Year : 2018 | Volume
: 41 | Issue : 2 | Page : 59--60
Use of hazard index parameters for assessment of radioactivity in soil: A view for change
Editor, RPE, Ex. Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
D D Rao
Editor, RPE, Ex. Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra
|How to cite this article:|
Rao D D. Use of hazard index parameters for assessment of radioactivity in soil: A view for change.Radiat Prot Environ 2018;41:59-60
|How to cite this URL:|
Rao D D. Use of hazard index parameters for assessment of radioactivity in soil: A view for change. Radiat Prot Environ [serial online] 2018 [cited 2020 Apr 6 ];41:59-60
Available from: http://www.rpe.org.in/text.asp?2018/41/2/59/239688
Commonly, gamma radioactivity in soil/sediment is evaluated using gamma-ray spectrometry utilizing high-resolution HPGe or NaI (Tl) detectors. The assessment of the radioactivity is carried out by computing several parameters such as “External Hazard Index (Eex),” “Internal Hazard Index (Ein),” gamma absorbed dose, annual effective dose, radium equivalent (Raeq), and Activity Concentration Index (I). These parameters are compared with available relevant standards or reference values.
UNSCEAR (2008) gives formulae for absorbed dose rate (nGy/h) evaluation at 1 m above the ground for uniform distribution of activity in soil. The effective dose computed from this radioactivity is compared with the world average annual effective doses.
External Hazard Index and Internal Hazard Index parameters and other indices are evaluated using formulae detailed in several publications.,,, The radioactivity levels are generally of ambient background levels and use of term like “Hazard” is highly exaggerating. The Eex and Ein values need to be less than unity for insignificant effect on health. However, even if they are ten times higher, they do not pose any serious adverse effects or cause any significant health hazards except that the risk of stochastic effect may increase marginally. They can still be called insignificant.
In comparison, even conventional pollution indicators, whose hazards are generally felt instantly, when threshold limits are reached and are exceeded, do not use words like “Hazard” in their standards. Their standards are expressed as threshold limit values (TLVs), permissible values, or as air quality standards. Conventional pollutants such asSOx, NOx, or TSPM when exceeding their corresponding TLVs/standards definitely cause some adverse effects on health of human. They may cause throat irritation or irritation in the eye or skin, etc.
International documents notably, UNSCEAR (2008), ICRP 103, IAEA (GSR Part III), etc., do not use the word “Hazard” for such ambient exposures, except that they specify limits for annual doses or radioactivity levels.
The index parameter Raeq is related to exposure to radiation and has been defined to compare the specific activity of material containing different activity levels of 238 U,232 Th, and 40 K. A value of 370 Bq/kg of Raeq corresponds to 1.5 mGy/a of absorbed dose. Similarly, the Eex and Ein parameters of unity also correspond to 1.5 mGy/a of radiation exposure. Thus, Eex and Ein when exceeding unity, it does not cause any significant exposure which may result in any kind of adverse health effects. To cause any kind of adverse health effects, the index should approximately exceed about a million. Thus, the use of “Hazard” word in exposure indices is completely inappropriate for ambient background exposures. The inappropriateness of computation of ECLRs for ambient exposures has already been discussed elsewhere in this journal. The OECD document which originally gave formulae for the gamma exposure indices do not use the word “Hazard” and instead mention as first enhanced level or second enhanced level.
The European Commission's Radiation Protection Report-112 gives the Activity Concentration Index (I) for representation of activity concentration due to 238 U,232 Th, and 40 K in building materials corresponding to a dose criterion. For instance, I = 1 corresponds to an annual effective dose of 1 mSv. Therefore, since all the index parameters are interrelated and correspond to a dose criterion, it is not necessary to use the decades-old Eex and Ein in terms of Hazard Exposure Index. The following recommendations are given for representing or assessing the soil/sediment radioactivity in terms of index parameters as may be needed.
Use of Raeq parameter to generalize and interrelate the activity due to 238 U,232 Th, and 40 K with a single parameterCompute absorbed gamma dose (nGy/h) and compare with annual world average exposure of of 57 nSv/h.Compute annual effective dose (indoor + outdoor) and compare with world average exposure of 0.48 mSv/a.Compute Activity Concentration Index (I) as per European Commission Report-112Finally, if it is essential, replace Eex with External Exposure Index (EEI) and Ein with Internal Exposure Index (IEI) instead of hazard index.
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