Background
The Environment Agency (EA) is the principal regulator responsible for monitoring and assessing chemical contaminants in surface waters and groundwater in England. Its approach has historically been guided by the European Union Water Framework Directive (WFD), which established a harmonised framework for monitoring the status of aquatic ecosystems across the European Union. Although the UK has left the EU, the core principles and monitoring structures derived from the WFD remain largely in place, with adjustments occurring through domestic legislation such as the Environment Act 2021 and oversight by the Office for Environmental Protection (OEP).
The EA organises its chemical monitoring programmes into three main categories:
Surveillance monitoring aims to provide long-term trend data and a comprehensive picture of chemical status across water bodies. It typically involves fixed sites sampled on a regular schedule to detect spatial and temporal trends.
Operational (compliance) monitoring targets specific sites where there is a risk of failing to meet environmental objectives. It focuses on assessing compliance with EQS and the effectiveness of management measures.
Investigative monitoring is undertaken in response to pollution incidents, suspected sources of contamination, or unexpected monitoring results. It helps to diagnose causes of non-compliance and inform remedial actions.
Sampling typically relies on grab samples collected at fixed intervals, but may also include automated composite samplers to capture temporal variability. Analytical work is conducted in UKAS-accredited laboratories, typically using liquid or gas chromatography-tandem mass spectrometry for organic contaminants and inductively coupled plasma mass spectrometry for metals. Monitoring strategies also follow strict quality assurance and quality control protocols, including defined limits of detection (LOD) and quantification (LOQ) and chain-of-custody procedures.
A central component of the EA’s approach to classifying chemical status of water bodies has been the use of Environmental Quality Standards (EQS) for specific substances, including priority substances identified under the WFD. EQS-values represent concentration thresholds for chemicals designed to protect aquatic life. Chemical monitoring data are compared against these EQS-values to assess whether water bodies achieve “good chemical status” as defined in River Basin Management Plans (RBMPs). These RBMPs are updated on a six-year cycle and set out objectives, monitoring strategies, and measures for each river basin district.
Chemical status assessments in England continue to rely on comparing measured concentrations of priority substances against their Environmental Quality Standards (EQS), but the method used to determine overall status changed significantly in 2019. Under the WFD framework, a water body only achieves “good chemical status” if concentrations of all assessed substances meet their EQS—failure for a single substance leads to overall failure (“one out, all out”). In the 2019 classification, the Environment Agency incorporated several ubiquitous, persistent, bioaccumulative and toxic substances—notably mercury and certain PBDEs—using biota standards and a presence-based approach, rather than site-specific water measurements. Because these substances are present above EQS across the country due to long-range atmospheric deposition and historical contamination, all surface water bodies were classified as failing chemical status by default. EQS comparisons for other priority substances are still carried out and reported, but the inclusion of these ubiquitous pollutants now dominates the headline chemical status results, masking local variation and improvements.
In recent years, the EA has explored innovative approaches to supplement traditional monitoring, including citizen science partnerships and non-target analytical techniques. These are seen as complementary tools to improve spatial coverage and detect emerging contaminants. Overall, the EA’s approach reflects a structured and standards-driven monitoring system, balancing statutory obligations with evolving environmental challenges.
Recorded Lecture
John Wilkinson, who is an analytical chemist at the University of York gives an overview of the approaches for regulatory monitoring of chemicals in England.
Key Reading
Hering D, et al. (2010) The European Water Framework Directive at the age of 10: a critical review of the achievements with recommendations for the future. Sci Total Environ. 408(19):4007-19. https://doi.org/10.1016/j.scitotenv.2010.05.031
JNCC (2024) Surface water status
Office for Environmental Protection (2024) A review of implementation of the Water Framework Directive Regulations and River Basin Management Planning in England
Rivers Trust (2025) WFD River, Canal and SWT Waterbody Classifications (2019)