Pesticide / Herbicide Plants Spraying

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BOSTON — DEET, the most widely used active ingredient in insect repellents, may pose serious risks to human reproduction. Scientists have linked the chemical to potential issues, including infertility, miscarriages, and birth defects.

A team at Harvard Medical School conducted studies on C. elegans worms, which have shown to be a relevant model for understanding how environmental toxins impact human reproduction. They discovered that DEET adversely affects meiosis, the cell division process that produces eggs and sperm, in these worms.

The researchers noted that similar levels of DEET in human blood could potentially lead to miscarriages, stillbirths, infertility, and genetic disorders like Down syndrome. Despite these findings, the team emphasized the necessity for further research before advising against using products containing DEET, due to its effectiveness in preventing insect-borne diseases.

N, N-Diethyl-meta-toluamide (DEET), the primary active ingredient in commercial insect repellents, is crucial in protecting against diseases transmitted by insects, such as malaria, Lyme disease, West Nile virus, and Zika virus.

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The Harvard Medical School research team specifically tested DEET’s effects on C. elegans worms’ meiosis. They found that DEET significantly alters gene expression in the worms, leading to oxidative stress and abnormal chromosome structure, which hinders proper chromosome separation during cell division. This resulted in less healthy egg cells and worm embryos.

Dr. Monica Colaiácovo, a senior author of the study and a professor of genetics at the Blavatnik Institute at Harvard Medical School, highlighted the importance of studying DEET’s impact, given its high prevalence in our environment and potential effects on meiosis.

DEET was one of our top hits in terms of chromosomes not separating properly, so eggs end up with abnormal numbers of chromosomes. In humans, this can cause miscarriage, stillbirth, infertility, and genetic conditions such as Down syndrome. We knew we had to look at this carefully,” Dr. Colaiácovo explains in a media release.

“Research has shown that DEET products can have neurologic effects on people who use them, but no one had really looked at what DEET is doing in meiosis. We wanted to understand whether it would cause a problem. Only a few human studies have been done, and practically everyone uses DEET, so the possibility that it could affect reproduction felt palpable for people in our lab.”

Dr. Colaiácovo adds that the same results could also apply to humans, as we share many equivalent genes with the worms.

C. elegans have been instrumental in uncovering how environmental toxicants such as the plastics chemical BPA can harm reproductive health,” the researcher says. “Many human genes have equivalents in C. elegans, and worms are a powerful model for looking at effects on reproduction.”

“We observed the changes in meiosis when the levels of DEET inside the worms were the same as, and in some cases lower than, what you find in blood or urine samples from the regular human population. That said, the paradigm for exposure wasn’t the same as it is for most people. The worms were exposed to DEET for 24 hours at a time, which may not apply to anyone, or apply to only certain groups, such as agricultural workers. And there are some metabolic and physiological differences between worms and humans.”

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Dr. Colaiácovo notes that future studies of the chemical are still necessary to properly advise and regulate ingredients in products which could be harmful to humans.

“A very important thing from our studies is that we’re providing reproducible, well-controlled, substantial data. Other groups can take up this work in mice or other animal models and further advance our understanding of what DEET may be doing in human reproductive systems. We can also build on this evidence to flag chemicals of concern for policymakers,” Colaiácovo continues.

“DEET exposure led to missing, aggregated, and abnormal eggs in the worms.”

The research team also recognizes the importance of DEET products in preventing the spread of harmful tropical diseases and does not want to see them pulled from the shelves just yet. However, Dr. Colaiácovo does suggest that updated advice could be given to pregnant women using DEET products.

“I want to make sure people are not scared away from being careful. So-called tropical diseases transmitted by insects are moving into new regions of the world as the climate changes, putting more and more people at risk. The consequences of stopping the use of insect repellents can be very serious,” Dr. Colaiácovo says.

“We want prevention. We want repellents. And DEET is a very effective option we have right now. At this moment, I would say we should be aware of the potential reproductive risks of DEET-containing products and be sure to follow the application instructions when using them. Our work suggests this is very important for pregnant women because female meiosis begins in the developing fetus in the womb.”

“I would love to see research give rise to best practices for applying DEET products during pregnancy, when there’s often so much confusion and anxiety about what to do or not do,” Colaiácovo concludes.

“I also hope our work helps drive the development of DEET alternatives that are safe and effective. It would be great to have an effective insect repellent that doesn’t make us worry about our health or that of our children.”

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South West News Service writer James Gamble contributed to this report.

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