United Kingdom food authorities said about 700,000 suspicious eggs had entered the country.
The WHO considers Fipronil to be moderately toxic, and says very large quantities can cause organ damage.
The eggs came from farms in the Netherlands and were used as one ingredient in processed foods, such as sandwich fillings.
Eggs contaminated by the insecticide were first found in the Netherlands and Belgium in early June, 2017. "Because the content is illegal, Danæg Products must withdraw the eggs from their customers".
Eggs with traces of the insecticide have been found in the Netherlands, where they are thought to have originated from.
He said: "At that time there was no indication of an acute danger to food safety".
Dutch prosecutors added that they were working in coordination with Europol, and in tandem with a similar investigation in Belgium, where authorities also raided several businesses today.
Fipronil is not permitted for use around food-producing animals like hens.
The Dutch food safety authority, NVWA, confirmed to the Ranger that the public prosecutor had begun a criminal investigation into a company involved in treating layers against red mite.
Fipronil is a widely-used anti-lice agent used to spray farm animals, is absorbed into the skin, and passes into hatched eggs.
Chickfriend is yet to comment. However, no cases have been reported of people falling sick. On the 24th of July, administrative documents have been seized from a person suspected of being the dealer of the product in the region of Uden, in the south-east of the netherlands.
Major supermarkets across the country are urgently recalling millions of fresh salads, sandwiches and fillers after the Food Standards Agency revealed that around 700,000 eggs linked to a contamination scare on European farms have been sent to the United Kingdom and may have already been eaten by British consumers.
But it said it was very unlikely that there was a risk to public health.
Supermarkets in Belgium, the Netherlands and Germany have also withdrawn millions of eggs from sale after concerns about contamination.
A major product recall in now underway in the United Kingdom off the back of the British Food Standards Agency's announcement about the levels of contamination there.
Belgian investigators meanwhile identified 26 people or companies as suspects during the 11 raids by police and food safety agency officers, for offences including fraud and breaking European Union food laws.