Here, exposure means the effect of electromagnetic fields on biological organisms. The first presentations explained the most important factors to be taken into account – on one hand, when determining the exposure of living organisms in the field and, on the other hand, when determining the exposure parameters for laboratory tests. The importance of accurate exposure assessment in all relevant studies was emphasised.

Because of the different biological effects, amongst other reasons, the various frequency ranges of electromagnetic fields are always treated separately.

Static and low-frequency electric and magnetic fields

Static and low-frequency electric and magnetic fields are relevant for the expansion of power grids. For outdoor studies on the possible effects of these fields in the vicinity of power lines, it must be taken into account that the distance to a power line alone is not a good measure of the intensity of the electric and magnetic field because the propagation of these is complex and depends on the load and arrangement of the conductor cables.

The magnetic fields emitted by power lines affect humans and animals by creating electric fields and currents in the body. This process depends on body size; thus, in small animals, weaker body currents are induced under the same current line.

High-frequency electromagnetic fields

Mobile communications transmitters generate high-frequency electromagnetic fields. Their field strength can also not be reliably estimated based on the distance. In general, it decreases with distance; however, the main beam direction, the inclination of the antenna, and the objects in the vicinity also play a role. The effect of high-frequency electromagnetic fields is based on energy absorption and heating. The energy absorption depends on the body size; for example, the better the body size corresponds to half the wavelength, the more energy the body absorbs.

A Belgian researcher explained how the energy absorption resulting from exposure to high-frequency electromagnetic fields can be simulated in three-dimensional models of animals. He showed that insects will absorb more energy when exposed to millimetre waves, which will be used for the new 5G technology, than at the lower frequencies currently used. However, even this higher energy absorption is in the range of a few nanowatts and insects are not expected to be exposed to excessive heating.

Intermediate frequencies

Another lecture deals with the intermediate frequencies (i.e. the frequency range between the low-frequency and the high-frequency fields). These play a role for electromobility, amongst other things. It was shown that in future stations for the inductive charging of electric cars, there is generally no need to fear any dangerous effects on animals even if they get caught in the gap between the car and the induction loop in the ground during charging. However, if the animals contain metallic objects (e.g. artificial joints), which can happen with pets, there could be significant heat generation.

Field studies

For all field studies, in contrast to laboratory studies, it is not possible to adhere to standardised experimental conditions. The exposure can be estimated; however, in most cases it cannot be influenced. Likewise, blinding is usually not possible.

It is well documented that certain organisms (e.g. migratory birds) can perceive the Earth’s magnetic field and orient themselves to it. It cannot be ruled out that this perception is disturbed by electric and magnetic fields generated by humans or that the fields also exert other effects on organisms.

Biophysical mechanisms

Three mechanisms have been discussed as biophysical mechanisms for the effects of magnetic fields: the radical pair mechanism, a mechanism via the mineral magnetite (Fe₂O₃), which occurs in animals and plants, and the induction of electric fields in organisms (see above).

The radical pair mechanism

The radical pairing mechanism is a complicated process in which quantum effects play a role. The basic idea is that photo-induced redox processes in the cell create free radical pairs (i.e. two molecules, each with an unpaired electron in its outer shell). These form either a singlet or triplet state, which then recombines into different reaction products. The ratio of the two reaction products obtained in this way can be influenced by external magnetic fields. Cryptochromes, a class of proteins first discovered in plants in 1993 by Canadian researcher Margaret Ahmad, were named as candidates for the corresponding molecules. These blue light receptors are also involved in the circadian rhythm of animals. Physically, spin – a property of particles described in quantum mechanics – plays the decisive role in the radical pair mechanism because it couples to the external magnetic field.

The mineral magnetite

The mineral magnetite is found concentrated in the beak of migratory birds. It is itself magnetic and therefore interacts with magnetic fields. It is therefore also a candidate for a biophysical mechanism for the perception of magnetic fields by organisms. For example, some bacteria are able to align and move along the Earth’s magnetic field. In these bacteria, long chains of magnetite are found in specialised structures called magnetosomes.

