"Handed" Pesticides Feminize Fish

by Mika Pringle Tolson

Mae Grace Nillos and her group at UC Riverside separated chiral pesticides and found estrogenic effects on male fish

Pyrethroids are a group of chiral pesticides commonly used to control insects like ants and mosquitos. They were considered a safer replacement for organophosphate pesticides, but some properties of pyrethroids have been ignored and their effects on the environment are largely unknown.

Chiral pesticides have a mirror image molecular structure called enantiomers that are non-superimposable, much like human hands. Only one enantiomer of most chiral biological compounds is present in nature. As a result, different enantiomers of a compound may have substantially different biological effects.

"Chiral pesticides are often viewed as a single chemical compound, even though they are actually mixtures of enantiomers," says Mae Grace Nillos, doctoral student in Environmental Toxicology at UC Riverside.

Nillos received a fellowship from TSR&TP to study the complex chemical structure of pyrethroids and assess their environmental fate and effects in aquatic environments.

Previous studies on chiral pharmaceuticals and insecticides have revealed enantioselective biological effects. These characteristics have only recently been recognized in chiral pesticides as the technology became more available. "It's a rapidly growing field of study," says Nillos.

Analyzing the enantiomers separately is critical to discern their effects. "One enantiomer may possess all the desired pesticidal activity," says Nillos, "but if you just ignore the other component, you don't know its effects to non-target species in the environment." Nillos and her research group have separated the enantiomers in pyrethroids and discovered significant estrogenic effects in fish with the inactive enantiomer.

By separating the enantiomers, compounds can be developed that are more effective and reduce unnecessary chemical load to the environment. Nillos eplains, "If you can do away with the pesticidally inactive enantiomer, you will have a more potent and more specific chemical. My research will hopefully lead to more responsible use of chiral pesticides."

Nillos plans to return to her native Philippines and apply the techniques she has learned with her doctoral training. "The importance of toxicology in environmental research and protection is only starting to be appreciated in developing countries. We're monitoring chemical levels in the environment, but not looking at the effects as much. Hopefully, I can help change that when I get home."

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