Deposited energy distributions for ²²⁶Ra (orange) and ²²²Rn (blue) in the benthic mixture for diatoms.

Solid lines: total deposited energy, Dotted lines: ion ionisation, Dashed lines: electron ionisation.</p

Electrons specific energy probability distributions (Gy⁻¹) for nucleosomes (90% porosity).

Orange: electrons solvation, Purple: electrons excitation, Black: electrons ionisation.</p

Number of DSB per Gray per Mbp as a function of the energy of <i>α</i>-particles.

(+): different values of the SPointProb parameter in our work, (○): simulations using other codes found in the literature [67–70], (□): experiments found in the literature [71–73].</p

Kinetic and deposited energy of <i>α</i>-particles at the nucleus for different environments (when considering frustule, values are provided in the parentheses).

Kinetic and deposited energy of α-particles at the nucleus for different environments (when considering frustule, values are provided in the parentheses).</p

Total specific energy probability distribution (Gy⁻¹) for nucleosomes (90% porosity).

Total specific energy probability distribution (Gy−1) for nucleosomes (90% porosity).</p

Dose rates to diatom in the benthic mixture.

Blue bar: 222Rn contribution, Orange bar: 226Ra contribution.</p

Summary of GATE simulation characteristics.

Mineral springs in Massif Central, France can be characterized by higher levels of natural radioactivity in comparison to the background. The biota in these waters is constantly under radiation exposure mainly from the α-emitters of the natural decay chains, with 226Ra in sediments ranging from 21 Bq/g to 43 Bq/g and 222Rn activity concentrations in water up to 4600 Bq/L. This study couples for the first time micro- and nanodosimetric approaches to radioecology by combining GATE and Geant4-DNA to assess the dose rates and DNA damages to microorganisms living in these naturally radioactive ecosystems. It focuses on unicellular eukaryotic microalgae (diatoms) which display an exceptional abundance of teratological forms in the most radioactive mineral springs in Auvergne. Using spherical geometries for the microorganisms and based on γ-spectrometric analyses, we evaluate the impact of the external exposure to 1000 Bq/L 222Rn dissolved in the water and 30 Bq/g 226Ra in the sediments. Our results show that the external dose rates for diatoms are significant (9.7 μGy/h) and comparable to the threshold (10 μGy/h) for the protection of the ecosystems suggested by the literature. In a first attempt of simulating the radiation induced DNA damage on this species, the rate of DNA Double Strand Breaks per day is estimated to 1.11E-04. Our study confirms the significant mutational pressure from natural radioactivity to which microbial biodiversity has been exposed since Earth origin in hydrothermal springs.</div

Measured mass activities of radionuclides present in sediments in five mineral springs in Auvergne (Massif central).

Measured mass activities of radionuclides present in sediments in five mineral springs in Auvergne (Massif central).</p

Absolute doses and normalised dose rates to microorganisms in all environments (when considering frustule, values are provided in the parentheses).

Absolute doses and normalised dose rates to microorganisms in all environments (when considering frustule, values are provided in the parentheses).</p

Kinetic energy of <i>α</i>-particles reaching the microorganism for different environments (when considering frustule, values are provided in the parentheses).

Kinetic energy of α-particles reaching the microorganism for different environments (when considering frustule, values are provided in the parentheses).</p