Addressing the 9-years Gap: The Long-Awaited Proposal on Safeners and Synergists

Addressing the 9-years Gap: The Long-Awaited Proposal on Safeners and Synergists

Safener, for who? Synergist, with what? Overlooked yet important for public health and especially for the environment, a proposal from the European Commission (EC) could be voted on by European Member States by the end of January. The focal point? Finally implementing, with a staggering 9 years delay, the provisions of the EU Pesticide law relating to the safety check of safeners and synergists. So far these potentially harmful pesticide ingredients fly below the radar and of course we welcome the proposal. However, we have identified limitations in the draft Regulation that need to be fixed to ensure compliance with the EU Pesticides Law. In this blog post, we break down the basics of safeners, synergists, and delve into the strengths and the flaws of the European Commission's proposal.

What are safeners and synergists ?

Pesticide products are composed of different ingredients. The active substance is declared as acting against the targeted 'harmful' organism (ie: glyphosate against weeds). Safeners and synergists are part of the ingredients that can be contained in, mixed together or applied before  pesticide products (formulations) to enhance their efficiency. They can be a single substance or a mixture of several components. Although they are always mentioned jointly in the EU Pesticides Regulation, safeners and synergists serve a different function.


A safener is a substance added to pesticide formulations to eliminate or reduce the harmful effects of the pesticide active substance on specific crops. These safeners are often applied to seeds or used in combination with herbicides. Their main function is to enhance the crops' ability to quickly break down herbicides through metabolic processes. This enhancement works by amplifying the biological pathways in the crops responsible for breaking down herbicides [1]. The goal is to speed up the degradation of herbicides within the crop, preventing them from reaching concentrations that could be damaging [2]. Safeners have primarily been developed for cereal crops such as maize, rice, and sorghum, particularly to protect against specific herbicides applied to crops before the plants emerge from the soil (pre-emergence herbicides).


Synergists are chemicals that in theory lack pesticidal properties on their own but which can increase the activity of the active substance(s) in a pesticide formulation. There is little information available on synergists, most of it refers to insecticide synergists [3]. A commonly used commercial insecticide synergist is piperonyl butoxide (PBO). PBO is  applied before using specific insecticides (e.g. pyrethroid or neonicotinoid insecticides). It works by inhibiting the insects’ ability to break down the insecticide molecules, thus making them hypersensitive to the insecticide [4]. Without this substance, insects would be more likely to degrade the insecticide before they die, and recover from the poisoning. Problem is, the use of synergists can affect other insects.

Evidently, safeners and synergists are not “inert” compounds. They can have unintended effects on living organisms and biological processes. For example, synergists could have harmful effects on honeybees, by inhibiting their defensive detoxifying enzymes and ability to resist the toxicity from insecticides [5]. Therefore, a thorough risk assessment of their potential toxicity to non-target species is absolutely critical! However, a significant deficiency exists, as this assessment so far has been very diverse among EU member states and therefore largely insufficient. 

The root of discrepancies in assessment across EU Member States

A harmonised EU risk assessment for safeners and synergists was never put in place. Shockingly, a Regulation addressing this issue should have been adopted by 14 December 2014, as stipulated by the EU Pesticides Regulation (Reg. (EC) 1107/2009, Article 26). However, the European Commission failed to come up with a proposal until just at the very end of last year. In the absence of such a Regulation, the national legislations have remained in place.

Practically, this means that to date EU Member States use different criteria and assessment methods to authorise safeners and synergists. Currently, there are 21 safeners and 13 synergists known to be used in pesticide products authorised in EU Member States [6]. There is no information regarding whether these substances have been properly assessed for their toxicity. This data gap is concerning, especially since we know that the complete formulations containing synergists and/or safeners are not thoroughly assessed for their potential impact on human health via long-term toxicity studies. As a result, the impact of these substances when used in formulations remains largely unknown.

Proposal for regulation 

However, this could change in the near future. In November 2023, with a 9-year delay, the European Commission published its draft Regulation. The aim of the text is to define the data requirements for the approval of safeners and synergists. It also establishes a work programme for  reviewing the authorisations of those already marketed or in use in EU Member States.

In a nutshell, the proposal foresees the establishment of a comprehensive and publicly available list of the safeners and synergists authorised in the European Union. This will serve as a basis for the establishment of a work programme, whose different steps and duration are detailed. The data requirements defined for the risk assessment of safeners and synergists align with those for active substances (Regulation (EU) No 283/2013). Studies from the scientific peer-reviewed open literature within the last 10 years are also requested. Additionally, specific supplementary data are also requested for the dossier to address the function and need of safeners and synergists in pesticide products.

PAN Europe’s expert analysis 

PAN Europe considers the draft Regulation to be satisfactory in terms of setting data requirements at the same high level as for active substances. Nevertheless, we have identified important limitations that need to be addressed to ensure compliance with the safety provisions of the EU Regulation on Pesticides.

These include:

  • An additional and very lengthy 6.5 years period to review the safeners and synergies currently on the market, 
  • The lack of setting protective Maximum Residue Levels for residues of these substances in food or specific limits for groundwater. 
  • Very importantly, omitting to explicitly state that safeners and synergists should have no harmful effects on human and animal health, and/or the environment and that the regulation is underpinned by the precautionary principle. 

PAN Europe voiced its concerns directly to the EC by participating in the open consultation on the proposal in December 2023. For a more detailed analysis of the proposal’s shortcomings, you can read our briefing linked at the end of the blog [7]. Given the substantial delay of this Regulation, it is welcome for the Commission to move forward. However, the proposal must be amended before it is voted on in order to provide for a high level of protection of human health and the environment. The EC's proposal is already up for discussion at the upcoming SCoPAFF meeting on January 30-31, with a potential vote by Member States. Nevertheless, the timeframe has evidently been too short for the Member States to thoroughly assess the input provided during the public consultation and incorporate it in the draft Regulation. At the moment, it remains uncertain whether the proposal has been modified to address the concerns raised by PAN Europe and other NGOs during the public consultation. 


  1. Duhoux, Arnaud et al. 2017. ‘Herbicide Safeners Decrease Sensitivity to Herbicides Inhibiting Acetolactate-Synthase and Likely Activate Non-Target-Site-Based Resistance Pathways in the Major Grass Weed Lolium sp. (Rye-Grass)’. doi:10.3389/fpls.2017.01310.  
  2. Rosinger, Christopher. 2014. ‘Herbicide Safeners: an overview’. Deutsche Arbeitsbesprechung über Fragen der Unkrautbiologie und - bekämpfung. doi:10.5073/jka.2014.443.066.
  3. National Pesticide Information Center (NPIC). 2020. ‘Synergists’. 
  4. Alptekin, S., Philippou, D., & Field, L. (2015). Insecticide synergists: Good or bad for honey bees? Outlooks on Pest Management, 26(2), 75–77. doi: 10.1564/v26_apr_07.
  5. bid 4.
  7. PAN Europe’s reaction to the EC’s proposal on safeners and synergists

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Pesticide Action Network Europe (PAN Europe) gratefully acknowledges the financial support from the European Union, European Commission, DG Environment, LIFE programme. Sole responsibility for this publication lies with the authors and the funders are not responsible for any use that may be made of the information contained herein.