The usefulness of LNT approach

There is controversy over the use of (Linear No-Threshold (LNT) hypothesis to estimate the stochastic risk of exposure to ionizing radiation. The approach is not universally accepted. However, the usefulness of the LNT approach for radiological protection is very significant. The concepts used in radiation protection are strongly based on the LNT hypothesis. For example, LNT allows radiation doses: (i) to be averaged within an organ or tissue, (ii) to be added from different organs, and (iii) to be added over time.

The LNT also underpins the concepts of absorbed dose, effective dose, committed dose, and the use of dose coefficients used to estimate internal dose from the intake of radionuclides.  

Calibration of dosemeters and doserate meters

International Standard ISO 29661:2012 defines terms and fundamental concepts for the calibration of dosemeters and equipment used for the radiation protection dosimetry of external radiation, in particular for beta, neutron and photon radiation. It defines the measurement quantities for radiation protection dosemeters and doserate meters and gives recommendations for establishing these quantities. For individual monitoring, it covers whole body and extremity dosemeters (including those for the skin and the eye lens), and for area monitoring, portable and installed dosemeters.

Guidelines are given for the calibration of dosemeters and doserate meters used for individual and area monitoring, in reference radiation fields. Recommendations are made for the position of the reference point and the phantom to be used for personal dosemeters. ISO 29661:2012 also deals with the determination of the response as a function of radiation quality and angle of radiation incidence. ISO 29661:2012 is intended to be used by calibration laboratories and manufacturers.

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Basis for protection standard for uranium

Basis for protection standard for uranium

Uranium, a terrestrial radionuclide, is naturally present in the environment – in soil, rocks, in sea water, ground water, in food in the human body itself. The mass concentration of uranium varies from place to place depending on the environmental conditions. Natural uranium consists of three isotopes of uranium-²³⁸U, ²³⁵U and ²³⁴U with different half-lives. The longest-lived ²³⁸U has a half-life of 4.5 billion years. Typically, the soil concentration is about 3 parts per million (ppm).

In addition to its radioactive nature, it is, as water soluble uranium compounds, is chemically toxic. Uranium gets deposited in the kidneys due to its physicochemical properties. The US EPA (2001) and WHO (2011) standard for uranium in drinking water is 30 micrograms per liter which is equivalent to 0.75 Bq/liter. The threshold limit value (TLV) (ACGIH, 1994) in air in work environment for insoluble uranium is 0.2 mg/m³.

The protection standards for uranium (soluble) is limited by the chemical toxicity, while for insoluble compounds, the protection standards are based on radiological considerations. 

Exposure to EMF radiation

During use mobile phones and cord-less phones emit RF radiation. Other sources of the radiation are mobile phone base stations, Wi-Fi access points, lap tops and tablets. The exposures to RF radiation can be long-term or round-the -clock.  Cancer risks of radio-frequency radiation [RF] emitted by some devices in the frequency range of 30 kHz -300 GHz was also evaluated by the IARC for any possible risk for head and brain tumours. It was found that it is Group 2B – a possible human carcinogen. The data based on animal studies and epidemiological studies.

It is important that ambient levels of RF radiation in different locations should be measured to address the public health concern of RF radiation.  International Commission on Non-Ionizing Radiation Protection [ICNIRP] standards are implemented by the industry to ensure public safety. However, as of now, the standards are based on thermal effects of RF radiation and non-thermal biological effects [stochastic] to the brain as a target organ are not considered. 

The guidelines provided by ICNIRP, the threshold level for behaviour changes in animals quoted is not a clear line between safety and hazard. It only indicates that EMF exposure below the threshold is safe. However, it is not correct to assume that above the given level the exposure is harmful. A safety factor of 10 is applied to the threshold level to obtain the occupational exposure limit. A safety factor of 50 is applied to obtain the guideline limit for the general public.

The Radio-frequency fields (measured in the units of microwatts/cm²) are generated by most of the mobile towers and modern wireless gadgets. The mobile towers catering to the upcoming 5G system for seamless connectivity will emit enhanced levels of RF fields, which will be of major public health concern. 

