Police in the Netherlands have detained two men suspected of being involved in the illegal use of a pesticide in the poultry industry. Millions of fipronil-contaminated eggs have been recalled since the scandal broke.

Dutch prosecutors said in a statement on Thursday that the men are directors of a company that allegedly used an unauthorized insecticide at poultry farms.

Investigators in the Netherlands and Belgium made the arrests during a string of coordinated raids linked to their probe into how fipronil, which can be harmful to humans, made it into the food chain.

“The Dutch investigation focused on the Dutch company that allegedly used fipronil, a Belgian supplier as well as a Dutch company that colluded with the Belgian supplier,” the prosecutors said.

“They are suspected of putting public health in danger by supplying and using fipronil in pens containing egg-laying chickens.”

Authorities in the Netherlands, Belgium and Germany recalled millions of eggs at the start of the month after the discovery of fipronil in batches delivered to supermarkets. Dozens of poultry farms, mainly in the Netherlands but also in Belgium, have been closed down, while supermarkets have cleared tainted eggs from their shelves.

The French agriculture ministry confirmed on Friday that 250,000 contaminated eggs had been “on the market” in France between April and July. Five companies using egg products were been involved. A first batch of 196,000 eggs from Belgium had been placed on the market between April 16 and May 2 and a second lot from the Netherlands of 48,000 eggs had been sold through Leader Price shops between July 19 and 28.

The insecticide is a common ingredient in anti-lice treatments, but it is banned from being used on animals destined for human consumption. Fipronil can be hazardous to humans’ kidneys, liver and thyroid glands, according to the World Health Organization, but only if consumed in large quantities.