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Professor Dennis Henshaw on high-voltage powerlines

Sunday, May 27, 2001
60 Minutes presents a live chat with British professor, Denis Henshaw. Professor Henshaw is here to answer your questions about the possible health risks associated with living near high voltage powerlines.

Professor Henshaw, thank you for joining us tonight, and good morning to you.

Host Denis_Henshaw: Good morning.

Host amicus_9msn: We will go directly to the questions from our chat guests as they have been eagerly awaiting your arrival.

sneddo: How do they measure the electric field that surrounds the powerlines?

Host Denis_Henshaw: It's just called an Electric Field Meter. It's a meter you can buy for around 200-300 pounds.

zapped: Would burying the power cables in built-up areas eliminate the health risks to the community?

Host Denis_Henshaw: It would eliminate any electric field or corona ion effect and magnetic fields are considerably reduced, so burying is the best solution.

wazza: If this is so dangerous, why do local councils build houses near or under these high voltage deathtraps?

Host Denis_Henshaw: In Sweden there is a prudent avoidance distance of 150 metres and in many states in the USA, there is also the practice of avoiding building houses near high voltage powerlines. But in other countries, Great Britain especially, there has been a reluctance to accept that there are any adverse effects from high voltage powerlines.
But recent international analysis has confirmed that there is a doubling of child leukemia at magnetic field exposure, much less than experienced under powerlines, and furthermore, the UK Government has indicated that it will set up a special committee to look into the other effects that we in Bristol have been talking about — adult cancer, depression, suicide etc.
In Switzerland they do recommend limiting magnetic field exposures to one micro-Tefla and that is about 20 percent of what you receive under high voltage powerlines, so the practical effect is to avoid building new houses near powerlines. In Italy some politicians have suggested a sever limit of "half a micro-Tefla".

Greg_Marlow: Professor, is it true that scientists have been unable to recreate the exact environment in a lab to obtain conclusive proof of your findings?

Host Denis_Henshaw: It's been difficult to obtain conclusive proof on humans because humans are exposed for many years in an outdoor and indoor environment and these are not easily reproduced in the laboratory. But as regards our latest work on how increased exposure to air pollution is caused by corona irons, then the behaviour of corona irons in the atmosphere has been extensively investigated by the power industry itself, notably during the 1980s.

Alf: Professor Henshaw, what frequency radio waves do these high-voltage powerlines give out?

Host Denis_Henshaw: They're very low frequency in Europe — they are 50 cycles per second; in USA/Canada they are 60 per second. This is a very low frequency and therefore the powerlines don't really emit radiation; what they have around them is a magnetic field, rather like the magnetic field around a bar magnet (except of course it is alternating 50 times per second) and a separate electric field (rather like the area of static charge on a TV set screen.)

Noodles: Professor Henshaw, would putting the elecric current through a transformer so that it was high amperage, but low voltage, affect the dangerous output level?

Host Denis_Henshaw: The low voltage would certainly mitiate against the electric field and corona iron effects; this is true. However, there will be an increased amount of electric current and this we know to be linked to childhood leukemia and also to depression in adults. Childhood leukemia is thankfully a very rare disease, but depression is very common. It is estimated that around 15 percent of adults in developed countries have one depressive episode per year, so this is an important cost to public health and any increase as a result of magnetic fields is clearly of public health importance.

Lineworker: l have worked on high voltage powerlines (22kv to 66kv) for the last eight years. Could this be affecting my health?

Host Denis_Henshaw: There have been extensive occupational studies of powerline workers; some of these studies have shown an increased risk of leukemia and of depression. However, in the case of leukemia, this is only after lifetime occupational exposure, for example more than 20 years. I think the risk to yourself is very small and not a cause to worry about, but what you must of course do is to visit your doctor if you do in any way feel unwell, so that your own health is carefully monitored.

Shaboom: Doctor, do you have any straightforward testing processes that could be used by the average citizen to test for harm at the molecular level?

Host amicus_9msn: Is there any correlation between irradiation of food with its subsequent damage to proteins and the effects of strong magnet fields from powerlines?

Host Denis_Henshaw: (First question), unfortunately the measurement of powerline health effects is complex and it's not really possible for individual members of the public to do this themselves. I don't think there is any link between high voltage powerline magnetic and electric fields food irradiation.

THEO: From the research you have done, what particles in the air are more prevalent to bind and is there a size range that is more binding?

Host Denis_Henshaw: Pollution exists in the air in the form of small particles we call aerosols and the peak size of these is in the range 100 - 200 nano-metres (one billionth of a metre). The corona iron from the powerline starts as a single ionised air molecule (oxygen or nitrogen), this ionised molecule attracts a small cluster of molecules in the air, usually water vapour molecules. On a subsequent time scale of a few minutes this electrically charged cluster of molecules attaches itself to the aerosol particles of air pollution. The technical details of this attachment process are highly complex but aerosols in the 100-200 nano-metre size range usually attract only one ionised molecule (ie. they support only one charge). For larger polluted aerosols in the air eg. one micron, these can support many electric charges.
However, the relative number of aerosols in this size range is much lower than for the 100-200 nano-metre aerosols. Once these aerosols have obtained their charge from the corona irons, it takes up to one hour before they lose their charge — in other words, near a powerline there is always a pool of pollutant aerosols that carry excess charge due to corona irons.

