Foreword: Radioactivity Dose Calculation and Water Quality Evaluation Guideline for Domestic Water Use

While radioactivity in water is relatively easily measured, given the appropriate equipment and radio-analytical expertise, the interpretation of the significance of the measured radioactivity to the domestic water user is beset with uncertainties and imponderables, especially when it comes to evaluating the actual risk to the consumer. There are many reasons for this, a basic one being that the dose-effect response assumes large statistical error-bars and indeterminacy when one extrapolates to the typically minimal radioactivity condition found in most water samples. The international criteria for radioactivity in drinking water present a plethora of different approaches, and are not very helpful in this regard.

The international approach to drinking water radioactivity has tended to focus on one or two selected radioactive nuclides in water, and has not offered much guidance in terms of total dose evaluation for all the common natural radionuclides present in water samples.

The approach used for radioactivity dose evaluation in this guideline builds on the total dose approach first developed for the Mooi River water radioactivity study, and serves to expand upon and clarify the uncertainties in assumptions met with in that study. The radioactivity dose is evaluated in terms of the five-colour classification approach well accepted for chemical and microbiological water quality in South Africa for classification of the water quality in the classes: Ideal (blue), good (green), marginal (amber), poor (red) and unacceptable (purple).

During the production of this document there was much discussion and controversy as to whether the department should adopt the life-time age weighted method of evaluating the significance of the radioactivity dose, or should rather be conservative and adopt the dose to the most sensitive user (usually infants under one year of age) for the purposes of classification.

The majority opinion has been adopted of using the lifetime age-weighted approach yet while also explicitly showing the dose values for all the specific age groups, should the user of the guideline wish to make either more or less conservative evaluations of water radioactivity in specific age group situations.

It is hoped that this guideline, with the associated computer software routine, should make it easier for hydrologists, and all those concerned with evaluation of radioactivity in water to assess the fitness for use of drinking water for radioactivity parameters.

Acknowledgements

Glossary of Terms

Action Level		The level of dose rate or activity concentration above which remedial actions or protective actions should be carried out in chronic exposure or emergency exposure situations.
Alpha Radiation		This is emission of energy from the atomic nucleus as alpha particles. Alpha particles are comparatively large, positively charged nuclei of helium and have a low penetrating power, e.g. being stopped by a few centimetres of air or a sheet of paper.
Artificial radioactivity		Radioactivity not of a natural origin (see definition of NORM) and produced as a result of human technological processes, for example, inside a nuclear power reactor.
Background		The surrounding environment which is uncontaminated by a local source of pollution.
Background Radiation		The radiation in the natural environment, including cosmic and cosmogenic radiation and radiation from the naturally occurring radioactive elements. It is also called natural background radiation.
Beta Radiation		This is emission of energy from the atomic nucleus as beta particles. Beta particles are equivalent to electrons and are able to penetrate up to around a metre of air or a centimetre of water.
Bio-concentration		The process by which contaminants in the environment are concentrated up the food chain (e.g. from benthic organisms, to fish, to humans).
Cosmic radiation		Radiation of great penetrating power that come to the earth from all directions of space.
Cosmogenic radiation		Radiation that results from the interaction of cosmic radiation with the earth’s atmosphere, for example radioactive carbon –14 is created in the earth’s atmosphere.
Critical Group		A group of members of the public (in the general population) which is reasonably homogeneous with respect to its exposure for a given radiation source and given exposure pathway and is typical of individuals receiving the highest dose by the given exposure pathway from the given source.
Dose – Effective		A weighted measure of the radiation energy received or absorbed by the whole body and measured in units of Sievert (Sv)
Dose – Annual Effective, Age Specific		A weighted measure of the radiation energy received or absorbed by the whole body and measured in units of Sievert (Sv), following uptake of a certain amount of radioactivity in a year where the dose will be committed over the lifetime of the person taking into consideration the sensitivity of the human body at the age when the uptake occurred.
Dose – Annual Effective, Lifetime Average		A weighted measure of the average radiation energy received or absorbed by the whole body and measured in units of Sievert (Sv), assuming that uptake of a certain amount of radioactivity occurs in a year over the whole lifetime of a person and taking into consideration of the sensitivity the human body at different age intervals into consideration.
Dose Limit		The value of the effective dose to individuals from controlled practices or working activities that shall not be exceeded.
Dose rate		The amount of ionising radiation that may have been received over any period of time.
	Exclusion		Any exposure where the magnitude or likelihood is essentially not amenable to control. Examples are exposure from Potasium-40 (K-40) in the body, from cosmic radiation at the surface of the earth and from unmodified concentrations of nuclides in most raw materials.
Exposure		The act or condition of being subject to ionising radiation.
Exposure Pathways		The routes by which radioactive material can reach or irradiate humans.
Gamma Radiation		High energy, short-wave length electromagnetic radiation of nuclear origin. Gamma rays are the most penetrating when compared to alpha and beta radiation.
Groundwater		Water beneath the earth’s surface, accumulating as a result of infiltration and seepage, and serving as the source of springs, wells, etc.
Intake		The process of taking nuclides into the body either by inhalation (typically as dust in air) or by ingestion (drinking water and/or eating food).
Intervention		Any action intended to reduce or avert exposure or the likelihood of exposure to sources which are not part of a controlled practice or which are out of control as a consequence of an accident.
Intervention Level		The level of avertable dose at which a specific protective action or remedial action is taken in an emergency exposure situation or a chronic exposure situation. This may also include exposure to natural occurring radioactive material not caused by any human activity, i.e. extraordinary high background radioactivity.
NORM		Naturally Occurring Radioactive Material. The main contributions of human exposure to ionising radiation arise from natural sources – cosmic rays, the nuclides in the earth’s crust and the natural radioactivity of the human body. Of the natural nuclides in the earth’s crust (NORM), those which are found to be the main sources of human radiation exposure are Potasium-40 (K-40), Thorium-232 (Th-232), Uranium-235 (U-235) and Uranium-238 (U-238) and decay products from the latter three nuclides. Potassium is a common element and the radioactive isotope, K-40, constitutes 0.012% of all potassium in its natural form. The three heavy nuclides (Th-232, U-235 and U-238) decay to produce other elements, which in turn decay further through a chain which includes several elements, eventually to end in stable isotopes of lead. An example of a significant daughter nuclide in these decay chains is Radium-226 (Ra-226 in the U-238 chain) and which is soluble in water.
Nuclide/Radionuclide		A radionuclide is an element or isotope that is radioactive as a result of the instability of the nucleus of its atom (e.g. radium or uranium). In this document all reference to nuclides will assume these to be radionuclides.
Nuclide vector		A specific set of nuclides that is used for analysis and/or evaluation of water quality, e.g. a simple water analysis with the purpose of only obtaining an initial indication of water quality may consist of the nuclide vector {U-238; Ra-226}. A more complex analysis to determine the radiation dose more precisely may consist of more nuclides in the U-238, U-235 and Th-232 decay chains.
Pathways Analysis		A method of estimating the transfer of contaminants (e.g. radio-nuclides released in water) and subsequently accumulated up the food chain to fish, vegetation, mammals and humans and the resulting radiological dose to humans.
Potential Exposure		Exposure that is not expected to be delivered with certainty but that may result from an accident at a source of radioactive material, or owing to an event or sequence of events of a probabilistic nature.
Practice		Any human activity that introduces additional sources of exposure or exposure pathways or extends exposure to additional people or modifies the network of exposure pathways from existing sources, so as to increase the exposure or the likelihood of exposure of people or the number of people exposed. Some mining and mineral processing activities fall within this definition and are normally authorised and regulated in terms of the National Nuclear Regulator Act (Act No. 47 of 1999).
Radiation		The emission and propagation of energy through space or matter in the form of electromagnetic waves (gamma rays) or fast-moving particles such as alpha and beta particles.
Radioactive		The condition of a material exhibiting the spontaneous decay of an unstable atomic nucleus into one or more different elements (e.g. uranium decays into various isotopes of radium, thorium and lead).
Radioactive Waste		Material, whatever its physical form, remaining from practices or interventions and for which no further use is foreseen (i) that contains or is contaminated with radioactive substances and has an activity or activity concentration higher than the level for clearance or exemption from regulatory requirements, and (ii) to which exposure is not excluded from regulatory control.

