More evidence links pesticides & falling IQs | Pesticide Action Network
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More evidence links pesticides & falling IQs

Emily Marquez's picture
Kid walking on farm

A new study from researchers at the University of California, Berkeley found that when pregnant mothers live within one kilometer of fields where certain pesticides are used, their children are more likely to have lower IQs. These findings confirm those in several earlier studies. Which leads me to wonder: just how much evidence do we need before taking action?

This latest study looked at 283 seven-year-olds living in the Salinas Valley, an agriculturally intensive area along the Northern California coast. Researchers found that higher levels of organophosphate (OP) pesticide use in nearby fields during pregnancy lowered IQ scores by about two points. In the specific area of verbal comprehension, a nearly three-point decrease in IQ was observed.

In this study, proximity to agricultural pesticide use was used as a proxy for pesticide exposure. Based on past studies, pesticide use reporting data has been correlated with environmental pesticide concentrations in the home, suggesting that proximity to agricultural pesticide use is a meaningful indicator of pesticide exposure.

The conclusion of the study? Mothers living near agricultural use of neurotoxic pesticides during pregnancy may risk "poorer neurodevelopment" of their children.

Do we need more data?

The families involved in this particular study are part of the CHAMACOS (Center for the Health Assessment of Mothers and Children of Salinas) cohort study, which has been following a group of mothers and their children for about 16 years.

Pesticide use reporting data available from the state of California makes this type of work possible. Unfortunately, California is one of very few states in the country where pesticide use is reported on a yearly basis — and yet, California's use reporting system has room for improvement. For instance, the study we're talking about looked at pesticide use within one kilometer of the home. What if researchers had access to data that allowed for analysis at smaller distances (e.g., closer proximity to pesticides)? Would that tell us more?

An important first step is getting more data in other states. My Midwest PAN colleagues are working with a farmer-led coalition in Iowa, for example, that's pressing for better rules protecting farmers from pesticide drift and statewide pesticide use reporting.

It's definitely important to have more information, both so researchers can conduct studies with the best data available and also because the public quite simply has the right to know. But when it comes to environmental exposures to OP pesticides and other neurotoxic agents, I think we already have more than enough information to put health-protective policies in place right now. This is an injustice that we can and must address.

The big picture when it comes to kids' brains

I was part of a group of (mostly academic) scientists that recently issued a consensus statement on neurotoxic chemicals under the name of "Project TENDR," which stands for Targeting Environmental Neuro-Developmental Risks. OP pesticides were among the chemicals identified as "candidates for action" posing a threat to children's brain development.

Other candidate chemicals included those with a LOT of data, like lead (just to give you some context, Benjamin Franklin wrote about lead's neurotoxic properties). Project TENDR also identified candidate chemicals like poly brominated diethyl ether (PBDE) flame retardants, among others.

Project TENDR was convened by Maureen Swanson of the Learning Disabilities Association of America and Irva Hertz-Picciotto, a researcher at the University of California, Davis, in response to the concerning increase in learning and behavioral problems in children — and the fact that increased risks of these problems have been associated with a number of toxic environmental chemicals.

The basic premise of the consensus statement is that the risks to brain and nervous system development from neurotoxic chemicals are unacceptably high, and policies must be put in place to reduce exposures of children and pregnant women to these chemicals. The consensus statement called the current regulatory system "fundamentally broken."

We don't have to accept this as the status quo. Pesticide usage doesn't have to be a given for us to have a thriving agricultural system. But we do need deep changes in our current policies to support the real transformation needed — and this is a real challenge. Luckily, a growing number of farmers and advocates are tackling this challenge, and hopefully these numbers will continue to grow.

Emily Marquez
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Thomas's picture
Thomas /

An opportunity may exist to determine the extent of neurological damage to mammals from organophosphorus pesticides. The crude measure of IQ does not tell us if there are other significant structural changes to specific structures of the brain.  It might be beneficial to capture field mice in areas that have had pesticides applied and compare their neurological structures to those of wild field mice.  The hippocampus, the center for learnig and memory, would be of particular interest.
Best Wishes,
Thomas Evans
Author of: Alpha Land: Bullies, Males and how the angry rule.

Emily Marquez's picture
Emily Marquez /

Hello Thomas, thank you for taking the time to make a comment. There has been at least one study on prenatal chlorpyrifos exposure resulting in structural anomalies in human children's brains by Virginia Rauh and coauthors in 2012, which is summarized in this PAN blog.

You might also be interested in this 2014 review on neuroimaging that talks about the techniques that can be used to assess the impact of environmental chemicals on neurodevelopment.

risolom's picture
risolom /

As a retired psychologist with years of experience using intelligence testing with children, I must note that a 2-3 point difference in IQ scores may not be all that significant.  Other measures of cognitive/intellectual functioning should also be used to confirm this trend.  Ongoing follow up, longer term studies of these kids should also be done.  
 Intuitively, it makes sense to be concerned about pesticide exposure to pregnant women and very young children.  More thorough, ongoing research should be done to investigate this more carefully, however.

Emily Marquez's picture
Emily Marquez /

Thank you for your comment, RISOLOM. I wouldn't call the findings from the study a trend because it is a statistically significant finding, the authors did statistical analyses in their study population, which is a cohort that has been followed for about 16 years as of 2016.

PAN's Program Director Kristin Schafer wrote a blog on "When IQs fall," discussing a study where a researcher projected IQ drops to the whole US population, and an MD epidemiologist named Bruce Lanphear did this excellent video on why small shifts in IQ matter, where he talks about lead and other environmental contaminants such as OP pesticides.

The study I blogged about is one among others that have found a drop in IQ associated with exposure to organophosphate (OP) pesticides. In another paper from the same cohort study I blogged about, a seven point IQ drop was observed in the highest prenatal exposure group to OP pesticides when the children in the cohort were seven years old.

Results that parallel these findings were reported in another long-term cohort study from New York City where, as prenatal exposure to the OP chlorpyrifos increased, a 1.4% decrease was observed in the IQs of seven year old children and the effect on working memory, a component of IQ, appeared to be more pronounced. In the same NYC cohort, but back when the NYC children were three years old, a nearly seven point decrease was reported in the IQs of the group most highly exposed to chlorpyrifos. 


Emily Marquez is PAN's Staff Scientist. She is a biologist with a background in endocrine disruption and environmental toxicology in reptiles. In addition to supporting scientific research for PAN’s campaigns, Emily trains community members in using PAN’s Drift Catcher to monitor for pesticide drift. Follow @EmilyAtPan