Radon Risks Assessment with the Covid-19 Lockdown Effects

This work draws attention to the effects of the second cause of lung cancer which is also the largest source of exposure to ionizing radiation, radon, during the lockdown recommended by the World Health Organization (WHO) due to the Covid-19 pandemic. The basic assumption is that the exposure times have been assimilated to the 03-month lockdown time and the 02-week maximum incubation period of the disease. Doses during these periods and Relative Risk of Lung Cancer (RRLC), Lung Cancer Cases per year per million people (LCC) and Excess Lifetime Risk of Cancer (ELRC), were evaluated based on the concentrations obtained in high natural background radiation area in Cameroon. The existing exposure situation due to radon is then reevaluated and ranged from 0.76% to 17.55%. These results show that the reconsidered exposure time would be equivalent to the exposure time of a worker over one year, with their respective doses values becoming equivalent. The risks of developing lung cancer were also evaluated and it has been found that due to this pandemic it unfortunately increased.

tional Atomic Energy Agency (IAEA) and the whole of the world scientific community are working on how to stop the disease spreading and are making their contribution to mitigating the consequences, which are being felt on the health, economic and social levels. Due to this pandemic, there is for instance the use of CT scan and X-ray in the rapid diagnosis of advanced cases of Covid-19 [1] [2].
The conditions imposed by the Covid-19 such as lockdown recommended by WHO to limit the spread of Covid-19, increased the residence time of families and workers inside their homes. This would have the direct consequence by increasing exposure to radioactive gases such as radon 222, also increasing the health risks due to its inhalation [3]. In addition to air quality, tobacco consumption can also contribute to the rise of lung diseases and especially lung cancer [4].
Lockdown as a measure to limit the spread of Covid-19 forces people sometimes to breathe poor air quality that does not meet environmental criteria. If the air quality of gaseous and particulate pollutants is improved during the lockdown [5] [6] [7], radon exposure, which is the largest contributor to natural exposure to ionizing radiation and the second leading cause of lung cancer in confined spaces, may influence the risk of developing these diseases.
Radon ( 222 Rn) is a naturally occurring radioactive gas, which is inert, colorless, and odorless. It is generated primarily from radium ( 226 Ra), which results from the radioactive decay of uranium ( 238 U). Radon disintegrates into a series of short-lived alpha-emitting daughter radionuclides, such as 218 Po, 214 Pb, 214 Bi, and 214 Po. In non-smokers, radon is the primary cause of lung cancer. Radon occurrence in the environment is mainly related to the high-level radioactive background. Its global average outdoor level ranges between 5 -15 Bq/m 3 meanwhile the annual worldwide average radiation dose from exposure due to naturally occurring radiation sources, including radon, is 2.4 mSv [8]. The radon air concentration varies between 100 Bq/m 3 and 300 Bq/m 3 as recommended respectively by the WHO [9] and ICRP [10].
In Cameroon, several studies have been carried out to measure concentration of radon in dwelling. Many radon measurement campaigns in dwellings have been led across the country. They consisted to deposit nuclear solid state track detectors of radon (E-Perm Electret, Raduet, Radtrack) in the dwellings of different localities of Cameroon. These devices were hung for at least 3 months in dwellings.
The indoor radon, concentration was measured in 103 and 50 dwellings located respectively in Poli and Lolodorf with respective means concentration of 294 Bq/m 3 and 687 Bq/m 3 . For the both region, 80% of dwellings have radon concentration above the reference level of 100 Bq/m 3 . In Lolodorf, 50% of dwellings showed a radon concentration above 300 Bq/m 3 meanwhile in Poli it is 20% and 60% in the Bakassi oil-bearing peninsula [11]. Indoor radon concentrations in 15 dwellings of the Bakassi Peninsula present an average value of 1280 Bq/m 3 .
60% of dwellings have an indoor radon concentration above the reference level Journal of Applied Mathematics and Physics of 300 Bq/m 3 . An inhalation dose of 29.3 mSv/y was calculated [10]. The Arithmetic mean radon concentrations in 71 dwellings of Douala City were estimated to be 139 Bq/m 3 [12]. Indoor radon (Rn) concentration means measured in the gold mining areas of Betare-Oya using RADUET detectors and TnP monitors were 133 ± 39 Bq/m 3 . The 76% of houses for Rn exceed the WHO reference level of 100 Bq/m 3 and 3% of the houses exceed the ICRP threshold of 300 Bq/m 3 [13].
It is important to note that these results were obtained in the dwellings of Cameroon during normal periods before the advent of the Covid-19 pandemic. It should be noted that the risk of lung cancer based on the results obtained in certain localities can be evaluated differently and compared with recent statistics.
Therefore, we purpose in this study to conduct a risk assessment exposure to radon as a public health problem based on the available concentration measure in the high-level background radioactive areas in Cameroon during the lockdown caused by Covid-19. Thus, radon doses and risks will be re-evaluated based on these periods.

