We give here, where available, the abstracts of papers published by National Grid’s own research scientists. They are presented in chronological order, but to make it easier to find a paper, they are also indexed here by subject area.
Indexed by subject area
Reviews of the science
|Alternating electric and magnetic fields near electric-power equipment: are they a health hazard?||J C Male, W T Norris, B J Maddock, J A Bonnell|
|Power lines and health||J Swanson, D C Renew, N J Wilkinson|
|Biophysical mechanisms: a component in the weight of evidence for health effects of power-frequency electric and magnetic fields||J Swanson, L Kheifets|
|Childhood leukemia, electric and magnetic fields, and temporal trends||L Kheifets, J Swanson, S Greenland|
|Power-frequency electric and magnetic fields in the light of Draper et al. 2005.||J Swanson, T Vincent, M Kroll, G Draper|
|Future needs of occupational epidemiology of extremely low frequency (ELF) electric and magnetic fields (EMF): review and recommendations.||L Kheifets, JD Bowman, H Checkoway, M Feychting, M Harrington, R Kavet, G Marsh, G Mezei, DC Renew, E van Wijngaarden|
|Extremely low frequency electric fields and cancer: Assessing the evidence||L Kheifets, D Renew, G Sias, J Swanson|
Exposures at work and at home
Fields from Power Lines
|Overhead line design in relation to electric and magnetic field limits||B J Maddock|
|Magnetic fields from transmission lines: comparison of calculations and measurements||J Swanson|
Electric fields, ions and airborne pollutants
Note: Dr Jeffers has published further papers on this subject as a private individual since leaving National Grid, which are not listed here.
EMF Exposure Limits and Policy
|Basic restrictions in EMF exposure guidelines.||DC Renew, ID Glover|
|Exposure guidelines for low-frequency electric and magnetic fields: report from the Brussels workshop.||AR Sheppard, R Kavet, DC Renew|
|A transmission utility's experience of applying EMF exposure standards.||J Swanson|
|Comment on Valic et al., 2009||J Swanson|
|Risk Governance for Mobile Phones, Power Lines, and Other EMF Technologies.||Kheifets L, Swanson J, Kandel S, Malloy TF.|
|Health-Economics Analyses Applied to ELF Electric and Magnetic Fields||Kandel S, Swanson J, Kheifets L|
|Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study||Gerald Draper, Tim Vincent, Mary E Kroll, John Swanson|
|A Pooled Analysis of Extremely Low-Frequency Magnetic Fields and Childhood Brain Tumors.||Kheifets L, Ahlbom A, Crespi CM, Feychting M, Johansen C, Monroe J, Murphy MF, Oksuzyan S, Preston-Martin S, Roman E, Saito T, Savitz D, Schüz J, Simpson J, Swanson J, Tynes T, Verkasalo P, Mezei G|
|Childhood cancer and magnetic fields from high-voltage power lines in England and Wales: a case–control study||ME Kroll, J Swanson, TJ Vincent and GJ Draper|
|Pooled analysis of recent studies on magnetic fields and childhood leukaemia||L Kheifets, A Ahlbom, C M Crespi, G Draper, J Hagihara, R M Lowenthal, G Mezei, S Oksuzyan, J Schüz, J Swanson, A Tittarelli, M Vinceti and V Wunsch Filho|
|Could the geomagnetic field be an effect modifier for studies of power-frequency magnetic fields and childhood leukaemia?||J Swanson, L Kheifets|
|Residential mobility of populations near UK power lines and implications for childhood leukaemia.||J Swanson|
|Residential distance at birth from overhead high-voltage powerlines: childhood cancer risk in Britain 1962-2008||Bunch KJ, Keegan TJ, Swanson J, Vincent TJ, Murphy MFG|
|Childhood cancer and exposure to corona ions from power lines: an epidemiological test||J Swanson , K J Bunch , T J Vincent and M F G Murphy|
|Magnetic fields and childhood cancer: an epidemiological investigation of the effects of high-voltage underground cables||K J Bunch, J Swanson, T J Vincent, M F G Murphy|
Exposure response relationships
|Exploring exposure-response for magnetic fields and childhood leukemia.||Kheifets L, Afifi A, Monroe J, Swanson J|
Abstracts presented chronologically
Alternating electric and magnetic fields near electric-power equipment: are they a health hazard?
J C Male, W T Norris, B J Maddock and J A BonnellElectromagnetic fields from overhead power lines have long been of interest because of the potentials and currents which may be induced in neighbouring structures. Such potentials can give rise, for example, to momentary small discharges (microshocks) when a person touches a conducting object close to a line. If annoying, these can be prevented by appropriate screening or earthing. In recent years, however, questions have been raised concerning possible direct effects of the fields on health, though none has yet proved real, despite extensive studies. The authors first consider the nature and magnitudes of the power-frequency electric and magnetic fields near transmission lines or in substations and the effects they are known to produce in people exposed to them. The authors then outline the considerable world-wide research effort at present devoted to identifying possible health hazards that such fields may present. Finally, they consider the idea of introducing regulations to limit the field exposure of people who occupationally or otherwise spend time near high-voltage power-transmission plant.
Power-frequency magnetic fields: measurement and exposure assessment
D C Renew, J C Male and B J MaddockThis paper outlines a number of techniques for the assessment of residential power-frequency magnetic fields and describes a survey of personal magnetic-field exposures of Electricity Supply Industry staff in the UK. Some early results of the survey suggest that both internal and external sources contribute to residential exposure and that much of the personal exposure of ESI staff in all job categories is incurred in the home. One implication for epidemiological studies is that residential fields may have only limited validity as an exposure surrogate for people who go out to work.
