Kowalczuk C, Yarwood G, Blackwell R, Priestner M, Sienkiewicz Z, Bouffler S, Ahmed I, Abd-Alhameed R, Excell P, Hodzic V, Davis C, Gammon R, Balzano Q. Absence of nonlinear responses in cells and tissues exposed to RF energy at mobile phone frequencies using a doubly resonant cavity. Bioelectromagnetics. Jul 6, 2010. Ahead of print.
Guidelines and limits set by ICNIRP for exposure to radiofrequency (RF) fields are mostly to prevent well known thermal effects. A controversy exists that non-thermal effect could be of biological importance. It arises due to the lack of an established non-thermal interaction mechanism although several have been proposed. Another plausible mechanism for non-thermal effect is the demodulation of amplitude modulated (AM) RF fields by biological systems. If this mechanism was proven, and biological cells and tissues could demodulate an RF signal, this means that cells would be exposed to low-frequency fields similar to those of biological processes. Thus a potential for biological activity would be possible.
The objective of the study was to perform an experiment to test whether the electric and magnetic structures of biological cells exhibit the nonlinear responses necessary for demodulation.
A highly sensitive system employing a doubly resonant cavity was used, which has the advantage that the mechanism can be evaluated in living cells and tissues exposed to frequencies emitted by GSM mobile phones. Different biological materials, with varying degrees of electrical excitability, were used for the physical requirements of the double resonant cavity system which remained viable throughout exposure. Both cancer and non-cancer cell lines were included, and cells and tissues previously reported to exhibit responses to low-level RF fields. Samples were exposed to low-level RF fields in the 880–890MHz band at the resonant frequency, f, of the loaded cavity and verified for the generation of second harmonic signals at frequency 2f.
A total of 558 second harmonic tests were performed on cells, tissues, or media. The value of f varied from 882.594 to 883.890 MHz. No second harmonic was found in any sample type or phase of the study above the noise floor. Although five traces did meet the criterion for second harmonic, in these traces, the signal at 2f was very small in magnitude and not easily apparent from the noise floor. In addition, four of the five traces were measured shortly before replacing the malfunctioning filter. Since this system can generate spurious second harmonics, these responses are cannot be attributable to nonlinearities in the biological preparations. For example, cell viability of exposed samples was diminished compared to sham values, but not compared to control values for a cell type, and was significantly higher than control values for another. Trypan blue exclusion assays showed cell viability to be typically around 90–95%.
It remains unclear whether low-level exposures to RF fields could cause significant biological changes. The basic assumption is that any nonlinearities would likely occur as a consequence of the electrical properties of the cell membrane. A total of 17 different cell and tissue types were used in this experiment including different species and levels of organization, all of them with different potentials for cellular interactions mediated by cell membrane systems of changing complexity. More than 500 cell and tissue samples were exposed to continuous wave fields at the resonant frequency of the loaded cavity (near 883 MHz) and verified for second harmonic generation. This experiment did not show any consistent responses attributable to nonlinearities in the exposed biological samples. But, it is possible that exposure to very intense continuous wave or pulsed RF signals could produce a measurable response.
This study has not demonstrated nonlinear conversion of RF energy by biological materials in a wide range of biological materials. Thus, the results do not support the possibility that living cells have the nonlinear properties necessary to demodulate RF energy.