Fipronil

Fipronil is a broad-spectrum insecticide. It disrupts insects’ central nervous systems by blocking chloride channels that are gated by γ-aminobutyric acid (GABA) or glutamate. These receptors are weaker or nonexistent in mammals.

Fipronil has a chiral center at the sulfur atom in the sulfoxide group; the two enantiomers have been isolated and verified. The article of commerce is a racemic mixture of the two.

Fipronil formulations sold worldwide include flea-control products for pets, cockroach traps, and insecticides for agrciultural crops, lawns, golf courses, and the like. But despite its wide range of uses and relative harmlessness toward mammals, fipronil is a significant environmental hazard. It is highly toxic to fish and other waterborne wildlife, birds, and beneficial insects. It has been cited as one of the primary causes of honeybee die-off.

In 2017, fipronil was the culprit in a food-contamination scandal in the Netherlands. Molecule of the Week’s Dutch reader who suggested this molecule provided this narrative:

• Egg-laying chickens in the Netherlands are plagued by red mites (bloodmites, Dermanyssus gallinae), which cause anemia and reduce egg output.
• To combat these mites, farmers turned to a tiny company in the Netherlands called Chickfriend. The company offered an effective way to exterminate the mites by fumigation.
• Chickfriend helped hundreds of chicken farmers get rid of the mites for months.
• But—it turned out that Chickfriend’s fumigant contained fipronil, which was banned in the Netherlands. Contamination of Dutch eggs, which are sold worldwide, plunged the industry into a tailspin, with estimated damages running into the hundreds of millions of euros.

A recent article in the Dutch newspaper De Stentor chronicles the fipronil scandal, including the subsequent legal fallout and a better way to combat red mites. (Note: The article is in Dutch, but it is easily translated by major Web browsers.)