Understanding How Chemical Exposures Affect Children’s Brain Development
DERT Success Story
Aimin Chen, Ph.D., M.D.
NIEHS grantee Aimin Chen, Ph.D., M.D., studies how prenatal and early childhood chemical exposures affect brain development in children. Chen, an associate professor at the University of Cincinnati College of Medicine, published findings showing that prenatal exposure to polybrominated diphenyl ethers (PBDEs) from flame retardants is associated with lower IQ and more hyperactive behaviors in children.
From the 1970s to 2004, flame retardants containing PBDEs were used widely in U.S. consumer goods, such as polyurethane foam, furniture, carpet padding, and electronic devices. Although most PBDEs have now been removed from commercial products, the persistence of these chemicals means they can remain in the environment for many years. People can be exposed to PBDEs through house dust and by eating foods — such as fish, milk, and meat — coming from animals that have consumed contaminated food or water.
Linking early exposures with later effects
Chen is studying PBDE exposure in the Health Outcomes and Measures of the Environment (HOME) Study cohort, which was established in 2003 as part of the NIEHS/EPA Cincinnati Children’s Environmental Health Center, led by Bruce Lanphear, M.D. The HOME Study is unique because children were followed from the time they were in utero, with exposure levels and brain development checked at birth and every year until age 5 and again at age 8.
“The HOME Study is representative of the general population in terms of race and socioeconomic backgrounds. The cohort also reflects the general U.S. population in terms of children’s exposure levels, which means that findings can be applied to the general population,” says Chen. “Another strength is that it was designed to look at neurobehavior and thus it includes very comprehensive neurobehavioral assessments for the children at each follow-up visit.”
In 2014, Chen and colleagues published results from the HOME Study showing that a 10-fold increase in PBDE concentrations during early pregnancy, when the fetal brain is developing, was associated with a 4.5-point IQ decrement and a 3.3-point increase in the hyperactivity score at age 5. These results confirmed earlier studies in other cohorts that found PBDEs may be developmental neurotoxicants. In 2015, Chen and colleagues reported that maternal PBDE concentrations during pregnancy was associated with increased thyroid hormones in pregnant women, which are essential for early fetal neurological development. These findings support efforts to reduce PBDE exposures, especially for pregnant women and children.
Chen says several professional groups are working on raising awareness and decreasing exposures to PBDEs. “Because of PBDEs’ persistence, it will take a long time to reduce exposures,” he says. “Chemicals used to replace PDBEs also need to be studied since they may be of concern.”
Chen and his research team now are analyzing data from the HOME Study to see whether PBDE exposure affected the children’s language development and executive function, which is tied to how well a person organizes and plans. They also will soon analyze exposure findings from children at age 8. In future studies, Chen plans to study PBDE replacements and will look at the biomolecular mechanisms that might be involved in the chemical’s neurobehavioral effects.
Exposures from e-waste
Chen also studies exposures to contaminants related to informal electronic waste (e-waste) processing in low- and middle-income countries. It is often conducted in common areas or where people live using simple methods, such as a fire, acids, or hammering, to recover metals from electronic devices.
“Biomonitoring studies in these places have shown that pregnant women experience high levels of exposure to heavy metals, flame retardants, and organic pollutants,” Chen says. “I am looking at how the individual chemicals and the complex mixtures in a totality are associated with various outcomes in fetal and child development.”
So far, Chen’s work has shown that higher levels of metals in the air and dust are not confined to the place where processing is performed but are also found in the wider community area. This knowledge can inform interventions to reduce exposures to workers, as well as residents in the community, especially vulnerable groups such as children and pregnant women. His current work is to characterize the exposure mixture in pregnant women, reveal major risk factors related to high exposure to guide intervention, and investigate adverse fetal developmental outcomes.