Thielens, A., Greco, M.K., Verloock, L. et al. Radio-Frequency Electromagnetic Field Exposure of Western Honey Bees. Sci Rep 10, 461 (2020) doi:10.1038/s41598-019-56948-0
Abstract
Radio-frequency electromagnetic fields (RF-EMFs) can be absorbed in all living organisms, including Western Honey Bees (Apis Mellifera). This is an ecologically and economically important global insect species that is continuously exposed to environmental RF-EMFs. This exposure is studied numerically and experimentally in this manuscript. To this aim, numerical simulations using honey bee models, obtained using micro-CT scanning, were implemented to determine RF absorbed power as a function of frequency in the 0.6 to 120 GHz range. Five different models of honey bees were obtained and simulated: two workers, a drone, a larva, and a queen. The simulations were combined with in-situ measurements of environmental RF-EMF exposure near beehives in Belgium in order to estimate realistic exposure and absorbed power values for honey bees. Our analysis shows that a relatively small shift of 10% of environmental incident power density from frequencies below 3 GHz to higher frequencies will lead to a relative increase in absorbed power of a factor higher than 3.
Strengths and limitations
This manuscript presents several contributions to the state of the art in the field of RF-EMF exposure assessment of insects. First, to the best of the authors’ knowledge, this is the only paper where a numerical RF dosimetry is presented for different developmental stages of honey bees. Second, this is the only study that combined real, in-situ exposure measurements with numerical simulations of RF-EMF exposure of insects in order to estimate a realistic exposure of honey bees. In comparison to our previous study11, we considered a broader frequency range from 0.6 GHz up to 120 GHz, which is more in line with the frequencies used in the current telecommunication networks (3 G and 4 G). Finally, this study presents a unique quantification of real-life exposure of honey bees and estimations of how this might change if future frequency shifts in that exposure might occur.
A disadvantage of this study is that we did not executed dielectric and thermal measurements in order to obtain dielectric and thermal properties of the studied honey bees. We obtained dielectric properties from literature and were able to execute electromagnetic simulations. We did not perform thermal simulations in this study. Another disadvantage is that we modeled far-field exposure by a limited number of plane waves, while previous studies have shown that a large set of plane waves is necessary to properly model far-field exposure26. We did execute a validation of our exposure set up by comparing it with a set of random plane wave exposures and found good correspondence, certainly close to the mean/median. Finally, we used FDTD simulations that are faced with uncertainties29 and used models that have a limited spatial resolution. This is a disadvantage of any RF-EMF simulation study in comparison to a study that relies on measurements of real insects.
Future research
Our future research will focus on executing exposure measurements of insects in order to validate the RF-EMF Pabs values and the dielectric parameters. Additionally, we would like to execute thermal simulations of honey bees and other insects under RF-EMF exposure. Finally, we aim to work on the development of more insect phantoms, with more spatial accuracy and potentially several independently identified tissues.
Conclusions
Exposure of Western Honey Bees (apis mellifera) to radio-frequency (RF) electromagnetic fields was studied using a combination of in-situ exposure measurements near bee hives in Belgium and numerical simulations. The simulations use the finite-difference time-domain technique to determine the electromagnetic fields in and around five honey bee models exposed to plane waves at frequencies from 0.6 GHz up to 120 GHz. These simulations lead to a quantification of the whole-body averaged absorbed radio-frequency power (Pabs) as a function of frequency. The average Pabs increases by factors 16 to 121, depending on the considered phantom, when the frequency is increased from 0.6 GHz to 6 GHz for a fixed incident electric field strength. A relatively small decrease in Pabs is observed for all studied honey bees between 12 and 120 GHz. RF exposure measurements were executed on ten sites near five different locations with bee hives in Belgium. These measurements resulted in an average total incident RF field strength of 0.06 V/m, which was in excellent agreement with literature. This value was used to assess Pabs for those honey bees at those measurement sites. A realistic Pabs is estimated to be between 0.1 and 0.7 nW for the studied honey bee models. Assuming that 10% of the incident power density would shift to frequencies higher than 3 GHz would lead to an increase of this absorption between 390–570%. Such a shift in frequencies is expected in future networks.
From the study:
RF EMFs can be absorbed and can cause dielectric heating in insects and (ii) this absorption of RF-EMFs is frequency dependent. This frequency dependency is important since 5th generation (5 G) networks are expected to partially operate at higher frequencies (up to 300 GHz)12,13. This shift might induce a change in RF EMF absorption for insects11.