areas of both ionising and non-ionising radiation. The ELF WG is a working group preparing an Australian Standard for electromagnetic radiation from 0 Hz to 3 kHz) The paper from Gerald Draper et al considers a subject of great interest to my colleagues and I and has received significant press coverage in Sydney. I am interested in whether the authors have confidence that the distance from power lines is a true representation of the magnetic and or electric fields that may be experienced. Did the Authors take any spot measurements of fields to confirm whether there was a relationship? Was the countryside level, undulating, steep etc.? Could there have been influence from lower voltage lines or cables? Were the lines of the same configuration, did they consist of more than one circuit, and did they carry similar currents? If the Authors considered there was a relationship between magnetic fields generated by the High Voltage transmission lines and childhood leukaemias, what steps did they take to investigate the increasing relative risks between 300 and 599 metres? Our Working Group meet again on Tuesday 14th June and it would be valuable to us if we could open a dialogue by then. Competing interests: None declared |
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Adrian P Gaylard, Chartered Physicist Independant Researcher
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Draper et al do well to mention that their results do not show causation, rather association. Furthermore, they also point to the risks of chance association. Bradford-Hill(1) proposed nine tests to apply to statistical associations before causation could be asserted, namely: strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experimental evidence, and analogy. I would like to comment on plausibility. The issue is not just that there is as yet no plausible biological mechanism for the induction of leukaemia by the electric or magnetic fields associated with power lines. As the RR for CNS/brain tumours takes values either side of unity (and if we are to understand them as indicators of a real risk), any biological mechanism would also have to protect from CNS/brain tumours out to 199m, induce CNS/brain tumours from 200m-399m and then continue to protect against such between 400 and 499m, again causing them from 500m-599m. A similar, though less striking observation can be made for "other diagnoses". Alternatively, we would need separate biological mechanisms for the causation of individual types of cancer by power lines. Under these circumstances chance would seem to be a more likely explanation. (1) The Environment and Disease; Association or Causation? Hill Bradford AS (1965) Proc. R. Soc. Med.; 58: 295. Competing interests: None declared |
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Denis L Henshaw, Professor of Human Radiation Effects H H Wills Physics Lab, University of Bristol, Tyndall Ave, Bristol, BS8 1TL
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The finding of increased incidence of childhood leukaemia by birth address up to 600 metres from high voltage powerlines may have a causal origin in terms of both the associated electric and magnetic fields. A plausible explanation for the approximate 70% increased incidence in childhood leukaemia up to 200 metres from powerlines may be via the disruption in the body of the hormone melatonin. Russ Reiter of the University of Texas and I have just completed a review of this topic as part of last June's World Health Organisation meeting on EMF and Child Health held in Istanbul. Our review of 14 international studies in human populations are consistent in indicating that magnetic fields down to 0.2 microtesla or lower can suppress the nocturnal production of melatonin in the pineal gland. Melatonin is a powerful antioxidant which acts as a natural anti-cancer agent. The hormone has been shown to be highly protective of oxidative damage to human blood cells. In animals, melatonin has been shown to be highly protective of oxidative damage to the fetus, the site where initial leukaemic damage is believed to occur in children. Leukaemia has been induced in mice exposed to constant light, which also has the effect of suppressing nocturnal pineal melatonin. Full details of our review may be found on our website below. At Bristol, we are also researching the effects of corona ion emission from high voltage powerlines. These ions can be carried hundreds of metres from powerlines by the wind (they have been detected up to 7 km away) and this could explain the observed increased childhood leukaemia up to 600 metres from powerlines. Corona ions are produced by the ionisation of the air under the intense electric field on the surface of powerline cables. Once emitted into the atmosphere, corona ions attach themselves to particles of air pollution thereby increasing the electric charge on such particles. At ground level, when subsequently inhaled, these charged pollutants then have a much higher probability of becoming trapped in the lung by mirror-charge (static electricity) effects. We are particularly interested in pollutant particles in the approximate size range 20 - 300 nanometres since these predominantly contain the potentially carcinogenic polycyclic aromatic hydrocarbons (PAHs). Once in the lung, such particles would readily pass into the bloodstream. Ambient exposures to PAHs have been shown to produce heritable mutations in mice. In figure 3 of Fews et al 1999 we demonstrate that corona effects are prominent at 600 metres even from 132 kV powerlines which were not those mainly considered in the Draper et al study. The National Radiological Protection Board's report on corona ions concedes the plausibility of the above proposed scenario. There is substantial mechanistic evidence to suggest that air pollution is a causal factor in the incidence of childhood leukaemia. The ubiquitous nature of air pollution exposure is such that a link with childhood leukaemia has been difficult to demonstrate in an epidemiological study with case-control design. However, increased childhood leukaemia in relation to pollution hazard sites in the UK has been reported. Overall, the distance profile of childhood leukaemia rates observed by Draper et al could be fitted by a model comprising the fall-off of magnetic fields within 200 metres of powerlines and the continuing presence of corona ion effects up to 600 metres away. Full details of these scenarios may be found via our response statement to the Gerald Draper et al study at www.electric-fields.bris.ac.uk Key references 1. Henshaw D L and Reiter R J, 2005. Do magnetic fields cause increased risk of childhood leukaemia via melatonin disruption? Bioelectromagnetics (In Press). 2. Henshaw D L, 2002. Does our electricity distribution system pose a serious risk to public health? Medical Hypothesis, 59,39-51. 3. Fews A P, Henshaw D L, Wilding R J & Keitch P A, 1999. Corona ions from powerlines and increased exposure to pollutant aerosols. Int. J. Radiat. Biol, 75 (12), 1523-1531. 4. National Radiological Protection Board. Particle deposition in the vicinity of power lines and possible effects on health. Documents of the NRPB 2004, 15(1). Competing interests: None declared |
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tony fogarty, GP locum 202 Unthank Rd, Norwich,, NR2 2AH
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'Power lines may be linked to childhood leukaemia' and 'Leukaemia:avoid living near high voltage lines...' These headlines do a grave disservice to the thoughtful paper by Draper et al, distorting their cautious conclusions. They are a gift to the superficial fear-mongering elements in the media and will be quoted unquestioningly for years to come. 'Brain tumours more than halved by living near power lines' would be as valid and erroneous. Headlines which are seemingly written to catch attention rather than to convey the truth are not suitable for a serious scientific journal. Competing interests: None declared |
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Alan W Preece, Emeritus Professor University of Bristol, Bristol Oncology Centre, Horfield Road, Bristol, BS2 8ED, Mary G. Wright
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The elevation of leukaemia risk out to 600m does indeed make it unlikely that magnetic fields are associated with risk, but does not dismiss the possibility of a physical mechanism associated with high voltage. In the full text of this paper, the authors claim to have tested Fews at al (1) hypothesis albeit in an oversimplified model. To test this hypothesis correctly, the wind direction used to assign correctly up or down wind status to a case or control must reflect the predominant wind direction in that area. While for the country on average, southwest is the predominant wind direction, there are areas of England and Wales where the predominant wind direction is not southwest as demonstrated by the Meteorological Office’s wind roses. Incorrectly assigning up and down wind status will smear the result. Also, the authors have included only a small proportion of the 132kV lines. These lines like the 275 and 400kV will produce small air ions in as large quantities and are maybe 5 or 6 times as frequent as the higher voltage lines. Given that the study only includes a small fraction of the 132kV lines and the assumption that the prevailing wind is from the southwest for the whole country, this study cannot be said to test the hypothesis, and therefore there may still be a mechanism to be tested. (1) Fews AP, Henshaw DL, Wilding RJ, Keitch PA. Corona ions from powerlines and increased exposure to pollutant aerosols. Int J Radiat Biol 1999;75:1523-31 Competing interests: None declared |
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Wayne A. Hunter, EMC Engineer Agilent Technologies, Wilmington DE 19808
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The authors also did not indicate whether any of the power lines in question were in use in the 1940s and 1950s when the use of spray herbicides, which are now banned due to carcinogenic and other health effects, were sprayed under the power lines to assist with plant control. These materials also would have a similar effect of reduction in incidence of carcinogenic effects with distance. Since the bio-persistence of toxicity for many of these chemicals is over 100 years, the material is still available for inhalation and injestation. The effect on small children breathing trace amounts of vapor or inhaling dirt with the material could also be a significant impact to this study. It would be interesting to assess the data in regard to the age of the power line and use of herbicides for plant control as a possible source of the increase in incidence. Competing interests: None declared |
