Pesticides Affect Reproductive Health Over Multiple Generations

Ever since Rachel Carson penned "Silent Spring," the public has been aware that chemicals could drastically affect everything from plants to animals to people. Yet now, researchers have found a new reason why it's dangerous to use a certain chemical pesticide. They've found when an aquatic organism called Daphnia is exposed to the pesticids, the impacts can span multiple generations.

Also known as a "water flea," Daphnia is a keystone species in the environment, which means that it has wide-ranging impacts. It acts as an important food source for juvenile fish and other organisms. Without the creature, it's likely that animals higher up the food chain would need to find alternate food sources.

The water flea's sex is usually determined by environmental cues, which cause it to release a hormone called methyl farnesoate (Mf). The researchers discovered that this hormone bound with a certain protein receptor, called the Mf receptor. This receptor can regulate gene transcription and seems to be tied to the production of male offspring.

"We were looking at a model organism, identified an important pathway for environmental sex determination and found that there are chemicals that can hijack that pathway," said Gerald LeBlanc, lead author of the paper, in a press release.

In order to see how a pesticide might exactly affect the sex determination of the water flea, the researchers exposed the creatures to varying levels of pyriproxyfen, an insecticide that mimics the Mf hormone. The exposure actually resulted in more male offspring and fewer offspring in total, with higher doses exacerbating both effects.

"At high concentrations, we were getting only male offspring, which is not good," said LeBlanc in a press release. "Producing fewer offspring, specifically fewer female offspring, could significantly limit population numbers for Daphnia."

It wasn't just high concentrations that made the difference, though. Lesser concentrations of pyriproxyfen also had an impact. With concentrations as low as 71 nanograms per liter, or 71 parts per trillion, the water fleas would produce some female offspring. However, these females suffered long-term reproductive health effects, producing significantly smaller numbers of offspring despite the fact that they had not been exposed to the chemical since birth.

"This work supports the hypothesis that exposure to some environmental chemicals during sensitive periods of development can cause significant health problems for those organisms later in life-and affect their offspring and, possibly, their offspring's offspring," said LeBlanc in a press release.

The findings are published in the journal PLOS One.