Introduction

Radioactivity from several naturally-occurring and anthropogenic sources is present throughout the environment. Thus, water bodies (e.g. surface waters, ground waters, sea waters) can contain radionuclides of natural, human-made or both origins:

— natural radionuclides, including ⁴⁰K, ³H, ¹⁴C, and those originating from the thorium and uranium decay series, in particular ²²⁶Ra, ²²⁸Ra, ²³⁴U, ²³⁸U, ²¹⁰Po and ²¹⁰Pb can be found in water for natural reasons (e.g. desorption from the soil and washoff by rain water) or can be released from technological processes involving naturally occurring radioactive materials (e.g. the mining and processing of mineral sands or phosphate fertilizers production and use);
— human-made radionuclides such as transuranium elements (americium, plutonium, neptunium, curium), ³H, ¹⁴C, ⁹⁰Sr, and gamma emitting radionuclides can also be found in natural waters. Small quantities of these radionuclides are discharged from nuclear fuel cycle facilities into the environment as a result of authorized routine releases. Some of these radionuclides used for medical and industrial applications are also released into the environment after use. Anthropogenic radionuclides are also found in waters as a result of past fallout contaminations resulting from the explosion in the atmosphere of nuclear devices and accidents such as those that occurred in Chernobyl and Fukushima.

Radionuclide activity concentration in water bodies can vary according to local geological characteristics and climatic conditions and can be locally and temporally enhanced by releases from nuclear installation during planned, existing and emergency exposure situations^[¹^]. Drinking-water can thus contain radionuclides at activity concentrations which can present a risk to human health.

The radionuclides present in liquid effluents are usually controlled before being discharged into the environment^[²^] and water bodies. Drinking waters are monitored for their radioactivity as recommended by the World Health Organization (WHO)^[³^] so that proper actions can be taken to ensure that there is no adverse health effect to the public. Following these international recommendations, national regulations usually specify radionuclide authorized concentration limits for liquid effluent discharged to the environment and radionuclide guidance levels for waterbodies and drinking waters for planned, existing, and emergency exposure situations. Compliance with these limits can be assessed using measurement results with their associated uncertainties as specified by ISO/IEC Guide 98‑3^[⁴^] and ISO 5667‑20^[⁵^].

Depending on the exposure situation, there are different limits and guideline levels (GLs) that would result in an action to reduce health risk. As an example, during a planned or existing situation, the WHO GL for drinking water is 1 000 Bq·l⁻¹ for Ni activity concentration.

NOTE 1 The GL is the activity concentration with an intake of 2 l·d⁻¹ of drinking water for one year that results in an effective dose of 0,1 mSv·a⁻¹ for members of the public. This is an effective dose that represents a very low level of risk and which is not expected to give rise to any detectable adverse health effects^[³^]_.

In the event of a nuclear emergency, the WHO Codex GLs^[⁶^] mentioned that the activity concentration might not be greater than 10 000 Bq·l⁻¹ for Ni.

NOTE 2 The Codex GLs apply to radionuclides contained in foods destined for human consumption and traded internationally, which have been contaminated following a nuclear or radiological emergency. These GLs apply to food after reconstitution or as prepared for consumption, i.e. not to dried or concentrated foods, and are based on an intervention exemption level of 1 mSv in a year for members of the public (infant and adult)^[⁶^].

Thus, the test method can be adapted so that the characteristic limits, decision threshold, detection limit and uncertainties ensure that the radionuclide activity concentrations test results can be verified to be below the guidance levels required by a national authority for either planned/existing situations or for an emergency situation^[⁷^],[⁸^].

Usually, the test methods can be adjusted to measure the activity concentration of the radionuclide(s) in either wastewaters before storage or in liquid effluents before being discharged to the environment. The test results will enable the plant/installation operator to verify that, before their discharge, wastewaters/liquid effluent radioactive activity concentrations do not exceed authorized limits.

The test method(s) described in this document can be used during planned, existing and emergency exposure situations as well as for wastewaters and liquid effluents with specific modifications that can increase the overall uncertainty, detection limit and threshold.

The test method(s) can be used for water samples after proper sampling, sample handling and test sample preparation (see the relevant part of ISO 5667 series).

This document has been developed to support the need of test laboratories carrying out these measurements, that are sometimes required by national authorities, as they can need to obtain a specific accreditation for radionuclide measurement in drinking water samples.

This document is one of a set of International Standards on test methods dealing with the measurement of the activity concentration of radionuclides in water samples.

BS ISO 23655-1:2022

Water quality. Nickel-59 and nickel-63 - Test method using liquid scintillation counting

Current

Published:

30 Sep 2022