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Bonnie M McKinnon, Consultant Calgary, AB T3L 1L2
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I have been eagerly waiting for current information with respect to EMF's and any relation to health issues. I am not in the health field, and have been subjected to pouring over inconclusive research linking distances, wire codes, etc., now corona ion emissions. I am a consumer, looking to purchase a home which borders on a Transportation Utility Corridor. After reading all these reports, I have not been able to ascertain exposure at constant levels of X mG may or may not producing cause. I have received readings of 60 mG at the back of the lot, 30 mG mid-back yard, 15 mG at the back of the house, 10 mG mid-house, 8 mG front of house, and 3.7 mG at the sidewalk. Are these levels consistent with research which has not proven cause, or are the levels higher or lower? Competing interests: None declared |
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Marie B Mc Devitt, Public Health Specialist Stockport PCT, Regent House, Stockport SK4 1BS, England
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Although the authors of the paper on powerlines and childhood leukaemia (1) state that there is no accepted biological mechanism to explain the epidemiological results they found, there are a couple of points which may be of relevance. Firstly, according to a study on occupational mortality in Great Britain (2) two major groups of electrical occupations show raised standardised mortality ratios (SMRs) for both all leukaemias and for acute myeloid leukaemia. For electrical and electronic engineers the SMR for all leukaemias for men aged 20-64 years was 202 and similarly for electricians, fitters, plant operators etc the SMR for acute myeloid leukaemia was 155. Both SMRs were statistically significant at the 95% confidence level. Secondly, apparently all chemical reactions are basically electric in nature since they involve exchanging or sharing negatively charged electrons between atoms to form ions or bonds (3). Perhaps electric or magnetic fields are having some particularly sensitive effect on the electrical charges of the cells in the bone marrow? 1. Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: case control study. BMJ 2005;330:1290-3. 2. Office of Population Censuses and Surveys. Occupational mortality, decennial supplement 1979-80, 1982-83. Series DS no6. London: HMSO, 1986. 3. Vander A, Sherman JH, Luciano DS. Human Physiology-the Mechanisms of Body Function. McGraw-Hill, 1975. Competing interests: None declared |
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Les A Coulton, Senior Research Scientist University of Sheffield Medical School, Beech Hill Rd. Sheffield, S102RX
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Professor Henshaw suggests that the higher incidence of childhood leukaemia near power lines could be due to two independent phenomena namely suppression of nocturnal pineal melatonin and corona ion emission. Doesn’t it seem rather unlikely that to explain the distribution of leukaemia patients there needs to be invoked two unrelated biological mechanisms which by chance lead to the same uncommon disease whilst not affecting other childhood cancers? A report of the independent Advisory Group on Non-ionising Radiation (AGNIR) which investigated the possible effects of corona ions or electric fields on intake of radioactive particles or other airborne pollutants stated that the main health hazards of airborne particulate pollutants are cardiorespiratory disease and lung cancer. The report concluded: “However, it seems unlikely that corona ions would have more than a small effect on the long-term health risks associated with particular air pollutants, even in individuals who are most affected. In public health terms, the proportionate impact will be even lower because only a small fraction of the general population live or work close to sources of corona ions.” AGNIR is also considering the interaction between melatonin and electromagnetic fields and the report is currently in its final draft. Given that neither of the suggested mechanisms has yet been shown to be of significance to human health, and that Professor Henshaw’s construct relies on both of them, this hypothesis is not a strong candidate to explain the Draper findings. Competing interests: None declared |
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Dr JK Anand, Retired public health physician N/A
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Whatever be the mechanism involved, it seems desirable to conduct animal epidemiological studies. This suggestion was made by me fifteen years ago(1). JK Anand Reference. The Veterinary Record, 1993, 132/1,24 (2 January) Competing interests: None declared |
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Alasdair M Philips, Director of Powerwatch CB6 2QA
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Despite the statements of some scientists, the UKCCS [1] did find elevated incidence of childhood leukaemia close to powerlines. When the UKCCS data is plotted as simple Odds Ratios for 275 kV and 400 kV powerlines [2], it shows a similar peak as this latest study at 100 metres and, more importantly, rising again after 150 metres. 
