Research in the Netherlands confirms that worms are the main culprit

Today the Dutch health authorities confirmed what we suspected based on our analysis: PFAS accumulated in Earthworms are the main cause of high PFAS levels in eggs. This means that our approach of holding our chickens in a raised coop seems right on target. 

Read the news release | download the report 

Key conclusions (generated with Claude AI):

Earthworms are the primary culprit. The evidence pointing to earthworms is compelling and multi-layered:

  • Earthworms contained very high PFAS concentrations — summed levels ranging from 5.1 to 264 ng/gram, consistently 2 to 24 times higher than in the eggs from the same locations.
  • The types (profiles) of PFAS found in earthworms closely mirrored those found in eggs at every location.
  • Strong statistical correlations were found between PFAS in earthworms and eggs (Spearman's rho 0.50–0.90 across all locations; statistically significant for PFOA, PFHxS, PFOS, PFHpS, and PFDS).
  • The questionnaire confirmed: hens kept indoors and those with no access to earthworms had significantly lower PFAS levels in their eggs.
  • Hens with larger areas of unpaved ground to roam on had higher PFAS levels — consistent with greater earthworm consumption.

The chain of contamination is: PFAS in the soil → absorbed by earthworms → eaten by hens → PFAS end up in eggs.

Insects may also play a role — a single pooled insect sample showed high PFAS levels — but one sample is insufficient to draw firm conclusions.

Other sources are minor contributors:

  • Soil (direct): PFAS concentrations in soil were 1.5–11 times lower than in eggs at most locations, and the correlation with egg levels was weaker than for earthworms. Soil is likely an indirect source (through earthworms) rather than a direct one.
  • Water: Where detected at all (4 out of 10 locations), PFAS levels in water were 242 to 10,000 times lower than in eggs. Water is not a meaningful source.
  • Bedding and coop materials (wood chips, straw, sawdust, varnished wood): Only trace PFAS were found at a small number of locations, far too low to explain egg contamination levels.
  • Feed: No PFAS was found in commercial chicken feed (consistent with a prior Arcadis study), and the questionnaire showed no correlation between feed type and egg PFAS levels.
  • PFAS precursors: Barely detected in soil, water, or coop materials; minimally present in earthworms. Not a significant pathway.
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