Underground Radiobiology: A Perspective at Gran Sasso National Laboratory

Abstract

Scientific community and institutions (e. g., ICRP) consider that the Linear No-Threshold (LNT) model, which extrapolates stochastic risk at low dose/low dose rate from the risk at moderate/high doses, provides a prudent basis for practical purposes of radiological protection. However, biological low dose/dose rate responses that challenge the LNT model have been highlighted and important dowels came from radiobiology studies conducted in Deep Underground Laboratories (DULs). These extreme ultra-low radiation environments are ideal locations to conduct below-background radiobiology experiments, interesting from basic and applied science. The INFN Gran Sasso National Laboratory (LNGS) (Italy) is the site where most of the underground radiobiological data has been collected so far and where the first in vivo underground experiment was carried out using Drosophila melanogaster as model organism. Presently, many DULs around the world have implemented dedicated programs, meetings and proposals. The general message coming from studies conducted in DULs using protozoan, bacteria, mammalian cells and organisms (flies, worms, fishes) is that environmental radiation may trigger biological mechanisms that can increase the capability to cope against stress. However, several issues are still open, among them: the role of the quality of the radiation spectrum in modulating the biological response, the dependence on the biological endpoint and on the model system considered, the overall effect at organism level (detrimental or beneficial). At LNGS, we recently launched the RENOIR experiment aimed at improving knowledge on the environmental radiation spectrum and to investigate the specific role of the gamma component on the biological response of Drosophila melanogaster.

Keywords: DULIA-bio; Drosophila melanogaster; LNGS; RENOIR; low radiation environment; radiobiology; underground biology.

Figure 1

Measurements and simulations for the optimization of the Marinelli beaker. (A) Scheme of Marinelli beaker currently in use, placed inside the 10 cm thick lead hollow cylinder. Only the Drosophila vial in the center of the cylindrical hole is shown, with two sets of TLDs positioned at two different heights. Dimensions of Marinelli are in black, dimensions of Drosophila vial are in blue, dimensions of the cylindrical hole are in green and the heights of TLDs are indicated in red. (B) Geometry of the Marinelli beaker implemented in the simulation. The TLDs were simulated with dimensions 40 × 40 × 4 mm³, that is with the same thickness but much wider surface area than the real detectors, to get a reasonable compromise between statistics and computation time. (C) Spectrum of a tuff/pozzolana sample, measured with an HPGe detector. Some of the major peaks are shown as examples of the heterogeneity of the emitters in the sample.

Figure 2

Benchmark Drosophila fertility test, carried out in the reference external LNGS laboratory, aimed at checking the irradiation configuration and getting information for optimizing the design of the new device. Setting and design of the Drosophila fertility test: After mating and embryo deposition, pupae and adults were counted for the periods indicated by the blue lines. (A) Top view and (B) lateral view of eight tubes containing flies inside the Marinelli; (C) top view of eight tubes containing flies inside the phantom. Columns indicate the total number of pupae and adults (males and females) from five replicates (tubes) obtained in three independent experiments. Error bars represent the square root of the total counts. Statistical differences between the results obtained inside and outside the Marinelli beaker were analyzed using the Student's t test (p < 0.05). No significant differences were observed.