Overhead line design in relation to electric and magnetic field limits
B J MaddockDesigners of overhead power lines have to contend with many technical and economic factors in their work. More recently, yet another has been added to the list – electric and magnetic fields. This article points out the principal design features which affect the fields from lines and summarises the guidelines and standards which exist around the world for power-frequency fields. It is based on the author’s lecture to the IEE Power Division on the 20th February 1991.
Measurements of static magnetic fields in homes in the UK and their implication for epidemiological studies of exposure to alternating magnetic fields
J SwansonAbstract. The variation of static magnetic fields within and between 55 homes in an area of south east England was measured. In general, fields varied by up to +or-10 mu T from the unperturbed geomagnetic field. They varied more in the corners of rooms (standard deviation 2.6 mu T) than in the centres (1.2 mu T). The field in the bedroom was uncorrelated with the field in the living room of the same home. For this sample of homes, the spread of field within a typical home was greater than the spread between homes. Therefore it is not meaningful to categorise homes by a single value of static field. This finding casts doubt on the suggestion that confusing epidemiological results concerning childhood cancer and power-frequency magnetic fields could be explained by a resonance mechanism involving static fields.
Occupational exposures to power-frequency magnetic fields in the electricity supply industry
C J Merchant, D C Renew and J SwansonReports a survey of the exposure of staff in the UK Electricity Supply Industry to power-frequency magnetic fields. Two hundred and fifty-eight staff from a variety of jobs and locations wore a monitor for 1 week each. The results form a substantial body of data which adds significantly to the understanding of occupational exposures. The results show that fields encountered in shops, offices and distribution sites were roughly half those in power stations, which in turn were half those in transmission sites. Office workers based on transmission sites experienced higher fields (geometric mean of individual time-weighted average fields: 0.48 mu T) than those at headquarters offices (0.18 mu T). In power stations, electrical workers experienced higher fields (0.46 mu T) than mechanical workers (0.25 mu T). Amongst transmission and distribution staff, the highest fields (1.16 mu T) were experienced by transmission substation attendants and the lowest fields (0.17 mu T) by staff working predominantly in domestic environments.
Exposures to power-frequency magnetic fields in the home
C J Merchant, D C Renew and J SwansonPower-frequency magnetic fields in homes come from a variety of sources, internal (appliances and domestic wiring) and external (electricity distribution and transmission circuits). The authors present results from a survey of the fields encountered at home by 258 adults over one week each. Information on the major electrical features of each of the homes was collected and related to the exposures incurred. The strongest identified factor influencing exposure at home was the presence or absence of overhead lines at voltages of 132 kV or above within 100 m of the home (geometric-mean TWA field encountered by participants 208 nT near lines, 54 nT not near lines). Occupants of homes near overhead lines or supplies from 415 V to 66 kV did not on average encounter fields significantly different to those in homes without such lines (50 and 54 nT, respectively). Occupants of flats incurred greater exposures than those incurred by occupants of semi-detached and terraced houses, which were in turn greater than those incurred by occupants of detached houses (109, 60, 56 and 43 nT, respectively).
Allocating extremely-low-frequency magnetic-field exposure between sources
C J MerchantWhere a person is exposed to extremely-low frequency magnetic fields from a number of sources, the question of how to allocate their total exposure between the sources may arise. This is not trivial, because the total magnetic field is the square root of the sum of the squares of the resultants of the phasor addition of the three spatial components of field, i.e. is not simply the linear addition of the field from each source in isolation. Each source produces an alternating field in three dimensions of space with a certain phase. In other words, the resulting field is described by a vector. An expression attributes the field between sources in a way that treats all sources equivalently. It can be applied in carrying out detailed exposure assessments of a person subject to fields from a number of appliances and background sources.
Correlation of residential magnetic fields, road type and traffic in the UK
C J MerchantTraffic has been proposed as a confounding factor in studies of residential power-frequency magnetic fields and ill health. For confounding to be possible, magnetic field and traffic must be correlated. This paper shows that there is some correlation in the UK. The power-frequency magnetic fields from electricity distribution are lower in homes on cul-de-sacs than in those on residential through roads. There is a tendency for there to be higher magnetic fields in homes on residential through roads expected to carry more traffic. This may reflect the fact that the routes followed by traffic and electric-power distribution within residential areas are often related. The correlation of magnetic field and traffic density was not shown to extend to homes on main roads.
Magnetic fields from transmission lines: comparison of calculations and measurements
J SwansonAn experiment has been performed to compare the calculated and measured magnetic fields produced by a double-circuit 400 kV transmission line. The phase currents were measured in the substation at one end of the line, taking particular care to measure the zero-sequence currents accurately, and the earth-wire current was measured at the span where the experiment was conducted. These currents were used to calculate the magnetic fields, using a number of computer programs based on Ampere’s law. the magnetic field was measured at 22 positions ranging from 100 m on one side of the line to 500 m on the other side. Measured and calculated fields generally agreed well. The largest errors were ±7% ±1 nT. These errors are attributed to a mixture of random errors in the calibration, resolution and synchronisation of the measuring instruments, and systematic errors stemming from the measurement of zero-sequence currents.
Do the electric and magnetic fields created by power lines cause cancer?Power lines and health
J Swanson, D C Renew and N J Wilkinson
Long-term variations in the exposure of the population of England and Wales to power-frequency magnetic fields
J SwansonThis paper estimates the change in the average exposure of the population of England and Wales to power-frequency magnetic fields between 1949 and 1989. If magnetic fields are causally linked to disease with a linear exposure - response relationship, this quantity is related to the incidence rate of the disease. The exposure is divided into components attributable to a number of sources, principally residential background fields and fields from domestic appliances and the transmission system. The 1989 average exposures from these sources are estimated as 45 nT, 20 nT and 4.2 nT respectively. For each source, an understanding of how fields arise is combined with statistics on the use of electricity and demographic statistics to estimate the change in exposure from that source. These individual changes are then combined, weighted according to the average exposure from that source. The estimated increase in overall average exposure is by a factor of 4.5, which applies to the whole population and also just to children. This increase is slightly greater than the result obtained by the simpler method of taking average domestic electricity demand per consumer, and can be treated with more confidence. There are still numerous approximations involved, some of which are identified and discussed, with the conclusion that the estimated increase is probably an underestimate.
