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T.Kleine Ostmann Field exposure and dosimetry in search of genotoxic effects of THz radiation in vitro
Thomas Kleine-Ostmann Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38112 Braunschweig, Germany
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Abstract—Many different studies on bio-electromagnetic interaction research in the THz frequency range exist that come to controversial results. Here, the results of a large exposure campaign searching for genotoxic effects in vitro and the experimental hurdles with regard to sample exposure and dosimetry that needed to be addressed to obtain reliable results are reviewed.
I. INTRODUCTION
The International Commission on Non-Ionizing Radiation Protection (ICNIRP) limits the exposure to electromagnetic fields up to frequencies of 300 GHz [1] and beyond [2] based on well-studied thermal effects. However, independent of the frequency of non-ionizing exposure, many studies claim nonthermal bio-electromagnetic effects without being able to identify the physical mechanism of the effects and a doseresponse relationship. In the THz frequency range, many studies of different quality on living organisms, model systems and cells have been performed that do not provide a clear picture whether non-thermal effects exist [3-5].
Based on findings in the THz Bridge Project, KorensteinIlan et al. [6] reported increased genomic instability in human Lymphocytes after exposure to mm waves below the safety limit. This initiated a larger experimental campaign financed by the German Federal Office for Radiation Protection (Bundesamt für Strahlenschutz BfS) and conducted by a cooperation of the University of Würzburg, the Helmholtz Centre for Infection Research, the University of Marburg and PTB. In three independent exposure campaigns on two different types of skin cells (primary dermal fibroblasts (HDF) and a keratinocyte cell line (HaCaT)) at frequencies of 106 GHz [7], 380 GHz and 2.52 THz [8], no genotoxic effects were found.
II. EXPERIMENTAL HURDLES AND DOSIMETRY
Many studies on bio-electromagnetic interaction research have severe shortcomings [9]. Very often, the electromagnetic field in the exposure location is not known quantitatively or the cells are not fixed in an inhomogeneous field. The exposure conditions with regard to source stability, temperature, pressure, humidity, CO2 content of the surrounding atmosphere but also unwanted fields from cell phones and electrical appliances are not monitored. Furthermore, there are often inadequate study designs with regard to insufficient sample and cell statistics, missing positive and sham controls and missing blinded procedures.
In the experimental campaign Genotoxic Effects of Terahertz Radiation in vitro, many of these critical points were addressed as adequate as possible. The dosimetry was based on numerical calculation of the field distribution in the sample using CST Microwave StudioTM and measurements of the power density traceable to the SI units [10].
III. RESULTS OF THE EXPOSURE CAMPAIGN
Not only the results of the THz Bridge Project but also results from an earlier exposure campaign at PTB with mobile communication signals indicated that there might be nonthermal effects [11]. Spindle disturbances in a HumanHamster hybrid (AL) cell line were found induced by the electrical field component of a standing wave in a TEM waveguide [12]. Later, these spindle disturbances were found after exposure of cells to THz radiation, as well [13]. Although spindle disturbances were expected to lead to micronuclei formation, no statistically significant genotoxic effects were found using the micronuclei test and the comet assay as end points after exposure with different times and levels at and below the safety limit.
IV. SUMMARY
In this contribution we reviewed a series of field exposure experiments that were conducted to clarify whether exposure of skin cells with THz radiation leads to genotoxic effects. No such effects were found.
REFERENCES
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Genotoxic Effects of THz Radiation in Vitro, Braunschweig, Germany,
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