Recent Publications from the Group

The following have all been recently submitted, accepted for publication or have now been published:

Comparisons of ground level measurements of ion concentration and potential gradient upwind and downwind of HV power lines in corona.

James C. Matthews, Alison J. Buckley, Matthew D. Wright and Denis L. Henshaw

Journal of Electrostatics, 2012, vol 70(4), pages 407-417


Simultaneous ion concentration and potential gradient measurements were made at AC high voltage power lines using ion mobility spectrometers and electric field mills. A significant (p < 0.01) change in central tendency and variability of ion concentration and potential gradient can occur downwind of power lines. In 3 out of 8 downwind measurements, there was a discrepancy of sign between the overall mean of these quantities, attributed to ion dispersion and ion-aerosol attachment. While ion concentrations give a greater indication of personal exposure, potential gradient measurements are more appropriate for assessment of the behaviour of a power line.

The effect of weather on corona ion emission from AC high voltage power lines

James C. Matthews

Atmospheric Research, 2012, vol 113, pages 68-79


There is a natural potential gradient caused by global thunderstorm activity that can be measured from the ground using electric field mill meters. High voltage power lines can produce corona ions by ionising the air, depending on the ambient weather conditions. A fixed site monitoring station recorded atmospheric potential gradient and weather conditions near to two AC high voltage power lines throughout 2008. High humidity correlated with negative potential gradient both upwind and downwind of power lines and high wind speed correlated with greater potential gradient disruption. Rain caused the greatest disruption to potential gradient, causing negative fields and an increased standard deviation. Multiple regression analysis also showed that that humidity and wind speed have an effect on the production of corona ions and quantile regression plots indicate a clear trend of decreasing mean potential gradient with increasing wind speed and relative humidity.

Diurnal variations of atmospheric potential gradient disruption near to high voltage power lines

James C. Matthews

Journal of Atmospheric and Solar-Terrestrial Physics, 2012, vol 77, pages 235-240.


The Earth's background potential gradient (PG) has a diurnal cycle (the ‘Carnegie curve’) that can be exhibited in fair weather when there are no local sources of space charge. High voltage power lines can create corona ions which are released into the atmosphere and can disrupt the natural PG. A fixed site monitoring station measured the vertical potential gradient at 1 s intervals alongside local weather conditions to investigate the time of day at which corona production is greatest downwind of a power line. In upwind conditions, the average PG curve returned correlates well with the Carnegie curve, but this is masked under downwind conditions. Overnight, the PG downwind of the monitoring station is more variable and more negative than upwind. Downwind of the power line there is significantly more variability of potential gradient after sunrise and before sunset on most days.

Corona ion induced atmospheric potential gradient perturbations near high voltage power lines

James C. Matthews, Jonathan P. Ward, Paul A. Keitch and Denis L. Henshaw

Atmospheric Environment, 2010, vol 44(9), pages 5093-5100


High voltage power lines are known to produce corona ions that can be carried from the line by the wind, progressively attaching to ambient aerosol particles and causing fluctuations in the Earth’s atmospheric potential gradient. A fixed site monitoring station was installed near two power lines, which recorded the potential gradient at 1 s intervals and the ambient weather conditions every 10 min. The station ran continuously from January 2007 to December 2008, accumulating long-term data. Results from 2008 show an increase in potential gradient variability when a wind is blowing across the power lines towards the station, indicating that corona ions may be present in this environment.

A technique for rapid estimation of the charge distribution of submicron aerosols under atmospheric conditions

Alison J. Buckley, Matthew D. Wright and Denis L. Henshaw

Aerosol Science & Technology 2010, vol 42(12), pages 1042-1051.


A portable technique is presented for rapid estimation of the charge distribution of submicron aerosols under atmospheric conditions, using two Differential Mobility Analyzer (DMA) systems in parallel. Simultaneous measurement of the aerosol mobility and size distributions are made by using one DMA with a neutralizer and the other without. An estimate of the aerosol charge is obtained by a fitting procedure, in which the size distribution and an expression for the charge distribution are used to calculate the mobility distribution of the sample. The parameters in the theoretical charge distribution are varied iteratively until the calculated and measured mobility distributions match. Validation was undertaken with separate measurements of ion mobility and concentration used in the charging expression. Results are presented for ambient indoor air, unipolar ion production by an ionizer and downwind of a high-voltage overhead AC powerline.

Aggregating disparate epidemiological evidence: comparing two seminal EMF reviews

Mike J. O’Carroll & Denis L. Henshaw

Risk Analysis 2008, vol 28(1), pages 225-234.


