02. June 2026, Topic: Aquatic Ecotoxicology Risk Assessment

Inconsistent risk assessment of chemicals compromises water protection in Europe

A new study highlights significant room for improvement in European chemicals regulation. The environmental risk assessment for a single substance can vary considerably depending on the regulatory context. This has direct implications for water protection.

In the EU – and also in Switzerland – chemicals are subject to different legal frameworks depending on their intended use. However, the same chemical may be suitable for various purposes: for example, an insecticide may be used as a plant protection product to protect crops, as a biocide to protect textiles, or as a veterinary medicine to protect pets or farm animals, and may also be used in an industrial context.

This means that individual substances are regulated under different sets of regulations, which can lead to differences in assessment. As part of the EU PARC project, the Ecotox Centre, together with partners from authorities in Switzerland, Germany and France, has investigated the causes of such differences in more detail. The two insecticides deltamethrin and imidacloprid served as case studies. The study compares the environmental risk assessment of the substances for water bodies across five key regulatory frameworks: REACH for industrial chemicals, PPPR for plant protection products, BPR for biocides, VMPR for veterinary medicines, and the Water Framework Directive for the assessment of water bodies.

Case study: Deltamethrin – Extreme differences in limit values

For the insecticide deltamethrin, the derived threshold value for aquatic organisms varied by more than three orders of magnitude across the regulatory frameworks – from very low concentrations of 1.7 pg/L in the Water Framework Directive to 3200 pg/L under the PPPR. These differences directly influence the risk assessment: depending on the regulatory framework, this results in either non-critical levels of water pollution or massive exceedances of threshold values, indicating a significant risk to aquatic organisms. For imidacloprid, the threshold values in the various regulations ranged between 4.8 and 9 ng/L, i.e. very close to one another.

Different data sets, methods and protection objectives

Several factors were responsible for the inconsistent assessment: The data sets differ, as not all available studies are taken into account in all procedures or are sometimes difficult to access. Regulatory studies are not automatically shared between the competent authorities, and only data officially submitted during the authorisation process are considered in the procedure. The assessment methods used in the procedures are not comparable: different models, assumptions and safety factors lead to differing results. Furthermore, the protection objectives differ, which is why different risk levels are considered acceptable.

Another problem is that new scientific findings are only incorporated into regulatory decisions after a delay. One example is deltamethrin: despite indications of risks to aquatic organisms, its authorisation has been extended several times – the last authorisation was granted more than 20 years ago.

Harmonised assessment as a solution

Under the slogan “One Substance – One Assessment”, the European Commission has proposed a uniform assessment of chemicals across all regulatory frameworks. The authors of the study support the creation of a shared database that makes all available studies accessible across the various regulatory frameworks and recommend, among other things, greater harmonisation of assessment procedures, better integration of monitoring data, and automated mechanisms to update risk assessments in the light of new scientific findings. “There needs to be more cooperation between authorities on the authorisation and assessment of chemicals,” says Alexandra Kroll. “This is the only way to identify risks to water bodies and biodiversity at an early stage and limit them effectively.”

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