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Planning Your Drinking Water Residue Testing
Get Ahead of Upcoming Regulatory Requirements
Drinking water residues and water treatment transformation products (tTPs) are the focus of recent EFSA and ECHA guidance, set to be a requirement starting April 1, 2026. Drinking water residues can be formed when active substances and their metabolites, referred to as environmental transformation products (eTPs), undergo reactions during the water treatment process. This may lead to the formation of tTPs that can cause harm to human and animal health through the consumption of drinking water.
Although the process that results in these tTPs is understood, the water treatment studies to assess possible tTPs can be more complicated to grasp.
Watch this presentation on drinking water residues and the testing needed to assess them.
Determining Which Products Meet Testing Criteria
If the predicted environmental concentrations for the active substance, eTPs or substances of concern in surface and/or groundwater exceed a threshold, typically 0.1 µg/L, a more in-depth investigation is needed into the potential formation of harmful tTPs during drinking water treatment.
Some chemical and biocide companies may be able to assess the possibility of tTPs in-house. However, Charles River’s regulatory affairs team is also available to help manufacturers with guidance on whether further assessments are needed.
Steps to Take When Further Assessment is Needed
If you need to further assess possible water treatment transformation products, an initial multi-step assessment is needed. This would combine literature search, predictive modeling and experimental approaches. Publicly available information and QSAR predictions will be used as input for the analyses conducted in the TP formation experiments.
The experimental work is essential to clarify tTPs formation at high and environmentally relevant concentrations. The most effective analytical method is then used to identify the tTPs detected at levels exceeding 0.075 µg/L in the environmental experiments. These experiments simulate water treatment disinfection processes like:
- Chlorination with NaOCl
- Chloramination with NH2CI
- Oxidation with CIO2
- Combined processes (pre-oxidation with CIO2 followed by chlorination or chloramination)
- Ozonation
- UV
- Biodegradation during sand filtration
The identified tTPs that exceed 0.075 µg/L are then subject to drinking water hazard and risk assessment.
Hazard and Risk Assessment
To assess the hazard and risk of tTPs, a tiered approach is proposed consisting of genotoxicity screening (Tier 1) followed by a general toxicity assessment (Tier 2). If the tTPs need additional assessment, a targeted toxicity assessment for specific endpoints is conducted (Tier 3).
Depending on the level of existing information for a studied tTP, the toxicological assessment may involve the generation of further data from in silico, in vitro, or in vivo testing to complete the hazard assessment and to ideally set a specific oral health-based guidance value (HBGV) or Margin of Exposure (MoE).
Test for Drinking Water Residues with Confidence
Charles River is committed to helping you maintain your presence on the plant protection product or biocide market. Investment in the best quality equipment for water treatment studies ensures we can provide high quality testing and data to ensure your products meet ECHA and EFSA guidelines. For example, the use of the defined ozone dosage method; as well as investment in an Opsytech® Collimated Beam Device, to allow for reproducible ozone and UV dose rates.
A high-quality data set, with demonstrated reproducibility, limits the risk of repeated studies. It is widely acknowledged that the analytics of water treatment studies could result in complex data sets that require the most advanced equipment and software to identify and quantify water treatment transformation products. At Charles River, we have invested in mass spectrometers, such as Sciex 7500+ triple quadrupole, Thermo Scientific™ Orbitrap Fusion™ Lumos™, and Tandem Supercritical Fluid MS to achieve this.
Our scientific expertise has made us a trusted partner for our clients with plant protection products and biocides. Our team have up to 20 years of mass spectrometry experience, enabling us to deliver the insights and solutions tailored to your needs. We are dedicated to the success of your water treatment studies, helping you plan, budget, and execute your testing strategy, ensuring optimal efficiency to meet the April 2026 deadline. Find out how we can support you in planning and executing the most efficient testing program.