Such structures have not yet been discovered in the cells of animals and plants. More generally, no structure containing magnetite that is associated with the nervous system or a signalling system has been identified in animals or plants. At the workshop, the possible discovery of large cells in animals and humans containing magnetite particles was reported; however, the data were inconclusive. At the cellular level, there are also no molecules that could interact with magnetite and thus further process the corresponding signals.

The magnetic compass of migratory birds

Under laboratory conditions, it has been demonstrated that electromagnetic fields generated by humans can interfere with the magnetic compass of migratory birds. However, the fields caused by power lines or mobile communications cannot cause these effects. The frequencies of the low-frequency fields of the power lines (16.7 Hz and 50 Hz) or the high-frequency fields of mobile communications (currently from about 900 MHz to several GHz) are explicitly not in the range in which an influence on birds has been proven. In experiments carefully conducted over a decade, electromagnetic fields in the frequency range from 400 kHz to 10 MHz were shown to affect the magnetic compass of migratory birds that begin their flight at night.

Circadian rhythm

In cockroaches, an effect of electromagnetic fields in the frequency range up to 10 MHz on the circadian rhythm was shown under laboratory conditions.

Thermal stress

Another known mechanism that can lead to biologically relevant effects is thermal stress, which can be induced by high-frequency electromagnetic fields.

In his presentation, a scientist reported results showing that high-frequency electromagnetic radiation can induce heat stress in rodents when the outside temperature was close to or above the body temperature of the rodents. There was an interesting effect on the metabolism of the animals. When outside temperatures were below the body temperature of the rodents, the additional heat energy provided by high-frequency fields was used to warm the animal’s body, which reduced its metabolic rate. A reduced metabolic rate leads to less metabolic damage. A reduction in metabolism would therefore lead to a reduction in such damage and could explain the higher life expectancy of the male rats exposed to electromagnetic fields in the NTP study. This should be further investigated.

In its statement on the NTP study, the BfS noted that it cannot be ruled out that at the very high exposures used in the study, the body temperature of the animals studied was exposed to fluctuations that exceed the tolerance range of normal physiology. The heat balance of animals depends, amongst other things, on the surface-to-volume ratio and thus on weight. This could explain why effects were found only in the comparatively large and heavy male rats in the study and not in the smaller female rats or in mice.

Marine animals

Some fish species (e.g. eels and salmon) migrate over long distances. It has been observed that they hesitate briefly when crossing submarine cables. However, these do not constitute a barrier for them. Sharks and rays sense magnetic fields with special organs called Lorenzini ampoules, which are based on the principle of electromagnetic induction, and use the magnetic fields when hunting. They react to fields of submarine cables in a similar way to prey. Sharks have been observed biting into submarine cables but quickly learn that they are not prey. The effects observed do not pose a danger to the respective animal species. However, it should be noted that the number of submarine cables is increasing and encounters with cables and interference with behaviour will occur more frequently. This development must be pursued further.

Birds

The orientation of robins was influenced by artificial magnetic fields under laboratory conditions. However, in field studies, no negative effect of weak magnetic fields on the orientation of robins has been proven. Migratory birds orient themselves to the Earth’s magnetic field. They also use the sun during the day and the stars at night to orient themselves and to memorise flight routes. These alternatives can be used to compensate for difficulties in orientation along the Earth’s magnetic field. However, in the field studies, the birds were exposed only to the artificial magnetic fields for a relatively short time, and the experiments were carried out at night under a starry sky. In cloudy conditions, the migratory behaviour of the birds could be affected by additional artificial magnetic fields. This will be investigated further.

Bats

A paper from the UK investigated a possible magnetoreception in bats compared with the magnetoreception in migratory birds. It turned out that bats also have magnetoreception. However, the polarity of the magnetic field plays the most important role. In contrast, the inclination of the Earth’s magnetic field serves as orientation for migratory birds.

It is therefore unlikely that the radical pair mechanism plays a role in the perception of magnetic fields by bats. However, the biophysical mechanism that enables bats to perceive magnetic fields is not yet known.

