Overview
ISO 4722-1:2023 - Water quality - Thorium 232 - Part 1: Test method using alpha spectrometry - specifies a laboratory method for determining the activity concentration of 232Th in environmental water (including sea water) and waste water prior to discharge. The method uses alpha spectrometry with 229Th as a recovery tracer and a chemical separation step to isolate and purify thorium from test portions. The standard also notes that the same principles can be applied to other alpha-emitting thorium isotopes (for example, 228Th and 230Th).
Key facts:
- Detection capability: for ~500 ml test portions, the detection limit is approximately 5 mBq·L⁻¹ with a counting time of about 200 000 s (adjustable for different operational needs).
- Emphasises proper sampling, handling and storage, chemical reagents and equipment, and rigorous quality control.
Key Topics and Technical Requirements
- Principle: addition of 229Th tracer, equilibration, chemical concentration/separation and alpha spectrometric measurement.
- Chemical separation and source preparation: methods to separate and purify thorium prior to electrodeposition or coprecipitation for counting (informative annexes provide guidance).
- Measurement and quality control:
- Chemical recovery assessment using the 229Th tracer.
- Background determination and counting efficiency.
- Spectrum analysis and calculation of activity concentration.
- Determination and reporting of standard uncertainty, decision threshold, detection limit, and coverage intervals.
- Sampling and sample volume: guidance for environmental and waste waters, with flexibility to modify volume/counting time to meet detection or regulatory limits.
- Reporting: content requirements for the test report, including results and associated uncertainties.
- Safety and competence: work should be performed by trained personnel following laboratory safety practices.
Practical Applications and Users
ISO 4722-1:2023 is intended for:
- Environmental and radiochemical laboratories performing routine monitoring of radioactivity in drinking water, surface water, groundwater and sea water.
- Regulatory agencies and water utilities assessing compliance with national or WHO guidance levels for thorium in drinking water and effluents.
- Nuclear industry, mining and waste management entities monitoring liquid discharges containing naturally occurring radioactive materials (NORM).
- Emergency response and research laboratories requiring reliable alpha-spectrometric determination of thorium isotopes.
Benefits:
- Provides a harmonized, traceable method for 232Th activity concentration measurement.
- Supports compliance assessment, public health protection and environmental monitoring programs.
Related Standards
Normative and informative references cited in ISO 4722-1:2023 include:
- ISO 5667 series (sampling and preservation of water samples)
- ISO 3696 (water for analytical laboratory use)
- ISO 11929-1 (characteristic limits for ionizing radiation measurements)
- ISO/IEC 17025 (laboratory competence)
- ISO 80000-10 (atomic and nuclear physics quantities and units)
For laboratories implementing ISO 4722-1:2023, refer to these related standards to ensure sampling quality, measurement uncertainty handling, and laboratory accreditation compliance.
