It’s long been known that children who live in poorer neighborhoods are more likely to be exposed to lead, industrial emissions, vehicle exhaust and other environmental pollutants. Now, scientists are beginning to suspect that low-income children aren’t just more exposed – they actually may be more biologically susceptible to them.
In a new study published in the journal Neurotoxicology and Teratology, researchers led by Columbia University’s Dr. Frederica Perera, PhD, DrPH, found that poor children who were exposed to high levels of PAHs (polycyclic aromatic hydrocarbons) during prenatal development scored significantly lower on IQ tests at age 5 than higher-socioeconomic status children with similar exposure to the pollutants.
PAHs are ubiquitous in the environment from emissions from motor vehicles, oil, and coal-burning for home heating and power generation, tobacco smoke, and other combustion sources. Exposure to the chemicals usually occurs by breathing contaminated air or eating grilled foods. With over 100 chemicals classified as PAHs, the health effects vary widely; past research has linked long-term exposure to the pollutants with serious health problems including cataracts, decreased immune function, kidney and liver damage, skin irritation and inflammation, and several types of cancer.
Exposure to PAHs during pregnancy is of particular concern, as some of the chemicals can cross the placental barrier and potentially affect fetal development. Previous studies indicate that prenatal exposure to PAHs may be a risk factor for adverse birth outcomes such as low birth weight, intrauterine growth restriction, and premature delivery. More recently, evidence has emerged that the effects of PAH exposure during pregnancy may extend into childhood, as well. In a study published in March, Dr. Perera’s team reported that that prenatal exposure to airborne PAH during gestation was associated with development delay at age 3, reduced verbal and full scale IQ at age 5, and symptoms of anxiety and depression at age 7.
In this latest study, the team followed 276 mother-child pairs from minority communities in New York City — a subset of a larger, ongoing urban birth cohort study — from pregnancy through early childhood. Prenatal exposure to PAHs was measured by assessing levels of PAH-DNA adducts (altered forms of DNA that are bonded to the chemical) in cord blood. Several times throughout the study, mothers were asked a series of questions about their material hardship, a poverty indicator used to assess an individual’s unmet basic needs with regard to food, clothing, and housing. Then, at age 7, children’s IQ scores were measured using the Wechsler Intelligence Scale for Children (WISC).
The researchers found that, among children whose mothers reported greater material hardship (indicative of higher levels of poverty), the group with higher levels of prenatal PAH exposure scored significantly lower on tests of full scale IQ, perceptual reasoning, and working memory compared to those children with lower levels of PAH exposure. Statistically significant interactions were observed between both prenatal and recurrent material hardship and high levels of PAH exposure on children’s IQ scores and working memory scores, meaning that the adverse effects of high levels of PAH exposure were a function of high material hardship, or poverty. These relationships were not significant for higher-socioeconomic status children (those whose mothers reported lower levels of material hardship), providing further evidence that poverty increases not only the risk of exposure to the pollutants, but also the negative health effects.
The findings add to a growing body of evidence showing that socioeconomic disadvantage — which acts as a toxic stressor — can exacerbate the adverse effects of toxic physical stressors like air pollutants. It is thought that the chronic stress of poverty fundamentally alters the way the body reacts to pollutants, especially when exposure occurs during critical periods of development such as before birth and during early childhood. When combined with certain pollutants, this poverty-related stress appears to produce a much greater health effect than either stress or pollution alone. Several studies have found that such stress exacerbates the effects of lead on children’s developing brains, while others have reported more asthma symptoms in kids with simultaneous exposure to air pollution and socioeconomic problems. Now, we have evidence that this also occurs in children exposed to both poverty and PAHs in the womb.
Poverty, however, is not the only toxic stressor — in fact, in most cases it co-occurs with additional sources of chronic stress including racism and discrimination, domestic violence, parental incarceration, and other adverse childhood experiences. Scientists say these toxic stressors can wear down the systems responsible for controlling immunity and hormones. Hormone levels needed for proper brain development may be altered, or the immune system may continually release inflammatory molecules into the blood. During prenatal development and early childhood, exposure to these stressors can permanently alter the way the body responds to future stressors, including chemical exposures. It also may weaken the immune system or trigger inflammation, thereby increasing vulnerability to environmental asthma triggers, such as mold, vehicle emissions, and secondhand smoke exposure.
Based on this growing line of research, experts warn that more needs to be done to reduce the harmful effects of pollutants among vulnerable children. Current policies, which typically focus only on chemical exposures without considering social risk factors, do not offer sufficient protection for children with increased susceptibility due to poverty, racism, and other toxic stressors, said Dr. Perera. She points to the need for a multifaceted approach involving “policy interventions to reduce air pollution exposure in urban areas as well as programs to screen women early in pregnancy to identify those in need of psychological or material support.”
Given the ubiquity of environmental toxins and the severity of the associated health effects, experts say exposures during prenatal development and early childhood could have profound implications for the future of individuals and society. As environmental health researchers Dr. Philippe Grandjean, of Harvard University, and Dr. Philip Landrigan, of Mt. Sinai Hospital, told The Atlantic:
“Our very great concern… is that children worldwide are being exposed to unrecognized toxic chemicals that are silently eroding intelligence, disrupting behaviors, truncating future achievements and damaging societies.”