The high concentration of PFAS chemicals in the eggs of hens kept as a hobby is down to their earthworm diet, according to research by public health institute RIVM.

Initial research published by engineering group Arcadis in 2024 said that worms were probably to blame. The researchers were looking for potential sources of PFAS, forever chemicals which have been linked to cancer, close to the Chemours factory in Dordrecht.

The RIVM extended the research project nationwide and now says it has confirmed that worms are an “important source” of PFAS in eggs. The institute did not research the source of the PFAS which the worms had consumed.

The RIVM is also investigating how much PFAS people in the Netherlands currently ingest as well as where it comes from. The aim is to identify which measures could help reduce exposure to PFAS.

The RIVM said its recommendation that people don’t eat the eggs of hens which roam outside and eat worms remains in place.

Court case

Last month, judges in The Hague ruled that the Dutch state is acting within the law in its work on preventing the spread of PFAS. Five environment and clean water campaign groups had said they were holding the state responsible for the spread of PFAS pollution and its impact on health.

The groups want the the state to stop issuing PFAS discharge licences, map existing pollution and begin clean-up operations. They argue the government had failed in its duty of care and asked the court to recognise the fundamental right to a healthy living environment.

There is currently no complete overview of where PFAS pollution exists in the Netherlands and dozens of companies have refused to cooperate with research projects.

Research by the Financieele Dagblad and Investico last year suggested that cleaning up PFAS pollution in the Netherlands is set to cost billions of euros, given the “forever chemicals” could be present in up to 1,000 locations.