Alf: Professor Henshaw, what causes the damage — the radio frequency energy from the powerlines or the ionised free O and N atoms? Are the N2 and O2 molecules split up into free atoms around powerlines?

Host Denis_Henshaw: Taking the last part of the question first, my answer to the previous question explains how the electrically charged aerosol evolves from the initial nitrogen and oxygen ionised molecules. The danger arises, we believe, because it is known that when you inhale electrically charged aerosols, these have a higher chance of sticking to your lung. For example, if you watch a smoker smoke, they may inhale cigarette smoke, but you see them exhaling a smoke also. In other words, not all of the inhaled smoke is trapped in the lung. For air pollution in the 100-200 nano-metre range, only 30 percent of what is inhaled is trapped in the lung. If however, you were to put an electrical charge on all of those aerosols, then the amount deposited in the lung becomes 100 percent. Under the powerlines we have measured we think only around 10 percent of pollutant aerosols become charged by corona irons, so this leads to a relatively small increase in lung deposition on inhalation. However in public health terms, this is sufficient to cause a sizeable increase in the illnesses associated with air pollution in a population living near high voltage powerlines. Research underway at Brisol by my colleague, Dr Alan Preece, suggests that there is a 30 percent increase in lung cancer in people living near high voltage powerlines in South West England. The effect here is mainly on the downwind side of the powerline, on the eastern side because of the experience of a prevailing south westerly wind across the UK. The measurements by Alan Preece, if extrapolated to the whole of the UK, would suggest about 300 lung cancers per year caused by powerlines in populations living within 400 metres.

bemused: Prof Henshaw, how do ionised particles cause depression?

Host Denis_Henshaw: Depression is linked to the magnetic fields from powerlines, not the corona ions. The human body produces an agent called melatonin, which is both a natural anti-cancer agent and an agent which controls moods. It is produced in the pineal gland in the brain and the production is 50-70 times greater at night when you are sleeping. Melatonian deficiency" is linked to depression. There have been experiments on humans which show that melatonian production is reduced by magnetic fields. Therefore the action of magnetic fields from powerlines in causing increased depression is biologically plausible.
Populations living near powerlines are more affected than powerline workers because by definition, the workers would be working in the daytime when their bodies are producing low melatonin, but populations living near powerlines are also exposed at night when their peak melatonian production takes place. Coming onto cancer, many scientists disagree that the action of magnetic fields in depressing body melatonian can lead to cancer.
However, a German study published last month showed a significant increase in childhood leukemia when looked at in relation to nighttime exposure of the children to magnetic fields. This is very interesting research which is ongoing.

yak: Prof, with research into 1,000,000 volt transmission lines occurring in the USA, what is the optimum voltage in terms of transmission for minimal affect on people?

Host Denis_Henshaw: I think you have to say that there is a conflict of interest here. The optimum voltage would be a very low voltage, something like 10,000 or 20,000 volts, however it is far too low to be of any use for transmitting power.
The answer is to bury the powerlines. The US research is exploiting the well-known fact that the higher the voltage, the more efficient the transmission. However, with 1,000,000 volts, I would expect corona ion emission could be a major problem. If these lines are to go over ground, they clearly must be well away from populated areas. The only real solution is to bury the powerlines; the technologies are established, but as always, it is a matter of cost. However, in cost benefit terms, it is clearly preferable to have lines buried in populated areas. For example, I was in Stockholm, Sweden last year and I suggested we went to a powerline to make some measurements to use in my invited lecture at the Carolinska Institute. My host burst out laughing and said, "You know there are no powerlines in Stockholm; in Sweden we do not put them near houses".

Chook: Professor, where may we obtain more documentation on your research in order to justify a complaint to authorities who plan to erect high voltage powerlines 22 metres away from my father's house at Coffs Harbour?

Host Denis_Henshaw: Our website is and we have started putting far more information for the public on this website in addition to the technical information and we are trying to extend the information in the coming weeks so please keep an eye on the site. There's also an email address there for people to make enquiries.

SpongeBob: Professor, in your personal opinion, what is a safe distance to live from these powerlines?

Host Denis_Henshaw: Well, in most cases, the effect of corona ions extends to no more than 400 metres from powerlines. However, in our experience, older powerlines are more prone to corona and in one case in a line not far from Bristol, we measured substantial corona ion effects up to 2.7km away.

birdy: Professor, have you any addresses we can contact concerning this in Australia?

Host Denis_Henshaw: Unfortunately no I don't, but there is another UK site, it's and there are links to other sites with information regarding childhood cancer. Power Watch is a consumer organisation with extensive knowledge.

Host amicus_9msn: Professor Henshaw, thank you for joining us tonight and presenting a plethora of information. Do you have any last words for our guests before we finish?

Host Denis_Henshaw: Thank you so much for such interesting questions. If you want me to add to anything I've said, do contact me via email, via our website. Thank you very much to all of you.

Host amicus_9msn: Again Professor Henshaw, thank you and goodnight. This concludes our 60 Minutes live chat with Denis Henshaw, May 27, 2001.

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