Net currents in underground distribution circuits in the UK: implications for assessing magnetic-field exposures
J SwansonReceived 2 May 1996, accepted for publication 15 September 1996In the majority of homes in the UK, background power-frequency magnetic fields come from currents in final distribution circuits. In these circuits, load currents produce a negligible external magnetic field. The fields in homes arise from net currents, produced when neutral currents divert out of the distribution cable through earth connections.This paper reports statistics on the prevalence of neutral-to-earth connections and measurements of net currents. Neutral-to-earth connections occur as part of protective multiple earthing, which is applied to 64% of underground circuits and 32% of domestic consumers' installations, and also occur accidentally within up to 20% (and probably substantially more) of homes. The 48 h average net current in a sample of 21 circuits was 3.6 A.Because net currents are produced by diverted neutral current, they vary as loads vary. However, neutral current is proportional not to total load but to the unbalance between the three phases, and this weakens the correlation between net currents and loads. Individual unbalanced loads can lead to disproportionately high net currents. These considerations suggest that the best way of assessing average magnetic fields in residences (which is necessary for epidemiological studies) remains by direct measurement over at least 24 h.
Comment on the paper: enhanced deposition of radon daughter nuclei in the vicinity of power frequency electromagnetic fields.
Net currents in underground distribution circuits in the UK
R F Cook, D C Renew and J SwansonReceived 1 June 1997, accepted for publication 2 July 1997
Does the exposure of children in the UK to background residential power-frequency magnetic fields differ from that of the whole population?
J SwansonBackground power-frequency magnetic fields in homes in the UK vary with the category of accommodation. The categories considered, in ascending order of average field, are detached, semidetached and terraced houses and flats. Because children occupy a different distribution of accommodation compared with the population as a whole, they will on average be exposed to a different background field. Using data on fields from a survey of two hundred people and on distribution of accommodation types from national statistics, it is estimated that this effect leads to children being exposed to background fields which are lower than those experienced by the population as a whole, 54.2 nT, by an average of , a difference which is barely significant.
Comment on the paper: High-voltage overhead lines and radon daughter deposition.
Comparison of residential power-frequency magnetic fields away from appliances in different countries.
Swanson J, Kaune WT.The purpose of this paper is to review measurements of residential power-frequency magnetic fields made in different countries and to determine whether average magnetic fields away from appliances are higher in some countries than in others. The paper includes 27 studies reporting measurements of residential magnetic fields in samples of homes: 14 from North America, 5 from the United Kingdom, and 8 from other European countries. Various factors that might make the results from individual studies unrepresentative of average fields in the relevant country are identified and discussed. Because distributions of magnetic fields generally are approximately log-normal, they are summarised by their geometric means. The best estimate of the geometric means of long-term average background fields in the United States is 60-70 nT and in the United Kingdom approximately 36-39 nT. In other countries, there are insufficient studies to draw firm conclusions on average fields. Measurements of personal exposure are higher than measurements of background fields, perhaps because they include exposures from appliances and other sources in the home. The ratio of personal exposure to background field seems, on average, to be approximately 1.4.
Possible mechanisms by which electric fields from power lines might affect airborne particles harmful to health.
Swanson J, Jeffers D.Power lines produce alternating electric fields and modify static electric fields in their vicinity. These electric fields, if large enough, can alter the concentration or transport of airborne particles (including particles harmful to health), for example by causing deposition of charged particles, polarisation of neutral particles, or by production of ions. It has been suggested that this could lead to adverse health effects being associated with power lines. Theoretical considerations and experimental evidence relevant to eight separate postulated mechanisms involving power lines and airborne particles are examined. On theoretical grounds, none should lead to any adverse health effect, primarily because the effects produced are very small and are swamped by air currents or by gravity, and because people spend limited time in the relevant conditions. The experimental evidence also weighs against any adverse health effects. Further, even if significant health effects were produced, they would be different from those suggested by existing epidemiology concerning power lines.
Residential Power-Frequency Electric and Magnetic Fields: Sources and Exposures.
J Swanson.The power-frequency magnetic fields found in homes are surveyed, concentrating on background fields. The aim is to survey the present state of knowledge and to highlight aspects of the fields in homes which are relevant to epidemiological studies. Wherever possible, emphasis is given to comparisons between different countries. Aspects of fields which are considered are: the sources of background fields; the strengths of average background fields in different countries; other features of the fields - harmonics, ellipticity, direction, relation to the static field - and other factors which are associated with the strength of the field in a home; the relative contribution of different sources of field to total personal exposure, assuming various exposure-response relationships; the way in which fields vary over time; and finally, the ways in which electric fields differ from magnetic fields, and the sparse information available on average electric fields.
Effects of wind and electric fields on 218Po deposition from the atmosphere.
Jeffers D.National Grid Company plc, Surrey, UK.PURPOSE: To estimate, under atmospheric conditions, 218Po deposition on a sphere representing the human head and compare with the effects of the maximum electric field to be found under a transmission line. METHOD: The effect of the wind in the absence of electric fields was calculated using the Reynolds Analogy between heat and mass transfer. The effect of the electric field was shown to be large compared with that of turbulence. A 'capture radius' due to the field was then estimated and charged 218Po particles blown into this region were assumed to be captured. RESULTS: The deposition ratio was proportional to gammaV0.4E0(0.67), where gamma = charged fraction of 218Po, V = velocity and E0 = surface electric field. With the charged fraction ranging from 0.9% to 3.2%, a surface field on 280 kV m(-1) and a wind speed of 3 m s(-1), the deposition ratio ranged from 3.4 to 9.3. The surface field is several orders of magnitude higher than the average personal exposures that have been measured in epidemiological studies and the effect does not appear to be of epidemiological significance. At low velocities, the predictions of this model are in agreement with the measurements of Henshaw et al. CONCLUSIONS: 218Po deposition by environmental AC fields cannot be advanced as an explanation for the reported associations between childhood leukaemia and electrical installations.
