When it comes to what causes some mental health disorders, like autism and attention deficit hyperactivity disorder (ADHD), scientists are still in the dark. However, they do know conditions like these are caused in part by genetics, and in other parts, by the environment. A new study shows how the environment can cause ADHD, by finding an association between its development and exposure to a common household pesticide.

“Although we can’t change genetic susceptibility to ADHD, there may be modifiable environmental factors, including exposures to pesticides, that we should be examining in more detail,” said lead author of the study Jason Richardson, an associate professor in the Department of Environmental and Occupational Medicine at Rutgers Robert Wood Johnson Medical School, in a press release.

When he and his team investigated this link, they found children exposed to pyrethroid pesticides like deltamethrin in utero or while breastfeeding were more likely to exhibit signs of ADHD, such as hyperactivity, problems with working memory, impulsivity, and attention deficits. Many of these problems, it seems, emerged from imbalances in the kids’ brains’ dopamine signaling systems, which are responsible for these processes as well as being motivated.

Richardson and his team’s findings are especially important because they found links between exposure to the pesticide and ADHD not only in humans but mice too. They culled data on 2,123 kids and teens who participated in the National Health and Nutrition Examination Survey (NHANES), specifically looking at health care questionnaires and urine samples. They then asked parents whether their child had ever been diagnosed with ADHD by a physician, and looked at prescription drug records to see who had filled prescriptions for ADHD medications.

They found children who had more metabolites to pyrethroid pesticides in their urine were twice as likely to be diagnosed with ADHD. When they experimented on mice, they found those exposed to the pesticides were also more likely to develop symptoms of ADHD, with a prevalence among males — this finding mirrors current rates of ADHD in humans, with boys being four to five times more likely to have the condition. The most concerning part, however, was that these symptoms persisted through adulthood even though the pesticides were completely out of their systems.

Pyrethroid pesticides are used in a wide range of places, from the farm to the home and gardens to lawns. They’re also used for bed bug control. But whether you live in a city or elsewhere, there’s a good chance of being exposed to the chemicals, as our diets are a predominant driver of that exposure.

Speaking to Rodale in 2011 about another study linking pesticides to ADHD, Dr. Phil Landrigan, professor and chair of the Department of Community and Preventive Medicine at Mount Sinai School of Medicine, said: “It’s been shown that people who switch to an organic diet knock down the levels of pesticide byproducts in their urine by 85 to 90 percent.” That 2010 study, by the way, found a 35 percent increase in ADHD risk for every 10-fold increase in urinary concentrations of pesticide metabolites.

Reducing exposure, among other precautions, is paramount to ensuring a healthy pregnancy. Women and children may be especially vulnerable because their bodies don’t metabolize the pesticides as efficiently, Richardson said. Future research on humans will determine how risky that exposure is. In the meantime, “We need to make sure these pesticides are being used correctly and not unduly expose those who may be at a higher risk,” Richardson said.

Source: Richardson J, Taylor M, Shalat S, et al. Developmental pesticide exposure reproduces features of attention deficit hyperactivity disorder. The FASEB Journal. 2015.