Leiden research that matters: how science is shaping European pesticide policy
Changemakers
Leiden ecotoxicologist Martina Vijver helped shake a European policy proposal in a single weekend. Not with a new experiment, but with years of research on pesticides – and an urgent letter that reached Brussels.
Vijver has been studying pesticides for years. Her key question: what happens when substances that seem safe in the lab end up in the real world? ‘In the lab, you can control many variables,’ Vijver says. ‘But real-life conditions are far more complex and not always predictable.’
Back in 2017, her research group published work highlighting the importance of a ‘safety lock’ in pesticide approval. New products are tested in the lab and assessed using models. That makes sense: if a substance is not yet on the market, you cannot measure its real-world impact.
Still, the researchers identified a risk. ‘The step from lab to field is bigger than often assumed. That is why we argued for a safety lock: continue monitoring and reassessing even after approval.’
‘That set off alarm bells for us’
Fast-tracking approval without reassessment: a bad idea
In November 2025, a proposal from the European Commission was leaked. Within a so-called omnibus package – a bundle of measures designed to speed up regulation – were changes to pesticide rules that could undermine safety.
Currently, with both European and national approval required, it takes five to ten years for pesticides to reach the market. The new plan proposed less administrative work and no mandatory reassessment after launch. ‘That set off alarm bells for us,’ Vijver explains. ‘Because we know how lab and field conditions can differ, and how difficult it is to predict long-term effects. We rarely foresee all the consequences of our actions; substances often have effects that only become visible years later.’
According to Vijver, this issue goes beyond pesticides alone. ‘With developments such as nanotechnology or mixtures of pesticides with PFAS, we are using small amounts of highly reactive substances. A lower dose does not automatically mean lower risk.’ That is why reassessment remains essential, she says.
An urgent letter in one weekend
The proposal surfaced on a Friday. That same weekend, Vijver contacted fellow scientists and civil society organisations. Together, they drafted an urgent letter. By Monday, a text had been signed by six experts, including ecologist and former university leader Geert de Snoo and Parkinson’s researcher Bas Bloem, with support from organisations such as Natuur & Milieu, FNV and Parkinson Alliantie Nederland.
Through Members of Parliament Anne-Marijke Podt and Laura Bromet, the letter was submitted as a parliamentary motion. On the final meeting day before Christmas, the motion was adopted. The Netherlands will vote against the proposed relaxation in Brussels in early 2026.
But the work did not stop there. Pressure also needed to be applied in Brussels. Within four days, Vijver and her colleagues gathered 200 signatures from scientists across Europe. The letter was sent to Commission President Ursula von der Leyen and to Members of the European Parliament. At the end of February, Vijver was also invited to speak with MEPs. Now, they await the vote – and whether the Netherlands will indeed oppose the changes.
‘As a scientist, you also have a responsibility to society. This is how my work can truly make a difference.’
The downside of science in the public arena
The network Vijver drew on for these efforts was built over many years through lectures, collaboration and public engagement. ‘We know each other and know who to involve in moments like this.’
But public visibility also has its drawbacks. It is demanding, takes place alongside her regular work, and can become personal. In a professional journal, she was labelled a ‘scientivist’. ‘I wear that title with pride. As a scientist, you also have a responsibility to society. I am concerned about our planet and how we leave it for the next generation. This is how my work can truly make a difference.’