This new study supports a likely magnetic field effect on child leukaemia incidence near to powerlines. 100 metres is beyond the typical 400 nanotesla point, but this is without taking polarisation / ellipticity of the field into account which induces higher currents in people and will be likely to increase the effective distance [3]. After a dip, both studes then show an ongoing rise in incidence after a few hundred metres which would closely fit the Henshaw charged aerosol hypothesis. Actual measurements [4] have found charged aerosol effects from about 150 metres to several km from powerlines before diffusing to ground level - a long way from the source of the corona ions and affecting a significant number of people. If Henshaw is right, then the adverse health effects of powerlines will extend to well over 1 km from the powerlines. It would be easy to test for this by extending the analysis of the Draper data up to a distance of at least 2km to see how far the elevated risk continues. Refs: [2] Graph available at: [3] Ainsbury, E, et al, Conference poster, [4] Fews A.P., et al, Modification of atmospheric DC fields by space charge from high voltage power lines, 2002, Atmospheric Research, 63: 271 - 289 Competing interests: Powerwatch comments on potential health effects of electromagnetic fields |
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Gerhard Juli, Engineer Public Utility 87435 Kempten, Germany
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Like many of similar studies (e.g. Ahlbom, Feychting), Draper, Vincent et alt. lack a relation between the dose and effect. Not calculated is the duration of living close to power lines. Excluded is the 11 kV (kilovolt) system, which is much more widespread then higher voltage systems. The magnitude of the magnetic fields of 11 kV-systems is the same like those of higher voltages. This is true also for cables lying underground because of the proximity to the public (around 1m). At a distance of about 50 ... 100 m from the axis of a overhead powerline system the strength of the electric and magnetic fields fall to the background level. When measuring electromagnetic fields, I always found the highest levels (out of occupational locations) in households, especially close to devices whith magnetic components like dishwashers, transformers (battery chargers), speakers, computers. What about trains? Because they use 25 kV single-phase low frequency alternating current (ac), the fields of those powerlines are a multiple of that of “ordinary” powerlines. Even systems not intended to carry electric current like central heating, gas pipes, water pipes can produce magnetic fields of considerable strength due to balancing currents. Competing interests: None declared |
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Michael J O'Carroll, Professor Emeritus University of Sunderland (home address) Garden House, Welbury, Northallerton DL6 2SE
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Introduction These comments are primarily from the viewpoint of a mathematician. While the paper reports a major study in scale, some of the statistics are weak, particularly in the findings at greater distances from powerlines. On the other hand some responses have seized upon those results at greater distances (up to 600 metres), where associated fields may be negligible, to dismiss any hypothesis for a magnetic field effect. Such dismissive claims do not stand up to mathematical scrutiny. Such claims also overlook the possibility of associated exposure in time spent closer to the line, for example at nursery or school. Further, while hastily relying on weak statistical results, such claims dismiss the stronger statistical association with childhood leukaemia established for flux densities above 0.4 microTesla. Possible understatement of potential effects The exposure metric in this study is proximity of birth address to National Grid power lines. That would seem an uncertain proxy for any particular field effects, compounded by uncertainty in the timing of exposure. Genetic evidence suggests, in many cases, a two-stage causal process of in-utero genetic damage followed by conversion in childhood to the disease. Address at birth may be better correlated with the first stage than the second. Uncertainties in relevant exposures would tend to dilute statistical evidence indicative of causation. General population studies which ignore susceptible subsets can greatly mask possible causal associations [1]. It would be helpful to study the relation of exposure in utero to incidence of genetic damage (identifiable by blood tests) and, separately, the relation of exposure prior to diagnosis in children with genetic damage to incidence of the disease. The risk in these two subset-related stages could be in the region of 1 in 200, in contrast to the whole population risk of 1 in 20,000 per year, with potentially much greater statistical resolving power for small relative risks. Statistical features Table 1 shows some odd features in the data. Firstly, the