Terahertz radiation: no genotoxic effect on skin cells

An increasing number of commercial applications, for example body scanners at airports, use the THz frequency range between 100 GHz and a few THz – which was previously diffi cult to access as the radiation was diffi cult to detect and to generate in the fi rst place. Although this type of radiation is not ionizing and, thus, cannot damage biological molecules directly, it had to be clarifi ed whether this type of irradiation can have negative impacts on the growth of cells. Since THz radiation penetrates into the body by less than 1 mm, skin cells were chosen for exposure experiments.

The partners were: the Institut für Hochfrequenztechnik (Institute of High-frequency Technology) of the Technische Universität Braunschweig, the Helmholtz Centre for Infection Research in Braunschweig, and the Department of Toxicology of the University of Würzburg. The scientists exposed two different human skin cell types (HaCaT keratinocytes and primary dermal fi broblasts) under well-defi ned ambient conditions to continuous THz radiation at different frequencies between 100 GHz and 2.52 THz. This took place in a modifi ed incubator at different power densities, i. e. below the safety limit, at the safety limit and slightly above the safety limit of the power density of 1 mW/cm2 as is presently defi ned up to 300 GHz. Both the ambient conditions and the exposure power densities were recorded during the exposure. The reliability of the results was ensured by "sham exposures" (without any fi eld) and positive controls (with a chemically induced effect) for the selected endpoints, as well as by the blinded analysis of the samples. Thanks to the SI-traceable measurements of the power density and to subsequent fi eld calculations in the sample container, exact dosimetry was performed for the fi rst time.

After an elaborate analysis of the three independent exposure campaigns, no genotoxic effects were detected at any of the endpoints used within the scope of the experiments. Also, neither were micronuclei detected in a corresponding test, nor could DNA fractions be found by means of comet assay. Within the scope of auxiliary experiments it was, however, noticed that the exposure of AL cells (of a humanhamster hybrid cell line) at 106 GHz leads to a disturbance of the spindle apparatus, i. e. cell division could be affected in one way or another. The project was prolonged by three months, and investigations of the relation between these disturbances of the spindle apparatus and the occurrence of micro-nuclei have begun.