Children's EMF Research Agenda
Extremely Low Frequency Fields
1. Epidemiological Studies
Something of an impasse has been reached in designing studies of ELF magnetic fields and childhood leukaemia. While existing epidemiological studies show a consistent association, most of the available studies are of case-control design and are thus potentially subject to selection bias. To move forward we need innovative approaches, which might include (1) designing studies capable of evaluateing selection bias (e.g., by collecting data on magnetic fields and participation) and/or minimizing it (e.g., a cohort study), or (2) identifying large, highly exposed populations (e.g., those living in apartments next to transformers), or susceptible subgroups (e.g., previously initiated populations in which magnetic fields act as a second ‘event’ in carcinogenesis). In addition, two hypotheses concerning causality (contact current and melatonin) were discussed at the Workshop. All of these approaches and hypotheses pose major challenges.
- Pooled analysis of childhood cancer studies. High Priority
Rationale: Pooled analyses of childhood leukaemia studies have been very informative. Although new studies would not fundamentally change the results of the previous pooled analyses, recent studies will add new countries and enough data to probe the results further. It might be possible to further explore the high end of the dose-response curve. Additionally, risk modifiers - for example, age - might be further explored. Brain cancer studies have shown inconsistent results; a pooled analysis of brain cancer studies may also be very informative, may inexpensively provide insight into existing data, including the possibility of selection bias, and, if appropriate (i.e., if studies are sufficiently homogeneous), may come up with the best estimate of risk.
- Further studies of ELF exposure and miscarriage. Medium Priority
Rationale: Two recent California studies have reported an increased risk of miscarriage due to maximum levels of ELF exposure, but the studies have areas of potential weakness in study design that can be improved. First we recommend studies to identify behavioural determinants of maximum fields. Further investigation, focusing on early pregnancy loss and using improved design, would also contribute to this area.
2. Volunteer studies
These recommendations address effects for which there is some supporting evidence in studies using adults.
- Laboratory-based studies of cognition and changes in electroencephalograms (EEGs) in children exposed to ELF fields in the laboratory, if ethical approval is possible. High Priority
Rationale: Studies of adult volunteers and animals suggest that acute cognitive effects may occur with short-term exposures to intense fields. Such effects are very important for the development of exposure guidance (e.g., McKinlay et al., 2004; WHO ELF Research Agenda) but there is a lack of specific data concerning field-dependent effects in children.
3. Animal studies
These recommendations focus on possible carcinogenic effects, particularly in relation to childhood leukaemia, and effects in key tissues and organs regarded as potentially susceptible to EMFs, particularly the developing central nervous system (CNS), haemopoietic (bone marrow) tissue and immune system. Experimental protocols should include prenatal and/or early postnatal exposure to EMFs.
- Further development and experimental investigation using appropriate animal models, including the use of transgenic animals (e.g., Carron et al., 2000), which develop a disease having similarities to childhood acute lymphoblastic leukaemia. (Animal studies carried out to date have not used such models.) Experimental studies to include the effects of prenatal exposure and the combined effects of ELFs and known carcinogens. High Priority
Rationale: The possible role of EMF exposure in childhood leukaemia development is a priority research area (e.g., AGNIR, 2001; WHO ELF Research Agenda). In addition the combined effects of ELF-EMFs and known chemical or physical carcinogens and/or mutagens have been reported in many studies (IARC, 2002).
- Studies of developmental effects of pre- and postnatal exposure to low-frequency EMFs on immune function and on the induction of minor skeletal variations. Effects of prolonged, intermittent exposure from the early postnatal period on subsequent cognitive function in animals. Medium Priority
Rationale: An increase in minor skeletal anomalies is the only consistent finding from a number of developmental EMF studies in mammals (e..,g Juutilainen, 2003). The immune system continues to develop postnatally; Study of the effects of ELF fields on this system is thus a useful means to evaluate them as possible immunotoxicants. Behavioural studies with immature animals provide a useful and established model for studying possible cognitive effects in children.
- Further study of possible ELF carcinogenic mechanisms, including exposure to intermittent fields and transients, both alone and in combination with known carcinogens. Low Priority
Rationale: The possible carcinogenicity of EMFs remains an issue of concern (e.g., IARC, 2002), although the experimental evidence for carcinogenic effects is weak. However, hypotheses such as those involving the role of signal intermittence, transients or contact currents have not been widely investigated and the possibility for co-carcinogenicity must be clarified.
4. In vitro studies
Areas requiring further ELF in vitro study include possible electric field and (contact) current effects on carcinogenic processes, especially pathways involved in haemopoietic cell differentiation and proliferation, and on nerve cell growth and synaptogenesis. In addition, further exploration of the possible role of melatonin in free-radical scavenging is required.
- Studies of ELF magnetic field and induced electric field effects on cell differentiation (e.g., during haemopoiesis in bone marrow) and on nerve cell growth using brain slices or cultured neurons. High Priority
Rationale: As in the recommended animal studies, possible effects on pre- and post-natal cellular differentiation and tissue development are a priority research area. Cell differentiation is inhibited during neoplastic progression; cell orientation and migration are both key processes in development. The developing nervous system and bone marrow are thought to be key tissues in this respect.
- Effect of EMF exposure on the protectiveness of physiological levels of melatonin against oxidative damage from free radicals, reactive oxygen species, etc. during haemopoiesis in foetal and postnatal tissue. Medium Priority
Rationale: Melatonin has been shown to be highly protective against oxidative damage to human lymphocytes in vitro (e.g., Vijayalaxami et al., 1996, 2004) and similar damage to the brain tissue of rat foetuses in vivo (Wakatsuki et al., 1999, 2001), possibly by increasing the concentration of known radical scavengers such as superoxidase dismutase (Okatani et al., 2000). The possibility that EMF exposure may affect the ability of melatonin to suppress oxidative damage in foetal or postnatal tissue should be investigated.
- Further studies of possible carcinogenic mechanisms for ELF fields, particularly in combination with known carcinogens. Low Priority
Rationale: The possible carcinogenicity of EMFs remains an issue of concern (e.g., IARC, 2002), although the experimental evidence for carcinogenic effects is weak. The combined effects of ELF-EMFs and known chemical or physical carcinogens and/or mutagens have been reported in many studies (IARC, 2002). In addition, hypotheses such as those involving the possible role of signal intermittence or transients have not been studied.
5. Dosimetry and exposure assessment
A better understanding of the prevalence of earth leakage currents and the potential consequences of exposure to contact currents in small children (e.g., when bathing), is needed. Work is in progress to examine the prevalence of contact currents in countries other than the United States (e.g., in European and Asian residential electrical systems). If exposure to contact currents is a global issue and some mechanism can be demonstrated, the model should be further examined.
- Dosimetric modelling of the interaction between induced or injected current and juvenile limbs should be undertaken, taking account of reduced surface resistance, lack of bone calcification and the presence of active marrow. High Priority
Rationale: The extent to which electric current flows through the bone marrow of small children as a consequence of contact which allows an earth leakage current to flow through their bodies should be further studied.
- Assess exposure to the 217-Hz nonsinusoidal magnetic fields from mobile phones. Low Priority
Rationale: The pulsating battery current in a mobile phone generates a low-frequency nonsinusoidal magnetic field (Jokela 2004) in the vicinity of the phone. The field penetrates without any effect on the skin into tissue. Some preliminary estimates show that the resulting exposure to induced currents in the head is not much lower than the ICNIRP limit. Furthermore, it has been suggested that mobile phones are an important source of ELF exposure, particularly to bone marrow in children’s hands. More detailed investigation of exposure is necessary to assess exposure quantitatively.