relative risk (RR) is more like a step function with distance (suggesting a possible exposure threshold) than an inverse power relation. Secondly, within the 200 - 600 metre range there is a strange counter-trend; as results in this range are barely statistically significant (CI 1.02 - 1.49) this suggests chance variations or chance events rather than something more systematic. The authors estimate, with qualifications, that about 1% of childhood leukaemia would be attributable to National Grid lines. That leads to about 5 attributable cases per year, some ten times higher than suggested by previous studies. The 1% of cases would reflect an average relative risk of about 1.25 on the 4% of children living within 600 metres. Discounting the contribution from the most uncertain range of 200 - 600 metres would leave a population of about 0.7 % of children (population is lower closer to powerlines) within 200 metres with a relative risk of about 1.7 of which 0.7 is attributable. That amounts to about 0.5 % of cases, which would only reduce the estimated attributable outcome to 2.5 cases per year. So the stronger statistical findings in the range 0 - 200 metres alone support about half the increased attribution. Table 1 shows large variations in the distributions of the three sets of controls. The controls need not be similarly distributed, as they match different case sets, but such differences are not explained. Maldistribution of controls would not wholly explain the finding, as the authors observe, but the differences remain disconcerting. Conclusions 1. The study is important in that it is on a large scale and deals with proximity of birth address to powerlines. In contrast, other key studies, which lie behind the statistical association of childhood leukaemia with magnetic flux density, refer mainly to pre-diagnosis exposures. The extent that this study might represent exposure to EMF in utero or pre-diagnosis is unclear. 2. The study finds statistically significant results of two kinds. First there are stronger results for birth addresses within 200 metres of a power line. Second there are weaker results in the range 200 - 600 metres with statistical quirks. 3. The results within 200 metres broadly reinforce the known doubling of risk of childhood leukaemia for pre-diagnosis exposure above 0.4 microTesla. However, they suggest the number of attributable cases from National Grid lines would be about 5 per year, some ten times more than previous estimates; this reduces to five times more using only the stronger results. This may be a reflection of a greater effect of pre- natal exposure compared with pre-diagnosis exposure, but this is not clear. There are uncertainties in both old and new estimates. 4. The results in the range 200 - 600 metres are likely to be spurious. They should not be relied on to support or deny an effect up to 600 metres. The argument that these results are incompatible with magnetic field levels should not be relied on to dismiss magnetic field hypotheses nor to counter the established statistical association with magnetic flux densities. 5. The uncertainty in exposure metric, and between pre-natal and pre- diagnosis exposure, would tend to understate any potential underlying causation. Better focused studies on the two stages would be helpful and could be much more robust statistically. Reference [1] M J O’Carroll, Searching for causes: focusing epidemiology, Paper P1-15, Children with Leukaemia: Scientific Conference 6-10 September 2004. Competing interests: None declared |
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Leeka Kheifets, Professor UCLA, Los Angeles, 90095, Maria Feychting , Joachim Schuz
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Re: Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study.
Leeka Kheifets1, Maria Feychting2, Joachim Schüz3
1. Department of Epidemiology, School of Public Health, UCLA, CA, USA
2. Institute of Environmental Medicine, Karolinska Institutet, Sweden
3. Institute of Cancer Epidemiology, Danish Cancer Society, Denmark
We have read with interest the paper from Draper and colleagues [1]. Given its large size the risk estimates in the paper should be stable. Furthermore, because contact with the subject was not necessary selection bias due to the differential participation among cases and controls, which plagued some of the previous studies [2], has been avoided. Thus we were particularly surprised by the dependence of the results on the chosen control group noted by the authors, (who used CNS and other cancer controls for leukaemia cases in one of the comparisons). To explore this further we combined all controls into one group and used it for comparison. We felt this is justified based on both theoretical and empirical grounds: exposure at birth among controls chosen for leukaemia, brain tumours and other cancers should not depend on the cancer subtype; crude odds ratios calculated by us did not differ (beyond first decimal) from the matched results presented by authors (data not shown).
