In July 2010, the United Nations General Assembly expressed concern that almost 900 million people worldwide do not have access to clean drinking water. The organization also voiced alarm that 1.5 million children under five die each year as a result of water- and sanitation-related diseases. In addition, it acknowledged that safe, clean drinking water and sanitation are integral to the realization of all human rights.
Climate change threatens freshwater reserves. According to the Intergovernmental Panel on Climate Change, general glacier retreat in many mountain areas, and increased risks of extreme weather events with droughts and heavy precipitation, pose a challenge to the safe supply of drinking water. Furthermore, in 2032 there may be a billion people more on this planet with whom water resources will have to be shared. To preserve water quality, therefore, we will have to manage it better.
Testing water quality
To ensure water is potable, monitoring through chemical analysis needs to be carried out regularly. This is done to : verify quality ; assess the impacts of agriculture, industry, tourism and other human activities; and evaluate the consequences of contamination and pollution.
In 2011, WHO published the fourth edition of its guidelines for drinking-water quality. This builds on over 50 years of WHO guidance on drinking-water quality, starting with the publication of the first International Standards for drinking water in 1958.
The WHO guidelines are based on the assumption that monitoring environmental quality and the protection of human health are inseparable. They are considered an authoritative basis for the setting of national regulations and standards for water safety in support of public health, including protection against ionizing radiation. Since the first edition, WHO has referred to ISO’s work on the measurement of water-based radionuclides.
The system of radiological protection, progressively developed with the increasing use of nuclear energy, was established early in this process. It is based on the assumption that any exposure to radiation involves some level of risk, and recognizes the link between environmental radioactivity and public health.
Today, before authorizing routine low-level liquid or gaseous radioactive discharges from a nuclear plant, an assessment is made of the potential exposure to ionizing radiation from the released radionuclides. The exposure models used take into account the characteristics of the expected radioactive source term, the possible conflicting use of natural resources including water, and the different routes by which potential exposure can affect people.
Subsequently, the measurement results obtained through the radionuclide monitoring of releases and of environmental and foodstuff samples, including drinking water, validate the estimates of the installation’s impact (in terms of exposure) and substantiate authorized discharge limits. The credibility of the exposure assessment is therefore based largely on the quality and reliability of the radionuclide measurement results.
National legislation of countries with nuclear facilities (industrial, medical, research and military) sets the rules for the continuous monitoring of radioactivity in the atmosphere, water and soil. This is to comply with the system of radiological protection elaborated by the International Commission on Radiological Protection (ICRP).
Each year hundreds of thousands of radioactivity measurements are performed on environmental samples and reported to national authorities for regulatory purposes and public information. Most of them concern monitoring of drinking water for radioactivity.
Dispersed by currents and winds, released radionuclides know no borders. This was sadly demonstrated during the Chernobyl and Fukushima accidents.
National stakeholders on nuclear issues, such as industry, control authorities, local associations and public information commissions, are linked with international stakeholders. Legal instruments require stakeholders to be informed of radioactivity levels in emissions as well as in internationally traded foods. Countries are more likely to place their trust in the quality of radioactivity data exchanged since they mutually recognize the services performed by accredited laboratories using common standards.
Tested and true
Standards on test methods for radionuclides are therefore reference documents and meet the technical concerns that arise repeatedly in the relations between economic, scientific, technical and social stakeholders, both nationally and internationally.
During a controversial situation, stakeholders are likely to carry out measurements on samples from the same sites. It is essential to use agreed and appropriate methods and procedures for : the sampling, handling, transport, storage and preparation of test samples ; the test method ; and calculating measurement uncertainty. This is covered in ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories.
In this framework, the normative approach aims to ensure the accuracy or validity of the test result through calibrations and measurements traceable to the International System of Units. This approach guarantees that radioactivity test results on the same types of samples are comparable over time and between different test laboratories.
Most International Standards are used by the laboratories that carry out radionuclide activity measurements required by national authorities, as they have to get specific accreditation for radioactivity measurement on food and/or drinking-water samples.