Childhood leukemia and electrical appliances.
Int J Radiat Biol 2000 Dec;76(12):1685-91
Comment on the papers: increased exposure to pollutant aerosols under high voltage power lines; and Corona ions from powerlines and increased exposure to pollutant aerosols.
Swanson J, Jeffers DE.
A note on the charging of aerosols by overhead line corona.
Jeffers D.Elevated concentrations of corona ions have been measured in the vicinity of high voltage overhead lines. It is shown that the integrated ion exposure of aerosols in the corona plume is of the order of (x/u)n(x) where n(x) is the ion concentration at distance x downwind from the line and u is the wind speed. Estimated ion exposures are of order 10(11) m(-3) x s, less then 1% of the 10(13) m(-3) x s needed to cause saturation charging of 20 nm aerosols. It is suggested that it is not valid to postulate that AC corona is a health hazard as a consequence of its charging aerosols in the size range 20-125 nm.
Basic restrictions in EMF exposure guidelines.
Renew DC, Glover ID.Different bodies have set guidelines restricting exposure to electric and magnetic fields. The limits at power frequencies recommended by these guidelines and the scientific basis and rationale for setting them have been reviewed, starting with the WHO Environmental Health Criteria 69 on Magnetic Fields, published in 1987. These guidelines are all designed to limit the induced current density to 10 mA m(-2), sometimes reduced by an additional safety factor of five for the general public. While published guidelines have, to date, universally adopted a restriction based upon induced current density, the internal electric field is the more fundamental quantity in determining biological effects. It is recommended that consideration be given to using the internal electric field rather than current density in future guidelines. Those who are responsible for setting guidelines need good scientific information on which to be able to set their limits. While there is already a significant weight of scientific evidence upon which exposure restrictions can be based, there is a need for more research to reduce uncertainties and to enable greater precision in the setting of limits. Some suggestions for future research directions, particularly aimed at further understanding of the interaction of electric fields with the nervous system, are suggested in this paper and are developed more widely in the following papers covering the proceedings of the EPRI Guidelines Science Workshop held in Brussels in June 2000.
Exposure guidelines for low-frequency electric and magnetic fields: report from the Brussels workshop.
Sheppard AR, Kavet R, Renew DC.The EMF Exposure Guidelines Science Workshop was held to evaluate the information base for guidelines for electric and magnetic field exposures at extremely low frequencies, to identify research needs, and to discuss how best to apply scientific knowledge in developing exposure recommendations. Although the existing guideline values are based on electrostimulation of nerve and muscle tissues, guidelines must also consider controversial studies of potential health effects from chronic exposures at environmental levels that are far too weak to cause electrostimulation. The size of the safety factor applied in specifying exposure limits reflects a variety of factors that introduce uncertainties. These include confidence in existing dose-effect relationships, population diversity, the reliability and precision of techniques to control over-exposure, and completeness of the information base, particularly regarding long-term effects. Specific research questions that can change the level of uncertainty meaningfully were identified in these areas: biophysical mechanisms of electrostimulation; the range of thresholds throughout exposed populations; cancer causation in children and adults, including a possible role for contact currents; cognitive, behavioral, and physiological effects on the central nervous system; improved dosimetry; and better understanding of electromagnetic interference with implanted biomedical devices such as pacemakers, defibrillators, and physiological monitors. This report introduces ten papers from the workshop that address these and related topics in detail.
A transmission utility's experience of applying EMF exposure standards.
Swanson J.National Grid, Leatherhead, Surrey, UK.Exposure standards for power-frequency electric and magnetic fields are often structured in terms of basic restrictions and investigation levels. For uniform exposures, investigation levels help the user operate within the standard without concern about exceeding the basic restriction. For non-uniform fields, however, numerical calculations of induced currents in the body may be necessary to determine compliance with the basic restriction. Utilities have strong incentives to apply exposure standards so that they do not impose unnecessary and unjustified constraints on their operations. They are therefore likely to be prepared to invest considerable effort in assessing compliance. However, the standards are based on round numbers, the values of tissue conductivity are not well characterized, and the calculations needed to apply the standards are still evolving. This suggests that, scientifically, this level of effort devoted to distinguishing compliant and non-compliant exposure scenarios is not justifiable.
A method for assessing occupational exposure to power-frequency magnetic fields for electricity generation and transmission workers.
Renew DC, Cook RF, Ball MC.A new method for assessing both current and historical occupational exposures to magnetic fields has been developed and used in health studies involving a cohort of electricity generation and transmission workers in England and Wales. The exposure values are derived by calculation from engineering and operational data about the power stations rather than from measurements. They are provided for each of 11 job categories for each year of operation of each power station represented in the cohort. The engineering data are used to determine the average magnetic fields in specified areas of work within the power station and then applied to information about the time spent in these areas by each of the job categories. The operational data are used to adjust the exposures for each year according to the power station output for the year. Earlier methods used measurements or the advice of panels of experts to provide exposure scores for a number of job categories across all power stations and years. Such methods were not able to distinguish exposures from different power facilities or during the different years of their operation. Measurement surveys at 10 power stations of the magnetic fields in the work areas gave confidence that the calculations were realistic. Exposure measurements on 215 workers at three power stations were compared in job groups with the exposures predicted by the method. The Pearson correlation coefficient was 0.86 and the slope and intercept of the line of best fit were 0.87 and 0.07 microT respectively. The method gives a good prediction of measured exposure and is being used for studies of occupational exposure to magnetic fields and leukaemia, and of cardiovascular disease, and a reanalysis of brain cancer.
Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study
Gerald Draper, Tim Vincent, Mary E Kroll, John SwansonObjective To determine whether there is an association between distance of home address at birth from high voltage power lines and the incidence of leukaemia and other cancers in children in England and Wales.
Cancer registry and National Grid records.
29081 children with cancer, including 9700 with leukaemia. Children were aged 0-14 years and born in England and Wales, 1962-95. Controls were individually matched for sex, approximate date of birth, and birth registration district. No active participation by cases or controls was required.
Main outcome measures
Distance from home address at birth to the nearest high voltage overhead power line in existence at the time. Results Compared with those who lived >600 m from a line at birth, children who lived within 200 m had a relative risk of leukaemia of 1.69 (95% confidence interval 1.13 to 2.53); those born between 200 and 600 m had a relative risk of 1.23 (1.02 to 1.49). There was a significant (P<0.01) trend in risk in relation to the reciprocal of distance from the line. No excess risk in relation to proximity to lines was found for other childhood cancers.
There is an association between childhood leukaemia and proximity of home address at birth to high voltage power lines, and the apparent risk extends to a greater distance than would have been expected from previous studies. About 4% of children in England and Wales live within 600 m of high voltage lines at birth. If the association is causal, about 1% of childhood leukaemia in England and Wales would be attributable to these lines, though this estimate has considerable statistical uncertainty. There is no accepted biological mechanism to explain the epidemiological results; indeed, the relation may be due to chance or confounding.
Biophysical mechanisms: a component in the weight of evidence for health effects of power-frequency electric and magnetic fields.
Swanson J, Kheifets L.Comparatively high exposures to power-frequency electric and magnetic fields produce established biological effects that are explained by accepted mechanisms and that form the basis of exposure guidelines. Lower exposures to magnetic fields (< 1 microT average in the home) are classified as "possibly carcinogenic" on the basis of epidemiological studies of childhood leukemia. This classification takes into consideration largely negative laboratory data. Lack of biophysical mechanisms operating at such low levels also argues against causality. We survey around 20 biophysical mechanisms that have been proposed to explain effects at such low levels, with particular emphasis on plausibility: the principle that to produce biological effects, a mechanism must produce a "signal" larger than the "noise" that exists naturally. Some of the mechanisms are impossible, and some require specific conditions for which there is limited or no evidence as to their existence in a way that would make them relevant to human exposure. Others are predicted to become plausible above some level of field. We conclude that effects below 5 microT are implausible. At about 50 microT, no specific mechanism has been identified, but the basic problem of implausibility is removed. Above about 500 microT, there are established or likely effects from accepted mechanisms. The absence of a plausible biophysical mechanism at lower fields cannot be taken as proof that health effects of environmental electric and magnetic fields are impossible. Nevertheless, it is a relevant consideration in assessing the overall evidence on these fields.
Childhood leukemia, electric and magnetic fields, and temporal trends.
Kheifets L, Swanson J, Greenland S.During the past 25 years concern has been raised about the possible health effects of extremely low frequency (ELF) electric and magnetic fields (EMFs), particularly regarding childhood leukemia. Comparison of changes in electricity consumption (a surrogate for exposure) to changes in childhood-leukemia rates, known as ecologic correlation, have been used to argue both for and against the association between magnetic fields and childhood leukemia. In this paper we explore what can be learned from such an ecologic approach. We first examine separately the evidence on trends in exposure to EMFs and on trends in leukemia rates, and then compare the two. Both incidence rates and exposures have increased, but there are so many approximations and assumptions involved in connecting the two trends that we cannot regard the ecologic evidence as providing any meaningful evidence for or against a causal link.
Power-frequency electric and magnetic fields in the light of Draper et al. 2005.
Swanson J, Vincent T, Kroll M, Draper G.Power-frequency electric and magnetic fields are produced wherever electricity is used; exposure is ubiquitous. Epidemiologic studies find an association between children living in homes with the highest magnetic fields and childhood leukemia, but bias is a possible alternative to a causal explanation. A new study, Draper et al., looks at residence close to high-voltage power lines, one source of exposure to such fields, and its design avoids any obvious bias. It finds elevated childhood leukemia rates, but extending too far from the power lines to be straightforwardly compatible with the existing literature. This leads to an examination of alternative explanations: magnetic fields, other physical factors, such as corona ions, the characteristics of the areas power lines pass through, bias, and chance. The conclusion is that there is currently no single preferred explanation, but that this is a serious body of science that needs further work until an explanation is found.
Investigation of the sources of residential power frequency magnetic field exposure in the UK Childhood Cancer Study.
Maslanyj MP, Mee TJ, Renew DC, Simpson J, Ansell P, Allen SG, Roman E.Health Protection Agency, Radiation Protection Division, Centre for Radiation, Chemical and Environmental Hazards, Chilton, DidcotOX11 0RQ, UK.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.
Methods used to calculate exposures in two epidemiological studies of power lines in the UK.
Two epidemiological studies of cancer (one for children and one for adults) and proximity to high-voltage power lines are being performed in the UK. We describe the methods used to calculate exposure to magnetic fields in these studies. We used grid references derived from addresses for subjects and compared these to the grid references of pylons to calculate distances to power lines. We gathered relevant data on the power lines and used these to calculate magnetic fields. This required information on loads in the years from 1962 to the present. The only such information now available is a prediction of loads made for each year in advance, and the use of predictions rather than actual loads is the biggest source of error in these calculations. For a recent year, we compare the loads used in these studies with actual loads to assess the accuracy of our calculations. These calculations were performed by industry, and we describe the steps taken to ensure their trustworthiness, including conducting them all blind to the case-control status of the subjects.