Two seminal reviews (IARC 2002, CDHS 2002) of possible health effects from powerfrequency EMFs reached partly different conclusions from largely similar epidemiological evidence. These differences can have an impact on precautionary policy. We examine the statistical aggregation of results from individual disparate studies. Without consistent exposure metrics, the advantage of meta-analysis and pooling to estimate magnitude of effect and confidence limits is lost. However, counting positive results and statistically significant results yields important information with p-values reflecting the overall strength of evidence. Representative results from 33 independent adult leukaemia studies tabled by IARC yielded 23.5 positives (p ˜ 0.01) and 9 significant-positives (p < 10-7). From 43 representative results from CDHS, there were 32 positive (p < 0.001) and 14 significantpositives (p < 10-12). There were no significant-negative results in either list. Results for adult brain cancer gave a similar, but less clear, message. Results for childhood leukaemia suggests they are not stronger, numerically, than those for adult leukaemia, and that formal pooling of coherent studies shows a stronger association than aggregating all the studies. CDHS did not note the number of significant positives, but noted the meta-analytic summary and the number of positives, forming a view about the strength of these findings. IARC shows no evidence of considering the aggregation of results other than subjectively. It considered individual studies but this led to a tendency to fragment and dismiss evidence which is intrinsically highly significant. We make recommendations for future reviews.

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Adult leukaemia near powerlines (letter)

M J O’Carroll and D L Henshaw

Internal Medicine Journal 2007, vol 37, page 841

Mini-Review: Can disturbances in the atmospheric electric field created by powerline corona ions disrupt melatonin production in the pineal gland?

D L Henshaw Jonathan P Ward and James C Matthews

Journal of Pineal Research 2008, vol 45, pages 341 - 350


Recent epidemiological studies have reported an increased risk of leukaemia in adults and children near overhead high voltage powerlines at distances beyond the measured range of the direct electric and magnetic fields. Corona ions are emitted by powerlines, forming a plume that is carried away from the line by the wind. The plume generates random disturbances in the atmospheric electric field of tens to a few hundred V m-1 on time scales from seconds to minutes. Such disturbances can be seen up to several hundred metres from powerlines. It is hypothesised that these random disturbances result in the disruption of nocturnal melatonin synthesis and related circadian rhythms, in turn leading to increased risk of a number of adverse health effects including leukaemia. In support of the hypothesis it is noted that melatonin is highly protective of oxidative damage to the human haemopoietic system. A review of electric field studies provides evidence that (i) diurnal variation in the natural atmospheric electric field may itself act as a weak zeitgeber; (ii) melatonin disruption by electric fields occurs in rats; (iii) in humans, disturbances in circadian rhythms have been observed with artificial fields as low at 2.5 V m-1. Specific suggestions are made to test aspects of the hypothesis.

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Small-ion and nano-aerosol production during candle burning: size distribution, concentration profile with time and charge state

Matthew D. Wright, A. Peter Fews, Paul A. Keitch and Denis L. Henshaw

Aerosol Science and Technology, VOL 41; NUMB 5, pages 475-484, 2007


The characteristics of small-ions and aerosols in the size range 0.4 nm to 1.1 µm, produced during burning of paraffin wax tea-light candles, were investigated using a custom-built aspiration condenser ion mobility spectrometer (ACIMS) and a sequential mobility particle sizer and classifier (SMPS+C) system. Peaks in the number concentration were observed at sizes 10 - 30 nm and 100 - 300 nm, consistent with ‘normal’ and ‘sooting’ burn modes. In addition, a smaller mode in the size range 2.5 - 9 nm was observed, interpreted as a soot-precursor species. When a fan was placed behind the burning candle to reduce the travel time to the measurement devices, a ‘modified small-ion’ signal was seen in the size range 1.2 - 1.8 nm. This was not observed without the fan present, suggesting this species has a short lifetime compared to the larger particles produced in the flame. During burning, aerosol concentration was elevated and small-ion counts were low. However after extinction of the flame, this trend was reversed and the number of small-ions increased to levels higher than those observed prior to burning, remaining so for up to 7 hours. The largest particles measured (> 100 nm) were found to carry greater charge than expected at room temperature equilibrium, but mid-sized particles (20 - 60 nm) carried lower than average charge.

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Author Posting. (c) Taylor & Francis, 2007.

This is the author's version of the work. It is posted here by permission of Taylor & Francis for personal use, not for redistribution.

