New EFSA-ECHA guidance on water treatment residues to impact biocides applications from April 1, 2026

April 8, 2025 

The new guidance from EFSA-ECHA represents a significant addition to the risk assessment requirements involving environmental exposure calculations for drinking water abstraction sites. It also includes testing for the formation of transformation products during water treatment and subsequent human health hazard testing/assessment for these substances. As the implementation date is the same for both active substance and product applications, in many cases, the biocidal product application stage will represent the first time the active substance(s) involved will be evaluated against the guidance. This adds further uncertainty to the registrability of the products.

When are assessments triggered under the new EFSA-ECHA guidance for biocidal product applications?

As per the first stage of the guidance, understanding the environmental exposure is key because it prompts subsequent testing for formation of water treatment transformation products and human health hazard assessment. This assessment is triggered for all products where active substances or metabolites are predicted to be present in groundwater or at drinking water abstraction points above 0.1 µg/L. This testing will be costly and complex to conduct. 

How can we ensure compliance with the EFSA-ECHA guidance for biocidal product applications?

Applicants and approval/authorisation holders are encouraged to review environmental exposure assessments as early as possible to determine the scale of further work that may be needed. This should include:

• A review of the exposure assessment for active substances, environmental metabolites and substances of concern to determine where concentrations exceed 0.1 µg/L in groundwater or at drinking water abstraction points
• An assessment of whether any refinements to the environmental exposure assessment can be supported to refine these concentrations
• An assessment of whether risk mitigation measures can be applied to refine these concentrations
• Determining which substances trigger assessment and planning the assessment according to the guidance, including any testing on formation of transformation products during water treatment and subsequent human health hazard testing  

How TSG can help

With extensive experience in environmental risk assessments of biocidal products, TSG is your trusted partner in navigating this new guidance. Our team is ready to assist you with environmental risk assessments, additional data generation, and any training or support your company requires. If you would like to learn more about how we can support you, contact TSG at [email protected], or reach out to your TSG consultant directly.