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Given the need to eat, drink and breathe, it can be nearly impossible to avoid the common chemicals of modern life.
Many of our crops – and our homes – are sprayed with organophosphate pesticides (OPs) to kill unwanted insects. Many hard plastic bottles and other containers, including linings for many canned foods, contain bisphenol A (BPA). Yet much remains unknown about how these and other chemicals interact with the human system.
How much health risk is posed by these exposures? What kinds of risks and at what stage of life? And if there are unacceptable risks, are there safer, practical, affordable alternatives? In attempting to reduce one threat, how do we know we are not introducing a new one?
A nationwide race is on to find answers to these questions, and scientists at Cincinnati Children’s are exploring how environmental toxicants can affect the developing fetus and growing children in ways that might not affect adults.
“There needs to be much more research in this area,” says Kimberly Yolton, PhD, a developmental psychologist and an expert in pediatric environmental health. “There’s a lot of hysteria, yet very few studies have been done on humans. Without more well-designed, longer term studies, it will be very hard to say which exposures are harmful and which are safe."
Three papers published in April 2011 in Environmental Health Perspectives report links between prenatal OP exposure and deficits in intelligence and behavior measured at age 7. The papers were published by research teams led by the University of California – Berkeley, Columbia University and Mount Sinai School of Medicine in New York.
“They saw effects in global IQ scores, areas of working memory, comprehension, processing speed and reasoning skills,” says Yolton. “The important point about their findings is that there is consistency in the results across different types of populations, so they are finding true effects.”
For example, the Berkeley-led team is studying a group of pregnant women and their children who live among low-income families in the agricultural region of Salinas Valley, Calif., where OP pesticides were commonly sprayed on crops including lettuce, strawberries, and grapes. Their latest study reported that children in the highest quintile of maternal OP exposure had an average deficit of seven IQ points compared with those in the lowest quintile. The effect was found in prenatal exposure, but not in postnatal exposure.
Yolton and others are working to expand upon these findings by looking into motor skills, language skills and behavioral factors. Funding for some of this work comes from a $1.5 million grant awarded to Cincinnati Children’s in 2009 as part of the American Recovery and Reinvestment Act.
“We are seeing some differences that vary by levels of exposure. Babies with higher exposure to OPs have less ability to self-regulate, are more excitable, have weaker reflexes, and are less able to pay attention to stimulation,” Yolton says.
To gather the data, Cincinnati Children’s is tapping into its HOME Study cohort, a group of nearly 400 pregnant women who were enrolled between 2003 and 2006 and their children. They are studying a variety of environmental exposures that may occur prenatally or in early childhood.
“One of the advantages we have is a population that includes an urban core, a suburban ring and rural areas all in one compact region,” Yolton says. “So we are comparing different categories of children to each other. It is likely that our inner city group has exposures to different OPs and at different levels than our rural group.”
To measure exposure, the researchers conduct urine tests at key milestone points to search for traces of six known metabolites that are created as the body processes OPs.
Adding a layer of complexity to the geographic variation, the team also is searching for variations in response based on genetic variation. “We want to know how the environment and the genes work together,” Yolton says.
Bisphenol A (BPA) has been used for more than 40 years to make hard plastic food containers such as baby bottles, reusable cups and the linings of metal food and beverage cans, including canned liquid infant formula.
The chemical is so common that a 2009 study by the federal Centers for Disease Control and Prevention (CDC) reported finding BPA in the urine of nearly every person they tested. In laboratory animals, BPA has been shown to affect the reproductive system, and a few studies suggest similar effects in humans.
Researchers at Cincinnati Children’s are studying how potential BPA effects on the endocrine system can lead to changes in behavior.
“In our HOME Study cohort, we have looked at prenatal BPA exposure. While we are seeing no impact during early infancy, we are seeing behavior problems rising in childhood with prenatal exposure. In particular, we are seeing increased aggression and hyperactivity among girls at age 2,” Yolton says. “At age 3, we also see an increase in depression and anxiety among girls. We don’t know yet if these are life-long effects or how behaviors may manifest differently at older ages.”
Measuring behavioral factors in children can be complex, she says. If BPA is linked to behavioral changes, when would those behaviors show up? Does it make more sense to test infants, toddlers or teens? Test the wrong group and the effect may not be detected.
“We’re not seeing toxic exposures at levels that hospitalize and kill people,” Yolton says. “We are looking at levels of exposure that resemble typical women and children and may have more subtle effects on development. That changes the way we study them, and what we do with the findings.”
Even then, linking a behavioral problem to a specific chemical exposure can be tricky business.
“Unlike a lab setting for animals, we’re not exposed to just one toxicant at a time,” Yolton says. “The risk isn’t just BPA, but BPA plus phthalates, plus lead, pesticides, tobacco smoke and everything else.”
This is why Yolton warns against reading too much into early-stage findings.
“Only handfuls of studies on BPA have been done in humans,” Yolton says. “Given the stakes involved, there’s still not enough evidence out there yet, but there is enough to be concerned and warrant more research.”
In past years, chemicals such as DDT were banned because of their potential health effects. But banning every product that poses a risk may not be the wisest approach.
“If you ban a really common product, what would be the alternative? The problem with a lot of newer, supposedly safer chemicals is that they get put on the market without adequate testing, so we’re not really sure what the effects are going to be,” Yolton says. “In effect, we may be replacing somewhat well-understood risks with largely unknown risks.”
Kimberly Yolton, PhD, is a developmental psychologist and expert in pediatric environmental health.
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