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Evaluation of Respiratory Exposure Dose of Uranium Dust Particles Filtered by Masks

by:GESTER Instruments     2021-04-07
Compared with ordinary mines, there are a large number of long-lived alpha radionuclides such as 234U, 238U, 226Ra, 230Th, and 210Po in radioactive uranium dust in uranium mines. These long-lived alpha radionuclides in uranium dust particles contribute a lot to the internal radiation dose caused by human respiration and cause great harm to the health of employees. At present, many scholars have evaluated the risk of respiratory exposure to uranium dust. Panigrahi et al. [1] conducted radioactive aerosol monitoring on the Jaduguda uranium mine in India. The monitoring results showed that the geometric mean concentration of radionuclides was 16.84 mBq/m3, with a standard deviation. Jha et al. [2] analyzed the monitoring data and found that there is a linear correlation between the total concentration of uranium dust and the concentration of nuclide, and the correlation coefficient is 0.43; Tomasek et al. [3] analyzed the uranium in various workplaces of Czech uranium mines. The mine dust was monitored, and the results showed that the AMAD range of radioactive aerosol activity was 2.0-9.2 μm (average value was 7.3 μm), and the corresponding geometric standard deviation was 2.1-6.5 (average value was 3.2). The 234U, 238U, 226Ra, 230Th, and 210Po long-lived alpha radionuclides in uranium dust are all fine particles. Masks have a certain filtering effect on fine particles. In the past studies, most of the previous studies neglected the filtering effect of masks on uranium ore dust, or for safety reasons, an empirical coefficient of 0.3 to 0.5 was adopted. If you ignore the influence of wearing a mask on the calculation of the human body exposure dose caused by uranium ore dust, this will inevitably lead to a high calculation result [4], and the selection of the safety factor lacks basis, and its accuracy and scientificity need to be proven. Therefore, this article uses two commonly used gauze masks and KN95 masks in uranium mines. Based on the real data of the mass concentration and particle size distribution of uranium dust after filtering by these two masks, the effect of uranium dust particles on breathing is calculated. The exposure dose to the human body and the risk index of respiratory exposure caused by uranium dust to the human body. The dose and risk values u200bu200bcalculated in this paper do not include the contribution of radon and its daughters. 1 Respiratory exposure risk assessment model Health risk assessment is based on the damage of pollutants to the human body, combined with toxicological data, to establish an assessment model of the degree of damage to human health caused by different types of pollutants. The International Agency for Research on Cancer divides pollutants into genetic substances (including radioactive substances and other carcinogens) and somatic toxic substances (non-carcinogens) [5-6]. According to different exposure routes, they can be divided into respiratory routes, dietary routes, and skin. Contact route. As the main step of occupational exposure risk assessment, respiratory exposure risk assessment is an important tool for evaluating the current or potential exposure of humans to hazardous substances, and it is also an integral part of epidemiological research. Respiratory exposure risk index is used to describe the degree of interaction between human body exposed to harmful substances and pollutants through respiratory pathways, and is an important parameter to evaluate the degree of risk of human exposure to external substances. The exposure risk evaluation model is expressed by formula (1) [ 7]: In the formula, R is the lifetime risk of equivalent death due to a certain harmful health effect; AAD (Average Annual Doses) is the average annual exposure dose of chemical pollutants, mSv/a; RFD is the pollutant in The reference dose under a certain exposure route, mSv/a. Among them, the pollutants involved in uranium mine workers are radioactive materials; the occupational exposure dose control value RFD in the uranium mining and metallurgy industry is 15 mSv/a [8]. The main occupational exposure of uranium dust is respiratory exposure, and the average annual exposure dose AAD can be calculated by the formula [9-10] as follows: where IR is the respiratory volume, m3/d; EF is the exposure frequency, d/a; ED Is the equivalent exposure duration, a; F is the filter efficiency of the mask, dimensionless; fi is the dose conversion factor of the i-th nuclide, Sv/Bq; Ci is the activity concentration of the i-th nuclide, Bq/m3. The internal exposure hazards caused by uranium ore dust to the human body mainly come from the long-lived alpha nuclide, but since the measured uranium ore dust concentration is a mass concentration, it needs to be converted into an activity concentration in order to calculate its exposure to the human respiratory tract. Therefore, the conversion is carried out according to the following formula: Strictly speaking, the mass fraction of uranium in uranium ore dust is not the same as the grade of uranium ore, but actual measurements have found that the mass fraction of uranium in uranium mine dust is not higher than the average grade of ore. It is reasonable and safe to substitute uranium grade for the mass fraction of uranium in uranium dust in equations (3) and (4). 2 Application of risk assessment model for respiratory exposure to uranium mine dust 2.1 Before the simulation results of field tests and monitoring, the APS 3321 instrument was used in a uranium mine to measure several representative locations through masks to obtain typical underground uranium mines. The relevant data of the mass concentration and particle size distribution of uranium ore dust filtered by masks in the workplace [13-14] are listed in Table 1.
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