1. Introduction to electromagnetic fields
- 1.1 What are electromagnetic fields?
- 1.2 Why and how have the health risks of electromagnetic fields been reassessed?
1.1 What are electromagnetic fields?
The source document for this Digest states:
3.1 Introduction
The purpose of the opinion is to update the CSTEE opinion of 2001 with respect to whether or not exposure to electromagnetic fields (EMF) is a cause of disease or other health effects and the purpose is not to provide a general review on electromagnetic fields and health. Recommendations regarding exposure guidelines or other risk management tools, including application of the precautionary principle are beyond the scope of the opinion. The methods that were used for the preparation of the opinion are explained below.
The objective of this section is to establish the scientific rationale that is necessary in order to provide an opinion in response to the request to the Committee, in particular to update the CSTEE opinion of 30 October 2001. This section therefore summarizes what was known at the time of the 2001 Opinion, reviews the scientific data that have been published after 2001, and assesses to what extent these new data affect previous conclusions. Following the Committee’s general principles, only studies published in peer reviewed journals have been considered.
The section is divided into four sub-sections according to frequency (f) range: radio frequency (RF) (100 kHz < f ≤ 300 GHz), intermediate frequency (IF) ( 300 Hz < f ≤ 100 kHz), extremely low frequency (ELF) (0 < f ≤ 300 Hz), and static (0 Hz) (only static magnetic fields are considered in this opinion). These frequency ranges are discussed in order of decreasing frequency, RF, IF, ELF, and static. For each frequency range the review begins with a description of sources and exposure to the population. This is followed, for each frequency range, by a discussion that is organized according to outcome. For each outcome relevant human, in vivo, and in vitro data are covered.
Source & ©: ,
Section 3.1 Introduction, p.11
Table 1 below illustrates some typical artificial sources of electromagnetic fields with frequency and intensity. Natural sources like the magnetic field of the earth are not included. Note, however, that big variations occur. For an explanation of some of the terminology used please be referred to the next chapter.
Table 1. Typical sources of electromagnetic fields
The Committee has been made aware of the military use of certain radiofrequency devices. Further consideration of this is outside the scope of this opinion.
Source & ©: ,
Section 3.1 Introduction, p 12
1.2 Why and how have the health risks of electromagnetic fields been reassessed?
The source document for this Digest states:
Methods
It is well recognized that there are established biophysical mechanisms that can lead to health effects as a consequence of exposure to sufficiently strong fields. For frequencies up to, say, 100 kHz the mechanism is stimulation of nerve and muscle cells due to induced currents and, for higher frequencies, tissue heating is the main mechanism. These mechanisms lead to acute effects. Existing exposure guidelines, such as those issued by ICNIRP, protect against these effects. The current issue is the possibility that health effects occur at exposure levels below those where the established mechanisms play a role and in particular as effects of long term exposure at low level. No further consideration is given to thermal effects.
Source & ©: ,
Section 3.1 Introduction, p. 11
As a general rule, scientific reports that are published in English language peer-reviewed scientific journals are considered primarily. This does not imply that all published articles are considered to be equally valid and relevant for health risk assessment. On the contrary, a main task is to evaluate and assess the articles and the scientific weight that is to be given to each of them. Only studies that are considered relevant for the task are commented upon in the opinion. Many more reports were considered than are cited in the reference list. However, only articles that contribute significantly to the update of the opinion are cited and commented upon. In some areas where the literature is particularly scarce it has been considered important to explain why the results of certain studies do not add useful information to the data base. The focus is on articles presented after the year 2000.
Relevant research for EMF health risk assessment can be divided into broad sectors such as epidemiologic studies, experimental studies in humans, experimental studies in animals, and cell culture studies. Also studies on biophysical mechanisms, dosimetry, and exposure assessment are considered. In a report of this nature it is not possible to consider the experiences of individuals. Nonetheless, such information often triggers a scientific study.
A health risk assessment evaluates the evidence within each of these sectors and then weighs together the evidence across the sectors to a combined assessment. This combined assessment should address the question of whether or not a hazard exists i.e., if there exists a causal relation between exposure and some adverse health effect. The answer to this question is not necessarily a definitive yes or no, but may express the weight of the evidence for the existence of a hazard. If such a hazard is judged to be present, the risk assessment should also address the magnitude of the effect and the shape of the dose-response function, i.e., the magnitude of the risk for various exposure levels and exposure patterns. A full risk assessment also includes exposure characterization in the population and estimates of the impact of exposure on burden of disease.
Epidemiological and experimental studies are subject to similar treatment in the evaluation process. It is of equal importance to evaluate positive and negative studies, i.e., studies indicating that EMF has an effect and studies not indicating the existence of such an effect. In the case of positive studies the evaluation focuses on alternatives to causation as explanation to the positive result: With what degree of certainty can one rule out the possibility that the observed positive result is produced by bias, e.g. confounding or selection bias, or chance. In the case of negative studies one assesses the certainty with which it can be ruled out that the lack of an observed effect is the result of (masking) bias, e.g., because of too small exposure contrasts or too crude exposure measurements; one also has to evaluate the possibility that the lack of an observed effect is the result of chance, a possibility that is a particular problem in small studies with low statistical power. Obviously, the presence or absence of statistical significance is only one factor in this evaluation. Rather, the evaluation considers a number of characteristics of the study. Some of these characteristics are rather general, such as study size, assessment of participation rate, level of exposure, and quality of exposure assessment. Particularly important aspects are the observed strength of association and the internal consistency of the results including aspects such as dose response relation. Other characteristics are specific to the study in question and may involve dosimetry, method for assessment of biological or health endpoint, the relevance of any experimental biological model used etc. Regarding experimental studies, additional important characteristics that are taken into consideration are the types of controls that have been used and to what degree replication studies have been performed. For a further discussion of aspects of study quality, refer for example to the Preamble to the IARC Monograph Series (IARC 2006). It is worth noting that the result of this process is not an assessment that a specific study is unequivocally negative or positive or whether it is accepted or rejected. Rather, the assessment will result in a weight that is given to the findings of a study.
The step that follows the evaluation of the individual studies within a sector of research is the assessment of the overall evidence from that sector with respect to a given outcome. This implies integrating the results from all relevant individual studies into a total assessment. This is based on the evaluations of the individual studies and takes into account, for each study, both the observed magnitude of the effect and the quality of the study. Note again, that for this process to be valid, all studies must be considered equally irrespective of their outcome.
In the final overall evaluation phase, the available evidence is integrated over various sectors of research. This phase involves combining the existing relevant pieces of evidence on a particular end-point from studies in humans, from animal models, in vitro studies, and from other relevant areas. The integration of the separate lines of evidence should take place as the last, overall evaluation stage, after the critical assessment of all (relevant) available studies for particular end-points. In the first phase, epidemiological studies should be critically evaluated for quality irrespective of the putative mechanisms of biological action of a given exposure. In the final integrative stage of evaluation, however, the plausibility of the observed or hypothetical mechanism(s) of action and the evidence for that mechanism(s) is a factor to be considered. The overall result of the integrative phase of evaluation, combining the degree of evidence from across epidemiology, animal studies, in vitro and other data depends on how much weight is given on each line of evidence from different categories.
Source & ©: ,
Section 3.2 Methods, p.12-13
The Three-Level Structure used to communicate this SCENIHR Opinion is copyrighted by GreenFacts asbl/vzw.