Pesticide Exposure May Span Generations

Chemical pesticides may actually span multiple generations, causing so-called "water fleas" to produce more male offspring and cause reproductive problems in female offspring. According to North Carolina State University researchers who have been studying aquatic organisms called Daphnia, they found that exposure to certain chemical pesticides can even lead to infertility, in some cases.

 "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 Dr. Gerald LeBlanc, a professor of environmental and molecular toxicology at NC State  and lead author of a paper on the work. "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."

Certain environmental cues can determine the sex of the Daphnia offspring. Researchers have been working to understand the mechanisms involved, including indentification of a hormone called methyl farnesoate (Mf) that Daphnia produce under various environmental conditions.

The researchers have now found that the hormone binds with a protein receptor called the Mf receptor, which can regulate gene transcription and appears to be tied to the production of male offspring.

In experiments, the researchers exposed Daphnia to varying levels of an insecticide called pyriproxyfen, which mimics the Mf hormone. The pyriproxyfen exposure resulted in Daphnia producing 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," LeBlanc said. " Producing fewer offspring, specifically fewer female offspring, could significantly limit population numbers for Daphnia."

Low exposure concentrations tended to have significant impacts, too. At pyriproxyfen concentrations as low as 71 nanograms per liter, or 71 parts per trillion, the Daphnia would still produce some female offspring. But those females suffered long-term reproductive health effects, producing significantly smaller numbers of offspring - despite the fact that they had not been exposed to pyriproxyfen since birth.

"We now want to know specifically which genes are involved in this sex determination process," LeBlanc said. "And, ecologically, it would be important to know the impact of changes in population dynamics for this species. Daphnia are a keystone species - an important food source for juvenile fish and other organisms."

The paper, "A Transgenerational Endocrine Signaling Pathway in Crustacea," was published in April in PLOS ONE.