Future needs of occupational epidemiology of extremely low frequency (ELF) electric and magnetic fields (EMF): review and recommendations.
Kheifets L, Bowman JD, Checkoway H, Feychting M, Harrington M, Kavet R, Marsh G, Mezei G, Renew DC, van Wijngaarden E.The occupational epidemiologic literature on extremely low frequency electric and magnetic fields (EMF) and health encompasses a large number of studies of varying design and quality that have addressed many health outcomes, including various cancers, cardiovascular disease, depression and suicide, and neurodegenerative diseases, such as Alzheimer disease and amyotrophic lateral sclerosis (ALS). At a 2006 workshop we reviewed studies of occupational EMF exposure with an emphasis on methodologic weaknesses, and proposed analytical ways to address some of these. We also developed research priorities that we hope will address remaining uncertainties. Broadly speaking, extensive epidemiologic research conducted during the past 20 years on occupational EMF exposure does not indicate strong or consistent associations with cancer or any other health outcomes. Inconsistent results for many of the outcomes may be attributable to numerous shortcomings in the studies, most notably in exposure assessment. There is, however, no obvious correlation between exposure assessment quality and observed associations. Nevertheless, for future research, the highest priorities emerge in both the areas of exposure assessment and investigation of ALS. To better assess exposure, we call for development of a more complete job-exposure matrix that combines job title, work environment and task, and an index of exposure to electric fields, magnetic fields, spark discharge, contact current, and other chemical and physical agents. For ALS, we propose an international collaborative study capable of illuminating a reported association with electrical occupations by disentangling the potential roles of electric shocks, magnetic fields, and bias. Such a study will potentially lead to evidence-based measures to protect public health.
Bioelectromagnetics. 2009 Jul 14. [Epub ahead of print]Comment on Valic et al., 2009.
No abstract available.
Extremely low frequency electric fields and cancer: Assessing the evidence.Kheifets L, Renew D, Sias G, Swanson J.
UCLA School of Public Health, Department of Epidemiology, Los Angeles, California.Much of the research and reviews on extremely low frequency (ELF) electric and magnetic fields (EMFs) have focused on magnetic rather than electric fields. Some have considered such focus to be inappropriate and have argued that electric fields should be part of both epidemiologic and laboratory work. This paper fills the gap by systematically and critically reviewing electric-fields literature and by comparing overall strength of evidence for electric versus magnetic fields. The review of possible mechanisms does not provide any specific basis for focusing on electric fields. While laboratory studies of electric fields are few, they do not indicate that electric fields should be the exposure of interest. The existing epidemiology on residential electric-field exposures and appliance use does not support the conclusion of adverse health effects from electric-field exposure. Workers in close proximity to high-voltage transmission lines or substation equipment can be exposed to high electric fields. While there are sporadic reports of increase in cancer in some occupational studies, these are inconsistent and fraught with methodologic problems. Overall, there seems little basis to suppose there might be a risk for electric fields, and, in contrast to magnetic fields, and with a possible exception of occupational epidemiology, there seems little basis for continued research into electric fields. Bioelectromagnetics, 2009. (c) 2009 Wiley-Liss, Inc.
Exploring exposure-response for magnetic fields and childhood leukemia.
Kheifets L, Afifi A, Monroe J, Swanson J.For 30 years, there have been suggestions that extremely low frequency magnetic fields such as those are produced by electric power systems may be associated with elevated risks of childhood leukemia. These suggestions are driven by epidemiological evidence, and it has been common to characterize that evidence as showing a threshold effect, with no increase in risk below a threshold, often 0.3 or 0.4 muT, and a constant risk above it. Such a threshold would, however, be biologically unlikely. We tested alternative dose-response relationships quantitatively. We obtained five exposure data sets, applied several candidate dose-response relationships to each one, and performed a regression analysis to see how well they fit each of the three epidemiological data sets. Threshold dose-response relationships performed only moderately. Linear relationships were generally even poorer. The fit was improved by adding quadratic terms or performing non-linear regression. There are limitations in our analysis, stemming from the available data, but addressing this issue in a data-based, quantitative manner should improve understanding, allow better calculations to be made of attributable numbers, and hence ultimately inform public policy making.
A Pooled Analysis of Extremely Low-Frequency Magnetic Fields and Childhood Brain Tumors.
Kheifets L, Ahlbom A, Crespi CM, Feychting M, Johansen C, Monroe J, Murphy MF, Oksuzyan S, Preston-Martin S, Roman E, Saito T, Savitz D, Schüz J, Simpson J, Swanson J, Tynes T, Verkasalo P, Mezei G.Pooled analyses may provide etiologic insight about associations between exposure and disease. In contrast to childhood leukemia, no pooled analyses of childhood brain tumors and exposure to extremely low-frequency magnetic fields (ELF-MFs) have been conducted. The authors carried out a pooled analysis based on primary data (1960-2001) from 10 studies of ELF-MF exposure and childhood brain tumors to assess whether the combined results, adjusted for potential confounding, indicated an association. The odds ratios for childhood brain tumors in ELF-MF exposure categories of 0.1-<0.2 muT, 0.2-<0.4 muT, and >/=0.4 muT were 0.95 (95% confidence interval: 0.65, 1.41), 0.70 (95% CI: 0.40, 1.22), and 1.14 (95% CI: 0.61, 2.13), respectively, in comparison with exposure of <0.1 muT. Other analyses employing alternate cutpoints, further adjustment for confounders, exclusion of particular studies, stratification by type of measurement or type of residence, and a nonparametric estimate of the exposure-response relation did not reveal consistent evidence of increased childhood brain tumor risk associated with ELF-MF exposure. These results provide little evidence for an association between ELF-MF exposure and childhood brain tumors.
