|Betreff: Consolidated Reply to concerns raised by Tsawwassen residents|
|Von: Iris Atzmon
|Datum: Fri, 6 Oct 2006 22:39:36 +0200|
In previous research, we found that rats acutely (2 hr) exposed to a 60-Hz sinusoidal magnetic field at intensities of 0.1-0.5 millitesla (mT) showed increases in DNA single- and double-strand breaks in their brain cells. Further research showed that these effects could be blocked by pretreating the rats with the free radical scavengers melatonin and N-tert-butyl-alpha-phenylnitrone, suggesting the involvement of free radicals. In the present study, effects of magnetic field exposure on brain cell DNA in the rat were further investigated. Exposure to a 60-Hz magnetic field at 0.01 mT for 24 hr caused a significant increase in DNA single- and double-strand breaks. Prolonging the exposure to 48 hr caused a larger increase. This indicates that the effect is cumulative. In addition, treatment with Trolox (a vitamin E analog) or 7-nitroindazole (a nitric oxide synthase inhibitor) blocked magnetic-field-induced DNA strand breaks. These data further support a role of free radicals on the effects of magnetic fields. Treatment with the iron chelator deferiprone also blocked the effects of magnetic fields on brain cell DNA, suggesting the involvement of iron. Acute magnetic field exposure increased apoptosis and necrosis of brain cells in the rat. We hypothesize that exposure to a 60-Hz magnetic field initiates an iron-mediated process (e.g., the Fenton reaction) that increases free radical formation in brain cells, leading to DNA strand breaks and cell death. This hypothesis could have an important implication for the possible health effects associated with exposure to extremely low-frequency magnetic fields in the public and occupational environments.
|Residential power-frequency magnetic fields (MFs) were labeled as a possible human carcinogen by the International Agency for Research on Cancer panel. In response to great public concern, the World Health Organization urged that further epidemiologic studies be conducted in high-exposure areas such as Japan. We conducted a population-based case-control study, which covered areas inhabited by 54% of Japanese children. We analyzed 312 case children (0-15 years old) newly diagnosed with acute lymphoblastic leukemia (ALL) or acute myelocytic leukemia (AML) in 1999-2001 (2.3 years) and 603 controls matched for gender, age and residential area. Weekly mean MF level was determined for the child's bedroom. MF measurements in each set of a case and controls were carried out as closely in time as possible to control for seasonal variation. We evaluated the association using conditional logistic regression models. The odds ratios for children whose bedrooms had MF levels of 0.4 T or higher compared with the reference category (MF levels below 0.1 T) was 2.6 (95% CI = 0.76-8.6) for AML + ALL and 4.7 (1.15-19.0) for ALL only. Controlling for some possible confounding factors did not alter the results appreciably. Even an analysis in which selection bias was maximized did not fully explain the association. Most of the leukemia cases in the highest exposure category had MF levels far above 0.4 T. Our results provided additional evidence that high MF exposure was associated with a higher risk of childhood leukemia, particularly of ALL. © 2006 Wiley-Liss, Inc.|
----- Original Message -----From: jack bullochSent: Friday, October 06, 2006 6:47 PMSubject: Re: Consolidated Reply to concerns raised by Tsawwassen residents.
That does not explain to me why California refuses to place lines overhead near schools and why Great Britain has recently decided to place a moratorium on power lines in built up areas? Considering costs, I am at a loss to understand why they are doing it. The Vancouver Sun also quoted Health Canada as stating "This position is consistent with the overall opinions from most national and international scientific bodies". How can this be true when the IARC (international agency of cancer research) classifies EMF chronic exposure at 2 to 4 mG as a possible carcinogen?Can you name me another country in the world which would attempt to place such a huge industrial project in residential backyards? Please just one.----- Original Message -----From: Robert P BradleySent: Friday, October 06, 2006 9:13 AMSubject: Consolidated Reply to concerns raised by Tsawwassen residents.
