September 26, 2017
Tractor working in field of wheat
Expert Q&A

The Risks of Pesticide Exposure

by Jeanine Barone  |  

Brenda Eskenazi, PhD, is the director of the Center for Environmental Research and Children’s Health (CERCH) at the University of California, Berkeley. She is a neuropsychologist and epidemiologist whose research has long focused on the effects of toxins, including pesticides, on human reproduction and child development. A long-running study of which she is the principal investigator, the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) Study, has looked at the effects of prenatal exposure to pesticides in a Mexican-American farmworker community in California’s Salinas Valley. We spoke with Dr. Eskenazi about what the study—which began in 1999—has found, and what we can all do to reduce our exposure to potentially dangerous pesticides.

Can you briefly describe the CHAMACOS study?

In 1999 to 2000, we enrolled 600 pregnant women who lived in the agricultural Salinas Valley. About 40 percent of the women were farmworkers, and most of the others lived in households where someone worked in agriculture. We followed their children every one to two years. And the children are now turning 16. During the pregnancy, we measured a biomarker of organophosphate pesticides (OP), a type of pesticide used in agriculture, in the urine of the mothers. This would indicate their exposure to OPs. We also did some measurement of OPs in the children between one and five years of age.

Because many OPs are used in agriculture, in our study we primarily looked at a non-specific metabolite of OPs. In other words, it would indicate exposure to OPs but not specify which one. We looked at the relationship between this biomarker and different aspects of child growth, neurobehavioral development, and respiratory illness.

What were your findings?

We found a relationship between a mother’s exposure to OPs during pregnancy and several outcomes in their children, including shortened gestation (the time interval from conception to birth), poor mental development in toddlerhood, autism-like symptoms at age two, poor attention at the start of school age, and lower IQ at age seven. We also found that exposure to OPs during childhood was linked with respiratory problems and poorer lung function. So it’s not just prenatal exposure that is cause for concern.

What are the main ways that children in the study are exposed to OPs?

We think that most of the exposure comes from residue on food and from living near the fields. In young children, exposure is likely to come from hands-to-mouth behavior. That is, the young children touch dust that’s contaminated and then put their hands in their mouths. Maybe some of it is inhaled, depending on how small the contaminated particles are. But, it’s likely that a good portion is coming from dust or contamination in food.

Can children be exposed to these agricultural chemicals even if they don’t live anywhere near the farms?

Yes. We did a study where we compared children living near the fields with children in Oakland, which is not near farmland. The children were all the same age, all Mexican-American, and had similar diets. We had them eat their usual food for a few days and then gave them organic food, which by definition is grown without the use of most conventional pesticides. We collected urine samples every day and measured the OP metabolites in them. We found that, in both the agricultural-area group and the Oakland group, OP levels were higher when the children were eating non-organic food vs. organic food—though the overall levels were higher among the children in the agricultural areas compared with those in Oakland. In other words, we showed that it’s not just where you live, but also whether you ate organic food that was related to the amount of OP metabolites in the children’s urine.

California is the nation’s biggest agricultural state. Has there been a push to reduce the use of OPs in food production?

Over the last decade in California, there has been a drastic decrease in the use of OPs in agriculture. Maybe it’s because of our study; we would like to think it contributed. Maybe it’s because of the cost of the chemicals. Or the EPA’s concern about these chemicals. But we are concerned about the increase in use of other pesticides that we know less about, such as a type called neonicotinoids.

California is special because we have access to publicly available Pesticide Use Reporting Data. We’re the only state that has this information so well organized and in such a complete system. Every pesticide used in the state is recorded in the database; we know where it’s applied, how much, on what day, and at what time. We have mapped the decreases in OPs and the increases in other pesticides. And now we’re thinking about how we’re going to look at the health consequences of these other pesticides that are replacing OPs.

Does exposure to a multitude of different pesticides make the outcome potentially worse for children or adults? In other words, is there a synergistic effect?

You are asking the $50,000 question. It is really hard to look at multiple chemical exposures. Many researchers—toxicologists and biostatisticians—are trying to develop innovative ways to look at this question. Here’s the problem with OPs: Not all have biomarkers; that is one of the reasons we decided to study these non-specific metabolites. But it doesn’t allow us to know which chemical is contributing to how much of the metabolites. Some are more toxic than others. So we have begun to look at the Pesticide Use Reporting Data to look at human exposure. We have GPS coordinates of where the mothers in our study lived during their pregnancy, and where pesticides were applied near their homes. We can then look for relationships between specific pesticides and the child’s development. In some ways it’s not as good as using a biomarker, but it allows us to look at different kinds of pesticides and specific pesticides. When we do that, we see that nearby use of certain pesticide mixtures are more likely to be linked with decreases in children’s IQ.

Can the effects of exposure vary by person?

Possibly. There may be people who are more susceptible because of genetics. Some may be less efficient at metabolizing OPs than others. So we have begun to look at gene interactions.

The EPA has recommended in recent years that a particular OP, chlorpyrifos, be banned in the U.S., in part because it (like other OPs) is chemically related to sarin nerve gas. But new EPA head Scott Pruitt in March signed an order that would allow farmers to continue using it. Can you share your thoughts on this development?

It is clear that the class of chemicals, OPs, has been associated in our study with a wide array of different developmental problems, from neurodevelopment to respiratory function. What we also know is that there has been a huge amount of data collected on chlorpyrifos in animals, although there’s limited human data. Those studies in rodents show quite clearly that there’s a relationship between early-life exposure and effects on development, and there’s also evidence of the mechanism of action. The risks have been discounted by some policy makers since the evidence is mainly in animals. But given the potential risks in humans, policy makers must consider the weight of evidence from these animal and mechanistic studies, on top of what human studies have found.

How can people reduce their exposure to organophosphates?

We have found that for people who live in agricultural areas, doormats make a difference. We recommend that people who’ve been working in the field wipe their feet and take off their shoes before entering their home. The EPA also recommends that farmworkers shower when they come home and change their clothes before they pick up their children. Launder the clothes you wear in the field separately from your family's clothing. Frequent vacuuming and damp dusting can also reduce pesticide residues in the home.

In addition, it’s essential to wash fruits and vegetables really well before you eat them—to remove pesticide residues from conventional produce, but also to remove bacteria, which can be on organic produce as well. Avoiding or eating less produce is not the answer. It is important that we all eat a diet high in fruits and vegetables, especially during pregnancy but the rest of the time too. So we want you to eat lots of fruits and veggies, but make sure they’re clean.

What could lead to a reduction in the use of pesticides in agriculture?

The more demand that we have for organic fruits and vegetables, which are grown without most synthetic pesticides, the more farmers will switch to organic production methods. Growing organically is more labor-intensive and, hence, more costly—and therefore more expensive to the consumer. So, not everybody can afford to buy organic. In California, we have seen not only a reduction in OPs but an increase in organic crop land. Organic agriculture doesn’t mean without chemicals; there are certain chemicals allowed. But farmers are increasingly using integrated pest management, which focuses more on the prevention of pests and the control of pests in less risky ways, including removing trash and standing water, rather than simply resorting to chemicals as the go-to tactic.

Also see Minimizing Pesticide Exposure on a Budget.