Radon Gas		A naturally occurring radioactive gas within the decay chain of U-238.
Receptor		A person living nearby to a source of pollution; the person who may receive any impacts resulting from an industrial activity.
Reference Level		This can be an action level, intervention level, investigation level or recording level. Such levels may be established for any of the quantities determined in the practice of radiation protection.
Remedial Action		Action taken to reduce radiation doses that might otherwise be received.
Risk		A multi-attribute quantity expressing hazard, danger or chance of harmful or injurious consequences associated with actual or potential exposures. It relates to quantities such as the probability that specific deleterious consequences may arise and the magnitude and character of such consequences.
Source		Anything that may cause radiation exposure, such as by emitting ionising radiation or releasing radioactive substances or materials. For example, natural materials emitting radon are sources in the environment.

Symbols and Abbreviations
Ac		Actinium
Bi		Bismuth
Bq		becquerel
IAEA		International Atomic Energy Agency
ICRP		International Commission on Radiation Protection
ILO		International Labour Organisation
mSv		10^-3 sievert
NNR		National Nuclear Regulator
Pa		Protactinium
Pb		Lead
pico		10^-12
Po		Polonium
Ra		Radium
Rn		Radon
Sv		Sievert
Th		Thorium
U		Uranium

The purpose of this document is to present a guideline for evaluating the quality of drinking water in respect of its radioactivity concentration. This document deals with naturally occurring radioactive material (NORM) in water. Artificial sources of radioactivity are outside the scope of this document although it is briefly discussed. Sediments that occur in natural water bodies, such as in river streams and that can trap NORM material, is also outside the scope of this document.

This document presents proposals for radioactivity monitoring and dose calculation methods that can be used to specify the quality of a water resource.

The annual radiological dose for a person drinking water that contains a certain level of radioactivity is calculated by an apparently simple equation as follows:

Annual Effective Dose (Sv) = Radioactivity Concentration in water (Bq/L) ´ Annual Consumption of water (L) ´ Radioactivity Dose Conversion Factor (Sv/Bq)

However, it is far from simple to obtain input data for the variables in the equation that will allow one to assess the quality of a specific water resource and quantify the dose for people using the water. The Mooi River and Klip River studies [1] provided ample proof of the complexities involved in studies to determine radioactivity concentrations in water and the associated health risk.

The main source of radioactivity impact on water is naturally occurring radioactive material NORM. It is present in all water resources and the impact is normally of a chronic nature. The proposed methods for the guideline therefore deal with water that contains NORM.

Some readers of this document may be unfamiliar with the subject of radiological protection and for this reason the document has been structured in three sections as follows:

· A first section that gives a general introduction to radioactivity and protection against ionising radiation.

· The second section provides background to the specific situation of chronic exposure situations as well as supporting information for assumptions made in the proposed guideline.

The reader who is familiar with radioactivity and radiation health hazards is advised to start at Section 2 of the document.