Bakker JF, Paulides MM, Christ A, Kuster N, van Rhoon GC. (2010). Assessment of induced SAR in children exposed to electromagnetic plane waves between 10 MHz and 5.6 GHz. Phys Med Biol. 55(11):3115-30.
To prevent adverse health effects of exposure to electromagnetic fields (EMFs), the International Commission on Non-Ionizing Radiation Protection (ICNIRP) has defined basic restrictions in terms of specific absorption rate (SAR). For the radiofrequency range, these restrictions are intended to keep the body temperature increase under 1°C, which correlates with a maximum whole-body-averaged SAR of 4 W/kg for 30 minutes in adults. To account for sensitive populations, such as children and the elderly, a safety factor of 50 is used for the general public, and this threshold is reduced to 0.08 W/kg. For practical exposure assessment, reference levels for the incident EMF have been derived from the SAR limits by simulation modeling of the human anatomy. Because of high variability of the human anatomy, it is difficult to generalize the results of this modeling to the entire population. In particular, anatomical models for children have not been sufficiently examined. Most previous child models were based on down-scaled adult models, which may lead to inaccuracies because children are different from adults not only in size, but also in proportions and tissue properties.
The objective of this study was to determine if the induced SAR in children remains below the ICNIRP basic restrictions upon EMF exposure at the reference levels.
Both whole-body-averaged SAR (SARwb) and the peak 10 g spatial-averaged SAR (SAR10g) were assessed in 6 child and 2 adult anatomical models using finite difference time domain (FDTD) modeling. The anatomical models of both genders with different body dimensions were developed from high resolution magnetic resonance imaging data. Tissue properties (volume density of mass, permittivity and conductivity) were included in the modeling. Plane waves were used with incident directions of the six sides: frontal, dorsal, left, right, bottom and top. Two orthogonal polarizations of the electric field per incident direction were used. SAR values were calculated for exposures to all the 12 orthogonal plane wave configurations at frequencies from 10 MHz to 5.6 GHz.
Results and Interpretation
An expanded uncertainty due to variations in simulation settings and tissue properties was estimated in a sensitivity study as 53% (SARwb) and 58% (SAR10g). For worst case exposure scenarios of small child models (configurations with the electric field aligned parallel to the main body axis) the ICNIRP basic restrictions on the SARwb were exceeded by a maximum of 45%. The maximum SAR10g values were within the ICNIRP limits for all studied exposure scenarios.
The authors point out that the overexposure of small children estimated in their study is minor compared to the safety factor of 50. “Fine tuning” may be needed to the recommended ICNIRP reference levels.