Earlier this week, a million Dutch eggs were stopped at the German border. It’s not the result of some bizarre trade embargo, but the latest development in what has become a massive egg recallsweeping through parts of Europe. While the full extent of the public health risk posed by the insecticide-laden eggs is still unknown, the situation is dire enough that a criminal investigation is underway. 

The crisis first hatched in the Netherlands, where droppings, blood and egg samples from a significant number of hen farms indicated high levels of fipronil. Though it’s the active ingredient in legitimate anti-tick and flea medications for pets, it’s illegal to use fipronil on chickens (or other animals) whose meat or eggs will be sold as food products. If consumed in significant quantities, fipronil can cause serious harm to the kidneys, thyroid glands and liver. Those risks prompted the Netherland’s Food Safety Board (NWVA) to declare that eating these contaminated eggs would “present a serious public health risk.” 

That risk has led to the recall of millions of eggs currently stored in the Netherlands, as well as neighboring Belgium and Germany. As far as Belgian authorities can tell from their preliminary criminal investigation, the culprits could be two different Flanders-based pesticide companies. It’s suspected that they willfully contaminated an anti-lice product legal for chicken use with fipronil in order to improve its potency. While a Dutch newspaper believes one of those pesticide producers may have clients in other EU countries, there’s no evidence yet to suggest the contamination has spread to farms outside of the Netherlands.

In the meantime, egg production has halted at 180 Dutch hen farms while the NWVA assesses the scope of contamination and tests more of the 600 samples collected so far. Some fear fipronil may have been in use on some such farms for a full year, and at this point the NWVA asserts it would be impossible to tell if any such toxic eggs wound up on European breakfast tables. Either way, it’s serious cause for concern for the country’s 11 billion egg a year industry.