Comment on “Developing Policy in the Face of Scientific Uncertainty: Interpreting 0.3 µT or 0.4 µT Cutpoints from EMF Epidemiologic Studies” by Kheifets et al. in Risk Analysis, 25(4), 927-935 (letter)

M J O’Carroll and D L Henshaw

Risk Analysis Vol. 27, No. 2, April 2007

Re: “Nighttime exposure to electromagnetic fields and childhood leukaemia: an extended pooled analysis” (letter)

M J O’Carroll and D L Henshaw

American Journal of Epidemiology 166: 859, 2007.

Observations on the relationship between magnetic field characteristics and exposure conditions

Elizabeth A. Ainsbury and Denis L. Henshaw

Physics in Medicine & Biology, 51, 6113-6123, 2006


The authors have been investigating metrics of extremely low frequency magnetic field exposure in different circumstances. In this paper, we describe the properties of magnetic fields in homes, in the vicinity of powerlines, on trains and from a library security system. We conclude that there are key differences between each of these fields. This suggests that there may be a characterisable pattern for magnetic fields in different situations.

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Static electric fields as a mediator of hospital infection

Allen, J. E., Close, J. J. and Henshaw, D. L.

Indoor & Built Environment, 14, 49-52, 2006


Static electric charge at the surface of nurses' plastic aprons was examined as a possible contributor to hospital infections in a bone marrow transplant ward. Transplant patients undergo high-dose chemotherapy and radiotherapy which compromises the immune system, rendering these patients highly susceptible to infecting organisms. Results of this pilot study showed that the velocity of a bacterium in air close to the apron surface was sufficient for swift attraction onto the surface. In addition, an electric field may be induced around the patient by the presence of the plastic apron, attracting airborne bacteria directly onto the patient. Tests showed that the polyethylene plastic aprons attracted about 83% more bacteria onto their surfaces during wear, compared with only 17% more acquired by aluminium foil aprons. We suggest that these results implicate static charge on aprons as a mediator of hospital infection.

A novel high resolution small ion spectrometer to study ion nucleation of aerosols in ambient outdoor air

A P Fews, N K Holden, P A Keitch and D L Henshaw

Atmospheric Research 76, 29-48, 2005


An electricity based ion spectrometer is described, capable of measuring particle sizes and mobilities from molecular ions (small ions) to aerosol particles across a size range of ~0.4 to 30 nm in diameter. It consists of a single cylindrical capacitor divided into three electrically insulated sections. The current arriving at the central section is measured by an electrometer and represents the ion flux over a known range of mobilities determined by the applied voltage. The applied voltage is scanned in steps to measure the ion fluxes over a large number of overlapping mobility ranges. The recorded signal and the response function of the instrument are unfolded using a maximum entropy procedure to give a high-resolution measured mobility spectrum. The maximum entropy approach offers a considerable improvement over traditional aspiration collectors and can approach the resolution of a drift tube system. In the way, the spectrometer successfully overcomes the diffusion limit to small ion resolution. Illustrative spectra are shown, demonstrating for the first time the presence of some resolved structure within the small ions falls in the range 0.8-2.0 x 10-4 m2 V-1 s-1. This represents a narrower range than that previously measured which is attributed to improved spectral resolution in the present work.

Do magnetic fields cause increased risk of childhood leukaemia via melatonin disruption?

D L Henshaw and R J Reiter

Bioelectromagnetics Suppl. 7: S86-S97; 2005


Epidemiological studies have reported associations between exposure to power frequency magnetic fields and increased risk of certain cancer and noncancer illnesses. For childhood leukemia, a doubling of risk has been associated with exposures above 0.3/0.4 µT. Here, we propose that the melatonin hypothesis, in which power frequency magnetic fields suppress the nocturnal production of melatonin in the pineal gland, accounts for the observed increased risk of childhood leukemia. Such melatonin disruption has been shown in animals, especially with exposure to electric and/or rapid on/off magnetic fields. Equivocal evidence has been obtained from controlled laboratory magnetic field exposures of volunteers, although the exposure conditions are generally atypical of neighborhood exposures. In contrast, support for the hypothesis is found in the body of studies showing magnetic field disruption of melatonin in human populations chronically exposed to both electric and magnetic fields associated with electricity distribution. Further support comes from the observation that melatonin is highly protective of oxidative damage to the human haemopoietic system. Aspects of the hypothesis are amenable to further investigation.

