July 13, 2015 -- Pyrethroids are chemicals commonly used in products aimed at killing insects, head lice, and fleas on pets. They were created to replace now-banned chemicals in insecticides and other products.
But new research is raising questions about their safety as well, linking them to brain development issues in children.
Pyrethroids are found in thousands of household insecticides, including sprays, foggers, and shampoos targeting ants, fleas, mosquitos, moths, hair lice, and fleas on animals.
Americans’ exposure to pyrethroids has doubled since 2001, when the Environmental Protection Agency phased out the use of earlier pesticides called organophosphates, according to a UC Davis study published in 2014.
The EPA in 2011 reviewed data on pyrethroids and said they're safe for children.
But last month in a published study, researchers said coming in contact with these chemicals may be linked to cognitive problems in children.
WebMD talked to a co-author of the study, French Institute of Health and Medical Research epidemiologist Cecile Chevrier, as well as environmental chemistry experts, insecticide producers, and the EPA to find out more.
What's the health risk to children from exposure to pyrethroids?
There was a statistically significant link between pyrethroid exposure at age 6 and a lower score on a test called the Wechsler Intelligence Scale, Chevrier says. That’s a well-known measure of children’s intellectual abilities, including verbal and memory skills.
These cognitive problems may interfere with later learning and social development.
The study took into account other things known to affect intelligence, including education, health, and socio-economic status of the children’s families.
How many children participated in the study?
There were 287 mother-and-child pairs. The families were part of a larger study in France examining the effects of environmental factors on children’s health.
How were the children exposed to pyrethroids?
That isn’t known. Possible sources were by eating it, by breathing it after the household use of insecticides, touching house dust with insecticide residue, or pets that had flea treatments. The children may have also been exposed through lice shampoo, Chevrier says.
How much of the chemicals did the children come in contact with?
The study couldn’t determine the exact level of exposure. It did find that the higher the concentration of pyrethroid in a child’s urine, the lower the child scored in terms of cognitive abilities, Chevrier says. Those abilities might include thinking, understanding, and remembering.
Are children more at risk than adults to pyrethroid exposure? Are adults at risk?
Children may be more vulnerable because they have higher exposures per pound of body weight, and their livers can't detoxify chemicals as quickly as adults, says Janie Shelton, an epidemiologist for the United Nations Office on Drugs and Crime at the Medical University of Vienna. Some people who've come in contact with pyrethroids have reported wheezing, coughing, and trouble breathing, according to the National Pesticide Information Center.
How significant is this study?
Shelton says it's significant because the researchers showed the children’s exposure through testing, and the study used widely accepted methods to test cognitive ability. But a small number of children participated. A larger study would help to clarify when children are at the most risk from exposure -- whether it's while in the womb or during early childhood, she says.
What are some other limitations to the study?
It’s hard to measure a child’s exposure to the chemicals over time, because the body gets rid of them within several days. Also, the study says that some children may have cognitive problems for other reasons, such as brain abnormalities, which were not tested for -- so the study results “should be interpreted with caution.”
Have there been other studies looking at the effect of pyrethroids on children’s health?
A 2011 study showed that children exposed in-utero to piperonyl butoxide, a common additive in pyrethroids, showed delayed mental development at age 3. A study earlier this year showed a possible link between pyrethroid exposure and ADD in children ages 5 to 15. But other studies have failed to find a link between these chemicals and cognitive issues.
Should people be worried about pyrethroids?
No, says Linda Froelich, a spokeswoman for the Pyrethroid Working Group, an alliance of eight pyrethroid makers. These chemicals are approved for sale in 100 countries around the world and are among the most researched commercial compounds, she says. And they've been studied by federal and state regulators, along with the EU and Latin American countries.
Pyrethroid makers are, in cooperation with the EPA and academia, doing a study on whether or not children are more sensitive to them, she says. The study is expected to be completed at the end of 2016.
Chevrier recommends adults limit their exposure to pyrethroid products, though.
The Pyrethroid Working Group offers some tips to do that:
- After you use a product, wash your hands before eating, drinking, chewing gum, or using the bathroom.
- Remove your clothing immediately if a product gets inside. Then wash thoroughly and put on clean clothes.
- Remove protective clothing or equipment immediately after handling a product. Wash the outside of gloves thoroughly before taking them off. As soon as possible, bathe and put on clean clothing.
- If you’re treating an area with a product, keep people and pets off the area until a spray has dried.
What does the EPA say?
The agency is reviewing pyrethroids and will do a human health-risk assessment as part of that review, says EPA spokeswoman Cathy Milbourn. The agency expects to publish a draft of the review in September 2016.
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