Endocrine disruptor classification under EU CLP

The EU Classification, Labelling and Packaging (CLP) Regulation requirements around specific hazard classes for EDs now apply to substances already on the EU market, not just new ones. So, companies need to ensure that existing classification decisions remain valid and are supported by robust scientific evidence.

Whether preparing a dossier for a new substance or reviewing an existing substance’s classification, careful interpretation of endocrine activity, adverse effects and mode of action (MoA) is critical.

Importantly, an apparent endocrine signal doesn’t necessarily mean ED classification is required.

A phased strategy for ED testing helps determine what the available evidence already shows, where gaps remain and whether additional studies are likely to resolve them. Getting this right can help avoid unnecessary testing and support proportionate classification decisions.

For some substances, particularly reactive chemicals such as strong oxidisers or those affecting multiple biochemical pathways, apparent endocrine effects may be difficult to distinguish from expected toxicological behaviour. In such cases, immediately moving to further testing may not provide meaningful new information.

That’s why ED assessment should be a staged process, starting with the existing evidence base and the specific concern that needs to be resolved. It may be useful to consider existing toxicological data, known chemical behaviour, read-across and mechanistic evidence before deciding whether further testing is necessary.

Where existing evidence is sufficient to address the regulatory concern, it may be possible to support a scientifically justified waiver from further testing under EU BPR or REACH.

In cases where new evidence is required, the way studies are selected and designed is key. The aim is to address specific uncertainties in the evidence base rather than simply to generate more data.

There are two critical questions at play here: does the available evidence support an ED classification, and is further testing needed to resolve any remaining uncertainty?

What determines endocrine disruptor classification?

Under EU CLP, ED classification depends on evidence of endocrine activity, an adverse effect, and a biologically plausible link between the two.

Substances may be classified Category 1 (known or presumed EDs) or Category 2 (suspected EDs), depending on the strength of the evidence. Where the evidence does not support either category, ED classification is not required.

Often, the most difficult aspect of this is determining whether an observed adverse effect is endocrine mediated. This is where MoA analysis becomes important.

Regulatory teams need to consider the strength and consistency of evidence across the full data package, rather than relying too heavily on individual findings. A single positive or equivocal finding should not be treated as conclusive if it is inconsistent with the wider toxicological profile.

Expert judgement is needed to determine what the overall evidence suggests and whether the case supports Category 1, Category 2 or no ED classification.

When is further endocrine disruptor testing needed?

If the available evidence does not provide sufficient clarity, additional studies may be needed. This could involve targeted in vitro or in vivo testing, or higher-tier studies, depending on the existing data and the nature of the concern. Studies should be proportionate and directly relevant to the specific question that needs to be resolved.

Where a study is unlikely to provide meaningful new information, is technically inappropriate, or the uncertainty can be addressed through existing evidence, it may be possible to support a scientifically justified waiver instead. In these cases, it’s important to clearly demonstrate why further testing is not needed, based on the full weight of evidence.

From ED classification to testing strategy

ED classification can be challenging, particularly where evidence is equivocal or several MoAs are plausible. With new CLP requirements now in effect, companies need to ensure their conclusions are scientifically defensible. Where uncertainties remain, the priority is to establish whether further testing is necessary and, if so, how studies should be selected, managed and interpreted.

Experts at Sagentia Regulatory have experience preparing scientific rebuttals to requests for ED studies, challenging inappropriate testing requirements, developing waiver justifications and carrying out mechanistic analyses to determine whether observed effects support an ED conclusion.

This is the first in a series of insights on endocrine disruptor assessment under EU regulations. Future articles will look at when ED study waivers may be justified under EU BPR and REACH, and how careful study selection, monitoring and interpretation can reduce the risk of ambiguous or misleading findings when further testing is required.