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An investigation into the vector ellipticity of ELF magnetic fields from appliances in UK homes

E .A. Ainsbury, E Conein and D L Henshaw

Physics in Medicine & Biology, 50, 3197-3209, 2005


Elliptically polarized magnetic fields induce higher currents in the body compared with their plane polarized counterparts. This investigation examines the degree of vector ellipticity of extremely low frequency magnetic fields (ELF-MFs) in the home, with regard to the adverse health effects reportedly associated with ELF-MFs, for instance childhood leukaemia. Tri-axial measurements of the magnitude and phase of the 0-3000 Hz magnetic fields, produced by 226 domestic mains-fed appliances of 32 different types, were carried out in 16 homes in Worcestershire in the summer of 2004. Magnetic field strengths were low, with average (RMS) values of 0.03 +/- 0.02 µT across all residences. In contrast, background field ellipticities were high, on average 47 +/- 11%. Microwave and electric ovens produced the highest ellipticities: mean respective values of 21 +/- 21% and 21 +/- 17% were observed 20 cm away from these appliances. There was a negative correlation between field strength and field polarization, which we attribute to the higher relative field contribution close to each individual (single-phase) appliance. The measurements demonstrate that domestic magnetic fields are extremely complex and cannot simply be characterized by traditional measurements such as time-weighted average or peak exposure levels. We conclude that ellipticity should become a relevant metric for future epidemiological studies of health and ELF-MF exposure.

Morphological features of the micro-distribution of naturally occurring 210Po and 226Ra in the teeth of children and juveniles

P R James, J J Close, P A Keitch, J E Allen, A P Fews and D L Henshaw

International Journal of Radiation Biology, 80(3), 185-198, 2004


Purpose: To examine the microdistribution of natural a-radioactivity in deciduous teeth of children and the permanent teeth of juveniles extracted for orthodontic purpose from across the UK. Materials and methods: The microdistribution of 210Pb-supported 210Po and 226Ra in 708 deciduous and permanent teeth and 32 foetal teeth was measured on 1442 TASTRAK a-particle track detectors. Results: Of the various findings, a number are of special interest. Around half of the 210Pb activity in the outer enamel of deciduous teeth appears to have been acquired in utero as a result of transplacental transfer. In deciduous and permanent teeth, 226Ra is concentrated mainly in the circumpulpal region, while the highest levels of 210Po are on the highly calcified outer enamel surface. Furthermore, activity concentrations recorded on this surface were ln-normally distributed. Conclusions: 210Pb-supported 210Po activity on the outer enamel surface of permanent teeth constitutes an assay of cumulative environmental exposure with which to assess exposure in bone, both in utero and in childhood. Such assessment can be used to study geographical variations in the a-activity in teeth. More work is also required to determine the concentrations of both 210Po and 210Pb in the foetal skeleton.

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Aspects of the geographical variations in naturally occurring 210Pb­supported 210Po in permanent teeth of juveniles in the UK

P R James, J J Close, P A Keitch, J E Allen, A P Fews and D L Henshaw

International Journal of Radiation Biology, 80(3), 199-208, 2004


Purpose: To study geographical variations in the level of naturally occurring 210Pb-supported 210Po in permanent teeth of juveniles in the UK. Materials and methods: Permanent teeth extracted from 278 juveniles for orthodontic purposes were obtained from 48 counties in the UK. 210Po activity concentration was measured on the outer enamel surface using TASTRAK a-particle-sensitive plastic track detectors. Results: Geometric mean¡SE activity concentrations in teeth from urban, suburban and rural areas, excluding the high radon area of Devon, were 8.41 z0.25/20.24, 7.76 z0.37/20.35 and 7.20 z0.49/20.46 Bq kg21, respectively. Overall, there was no significant association between a-activity on the outer enamel surface of permanent teeth and proximity to the major UK motorways. However, when the data were considered with respect to the prevailing south-westerly wind on the western side of the UK, a statistically significant association with respect to donors living downwind (on the easterly side) of the motorways was found. This effect was greater for sections of the M5 and M6 motorways that traverse urban areas. 210Po levels in teeth were also associated with domestic radon concentration. This effect was comparable with that from traffic and urban pollution. Conclusions: Higher levels of 210Pb-supported 210Po are seen in permanent teeth of juveniles near sources of increased exposure in the UK. Inhalation uptake is an important pathway of exposure, especially with respect to domestic radon exposure. The results might be important in assessing integrated exposure to 210Po in the skeleton and consequent high linear energy transfer dose to bone marrow.

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Health effects of high voltage powerlines

Henshaw, D. L. and Fews, A. P.

Electromagnetic Environments and Health in Buildings
Chapter 15, pp 295-306. Ed: Derek Clements-Croome
Published by: Spon Press, London, 2004. ISBN 0-415-31656-1