Research and analysis

Behaviour of radionuclides in wastewater systems: a laboratory study: summary

Published 31 July 2026

Applies to England

1. Chief Scientist’s Group report summary

This project examined how medical radionuclides separate themselves (partition) between different parts of the wastewater environment through laboratory experiments. It assessed the behaviour of lutetium-177 (177Lu) and iodine-131 (131I) during transfer to sewer pipes, concrete tanks, and river sediment from wastewater after a hospital discharge of radioactive waste to sewers.

The findings will help the Environment Agency to better understand the radiological impacts of medical waste discharges on people and the environment and to aid the regulation of the sectors that use medical radionuclides. This includes hospitals, universities, and other research institutions.

1.1 Background

Radionuclides that are used in medical procedures are ultimately discharged as liquid waste to sewers. The Environment Agency initially assesses the radiological impacts of these waste discharges on people and wildlife using a modelling tool that predicts the fate and transport of radionuclides in wastewater environments. However, information is lacking or outdated on the partitioning behaviour of 177Lu and 131I between solid and liquid phases in wastewater systems. Greater knowledge of the behaviour of these medical radionuclides in wastewater environments would strengthen the Environment Agency’s radiological assessments.

1.2 Approach

Laboratory rigs were established that simulated wastewater systems under controlled conditions. Wastewater, sewer pipe, concrete tank materials, and river sediment were sourced in or around one UK wastewater treatment works. Non-radioactive forms of Lu and I were added to the wastewater and their partitioning to the solids was determined by measuring their decreasing solution concentrations over time. The project evaluated the behaviour of Lu and I at three different stages of the wastewater collection and treatment process:

• partitioning to polyvinyl chloride (PVC) pipes that transport wastewater through a sewer network.
• partitioning to concrete tanks that store wastewater in a wastewater treatment works.
• partitioning to sediment in a river that receives treated effluent from a wastewater treatment works.

The project assessed the partitioning behaviour of organic and inorganic Lu and I compounds in each case.

1.3 Results

The experimental results show that, under the specific conditions of the study, Lu partitions to river sediment but not to PVC or concrete. Here, partitioning took 2 weeks, and the first step was the transfer of Lu from the dissolved phase to the particulate phase in the wastewater. A similar chemical conversion was seen in all laboratory rigs and means that Lu binds to particulate materials in the wastewater. Lutetium partitioning behaviour was consistent between different chemical compounds containing Lu, which may be explained by the rapid dissociation of Lu compounds in wastewater systems. The organic and inorganic forms of I appeared to have different partitioning properties under laboratory conditions. However, all solids leached I into the wastewater, introducing uncertainties into these results. All laboratory rigs used stagnant wastewater whereas liquid can rapidly flow in real world sewers and rivers. This means that radionuclides may have a different amount of contact with solid surfaces in actual wastewater systems, likely affecting partitioning processes.

1.4 Conclusions

The project investigated the partitioning of medical radionuclides in wastewater systems. It found that the contact time with solid materials and the radionuclide chemical form affect the behaviour of 177Lu and 131I, respectively. This is important for both the Environment Agency and those we regulate (such as hospitals) who  assess the radiological impacts of medical waste discharges on people and the environment.

1.5 Publication details

This summary relates to information from project SC250007, reported in detail in the following output:

• Report: SC250007
• Title: Behaviour of radionuclides in wastewater systems: a laboratory study
• Science manager: Adam Lang, Environment and Human Health Research, Chief Scientist’s Group
• Research contractor: McQuillan Environmental

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency