Gamma Radiation Hazards and Risks Associated with Industrial Wastes Materials ()
1. Introduction
“The occurrence of natural radionuclides 226Ra, 232Th and 40K in industrial solid waste is the source of the radiation hazard to the population and the environment [1] ”. Monitoring all sources of natural radiation in the workplace is essential to evaluate the potential environmental risk [2] . Some industrial activities produce a huge amount of wastes which might pollute the environment. In fact, “Industrial waste is the fastest growing materials which lead to doses of radiation exposure. If this waste is not organized and recycled, no areas will be available to store it [3] ”. The industrial solid waste product of Iron, Aluminium, Cooper and wood could be found as sharp pieces or as a powder. These products are formed either by filling the metals and woods, or by mending finished materials, or by several other methods, including automatic and manual ones. These waste materials may be the source of natural radiation for the workers at the workshops. In general, there is no control over the operation of these industrial workshops, and there is no specific approach to a guideline of natural radioactivity of industrial wastes. Thus, the first aim of this work is the measurement of the natural radionuclides (226Ra, 232Th and 40K) in different samples of industrial solid wastes (Iron, Aluminium, Copper and wood). The second aim is the assessment of the radiological hazard to the environment and the workers at the workshops that produce materials with enhanced content of natural nuclides. The significance of this study is to supply basic safety standards for the sake of workers and public health against the danger arising from such industrial waste.
2. Materials and Methods
Twenty-five of solid waste samples were collected from several Industrial workshops in Saudi Arabia, Jeddah city. The collected samples were oven dried at 110˚C for twelve hours and then packed in a Marinelli beaker and sealed for one month to reach secular equilibrium between 226Ra and 232Th with their decay products. The radionuclide activity concentrations in the prepared samples were measured using a high-purity germanium (HPGe) detector with an efficiency of about 25 %. A counting time of 36,000 s was used for measurements the Gamma-rays spectrum. The background concentration of the γ-rays was determined with an empty Marinelli beaker under the same measurement conditions. 226Ra activities were calculated from the activities of its short-lived daughters 214Pb at 295.2 keV & 351.9 keV and 214Bi at 609.3 keV. 232Th activities were measured by taking the mean activity of photo peaks of the daughter nuclides 228Ac (338.40 and 911.07 keV) and 212Pb (238.63 keV). Activities of 40K were determined directly from its gamma emission at 1460.83 keV.
The activity concentrations of the investigated samples were evaluated using the following equation [4] [5] :
(1)
where Nc is the net gamma counting rate (counts per second), ε the detector efficiency of the specific γ-ray, β the absolute transition probability of Gamma- decay and M the mass of the sample (kg).
3. Assessment of Radiation Hazard
3.1. Radium Equivalent Activity (Req)
To assess the radiological hazard of the concerning samples, it is useful to use the radium equivalent activity (Req) in Bq∙Kg−1 [5] :
(2)
where ATh, ARa and AK represent the activity concentrations of 232Th, 226Ra and 40K in Bq∙kg?1 respectively. Req is defined according to the estimation that 1 Bq∙kg?1 of 226Ra, 0.7 Bq∙kg?1 of 232Th and 13 Bq∙kg−1 of 40K produce the same gamma-ray dose [6] the permissible dose limit for the public is 1.5 mSvy−1 [7] .
3.2. Absorbed Gamma Dose Rate (D)
The absorbed gamma dose scale in air 1mabove the ground surface for the uniform distribution of radionuclides (232Th, 238U, and 40K) were computed by guidelines provided by [5] :
(3)
where ATh, ARa and AK represent the activity concentrations of 232Th, 226Ra and 40K in Bq∙Kg?1 respectively.
3.3. The Annual Effective Dose Equivalent (Deff)
The annual effective dose equivalent received by a member has been calculated from the absorbed dose rate by applying dose conversion factor of 0.7 Sv/Gy and the occupancy factor for outdoor and indoor as 0.2 and 0.8, respectively, [5] , using the following equations:
(4)
(5)
3.4. Excess Lifetime Cancer Risk (ELCR)
Excess Lifetime Cancer Risk (ELCR) was calculated by the equation below [4] [5] :
(6)
where Deff (outdoor), DL and RF are the outdoor annual effective dose equivalent, the duration of life (70 years) and the risk factor (Sv?1), fatal cancer risk per Sievert. For detriment-adjusted cancer risk of 5.52 × 10−2 Sv?1 for the whole population [5] .