Thank you for your comments which you sent to Dr. Art Thansandote regarding the current perspectives on the electric and magnetic field (EMF) issues arising as a result of the proposed transmission line upgrade in Tsawwassen. Following review by Dr. Thansandote and his staff, all your correspondence and their draft reply were forwarded to me for review. Since the themes in your separate emails are similar in nature, I would like to address them all at the same time.
As a family man and a member of my own community, I understand your concerns with respect to power lines. However, as scientists, I and the members of my Bureau involved in the ongoing evaluation of this subject must look at the issue from a scientific point of view and ultimately provide our recommendations to Health Canada based on our objective understanding of the current science. At the risk of stating the obvious, you should be aware that we take this responsibility quite seriously as the advice and recommendations resulting from our activities affect not only communities such as your own, but also the communities in which our families reside. At the end of the day all of us leave the lab to return home where we too are faced with the same impacts of our decisions as you and your neighbours.
To begin addressing your concerns let me first clarify why Health Canada (HC) has not produced guidelines for exposure to power line EMFs despite the fact that we have issued guidelines (or as we call them, Safety Codes) for radiofrequency fields, X-rays, etc. This will also explain why we take the position, as stated in our submission to the BC Environmental Assessment Office (EAO), that "there is no compelling scientific evidence".
Before developing a guideline for exposure to some agent a number of criteria must be met. These are:
1. A cause-effect relationship should be established,
2. A plausible mechanism which describes how the agent could possibly produce the effect should be available, and
3. A robustness of effect (the characteristic of being strong enough to withstand intellectual challenge) should be demonstrated.
I will discuss each of these in more detail.
In studying whether a cause-effect relationship exists and how robust it is, it is customary to take a weight of evidence approach when evaluating the scientific literature. That means that the whole body of peer-reviewed scientific evidence is examined including epidemiology (statistical studies of patterns of disease in human populations), animal studies and cell culture or in-vitro studies. Assessments are made on the quality of the study and the strength of evidence for or against an effect. Naturally, studies judged to be of poor quality are given little weight of evidence, while higher quality studies are given the more weight. This is irregardless of whether the studies found an effect, be it positive, negative or otherwise. There is a wide range of quality in the studies that are reported in the literature and part of the assessment process is to judge the quality of the experimental design, the protocols for data gathering and the analysis of all data acquired before the conclusions are even looked at. After reviewing the literature, which can take quite some time, it remains the reviewers' responsibility to apply their professional expertise and integrity to make a qualitative judgment about the amount of weight given to any and all studies. To be clear, this is a qualitative exercise, not a quantitative one, that results in the overall assessment of the issue and the formulation of the necessary recommendations. Fortunately, all of the Health Canada staff involved in the assessment of EMF health effects and preparation of relevant Safety Codes are experts in their specific areas with many years of research experience.
Our group at Health Canada has participated in scientific reviews on the national and international scene for such organizations as the World Health Organization (WHO), International Committee for Electromagnetic Safety (under the Institute of Electrical and Electronics Engineers or IEEE) and the Canadian Federal-Provincial-Territorial Radiation Protection Committee. In addition to these activities, we are engaged in carrying out our own research in the area of animal and cell culture EMF effects. This is invaluable not so much from the results that are produced, but rather from the insight it gives us into the potential pitfalls of doing EMF research and in evaluating the quality of the work of other groups. Our experience tells us that it is extremely difficult to do research in this area due to the number of potential confounding factors (things that enter into your experiment that can make the result false). For this reason, a great deal of weight is usually given to an effect if it can be replicated consistently by independent groups of researchers. This particular point is fundamental to the advancement of all science. It is normal practice for all scientists to question and repeatedly test the hypotheses of others. This constant review serves to strengthen our understanding of science by identifying the strong theories and eliminating the weaker ones.
