9. What is known about environmental effects of electromagnetic fields?
- 9.1 Are there new findings on environmental effects of radiofrequency fields?
- 9.2 Are there new findings on environmental effects of extremely low frequency fields?
The SCENIHR opinion states:
3.7. Environmental Effects
Studies on individual species living in close proximity to EMF sources are important in identifying whether ecosystems can be affected substantially by EMF. In addition such studies may be a potential source of information on the potential of EMF to cause adverse effects in man.
What was already known on this subject?
In the past the main themes of research have been:
- effects on reproduction
- influence on species that use magnetic fields for navigation purposes
Previous studies have given an indication that exposure of wild birds to EMF can under certain circumstances change their behaviour, reproductive success, growth and development, physiology and endocrinology and/or the parameters of oxidative stress. The literature on these effects is well reviewed by Fernie and Reynolds (2005) and Juutilainen (2005). However, the changes observed are neither all in the same direction nor consistent.
What has been achieved since then?
Since the previous opinion, only a few papers have been published, the majority of which have been on the effects of electromagnetic fields on birds.
9.1 Are there new findings on environmental effects of radiofrequency fields?
The SCENIHR opinion states:
Two independent field studies have focused on the causes of the well reported decline in the population of house sparrow in a number of European countries. Balmori and Hallberg (2007) examined the hypothesis that EMF from phone masts might play a role in this decline. They measured the electric field strength (1MHz-3GHz range) and the house sparrow population at 30 points in Valladolid, Spain. A clear inverse correlation was observed between field strength and the number of house sparrows. In this study, the logarithmic regression of the mean bird density vs field strength groups (considering field strength groups (field strength being described in 0.1V/m increments) was R=0.87 (P=0.0001).
A similar observation has been described for six residential districts in Belgium at 150 point locations (Everaert and Bauwens 2007). In this study the number of male house sparrows was negatively correlated with electric fields from both 900 and 1,800 MHz downlink frequency bands in six different study areas. These studies support an association between electromagnetic fields and the observed decline in house sparrow populations. A number of other factors have also been identified as possible contributors to the decline in house sparrow populations including pollution and loss of preferred food sources. The interaction between EMF and these factors warrants further study. A further issue to be resolved is why the decline in house sparrows is apparently not mirrored by a decline in other species of birds in major conurbations.
Reijt et al. (2007) studied breeding tits in nesting boxes around a military radar station compared with a control location. The exposure levels were reported as being from 2.0 to 5.0 W/m2. No change in breeding biology was observed. However there was a shift in the ratio of blue tits to great tits compared with the control location. Thus one interpretation of this study and those on house sparrows is that the electromagnetic fields may discourage some bird species from breeding there or alternatively might encourage other species to build their nests in the areas with higher RF EMF fields. It may be noted in this regard that there is some evidence that electromagnetic fields may modify the reproductive behaviour of insects (see for example Panagopoulos et al. 2007) that serve as food sources for various bird populations.
Radio telemetry is increasingly used to track species in the wild. For this purpose small transmitters are attached (often by a subcutaneous implant) to captured representatives of the species and the animals are then released back into the wild. In one such study in tufted puffins (Whidden et al. 2007) it was found that radio-marked adults tended to have poorer breeding success and the progeny had lower growth rates than puffins without transmitters. The cause of this difference is ascribed to the EMF from the transmitters.
Field studies from two independent sources suggest a correlation between the reduction in house sparrow population in urban areas and exposure to electromagnetic fields. However, there are a number of possible interpretations of this data and further investigations are needed.
9.2 Are there new findings on environmental effects of extremely low frequency fields?
The SCENIHR opinion states:
There have been a number of studies of the reproductive health of birds of prey living around overhead power lines. Conclusions from such studies vary widely. Key factors to explain these varying observations include duration and intensity of exposure, interspecies differences in sensitivity to the effects, breeding habits etc. Costantini et al. (2007) studied the breeding success of Eurasian kestrels living in boxes on overhead power lines. Traditional markers of breeding success such as body weight were determined. In addition, because oxidative stress has been hypothesised to be a coherent mechanism whereby EMF might produce adverse effects, serum antioxidant capacity and reactive oxygen capacity was also measured. In this study none of the parameters measured showed a correlation with field strength.
Publications on the effects of EMF on plants have continued to appear, however the prime interest has moved to the use of EMF commercially to facilitate plant growth in nurseries (De Souza et al. 2008, Florez et al. 2007, Ananta and Shantha 2008). The conclusions from such studies are that by application of magnetic fields the growth of several plant species can be promoted. Optimum growth was observed at levels of around 100-150 mT. From the published data it is difficult to assess the extent of variation in plant species’ response to EMF, or whether the effects are purely on plant growth.
Single publications from laboratory studies have identified detectable effects of ELF on bacteria (50 Hz, 0.1 -1.0mT: Cellini et al. 2008), Daphnia (50Hz and above: Krylov 2008), and in vitro preparations from fish and chickens (200 Hz and above, [1.5-5mT]: Cuppen et al. 2007).
One study (Scalenghe 2007) has examined the effects of a buried electricity transmission cable on soil quality. While the electric field was near to zero close to the cable the magnetic field flux density was 20 times higher than background levels. After six months the levels of organic carbon, total nitrogen and microbial activity were inversely related to the distance from the cable indicating a reduction in biological activity due to the magnetic field.
Several in vitro studies have shown changes in the mT range using preparations from fish, birds, Daphnia and bacteria. Two field studies have also detected some changes although their interpretation, in terms of environmental significance, is uncertain.
The current database is inadequate for the purposes of the assessment of possible risks due to environmental exposure to RF, IF and ELF.