Pesticide Exposure in Womb Linked to Lower IQ


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Updated: 1/30/2012 11:03 am Published: 9/19/2011 10:12 am


April 21, 2011 -- Children exposed to pesticides in the womb are more likely to have measurable problems with intelligence, memory, and attention, three new studies show.

The pesticides in question, a class of chemicals called organophosphates, have long concerned both scientists and regulators because they work by irreversibly blocking an enzyme that’s critical to nerve function in both bugs and people.

Even at relatively low levels, organophosphates may be most hazardous to fetuses and young children, where healthy brain development depends on a carefully orchestrated sequence of biological events.

To protect kids, the EPA banned most residential uses of organophosphates in 2001, but they are still sprayed agriculturally on fruits and vegetables. They’re also used to control pests like mosquitos in public spaces like parks and golf courses. They can be absorbed through the lungs or skin or by eating them on food.

The new, government-funded studies, from researchers in New York and California, have charted environmental exposures in hundreds of women and their children through pregnancy and into their grade school years.

Though each study used a slightly different way to track the pesticide exposures, they all reached strikingly similar conclusions -- that many children exposed to higher levels of organophosphates during pregnancy than their peers are more likely to have lower IQs and may have more difficulty focusing on tasks or solving problems.

In one study, researchers even found that genetics appears to play a strong role in whether exposure to organophosphates will cause damage.  Mothers carrying a particular gene that slowed their ability to metabolize the pesticides were more likely to have children with brain deficits than mothers whose genes made them quick metabolizers.

Animal studies had previously demonstrated that organophosphates could scramble brain function and behavior in baby rats.

And last year, two studies found that children exposed to higher levels of organophosphate pesticides than their peers were more likely to be diagnosed with attention deficit hyperactivity disorder (ADHD).

“This combination of three long-term studies looking at everyday exposures in American subpopulations is notable,” says Sonya Lunder, a senior analyst at the Environmental Working Group, a nonprofit advocacy group. 

“There have only been a couple of studies like this in the U.S. before, and it really increases our level of concern. It’s a pretty sobering look at pesticide safety,” says Lunder, who was not involved in the research.

Checking Markers for Pesticide Exposure

Researchers at Columbia University looked at markers for exposure for particular organophosphate, chlorpyrifos, in blood samples taken from umbilical cords in 265 inner-city mothers and infants in New York City.

“Our measure is a direct measure of fetal exposure via fetal blood,” study researcher Virginia Rauh, ScD, a professor at Columbia University’s Mailman School of Public Health.

The mothers were asked detailed questions about their lifestyle and health habits during the third trimester of pregnancy and then every year after that.

At age 7, the kids were given a battery of intelligence tests that measured IQ, working memory, verbal comprehension, perceptual reasoning, and processing speed.

For every increase in exposure of about 5 picograms per gram (pg/g) in their cord blood, the children’s IQ scores dipped by 1.4% and their working memory declined by about 2.8%.

“Keep in mind that we would consider this low-level exposure,” says Rauh. “This is not some sort of high-level industrial exposure.”

When researchers looked at other chemical exposures, including tobacco smoke or air pollutants called polycyclic aromatic hydrocarbons, they saw no associations between those levels and memory or IQ.

Clearing Pesticides From the Body

In the second study, which was also conducted in New York City, researchers at Mount Sinai Medical School looked for markers of pesticide exposure in urine in more than 400 mothers and infants. They also took samples of the mothers’ blood to analyze it for the gene that codes for an enzyme called paraoxonase 1 (PON1), which is involved in the metabolism of organophosphate pesticides.

Overall, about 30% of the mothers tested positive for a version of the gene that causes pesticides to be cleared more slowly from the body.

Their children were given tests for brain development at ages 1 and 2, and again between the ages of 6 and 9.

Overall, they found that increasing levels of pesticide metabolites in mothers during pregnancy were linked to greater deficits in IQ, perceptual reasoning, and working memory in many grade-school aged children.

Among children of genetically slow metabolizers, the deficits were worse compared to children of intermediate and fast pesticide metabolizers.

Study of Farmworkers

The third study was conducted in a community of California farmworkers.

Researchers at University of California, Berkeley measured metabolites of organophosphates in urine samples collected from 326 pregnant women and from their children at age 6 months and ages 1, 2, 3.5, and 5 years.

About 44% of the women worked on farms during the study, but they were not pesticide applicators.