Risk Governance for Mobile Phones, Power Lines, and Other EMF Technologies.
Kheifets L, Swanson J, Kandel S, Malloy TF.UCLA School of Public Health, Department of Epidemiology, Los Angeles, CA, USA.Power-frequency electric and magnetic fields (EMFs) have been present in industrialized countries since the late 19th century and a considerable amount of knowledge has been accumulated as to potential health effects. The mainstream scientific view is that even if there is a risk, it is unlikely to be of major public-health significance. EMFs from cellular communications and other radio-frequency technologies have increased rapidly in the last decade. This technology is constantly changing, which makes continued research both more urgent and more challenging. While there are no persuasive data suggesting a health risk, research and particularly exposure assessment is still immature. The principal risk-governance issue with power frequencies is how to respond to weak and uncertain scientific evidence that nonetheless causes public concern. For radio-frequency electromagnetic fields, the issue is how to respond to large potential consequences and large public concern where only limited scientific evidence exists. We survey these issues and identify deficits in risk governance. Deficits in problem framing include both overstatement and understatement of the scientific evidence and of the consequences of taking protective measures, limited ability to detect early warnings of risk, and attempted reassurance that has sometimes been counterproductive. Other deficits relate to the limited public involvement mechanisms, and flaws in the identification and evaluation of tradeoffs in the selection of appropriate management strategies. We conclude that risk management of EMFs has certainly not been perfect, but for power frequencies it has evolved and now displays many successful features. Lessons from the power-frequency experience can benefit risk governance of the radio-frequency EMFs and other emerging technologies.
Childhood cancer and magnetic fields from high-voltage power lines in England and Wales: a case–control study
ME Kroll1, J Swanson2, TJ Vincent1 and GJ Draper1BACKGROUND: Epidemiological evidence suggests chronic low-intensity extremely low-frequency magnetic-field exposure is associated with increased risk of childhood leukaemia; it is not certain the association is causal.
METHODS: We report a national case–control study relating childhood cancer risk to the average magnetic field from high-voltage overhead power lines at the child’s home address at birth during the year of birth, estimated using National Grid records. From the National Registry of Childhood Tumours, we obtained records of 28 968 children born in England and Wales during 1962–1995 and diagnosed in Britain under age 15. We selected controls from birth registers, matching individually by sex, period of birth, and birth registration district. No participation by cases or controls was required.
RESULTS: The estimated relative risk for each 0.2 mT increase in magnetic field was 1.14 (95% confidence interval 0.57 to 2.32) for leukaemia, 0.80 (0.43–1.51) for CNS/brain tumours, and 1.34 (0.84–2.15) for other cancers.
CONCLUSION: Although not statistically significant, the estimate for childhood leukaemia resembles results of comparable studies. Assuming causality, the estimated attributable risk is below one case per year. Magnetic-field exposure during the year of birth is unlikely to be the whole cause of the association with distance from overhead power lines previously reported from this study.
Pooled analysis of recent studies on magnetic fields and childhood leukaemia
L Kheifets, A Ahlbom, C M Crespi, G Draper, J Hagihara, R M Lowenthal, G Mezei, S Oksuzyan, J Schüz, J Swanson, A Tittarelli, M Vinceti and V Wunsch FilhoBackground: Previous pooled analyses have reported an association between magnetic fields and childhood leukaemia. We present a pooled analysis based on primary data from studies on residential magnetic fields and childhood leukaemia published after 2000.Methods: Seven studies with a total of 10,865 cases and 12,853 controls were included. The main analysis focused on 24-h magnetic field measurements or calculated fields in residences.Results: In the combined results, risk increased with increase in exposure, but the estimates were imprecise. The odds ratios for exposure categories of 0.1–0.2 μT, 0.2–0.3 μT and 0.3 μT, compared with <0.1 μT, were 1.07 (95% CI 0.81–1.41), 1.16 (0.69–1.93) and 1.44 (0.88–2.36), respectively. Without the most influential study from Brazil, the odds ratios increased somewhat. An increasing trend was also suggested by a nonparametric analysis conducted using a generalised additive model.
Conclusions: Our results are in line with previous pooled analyses showing an association between magnetic fields and childhood leukaemia. Overall, the association is weaker in the most recently conducted studies, but these studies are small and lack methodological improvements needed to resolve the apparent association. We conclude that recent studies on magnetic fields and childhood leukaemia do not alter the previous assessment that magnetic fields are possibly carcinogenic.
Could the geomagnetic field be an effect modifier for studies of power-frequency magnetic fields and childhood leukaemia?
J Swanson and L KheifetsEpidemiological studies find an association between power-frequency magnetic fields and childhood leukaemia. One candidate mechanism for a causal link is effects of magnetic fields on biological reactions involving free radicals. This mechanism predicts effects from variations in static, as well as alternating, magnetic fields, and therefore different consequences at different locations on the earth's surface due to variations in geomagnetic field. Testing this directly is problematic. Instead, we investigate whether geomagnetic field appears to be an effect modifier in studies of alternating magnetic fields. We find some, but rather limited and not statistically significant, evidence for this, and discuss the implications.
Residential mobility of populations near UK power lines and implications for childhood leukaemia.
J SwansonEpidemiological studies suggest associations between childhood leukaemia and living near high-voltage power lines, but the most obvious potential causative agent, the magnetic fields produced by the power lines, is not supported by laboratory studies or a known mechanism. An alternative hypothesised explanation is if there is greater population mobility near power lines, linking to the findings of Kinlen that population mixing increases leukaemia rates. We used the names recorded in electoral registers to see whether people near power lines move house more often than the population as a whole. We did find variations, but only small ones, and not such as to support the hypothesis.
