Overview
ISO 22515:2021 - Water quality - Iron-55 - Test method using liquid scintillation counting specifies a laboratory method for determining the activity concentration of iron-55 (55Fe) in all types of water using liquid scintillation counting (LSC). The standard defines measurement ranges achievable with current LSC technology (up to 120 mBq·L‑1 for typical counting regimes), recommended sample volumes (0.5–1.5 L) and counting times (7 200–10 800 s). It also explains how to measure higher activities by diluting samples or using smaller aliquots and highlights that detection performance depends on laboratory equipment, background, and the amount of stable iron present.
Key topics and technical requirements
- Principle: Chemical isolation of iron followed by LSC measurement to determine 55Fe activity concentration.
- Measurement range & sensitivity: Typical measurable range from the method detection limit up to ~120 mBq·L‑1 under the stated sample and counting conditions; higher activities require dilution or smaller aliquots.
- Reagents & equipment: Lists of standard solutions, holdback carriers, acid/base reagents, scintillation vials and liquid scintillation counters; specific separation reagents for iron purification are provided.
- Sampling & sample preparation: Requirements for representative water sampling and pre-treatment in line with relevant ISO sampling guidance.
- LSC set-up & calibration: Region setting, background determination, calibration procedures and detection efficiency determination for 55Fe.
- Quality control & reporting: Procedures for recovery checks, blank controls, uncertainties, decision threshold and detection limit calculations, and format of the test report.
- Dependence on laboratory conditions: Performance indicators (detection limits, efficiencies) are laboratory-specific and influenced by dissolved material and stable iron content.
Applications and users
ISO 22515:2021 is intended for:
- Environmental and water quality laboratories monitoring radionuclides in surface, ground and seawater.
- Regulatory agencies and drinking-water authorities verifying compliance with guidance limits (e.g., WHO guidance levels referenced in the standard).
- Nuclear facilities and wastewater treatment operators monitoring liquid effluents and routine discharges.
- Emergency response and radiological assessment teams needing validated methods for 55Fe in water.
- Research laboratories studying radionuclide behaviour and transport in aquatic systems.
Practical benefits include standardized procedures for reproducible 55Fe measurement, guidance to optimize detection limits, and a framework for reporting results with associated uncertainties.
Related standards and guidance
- ISO 5667 series (water sampling guidance)
- ISO/IEC Guide 98-3 (GUM - uncertainty estimation)
- ISO 5667-20 (sampling of waters - radiochemical analytes)
- World Health Organization (WHO) guidance levels for radionuclides in drinking water
Keywords: ISO 22515:2021, iron-55, 55Fe, liquid scintillation counting, LSC, water quality, radionuclide monitoring, detection limit, activity concentration.