RADON EXHALATION FROM SOIL AND ITS DEPENDENCE FROM ENVIRONMENTAL PARAMETERS

The dynamics of Rn-222 cyclic flow within the shallow geological subsurface media as a daily temporal variated source for exhalation into the air

Extensive research on the dynamics of radon gas (Rn-222) originating from the radioactive decay of radium (Ra-226) in geological subsurface media, sheds light on its periodic release into the atmosphere. Radon is a product of the uranium-238 decay chain found within rock and soil grains. While only a fraction of the generated radon escapes (emanates) into porous spaces due to nuclear recoil, it serves as the source for subsurface gas flows and for cyclic exhalation into the soil-atmosphere interface. Ongoing study of radon movement in shallow and deep subsoil, and its emergence at the surface, reveals complete semi-diurnal, diurnal, and seasonal gas flow cycles in the subsoil. Complementary emissions occur nocturnally as radon is released into the atmosphere. Moreover, two natural driving forces govern complex semi-diurnal and diurnal flows below and above the surface. Subsurface gas movement in porous media exhibits nonlinear behavior influenced by surface temperature gradients, resulting in downward flow to depths of up to 100 m. This flow exhibits daily periodicity with depth-dependent time delays, correlating with the diurnal surface temperature cycle. Additionally, pore gas transport into and out of open boreholes responds linearly to semi-diurnal barometric pressure changes, known as barometric pumping. Beyond subsurface phenomena, Europe and Australia increasingly employ nocturnal radon measurements to study atmospheric stability and air quality, assuming that variations in local stationary near-surface radon concentrations reflect atmospheric mixing processes. Recognizing mechanisms governing radon's temporal changes within geological subsurface media highlights the need for continuous underground radon monitoring to validate variations in daily radon exhalation to the surface. On the other hand, monitoring radon at considerable depths minimizes climatic contributions and enhances the ability to discern non-periodic pre-seismic radon signals, independent of atmospheric compulsion. This research offers potential insights into seismic precursors and the complex interplay between subsurface geodynamics and atmospheric conditions.

Oxidative genomic damage in humans exposed to high indoor radon levels in Northeast Brazil

Radon gas inhalation is the main source of exposure to ionizing radiation by humans. There is still lack in knowledge concerning the chronic and indirect effects of exposure to this carcinogenic factor. Therefore, the aim of this work is to analyze the levels of oxidative genomic damage in inhabitants of a medium-high background radiation area (HBRA) (N = 82) in Northeastern Brazil and compare them with people living in a low background radiation area (LBRA) (N = 46). 8-hydroxy-2-deoxyguanosine (8-OHdG) was quantified in urine, Ser326Cys polymorphism was determined in the hOGG1 gene and indoor radon was measured. HBRA houses had 6.5 times higher indoor radon levels than those from LBRA (p-value < 0.001). The 8-OHdG mean (95% confidence interval) were significantly different, 8.42 (5.98-11.9) ng/mg creatinine and 29.91 (23.37-38.30) ng/mg creatinine for LBRA and HBRA, respectively. The variables representing lifestyle and environmental and occupational exposures did not have a significant association with oxidized guanosine concentrations. On the other hand, lower 8-OHdG values were observed in subjects that had one mutant allele (326Cys) in the hOGG1 gene than those who had both wild alleles (Ser/Ser (p-value < 0.05). It can be concluded that high radon levels have significantly influenced the genome oxidative metabolism and hOGG1 gene polymorphism would mediate the observed biological response.

Temporal Variation in Indoor Radon Concentrations Using Environmental Public Health Tracking Data

ABSTRACT

Indoor radon is the second leading cause of lung cancer in the United States (US) after smoking and the number one for lung cancer in non-smokers. Understanding how indoor radon varies during the year reveals the best time to test to avoid underestimating exposure. This study looks at the temporal variation in 13 years of radon concentrations in buildings located in 46 US states and the District of Columbia (DC). In the dataset, radon concentration varies from 3.7 Bq m -3 (Becquerels per cubic meter) to 52,958.1 Bq m -3 , with an overall mean of 181.4 Bq m -3 . About 35.4% of tests have a radon concentration level equal to or greater than the US Environmental Protection Agency (US EPA) action level 4.0 pCi L -1 (148 Bq m -3 ). 3 Temporal variation in radon concentrations was assessed using the overall monthly mean radon concentration. The highest concentrations were found in January (203.8 Bq m -3 ) and the lowest in July (129.5 Bq m -3 ). Higher monthly mean indoor radon concentrations were found in January, February, and October, and lower in July, August, and June. This result is consistent with findings from other studies and suggests continuing to encourage radon testing throughout the year with an emphasis on testing during the colder months.