Residential distance at birth from overhead high-voltage powerlines: childhood cancer risk in Britain 1962-2008
Bunch KJ, Keegan TJ, Swanson J, Vincent TJ, Murphy MFGBackground: We extend our previous study of childhood leukaemia and proximity to high-voltage powerlines by including more recent data and cases and controls from Scotland, by considering 132-kV powerlines as well as 275 and 400 kV, and by looking at greater distances from the powerlines.
Methods: Case–control study using 53 515 children from the National Registry of Childhood Tumours 1962–2008, matched
controls, and calculated distances of mother’s address at child’s birth to powerlines at 132, 275 and 400 kV in England, Wales and Scotland.
Results: Our previous finding of an excess risk for leukaemia at distances out to 600m declines over time. Relative risk and confidence interval for leukaemia, 0–199m compared with >1000 m, all voltages: 1960s 4.50 (0.97–20.83), 2000 s 0.71 (0.49–1.03), aggregate over whole period 1.12 (0.90–1.38). Increased risk does not extend beyond 600 m, but may be present, albeit less strongly, for 132 kV lines.
Conclusion: A risk declining over time is unlikely to arise from any physical effect of the powerlines and is more likely to be the
result of changing population characteristics among those living near powerlines.
Relative accuracy of grid references derived from postcode and address in UK epidemiological studies of overhead power lines.
Swanson J, Vincent TJ, Bunch KJ.
In the UK, the location of an address, necessary for calculating the distance to overhead power lines in epidemiological studies, is available from different sources. We assess the accuracy of each. The grid reference specific to each address, provided by the Ordnance Survey product Address-Point, is generally accurate to a few metres, which will usually be sufficient for calculating magnetic fields from the power lines. The grid reference derived from the postcode rather than the individual address is generally accurate to tens of metres, and may be acceptable for assessing effects that vary in the general proximity of the power line, but is probably not acceptable for assessing magnetic-field effects.
Childhood cancer and exposure to corona ions from power lines: an epidemiological test
J Swanson1 , K J Bunch , T J Vincent and M F G Murphy
We previously reported an association between childhood leukaemia in Britain and proximity of the child’s address at birth to high-voltage power lines that declines from the 1960s to the 2000s. We test here whether a ‘corona-ion hypothesis’ could explain these results. This hypothesis proposes that corona ions, atmospheric ions produced by power lines and blown away from them by the wind, increase the retention of airborne pollutants in the airways when breathed in and hence cause disease. We develop an improved model for calculating exposure to corona ions, using data on winds from meteorological stations and considering the whole length of power line within 600 m of each subject’s address. Corona-ion exposure is highly correlated with proximity to power lines, and hence the results parallel the elevations in leukaemia risk seen with distance analyses. But our model explains the observed pattern of leukaemia rates around power lines less well than straightforward distance measurements, and ecological considerations also argue against the hypothesis. This does not disprove the corona-ion hypothesis as the explanation for our previous results, but nor does it provide support for it, or, by extension, any other hypothesis dependent on wind direction.
Journal of Radiological Protection 2015 Sep;35(3):695-705.
Magnetic fields and childhood cancer: an epidemiological investigation of the effects of high-voltage underground cables
K J Bunch, J Swanson, T J Vincent, M F G Murphy
Epidemiological evidence of increased risks for childhood leukaemia from magnetic fields has implicated, as one source of such fields, high-voltage overhead lines. Magnetic fields are not the only factor that varies in their vicinity, complicating interpretation of any associations. Underground cables (UGCs), however, produce magnetic fields but have no other discernible effects in their vicinity. We report here the largest ever epidemiological study of high voltage UGCs, based on 52,525 cases occurring from 1962-2008, with matched birth controls. We calculated the distance of the mother’s address at child’s birth to the closest 275 or 400 kV AC or high-voltage DC UGC in England and Wales and the resulting magnetic fields. Few people are exposed to magnetic fields from UGCs limiting the statistical power. We found no indications of an association of risk with distance or of trend in risk with increasing magnetic field for leukaemia, and no convincing pattern of risks for any other cancer. Trend estimates for leukaemia as shown by the odds ratio (and 95% confidence interval) per unit increase in exposure were: reciprocal of distance 0.99 (0.95-1.03), magnetic field 1.01 (0.76-1.33). The absence of risk detected in relation to UGCs tends to add to the argument that any risks from overhead lines may not be caused by magnetic fields.
Health-Economics Analyses Applied to ELF Electric and Magnetic Fields.
Kandel S, Swanson J, Kheifets L.
Extremely low frequency electric and magnetic fields (ELF EMFs) are a common exposure for modern populations. The prevailing public-health protection paradigm is that quantitative exposure limits are based on the established acute effects, whereas the possible chronic effects are considered too uncertain for quantitative limits, but might justify precautionary measures. The choice of precautionary measures can be informed by a health-economics analysis (HEA). We consider four such analyses of precautionary measures that have been conducted at a national or state level in California, the Netherlands, the United Kingdom, and Israel. We describe the context of each analysis, examine how they deal with some of the more significant issues that arise, and present a comparison of the input parameters and assumptions used. The four HEAs are methodologically similar. The most significant qualitative choices that have to be made are what dose-response relationship to assume, what allowance if any to make for uncertainty, and, for a CBA only, what diseases to consider, and all four analyses made similar choices. These analyses suggest that, on the assumptions made, there are some low-cost measures, such as rephasing, that can be applied to transmission in some circumstances and that can be justifiable in cost-benefit terms, but that higher cost measures, such as undergrounding, become unjustifiable. Of the four HEAs, those in the United Kingdom and Israel were influential in determining the country's EMF policy. In California and Netherlands, the HEA may well have informed the debate, but the policy chosen did not stem directly from the HEA.
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