Questions related to the exposure of people to electromagnetic waves remain topical, in particular with the deployment of 5G. The development of wireless communications systems has been going on for over 25 years now – GSM, 3G, 4G, and now 5G. What do we know today about this new technology and the fear of its impact on health?
The evolution of telecommunications networks must meet two requirements today:the widest possible coverage of the territory and the increase in the number of users, and an increase in speeds to meet new uses, with content requiring exchanges increasingly important data. Initially, we mainly transported voice, whereas today digital content has become ubiquitous, requiring large bandwidths. The latter define the ability of a system to convey a quantity of information, for example that contained in a video.
Wireless telecommunications are based on a radio link between two transceivers. This link is made via an electromagnetic wave which propagates for example between a smartphone and a base station called a "relay antenna". This propagation takes place in our environment without material support, that is to say in the air, and remains invisible to our eyes. For comparison, sunlight can also be seen as an electromagnetic wave, but it differs in higher frequencies and much higher energy than that used by telecommunications systems.
When an electromagnetic wave encounters matter, part of it is reflected and another part penetrates the matter. Depending on its properties, it can be absorbed and transformed into heat. This is the case in a microwave oven, or during the interaction of a wave with living things. However, between the microwave oven and the telecommunications systems, the powers involved are very different:around 900 watts for the domestic oven, and less than 2 watts for a smartphone.
Several frequency bands are used for these telecommunications systems. The first GSM systems operated on bands around 900 MHz, then the frequencies evolved between 700 MHz and 2600 MHz. At these frequencies, the links are made over a maximum of a few tens of kilometers, depending on the power of the transmitters, which implies a dense network of base stations to cover a territory.
The deployment of the 5G network will initially use a new frequency band around 3.5 GHz, quite close to that currently used for 4G. Subsequently, two new frequency bands, around 26 GHz, then beyond 60 GHz for short-distance links, will be used.
From a technological point of view, significant efforts are being made to reduce the energy required for the proper functioning of such a telecommunications network. We can cite the "power control" which will seek to reduce the transmitted power necessary for good communication, and an "optimization of the transmitter-receiver link" by concentrating the energy in a privileged direction, i.e. say that of the receiver.
The first type of exposure is related to base stations, where the exposure is considered "far field", i.e. one is far from the transmitter, a relay antenna for example. In this case, the field levels are weak, all the weaker as one moves away from the transmitting antenna (in first approximation, the amplitude of the electromagnetic field is inversely proportional to the distance between the transmitter and the place of exhibition).
The other possibility of exposure is related to the use of a device close to the user, for example a smartphone. To ensure a link with the base station, the power emitted will induce exposure levels generally higher than those of a far-field exposure. This is called local exposure, where the waves interact with the parts of the body closest to the source.
The interaction between an electromagnetic wave and the human body leads to an absorption of energy in the latter and, at these frequencies, to a more or less significant thermal effect depending on the power. To quantify this absorption, a reference physical quantity has been defined for frequencies below 10 GHz, the "specific absorption rate". This "SAR" is expressed in "watt per kilogram", and corresponds to the energy absorbed per unit of time and mass in the human body.
To guard against potential health effects related to exposure to electromagnetic waves, in particular those related to thermal heating, basic restrictions and exposure limit values have been defined. Compared to an exposure level that would result in a temperature rise of 1°C for the whole body after 6 minutes (compared to the body at 37°C), a factor of 50 is retained to guarantee the absence of thermal effect. For local exposures, the vascularization dissipates the heat linked to the absorption of microwaves. Some organs are more sensitive than others to heat (the eyes for example, which are less vascularized than other organs) and there are also limit values.
These limit values are based on recommendations from the International Commission on Non-Ionizing Radiation Protection, which are based on a detailed analysis of the scientific literature. The basic restrictions lead to values that must not be exceeded both for exposure in the far field (entire body) and for local exposure (device placed close to the head, for example). The restrictions reflect the powers absorbed in the human body , quantities that are difficult to measure directly. Therefore, "reference levels" have been defined:if they are not exceeded, it is known that the basic restrictions are respected. For example, for frequencies above 2 GHz, the SAR should be less than 0.08 watts per kilogram for whole body exposure and 2 watts per kilogram for localized exposure. These values ensure that there is no significant increase in body or tissue temperature.
The advent of 5G brings exposure to new frequencies. Regarding the band around 3.5 GHz, we are at frequencies close to and slightly higher than those used for 3G and 4G:the interaction mechanisms, as well as the exposed areas, will be similar to those studied up to here. At these frequencies, in the current state of knowledge, there is a consensus on the absence of proven health effects on the body related to exposure to electromagnetic waves. Collective expert appraisals are regularly carried out in France and around the world, to take into account technological developments and the latest results published in the scientific literature.
In recent years, questions remained mainly with respect to the exposure of children, pregnant women, and chronic exposures where we will focus on studying the effect of an exposure and a response of the body over the long term (several years or even a lifetime). Future expert reports, in particular that of ANSES, should provide some answers to these questions.
Regarding the new frequencies around 24 GHz and 60 GHz, the problem is changing. Indeed, the rise in frequency induces a lesser depth of penetration into the tissues and organs, of the order of 3 to 6 times less than the frequencies of 3G or 4G (where the SAR is typically attenuated by a factor 100 by 2-3 cm). This implies a new physical quantity of reference, namely the "power density of the electromagnetic wave", which is expressed in watt per m 2 . The latter characterizes the wave that will interact with an individual and must not exceed 10 watts per m 2 .
The other consequence is an evolution of the targets of interactions:the weaker penetration leads to being more attentive to the potential risks on the skin, the nerve endings and the blood circulation, and less on the brain for example.
Data are available in the literature in these frequency ranges and they are currently being analyzed by a working group set up by the National Agency for Food, Environmental and work, ANSES. This work on the possible effects of exposure to 5G should be completed in a few months.
These health issues remain relevant and to enrich knowledge on the possible effects of waves on the human body, studies are still in progress and they are supported in France within the framework of the National Environment-Health-Work Research Program of the 'HANDLES. At the same time, for its part, the National Frequency Agency (ANFR) ensures compliance with the limit values for public exposure to electromagnetic waves and lists the measurements carried out in the field, as well as the various transmitters deployed on the territory. On the basis of scientific reports, the European Union issues recommendations, which are subsequently transcribed into French law through decrees.