4. Results and Discussion
4.1. Activity Concentration
The results of 226Ra, 232Th and 40K concentrations in the waste samples were summarized in Table 1. From this Table, All samples under investigation, the average values of 226Ra ranged from 2.6329 Bq∙Kg−1 in (Copper) to 173.29 Bq∙Kg−1 in (Iron). 232Th average values ranged from 0.60 Bq∙Kg−1 in (Copper) to 141.99 Bq∙Kg−1 in (Iron) while the average values of 40K ranged from 29.99 Bq∙Kg−1 in (Copper) to 41.99 Bq∙Kg−1 in (Aluminum). Iron waste recorded the highest average values concentration of 226Ra and 232Th, and are much higher than the world average values 30, 35 Bq∙Kg−1 for 226Ra and 232Th respectively, as reported by [5] , which can be explained by adsorption on weathered ferromagnetic
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Table 1. Results of natural radioactivity concentration (Bq∙kg−1) in the waste samples collected from different industrial workshops, Saudi Arabia.
minerals, also iron scrap were used in high percentage [8] . For all the studied samples, the average values of K were lower than the world average values of 400 Bq/kg [5] . Different concentrations of radioactive nuclei in the samples refer to the sources and environmental acting on these samples. The average activity concentrations of 226Ra, 232Th and 40K in the waste samples under study are given in Figure 1.
4.2. Radiation Hazard from Waste Samples
The calculated average values of radium equivalent activity (Req), absorbed Gamma Dose Rate (D) and the Annual Effective Dose Equivalent (Deff), for all waste sample types and the total average values are shown in Table 2. The radiological hazards were compared with the recommended values by UNSCEAR 2000. From this table, we can establish the following:
1) Radium equivalent activity (Req)
The minimum average value of Req activity was 1.12 Bq∙Kg−1 for Copper waste while the maximum average value was 378.86 Bq∙Kg−1 for Iron waste, which is higher than the recommended maximum value of 370 Bq∙Kg−1 [5] . The highest value in Iron is attributed to the high activity concentration level of 226Ra and 232Th in Iron waste samples. The total average value of Req for all samples was 95.87 Bq∙Kg−1, this value is lower than 370 Bq∙Kg−1.
2) Absorbed gamma dose rate (D)
As shown in Table 2, the average value of the absorbed dose of all types of waste samples ranged from 2.79 nGyyh−1 (Copper) to 163.86 nGyyh−1 (Iron) with total average value 44.56 nGyyh−1. UNSCEAR 2000 reported that the world wild average value in an air of outdoor absorbed dose 55 nGyh−1 with at y-pical range from 10 to 200 nGyh−1. The average values for Copper, Aluminuim and Wood and the total average are lower than the recommended values by [5] . Table 2 shows that only for Iron waste samples, its absorbed average value is 3 times higher than the world average value. Figure 2 shows a comparison between the
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Figure 1. Average activity concentrations of 226Ra, 232Th and 40K for waste samples collected from different Industrial workshops, Saudi Arabia
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Table 2. Comparison of the average radiological hazard of the studied waste samples.
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Figure 2. Comparing the average and the total average values of absorbed dose rate (nGy/h), and Radium equivalent (Bq/Kg) of the waste samples with UNSCEAR 2000.
average and total average values of radium equivalent (in Bq∙Kg) and absorbed dose (in nGyyh−1) for the waste samples under investigation and the recommended values by UNSCEAR 2000.
3) The annual effective dose equivalent
The average annual effective dose of indoor and outdoor for all samples ranged from 0.012 mSvy−1 (Copper) to 0.73 mSvy−1 (Iron) and from 0.003 mSvy−1 (Copper) to 0.18 mSvy−1 (Iron) with the corresponding total average values of 0.20 mSvy−1 and 0.05 mSvy−1, respectively. These average values are less than the world average annual effective dose indoor 0.42 mSvy−1 and outdoor 0.07 mSvy−1 as reported by [5] . The maximum average values for outdoor and indoor effective doses were observed in Iron are higher than the world average effective dose for outdoor and indoor. This indicates that there is a significant effect for the workers in Iron workshops.
4) Excess lifetime cancer risk (ELCR)
The average values of ELCR ranged from 0.04 × 10−3 in Copper to 2.54 × 10−3 in Iron, with a total average value of 0.69 × 10−3. The average values of ELCR for all waste types are less than the world average (0.29 × 10−3) reported by [5] . The ELCR for Iron exceeded this value; this indicates that there is no risk to the general public and the workers in the industrial workshops which produce wastes of Copper, Aluminium and Woods and the workplace are still in zone of normal radiation, but there is a threat to the workers' health in Iron workshops.
5. Conclusion
The activities of the natural radionuclides 238U, 226Ra, 232Th and 40K in the solid waste samples collected from various industrial workshops in Saudi Arabia were measured by using a gamma-ray spectroscopy with HPGe detector. The total average values of radium equivalent, external hazard, absorbed dose and effective dose of all studied samples are below the internationally accepted values. The measured samples are still in the zones of normal radiation level, causing no threat to the environment, the human health, and the workers at the workshops except the Iron waste may create some radiological complications. The results may be useful in the assessment of the exposures and the radiation doses due to the natural radioactive content in industrial solid waste samples. They may provide a wide serve as a guideline for future measurement and assessment of possible radiological risks to human health.
Recommendation
We recommend two major steps to be taken into account: first, reducing the hours of operation at the workshops of iron; second, using ventilation and respirators in the workplace at all industrial workshops. Finally, there must be the radiological control on the operation of such industrial workshops.