Since 1978, ISO technical committee ISO/TC 147, Water quality, has developed standards on the metrological requirements to monitor the radioactivity of water intended for human consumption ; and since 1999, ISO/TC 85, Nuclear energy, nuclear technologies, and radiological protection, has developed standards on the measurement of radionuclides in the various environmental components.
ISO/TC 85 focuses on the drafting of standards on the radiological characterization of all sites, and the routine radiological monitoring of sites potentially affected by the discharge of radioactive effluent.
In most drinking water, since the activity concentrations of individual radionuclides are low and their determination is time-consuming, detailed analysis is normally not justified for routine monitoring. WHO therefore recommends the use of a preliminary screening procedure to determine the gross (total) alpha and beta radiation emitted by all radionuclides in water before identifying any specific radionuclide.
The test results are respectively compared with the screening levels and if justified with the specific guidance levels for radionuclide contained in the WHO guidelines.
When test results are below the screening levels of 0.5 Bq/l for gross alpha activity and 1 Bq/l for gross beta activity, there is no need for specific radionuclide measurement. Such concentrations will expose each person to well under 0.1 mSv/year, a level not expected to adversely affect health. If either of the screening levels is exceeded, then the specific radionuclides producing this activity should be identified and compared to their respective guidance levels.
The first edition of the WHO guidelines for drinking-water quality was published in 1984. Within ISO/TC 147, subcommittee SC 3 on radiological methods, set up in 1978, published its first standard on the determination of tritium activity concentration using a liquid scintillation counting method in 1989.
Three others standards were subsequently published, on the measurement of gross alpha activity and gross beta activity in 1992, and on gamma spectrometry in 1997. These standard test methods form the basis for the monitoring of drinking water as recommended by WHO since the first edition of the guidelines.
Following the publication of these four standards, SC 3 was disbanded. The ensuing periodic revision of these standards demonstrated the need for reviews. This was due to the availability of new equipment and procedures used to measure radioactivity in most laboratories that monitor drinking-water quality.
In 2002, it was decided to resume activities on radiological methods at working group level (WG 4). The initial mandate was limited to the revision of the four above-mentioned standards that were subsequently published.
New series of standards
In 2007, the need to draft new standards, in line with WHO recommendations, led to the adoption of a first set of new work item proposals (NWIP) on new test methods for gross alpha and gross beta activity used by test laboratories. A year later, a second set of NWIP was adopted on the measurement of strontium-90, polonium-210 and carbon-14.
As naturally occurring radionuclides in drinking water usually give radiation doses higher than those provided by artificially produced radionuclides, and are therefore of greater concern, in 2009 a third set of NWIP was proposed on test methods for radium-226, radon-222, lead-210 and uranium radioisotopes. These are currently being drafted.
The initial mandate of WG 4 was extended to a set of 15 new standards comprising 20 documents. This led to the proposal to reestablish SC 3 in 2010, which was adopted in 2011 with a new title, SC 3, Radioactivity measurements. The subcommittee aims to focus on priorities resulting from the latest WHO recommendations, taking into account the technical consequences of regulatory changes in drinking-water quality control. Six working groups are drafting test methods for the natural radionuclides lead-210, radon-222, radium-226, uranium, tritium and carbon-14, as well as the artificial ones plutonium and americium.
When published, this set of ISO standards on radioactivity measurement will answer the needs of test laboratories. They will adhere to WHO and ICRP recommendations on assessing drinking-water safety with respect to naturally occurring and artificial radionuclides. In addition, they will be used to identify spatial and/or temporal trends in the radiological characteristics of the water source, required to ensure adequate water management of the water quality for other uses such as crop irrigation and freshwater fish farming.
The above-mentioned ISO standards and NWIP rely on the trust built up between the two international organizations and experts representing monitoring laboratories in 23 countries. In the latest (2011) edition of the WHO guidelines, they are listed as references for the measurement of radionuclides in water in chapter 9 on radiological aspects.