Kids who were exposed to the highest levels of organophosphates during pregnancy had IQ scores that were an average of 7 points lower than the IQ scores of kids with the lowest pesticide exposures.

In fact, every tenfold increase in a pregnant mother’s pesticide exposure was associated with a more than 5-point drop in her child’s IQ at age 7.

There was no association between the pesticide levels measured in the children’s urine and learning or memory problems.

“This is not a trivial association,” says study researcher Brenda Eskenazi, PhD, professor of epidemiology and maternal and child health at the University of California, Berkeley.

Normal IQs range from 85 to 115. Children who score lower than 85 often need special education classes in school to make up for trouble with reading, comprehension, and attention.

“On a population basis, it means more kids are going to be driven down into the range that we’re concerned about,” Eskenazi says. “You’re going to have more kids below 85 IQ, which means that they may need to have special services.”

The studies were published in the journal Environmental Health Perspectives.

What the Findings Mean

“This range of effects that these three studies are reporting are very similar to the effects that we associate with lower levels of exposure to lead,” says Philip J. Landrigan, MD, a pediatrician and Ethel H. Wise Professor and Chair of the department of community and preventive medicine at the Mount Sinai School of Medicine, in New York City.

“These are kids who are going to be a couple of beats slower in thinking things through,” Landrigan tells WebMD.

“Their working memory, which is the aspect of memory that we use to deal with tasks in the here and now, is going to be somewhat diminished. They’re going to have a shorter attention span, which means that they’re going to have trouble concentrating on tasks, focusing in school,” he says.

Toxicology experts, however, noted that several caveats apply to the findings.

The first is that while the association between organophosphates and brain deficits looks suspicious, and is biologically plausible, the studies can’t prove that the pesticides are responsible for the problems. 

Most of the families in these studies were low-income and less-educated, groups that have been shown to be disproportionately impacted by learning and attention problems. Though researchers tried to tease out those influences, epidemiologists know that it can be tricky to completely eliminate their effects.

The second caution is that the studies were under way before the EPAs ban on residential use took effect, so it’s hard to know if the results are reflective of levels seen in homes today.

Still, researchers say that based on their investigations, a significant portion of the exposures was probably coming through pesticides eaten on fruits and vegetables.

“It is decreasing, but it is ongoing,” says study researcher Brenda Eskenazi, professor of epidemiology and of maternal and child health at the University of California, Berkeley.

The EPA is reviewing the restrictions on organophosphates to see if they are tight enough to protect public health.

Many feel the current regulations fall short.

“There are 10 million pounds of chlorpyrifos actually currently still being used annually,” says Rauh.

What Consumers Can Do

Experts say consumers can lower their exposure to organophosphates in several ways.

“These findings make it all the more urgent for people to buy organic fruits and vegetables whenever they can afford to do so,” Landrigan says. “It’s been very clearly shown, in studies conducted by CDC, that organic fruits and vegetables have 90% less pesticides than so-called conventionally grown.”

What’s more, Landrigan tells WebMD, “The CDC studies have shown that if people switch over to organic, the organophosphate pesticides are gone from their bodies in just a few days. These chemicals wash out quickly, and you can bring about change very fast.”

If organic fruits and vegetables are unavailable or too expensive, washing produce can definitely make a difference.

It’s more important for pregnant women to get the nutrition benefits of eating fruits and vegetables, Eskenazi says, than stop eating them because they’re afraid of pesticide residues.

“We want to absolutely make sure that pregnant women eat their fruits and vegetables but wash them extremely well, and that means using a scrub brush if necessary,” she says.

The U.S. Department of Agriculture (USDA) regularly tests and reports levels and kinds of pesticides found on washed or peeled fruits and vegetables.

Based on the latest available data, the Environmental Working Group, which analyzed the USDA’s data, finds that these are the fruits and vegetables that have the highest and lowest levels of organophosphate pesticides:

Highest Levels:

  • Green Beans (most residues detected)
  • Peaches
  • Sweet bell peppers
  • Celery
  • Nectarines
  • Pears
  • Apples
  • Blueberries
  • Cherries
  • Collard greens
  • Grapes
  • Kale

Lowest levels:

  • Sweet corn and onions (tied -- cleanest)
  • Pineapples
  • Grapefruit
  • Bananas
  • Oranges
  • Cauliflower
  • Potatoes
  • Winter squash
  • Broccoli
  • Carrots
  • Summer squash

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