A chemical monitoring wastewater programme led by UK Water Industry Research (UKWIR) has identified declining concentrations of several hazardous chemicals in wastewater systems across England and Wales.
The Chemical Investigations Programme (CIP) represents one of the most comprehensive industry-wide monitoring initiatives examining substances entering rivers and seas via wastewater systems.
Research linked to the UK water industry’s Chemical Investigations Programme examining hazardous chemicals in wastewater.
Analysis of monitoring data collected between 2020 and 2025 shows downward trends in concentrations for 19 of the 20 substances investigated.
The programme is a collaboration between water companies and regulators including the Environment Agency, Defra and Natural Resources Wales.
Monitoring programme highlights impact of chemical bans
The chemical monitoring wastewater programme indicates that regulatory bans and product phase-outs can significantly reduce environmental contamination over time.
One example is tributyltin (TBT), previously used in antifouling coatings on ship hulls. Following an international ban introduced in 2008, environmental concentrations have fallen significantly.
Monitoring data also shows reductions in perfluorooctane sulfonate (PFOS), part of the per- and polyfluoroalkyl substances (PFAS) family of persistent chemicals sometimes referred to as “forever chemicals”.
Although PFOS concentrations are declining, the compound remains detectable in some rivers due to its persistence and the continued release of residues from historic sources such as landfill sites.
Source control versus treatment upgrades
Researchers involved in the programme say the findings reinforce the importance of preventing chemicals entering wastewater systems in the first place.
Jenni Hughes, strategic programme manager at UKWIR, said monitoring data demonstrates the value of source control measures.
“The water industry isn’t the source of these chemicals, and our data shows that when there is rigorous source control, the environment heals without the need for carbon-heavy, expensive interventions from utilities.”
Long-term monitoring also helps utilities identify priority catchments where targeted interventions may be required.
Mark Craig, Severn Trent Water’s long-term asset strategy lead and UKWIR co-lead for wastewater, said monitoring provides valuable insight into environmental trends.
“With this trend monitoring, we have the power to show what is actually happening in our environment.”
Next phase to examine emerging contaminants
While most substances monitored showed declining concentrations, dissolved mercury was identified as increasing in environmental monitoring data.
Mercury can enter the environment through natural geological processes as well as industrial sources including mining, fossil fuel combustion and waste incineration.
The Chemical Investigations Programme is now entering its fourth phase, running from 2025 to 2030.
Future research will examine emerging issues including antimicrobial resistance, microplastic degradation within wastewater treatment works and the behaviour of PFAS compounds in sludge.