Bats avoid sources of electromagnetic fields in the gigahertz range. A field test in the vicinity of radar installations showed that in electromagnetic fields in the frequency range of 1–4 GHz (at a field strength of 2 V/m), the flight activity of bats is reduced. However, in this frequency range, there is not yet any known biophysical mechanism that could explain how the magnetoreception of bats can be affected by such fields. It is therefore currently assumed that the effects observed on bat behaviour have other causes.

Mammals in general

The question of which other mammals have magnetoreception was also discussed. It has been clearly demonstrated in some rodents. Also herd animals such as cows and pigs seem to align themselves with the Earth’s magnetic field when they are together in small groups. So far, no mechanisms that operate at the level of molecules or cells in mammals that could explain a perception of magnetic fields have been fully worked out. Therefore, experiments were carried out with rodents in order to clarify the exact mechanisms. In rodents, there is evidence that magnetite particles as well as the radical pair mechanism known from migratory birds may play a role.

However, it is still unclear whether the two mechanisms complement each other or occur differently depending on the species.

In mammals with poor eyesight (e.g. naked mole rats), the radical pair mechanism plays no role because it requires light. Magnetite particles seem to play a greater role here.

However, in mammals with well-developed eyes, the radical pair mechanism seems to play a more important role in the perception of magnetic fields. Because both mechanisms react differently to magnetic fields, detailed research into the types of magnetic field perception in different mammals is important in order to be able to assess whether magnetic fields generated by humans influence mammalian behaviour.

Human perception of magnetic fields

One of the pioneers of research into the effect of magnetic fields on living beings described the magnetite mechanism in his lecture and presented several studies on the perception of magnetic fields by humans starting in the 1970s. However, it was not possible to reproduce initial results from the 1970s, which indicated that humans can perceive magnetic fields. In the meantime, however, neuroelectrophysiological studies have shown characteristic changes in brain waves when people are exposed to magnetic fields. However, the fields are not subjectively perceived. The observable effects in humans are difficult or impossible to explain by the electric field induction theory or the radical pair mechanism. Instead, they point to a mechanism based on the magnetic mineral magnetite (Fe₂O₃). Magnetite accumulations were found in various human tissue samples, especially in the brain. Moreover, the mechanism seems to be quite old from an evolutionary perspective. However, so far, there is no evidence of direct connections between magnetite and nerve cells. It is also not clear whether magnetite plays a functional role in the human body at all.

The researcher also pointed out some methodological problems in assessing the effect of electric and magnetic fields on biological systems (e.g. the need for blinding and the selection of appropriate controls).

Insects, especially bees and bumblebees, were studied in this context because electrical signals are particularly important for them in foraging and communication. Lower animals such as crabs, snails, and mussels also perceive magnetic fields and use them for orientation.

Bees

The body of the bees is itself slightly positively charged with electricity because of the separation of charges caused by friction during flight. In addition, flowering plants from which bees obtain pollen and nectar are slightly negatively charged. The perception of electric fields emitted by plants helps bees to forage. There is also an electrical gradient between the ground and the atmosphere. All three mechanisms seem to play a role in the perception of electric fields by bees.

Another paper from Germany suggests that because of their electrically charged exoskeleton, bees produce electrical signals that pass on information to other bees during their communication movements (dancing). It has been shown that pesticides interfere with this signal generation and transmission. However, there is no evidence that electric, magnetic, and electromagnetic fields from power lines or mobile communications systems trigger a similar effect. The working group investigating electrical signals in bees has not received any feedback from bee-keepers about corresponding problems. The fact that radar with a frequency of 9 GHz can be successfully used to monitor the flight paths of bees also speaks against a harmful effect of these fields.

Plant growth

In a paper from Italy, the effect of magnetic fields on the growth of plants was investigated. There were minor effects on plant growth and metabolism. The effects on metabolism appear to be within normal variations and should be considered as a natural, non-harmful response of the plant to an external environmental influence – in this case, the magnetic field.