Use of the combined control group revealed a pattern different than the one presented in the original paper (Table 1). As would be expected, results for all cancers combined show no relation to the distance. For both leukaemia and brain cancer results at two distances are noteworthy: for the 50-100 meters category an excess of leukaemia and a deficit for brain tumours is observed. For the 500-600 meters category we observed a modest excess for both leukaemia and brain tumours. Of note is that the trend reported in the original paper is not present when the combined control group is used, thus indicating that the trend depended on the leukaemia controls rather than on the leukaemia cases. We agree with the authors that the results of this study do not support a possible magnetic field association, as has been reported by the IARC monograph [2]. However, distance is known to be a very poor predictor of magnetic field exposure, and therefore, results of this material based on calculated magnetic fields, when completed, should be much more informative.
Further insight might be gained by details on the methods used for the control selection and sensitivity analyses by age, sex and time period.
1. Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study. BMJ 2005; 330:1290-2.
2. Ahlbom A, Day N, Feychting M, et al. A pooled analysis of magnetic fields and childhood leukaemia. Br J Cancer, 83, 692-8 (2000).
3. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol 80 Non Ionizing radiation, Part 1: Static and Extremely Low – Frequency Electric and Magnetic Fields. 2002
Distance of address at birth from nearest National Grid line and estimated odds ratios using all controls combined
Leukemia CNS Other tumours All cancer combined All controls
Distance No. cases OR (95% CI) No. cases OR (95% CI) No. cases OR (95% CI) No. cases OR (95% CI) No. controls
0-49 5 0.94 (0.34-2.57) 3 0.83 (0.24-2.84) 7 1.00 (0.41-2.42) 15 0.94 (0.46-1.90) 16
50-99 19 1.73 (0.99-3.05) 4 0.53 (0.19-1.51) 15 1.04 (0.56-1.91) 38 1.15 (0.72-1.84) 33
100-199 40 1.18 (0.82-1.70) 26 1.12 (0.73-1.73) 37 0.83 (0.57-1.20) 103 1.01 (0.77-1.33) 102
200-299 44 0.93 (0.66-1.30) 38 1.17 (0.82-1.68) 66 1.05 (0.78-1.41) 148 1.04 (0.82-1.31) 143
300-399 61 1.23 (0.91-1.66) 35 1.04 (0.72-1.50) 79 1.21 (0.92-1.59) 175 1.18 (0.95-1.47) 149
400-499 78 1.15 (0.89-1.50) 40 0.86 (0.62-1.22) 80 0.89 (0.69-1.16) 198 0.97 (0.80-1.18) 204
500-599 75 1.24 (0.95-1.63) 54 1.31 (0.96-1.78) 86 1.08 (0.83-1.39) 215 1.18 (0.97-1.44) 182
™600 9378 1 (ref) 6405 1 (ref) 12406 1 (ref) 28189 1 (ref) 28252
Competing interests: For LK work for EPRI and consulting with utilities |
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Leeka Kheifets, Professor of Epidemiology UCLA, Los Angeles, 90095, Maria Feychting , Joachim Schuz
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Leeka Kheifets1, Maria Feychting2, Joachim Schuz3 1. Department of Epidemiology, School of Public Health, UCLA, CA, USA 2. Institute of Environmental Medicine, Karolinska Institutet, Sweden 3. Institute of Cancer Epidemiology, Danish Cancer Society, Denmark We have read with interest the paper from Draper and colleagues [1]. Given its large size the risk estimates in the paper should be stable. Furthermore, because contact with the subject was not necessary selection bias due to the differential participation among cases and controls, which plagued some of the previous studies [2], has been avoided. Thus we were particularly surprised by the dependence of the results on the chosen control group noted by the authors, (who used CNS and other cancer controls for leukaemia cases in one of the comparisons). To explore this further we combined all controls into one group and used it for comparison. We felt this is justified based on both theoretical and empirical grounds: exposure at birth among controls chosen for leukaemia, brain tumours and other cancers should not depend on the cancer subtype; crude odds ratios calculated by us did not differ (beyond first decimal) from the matched results presented by authors (data not shown). Use of the combined control group revealed a pattern different than the one presented in the original paper (Table 1). As would be expected, results for all cancers combined show no relation to the distance. For both leukaemia and brain cancer results at two distances are noteworthy: for the 50-100 meters category an excess of leukaemia and a deficit for brain tumours is observed. For the 500-600 meters category we observed a modest excess for both leukaemia and