References

Hardell, L., WHO, Radiofrequency radiation and health – a hard nut to crack [review], Int. J. of Oncology, 51, 2017, 405-413

ICNIRP EMF Guidelines for limiting exposures to time-varying electric, magnetic and electromagnetic fields-up to 300GHz, Health Physics, 74 [4], 1998, 494-522 [Being revised]

ICNIRP EMF Guidelines for limiting exposures to time-varying electric and magnetic fields, 1Hz-100kHz, Health Physics, 99[6], 2010, 818-836

Radiological safety in application of radiation in medicine

Positron Emission Tomography (PET)  is used as an imaging technique in a wide range of biomedical research applications in human patients and volunteers. Millions of PET scans are performed worldwide. Radio-tracer is introduced to the patient and its movement or deposition in the body is followed through a PET scan. A typical nuclear medicine procedure results in a radiation dose of around 25 mSv to a patient, while a CT scan using X-rays gives a dose of 5-8 mSv per scan, depending on which part of the body is scanned. To put risks in a proper perspective, natural background radiation dose is in the range of 2 to 3 mSv in year.

Radiation protection principle recommends optimization of the procedure to minimise patient dose. Some of possible ways of minimization of the dose is:

Ø Use highly sensitive and faster scanners for the procedure so that time spent is minimum for scanning so that the system can detect and perform scans at very low levels of emissions

Ø Optimise the radio-tracer dose to the patient to get a good scan

Ø Select a most suitable short-lived low energy photon emitting radiotracer

Ø Minimise radiation exposures of the healthy tissues/organs which are adjacent to the tissue/organ being scanned or treated. 

  

The procedures results in radiation dose (occupational exposures) to the medical, para-medical staff and technicians who are handling the radioactive material and who operate the machines for scanning. Scattered radiation from the primary beam is of concern, particularly to the eye lens, and needs to be monitored. Suitable radiation dosimetry technique should be used for the purpose. The hospital health physicist should ensure that the occupational exposures should be controlled and kept as low as reasonably achievable (ALARA).

Finally, the hospitals, the physicians/radiologist should avoid misuse of this technology for financial gains alone. In addition to the benefits to the patient from the procedure, the patients should be thoroughly briefed about the possible health effects from the exposure to radiation. Benefits should outweigh the risks of the exposures. 

NORM waste disposal needs to be regulated!

Waste containing Naturally Occurring Radioactive Material (NORM) is generated in industries which handle uranium and thorium containing raw materials. The waste contains radioactive uranium/thorium and their progeny and or K-40 which are naturally present in the earth crust in rocks, in ores/minerals and in coal. After recovery of the useful product elements, the waste contains traces of radioactive elements and can pose an environmental hazard. The fly-ash (waste product after burning of coal) also contains radionuclides in more concentrated levels as compared to their presence in coal. The ash waste is used to make bricks in some countries. The constraint is the emanation of radioactive radon gas from the traces of Ra-226/224 present in the fly ash.

There are regulatory limits on the radioactivity elemental concentration levels for disposal without any controls. However, in most of the industrial situations the activity concentration levels are much higher and are not safe to indiscriminate disposal in the environment. Disposal as road fillings is one of the uses of NORM waste.

It is time that national regulatory bodies wake up this public health concern and enforce appropriate controls on the disposal of the NORM waste.

Lung cancer fatality risk and smoking habits

It is well known that there is a strong relationship between the smokers and the incidence and lung cancer fatality. A US lung cancer mortality study indicated the mortality rate increased with age and the number of fatalities from lung cancer among smokers increased very significantly as compared to non-smokers.

Mortality rate per 100,000 person-years

Age group                Non-smokers          Smokers

55 – 59 y                   5.3                              206

60 – 64 y                   11.6                           361

65 – 69 y                   21.5                           581

70 – 74 y                   34.9                           909

It is indicated that the incidence of lung cancer is more prevalent amongst the uranium miners who are exposed to radon (radioactive gaseous decay product from uranium and thorium series) and its decay products. The risk of incidence of lung cancer varies with the different smoking habits. Studies have indicated that there is enhancement (synergistic effect) in the lung cancer risk due to radon exposure and the smoking habits of the exposed persons.

This means risk of lung cancer resulting from unit radiation dose due to exposure to radon for people who are smokers is substantially higher than that of people who never smoked.

Exposure to radon is much more injurious to heath if you are a smoker.