Role of the cryptochromes

Another paper from France dealt with the role of cryptochromes in the interaction of electric – and especially magnetic – fields with plants and animals. Mice were also studied for this paper. Cryptochromes thus seem to play a decisive role in the effect of magnetic fields in plants and animals. Magnetic fields can influence the growth of plants via cryptochromes. In mouse and human cells, magnetic fields are thought to trigger an increase in the number of reactive oxygen molecules via cryptochromes and thus cause oxidative stress. This also works to some extent in the dark. The magnetic field strengths at which this effect was seen are about 10 times higher than the natural magnetic field of the Earth. Further research is needed to find the threshold at which effects occur and to understand the biophysical mechanisms that mediate a possible effect of magnetic fields on the entire cell via the cryptochromes.

Genes and the shape and structure of plants

A paper from France looked at the effects of high-frequency electromagnetic fields on genes as well as the shape and structure of plants. It was shown that depending on the calcium concentration in a particular plant, a change in energy metabolism occurred when it was exposed to an electromagnetic field with a frequency of 900 MHz and a field strength of 5 V/m for 10 minutes. This response was observed throughout the plant and spread throughout the plant when the electromagnetic field acted locally on some areas of the plant and the rest of the plant was shielded from electromagnetic fields.

The presence of the plant hormone abscisic acid was necessary for the systemic response. In general, an increase in the activity of genes related to oxidative stress was observed. However, there was no effect on the morphology of the plants when fully grown plants were exposed to the electromagnetic fields. In contrast, still developing plants showed a reduction in growth. However, it was emphasised that the observed effects are not sufficient to assume a hazard for plants.

Ecological indicators

A literature review from Poland dealt with the possible ecological effects of high-frequency electromagnetic fields with a focus on plants. A number of possible ecological indicators that can be used in later studies were presented.

Tree damage and mobile communications base stations

In a short presentation, a paper from Germany was presented. This included a description of 60 specifically selected transmitter-damaged trees in the line of sight of a base station, 30 randomly selected trees, and 30 trees with low mobile communications exposure without damage. From this, a possible connection between tree damage and the proximity to mobile communications transmitters was postulated. The strength of the electromagnetic fields was measured.

From the perspective of the BfS, the paper has considerable methodological shortcomings such as the fact that the damaged and non-damaged trees were not all randomly and independently selected for proximity to the base station and that other factors that can damage trees were not discussed. The study design is not suitable for investigating a causal relationship between damage to trees and high-frequency fields from mobile communications base stations.

Cataracts in calves

Here, there was only one study from Switzerland about a possible connection between the formation of cataracts in calves on a farm near a newly erected mobile communications mast. At the site studied, many other factors that can also have an effect on calves before and after birth (motorway, oil pipelines, power lines, train connections) were present. The frequency of the cataracts on this farm was increased compared with the whole of Switzerland. The distribution of cataracts in calves in Switzerland showed a correlation with exposure to mobile communications transmitters; however, it remains unclear whether this correlation is causal. In an experimental study, 10 cows were exposed to GSM (900 MHz, 10–20 V/m), and the concentration of enzymes indicative of oxidative stress was determined in the blood. In some cows, the corresponding enzymes increased; in others, they were lowered, or there was no change. The values were mostly within the normal physiological range. The many confounding factors on the farm, the small number of cows examined and the inconclusive results mean that the study is not particularly meaningful from the point of view of the BfS.

Occurrence and diversity of pollinators

On the two Greek islands of Limnos and Lesvos, a study was carried out on the occurrence and diversity of pollinators in relation to the distance to mobile communications base stations. The fields generated by the mobile communications systems were measured and correlated with the occurrence of the insects.

The results were not uniform: the numbers of some insect species decreased with increasing electric field strength, whilst the numbers of other insect species actually increased. The effect on biodiversity varied from island to island.

Possible resonance effects

Future applications in the high-frequency range (5G applications > 20 GHz) will reach wavelengths that correspond to about half the length of insect bodies; this could cause resonance effects. It is therefore important to conduct further research in this area.