brain tumours. Of note is that the trend reported in the original paper is not present when the combined control group is used, thus indicating that the trend depended on the leukaemia controls rather than on the leukaemia cases. We agree with the authors that the results of this study do not support a possible magnetic field association, as has been reported by the IARC monograph [2]. However, distance is known to be a very poor predictor of magnetic field exposure, and therefore, results of this material based on calculated magnetic fields, when completed, should be much more informative. Further insight might be gained by details on the methods used for the control selection and sensitivity analyses by age, sex and time period. 1. Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study. BMJ 2005; 330:1290-2. 2. Ahlbom A, Day N, Feychting M, et al. A pooled analysis of magnetic fields and childhood leukaemia. Br J Cancer, 83, 692-8 (2000). 3. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol 80 Non Ionizing radiation, Part 1: Static and Extremely Low ¨C Frequency Electric and Magnetic Fields. 2002 Competing interests: For LK work with EPRI and consulting for utilities. |
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Leeka Kheifets, Professor of Epidemiology UCLA, Los Angeles, CA 90095, Maria Feychting, Joachim Schuz
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Re: Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study. Leeka Kheifets1, Maria Feychting2, Joachim Schuz3 1. Department of Epidemiology, School of Public Health, UCLA, CA, USA 2. Institute of Environmental Medicine, Karolinska Institutet, Sweden 3. Institute of Cancer Epidemiology, Danish Cancer Society, Denmark š We have read with interest the paper from Draper and colleagues [1].šš Given its large size the risk estimates in the paper should be stable. Furthermore, because contact with the subject was not necessary selection bias due to the differential participation among cases and controls, which plagued some of the previous studies [2], has been avoided.š Thus we were particularly surprised by the dependence of the results on the chosen control group noted by the authors, (who used CNS and other cancer controls for leukaemia cases in one of the comparisons).šš To explore this further we combined all controls into one group and used it for comparison.š We felt this is justified based on both theoretical and empirical grounds: exposure at birth among controls chosen for leukaemia, brain tumours and other cancers should not depend on the cancer subtype; crude odds ratios calculated by us did not differ (beyond first decimal) from the matched results presented by authors (data not shown). Use of the combined control group revealed a pattern different than the one presented in the original paper (Table 1).š As would be expected, results for all cancers combined show no relation to the distance.šš For both leukaemia and brain cancer results at two distances are noteworthy:š for the 50-100 meters category an excess of leukaemia and a deficit for brain tumours is observed.š For the 500-600 meters category we observed a modest excess for both leukaemia and brain tumours.š Of note is that the trend reported in the original paper is not present when the combined control group is used, thus indicating that the trend depended on the leukaemia controls rather than on the leukaemia cases.š We agree with the authors that the results of this study do not support a possible magnetic field association, as has been reported by the IARC monograph [2]. However, distance is known to be a very poor predictor of magnetic field exposure, and therefore, results of this material based on calculated magnetic fields, when completed, should be much more informative. Further insight might be gained by details on the methods used for the control selection and sensitivity analyses by age, sex and time period. 1.ššššš Draper G, Vincent T, Kroll ME, Swanson J. Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case- control study. BMJ 2005; 330:1290-2. 2.ššššš Ahlbom A, Day N, Feychting M, et al. A pooled analysis of magnetic fields and childhood leukaemia. Br J Cancer, 83, 692-8 (2000). 3.ššššš IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol 80 Non Ionizing radiation, Part 1: Static and Extremely Low – Frequency Electric and Magnetic Fields.š 2002 š š Distance of address at birth from nearest National Grid line and estimated odds ratios using all controls combined š
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