Exposure Times, Occupation and Equilibrium Factors
As the equilibrium factor depends on on-air exchange, the lockdown influence the way of life, most precisely ventilation in the home, especially in tight constructions and small houses. The occupancy factor with the instructions to stay at home can reach 100%. It is difficult to measure it in practice as it widely varied with age, occupation, state of health, climate and is usually higher in cold climate countries [17]. The default equilibrium factor is 0.4 and can vary from 0.2 to 0.7 [18].

Area of Study
Cameroon's mining potential [19] presents high natural background radiation areas that have been subjected to radon measurements. In order to cover the entire nation, some localities in 05 regions was concerned, in particular the locality of Poli in the North [11], those of Lolodorf, Bikoue, and Ngombas in the South [20], Bakassi in the South-West region [21], Betaré-Oya in the East [22] and the city of Douala, capital of the Littoral region [12]. To values obtained in these localities, we associate some limits concentrations of international institutions for comparison.

Evaluation of the Annual Effective Dose (AED), Effective Dose to Lung (EDL), Excess Lifetime Cancer Risk (ELCR) Lung Cancer Case (LCC), and Relative Risk Lung Cancer (RRLC)
Doses from inhaled radon (E inh (Rn)) were calculated according to the following The annual effective dose to the lungs will be calculated as follows: The radiation-weighting factor W T is 20 for alpha particles and W T is the tissue weighting factor (0.12 for lungs).
The excess lifetime cancer risk (ELCR) was calculated using the following formula [23]: where DL is the estimated average lifetime of 60 years in Cameroon and RF is the risk of fatal cancer per Sievert (5.5 × 10 −2 Sv −1 ) [24].
The relative risk of lung cancer (RRLC) due to indoor exposure to radon was calculated using the following equation [25]:

Radon Activity Concentration
The available values of indoor radon concentration reported in Table 1 [27]. Such high values found in High Natural Background Radiation Areas (HNBRA), must be confirmed to be the most consistent measurement. In fact, the number of dosimeters and dwellings can be increased in order to cover systematically all HNBRA in the country. Short-term and continuous measurements can help be carried out for more accuracy. We can notice that the few measurements done using EICs detector give high values than those obtained from Raduet detectors. Attention can be paid in the choice

Annual Effective Dose and Annual Effective Dose to Lung
According to

Lung Cancer Cases
The

Lockdown Effects on Doses and Risks
Based on the assumption made in Section 2, the doses and risks presented above have been reassessed and plotted in Figures 1(a) and 02 weeks, this amounts to receiving respectively 4.80% and 30.86% of annual dose over 7000 h/y during these periods. For all the evaluated quantities (Annual Effective Dose, Equivalent Dose to lung, Excess lifetime Cancer Risk, Relative Risk of Lung Cancer and Lung Cancer Cases per million person), with an occupancy factor varying from 0.6 to 1 and lockdown time of 03 months, we can expect a ratio of 4.87% to 112.85% of the value received in 7000 h/y of exposure. In a two-week quarantine, it range from 0.76% to 17.55%. The equilibrium factor could also be taken into account in this kind of approach but since it is more a natural decay process between radon and these progenies than human intervention, we choose not to vary it in our assessment.

Conclusion
The disturbances caused by Covid-19 are felt at several levels of human health.  (e) (f) Journal of Applied Mathematics and Physics Through this study, which aimed at estimating the effects of lockdown time on the inhaled doses of radon on humans and the associated cancer risk, we have demonstrated that the doses that will be received this year may increase from 0.76% to 17.55%. The dose from exposure to radon by ingestion through drinking water can also be taken into account to improve this type of study. Exposure time (8760 hr/y, 7000 hr/y and 2000 h/y) and occupancy factors can be adapted on a case-by-case basis for a more accurate assessment of indoor and outdoor exposures to re-estimate ambient doses received in the High Natural Background Radioactive Area. Ventilation and flooring retrofitting instructions against radon/thoron soil emissions are highly recommended and the attention given to the reading of this scientific essay contributes to the enrichment of the reader's safety culture. While any scientific study comes with its share of uncertainty and parameter approximation, it is nonetheless true that lockdown would influence radon exposure and associated risks.