Factors influencing radon transport in the soils of Moscow

This article delves into the factors that may influence radon flux, such as soil properties and weather conditions, on the example of two experimental locations with different soil compositions, composed primarily of clay and sand, respectively. The experimental location with sandy soil was previously observed to have anomalously high radon flux levels. Radon monitoring was performed routinely, approximately at the same time of day and in parallel on both of these locations to exclude the influence of diurnal variations. The results show that radon transport in these locations differs in mechanism: Location with clay soil has diffusive radon transport, with an average radon flux density of 37.4 ± 24.9 mBq m^-2 s^-1 and a range of 0.3-167.8 mBq m^-2 s^-1, while the location with sandy soil has convective radon transport with an average radon flux density of 93.6 ± 51.2 mBq m^-2 s^-1 and a range of 9.8-302.2 mBq m^-2 s^-1. This corresponds to about 8.3% of RFD measurements on site with clay soils exceeding the national reference level of 80 mBq m^-2 s^-1 and 45.6% exceeding them on the site with sandy soils. Average radon flux density values were then compared to meteorological variables using Pearson correlation analysis with Student's t-test. It was observed that radon flux density correlates the most with ambient air temperature both for diffusive and convective radon transport mechanisms, while a weaker inverse correlation is observed with atmospheric precipitation and wind speed for the diffusive mode of radon transport, but not for the convective. Radon activity concentration in soil air correlates with the radon flux density and air temperature in the case of convective radon transport, but does not correlate in the case of diffusive transport.

The possibility of the phosphogypsum use in the production of brick: Radiological and structural characterization

In this paper, phosphogypsum (PG) with the content of ²²⁶Ra of about 500 Bq kg^-1 was used as a clay additive in mass ratios of (0-40) % and its influence on the radiological and mineralogical characteristics of the obtained brick samples was monitored. After sintering the samples at 1000 ℃, the formation of the mineral phase gehlenite was observed, and its share increased with the share of PG in the samples. The Monte Carlo method was used to determine the gamma dose rates, and consequently annual effective dose, for a standard room, with dimensions 4 × 5 × 2.8 m, whose walls were built of brick with PG. The obtained values were in the range (0.22-0.35) mSv y^-1. In addition, the active device RAD7 was used to determine the radon surface exhalation rates from the samples, which were found to be in the range (63-150) mBq m^-2 h^-1. The estimated indoor radon concentrations were found to be drastically lower than 100 Bq m^-3, leading to low radon inhalation doses. However, estimated annual effective doses from external gamma exposure were found not to be insignificant.

Modeling of radon exhalation from soil influenced by environmental parameters

Atmospheric radioactive noble gas radon (Rn-222) originates from soil gas exhaled in the atmospheric surface layer. Radon exhalation rates from soil as well as corresponding meteorological and soil parameters were recorded for two subsequent years. Based on long-term field data, a statistical regression model for the radon exhalation and the most important influencing parameters soil water content, temperature of soil and air, air pressure and autocorrelation of the exhalation rate was established. The fitting result showed that the multivariate model can explain up to 61% of the variation of the exhalation rate. First, the exhalation rate increases up to 80 Bq m^-2 h^-1 with increasing soil water content. Later, at water content >10%, increasing soil wetness suppressed the exhalation rate: at values higher than 24% to approximately one third. The air temperature had a distinct positive effect while the soil temperature had a strong negative effect on the exhalation rate, indicating their different influencing-mechanisms on the exhalation. The air pressure was negligible. The lagged values of radon exhalation had to be included in the model, as the variable shows strong autocorrelation.