Getting back to the weight of evidence for EMF, we offer our views on the 3 criteria cited previously with emphasis on cancer (since that seems to be the principle concern here):
1. It is our opinion that animal and cell culture studies have not demonstrated that power line EMFs cause cancer. A number of groups including the International Agency for Research on Cancer (IARC), the US National Institute of Environmental Health Sciences (NIEHS) and other scientific bodies also conclude that there is no evidence of causation from the animal and cell studies.
2. We acknowledge that a number of epidemiology studies and meta-analysis studies (combinations of the data from separate studies) have suggested an association between power line magnetic fields (or some surrogate of the fields) with childhood leukemia. However, it is our opinion that the epidemiology data for this association is weak and/or non-existent because:
(i) many of the results are based on small numbers of cases (childhood leukemia is a relatively rare disease, which makes it extremely difficult to design an epidemiological study of sufficient statistical power to produce conclusive results),
(ii) different studies assessed exposure of subjects using several different methods or in some cases not at all, instead relying on surrogate measures such as wire codes or distance to the transmission line (good exposure data is critical to any epidemiology study and is routinely the most difficult aspect of a study to address, many published studies are regularly criticized for weakness in exposure determination),
(iii) in studies comparing a group of people with the disease against a group selected to be controls (case-control studies), there are problems with the control selection process which may result in biasing the results one way or the other, and
(iv) the resulting statistics, risk ratios or odds ratios, are too small to permit a conclusion that causation is due to magnetic fields. For instance, one of the most quoted studies in your enquiries, the Draper study of 2005, lends evidence against causation of magnetic fields because the elevated risk ratios extend out to distances from the power lines beyond the physical influence of the magnetic fields produced by the power lines. This point was noted by the authors of the study yet is often ignored when the results are quoted.
Thus, we are faced with no evidence for a cause-effect relationship from the animal and cell culture studies and weak evidence of an association (but not necessarily a causal one) from the epidemiology. These two points are why IARC decided the classification of 2B was warranted for power frequency magnetic fields and not the more serious 2A or 1 classifications.
In terms of the second criterion, "a plausible mechanism", attempts at demonstrating that such a mechanism exists have not been successful. One of the most quoted possible mechanisms, the melatonin hypothesis, is flawed by the fact that empirical data from human and animal studies have provided no consistent evidence that magnetic filed exposure can influence day-time or night-time melatonin production.
Finally, without the first two criteria being met, it is impossible to satisfy the third, i.e. the robustness of effect. For example, even the epidemiology results are inconsistent where many well-conducted studies, for example the BC cancer study conducted by Mary McBride, found no association with childhood leukemia.
For the reasons cited above, Health Canada has chosen not to issue guidelines for power line EMFs. This is not to say that we are ignoring the epidemiology evidence, only that the weight of scientific evidence does not satisfy the criteria for setting guidelines.
Nevertheless, given the heightened public concern over this issue, Health Canada, already having applied the Government of Canada "Framework for the Application of Caution in Science-based Decision Making about Risk", further endorses the Precautionary Principle (PP) as promoted by the WHO. The precautionary measures taken should be proportional to the level of risk and its associated uncertainty, the severity of the outcome, and the level of societal benefit. This is where the social debate begins. The decision by IARC to classify power line EMFs as "possibly carcinogenic to humans" (the same classification applied to coffee and pickled vegetables) based on the epidemiological evidence should be interpreted as an initiation of the implementation of the PP. Our position is that because childhood leukemia is relatively rare and the evidence for causation by magnetic fields is weak, PP measures for EMF should be low cost or no cost. In any event, it is up to all stakeholders in the VITR project debate to discuss the project details and reach an appropriate consensus solution. What the PP does not say is that exposures should be reduced by government regulation in the face of the weak scientific evidence.
In summary, it remains our opinion that there is no compelling scientific evidence that power line EMFs can cause adverse health effects such as childhood leukemia. I hope that this information clarifies our position with respect to power line EMFs and health.
Robert P Bradley, Director
Consumer and Clinical Radiation Protection Bureau
Product Safety Programme
Healthy Environments and Consumer Safety Branch