Absorbed energy distribution from radiofrequency electromagnetic radiation in a mammalian cell model: effect of membrane-bound water.

The spatial distributions of induced 27 or 2450 MHz radiofrequency (RF) electric fields (E-fields) and specific absorption rates (SARs) in a three-component spherical cell model (cytoplasm, membrane, extracellular space) were determined by Mie scattering theory. The results were compared to results for the same cell model but with 0.5 nm thick of bound water on the inner (cytoplasmic) and outer (extracellular) membrane surfaces (i.e., five-component cell model). The results provide insight regarding direct frequency-dependent RF radiation effects at the cellular level. Induced E-fields and SARs were calculated for two bound-water characteristic frequencies (400 or 1000 MHz) and ionic conductivities (1-1000 mS/m). In order to estimate the dependence of the results on bound water within the membrane per se, the model was revised to include bound water within the inner and outer membrane surfaces. The results were as follows: 1) on the x-axis, the y- and z-components of the induced E-field were of insignificant magnitude compared to the x-component for an incident E-field parallel to the x-axis; 2) the ratio of transmembrane E-fields induced by 2450 MHz vs. 27 MHz RF [i.e., Ex (2450 MHz)/Ex (27 MHz)] was 0.1; 3) for the three-component cell model, the corresponding SAR ratios [SAR (2450 MHz)/SAR (27MHz)] in the cytoplasm and extracellular space were 1.66 and 5.0, respectively; 4) the SAR rations [SAR (2450 MHz)/SAR (27 MHz)] for the cytoplasm and extracellular space for the five-component cell model were 1.66 and 5.0, respectively; 5) the ratio of the E-fields induced in the cytoplasmic and extracellular layers of bound water in the five-component cell model [E (2450 MHz)/ E (27Mhz)] were 0.62 and 0.63, respectively; 6) the SAR ratios [SAR (2450 MHz)/SAR (27 MHz)] for the cytoplasmic and extracellular bound-water layers were 66 and 65.3, respectively; and 7) variation of bound-water characteristic frequency, ionic conductivity, or bound-water incorporation inside the membrane surfaces, per se, did not significantly affect the E-field or SAR ratios. These results indicate that frequency-dependent nonuniformities may occur in the distribution of induced RF E-fields and SARs at the cellular level.