Research has demonstrated that babies exposed to high levels of polycyclic aromatic hydrocarbons (PAHs) and secondhand smoke while in the womb are born smaller than infants exposed to lower levels. A natural next question may be: what effect do these pollutants have on prenatal neurodevelopment? Recently, scientists from the Mailman School of Public Health at Columbia University found an answer.

They discovered that exposure to airborne PAHs combined with maternal stress during pregnancy may be linked to behavioral problems in children.

What are PAHs?

The Environmental Protection Agency (EPA) describes polycyclic aromatic hydrocarbons, in part, as chemicals that are often found together in groups of two or more. PAH, then, does not define a single, precise chemical but a category of pollutants that can exist in over 100 different chemical combinations. Although PAHs are found naturally in the environment, they can also be created when products like coal, oil, gas, and garbage are burned, though burned incompletely. PAHs, then, can easily be breathed into the lungs, which is one of the most common ways they enter the body. In fact, anyone living near a hazardous waste site is probably breathing air contaminated by PAHs.

Pregnant mice, according to the EPA, exposed through their food to 308 parts per million of one particular type of PAH (benzo (a) pyrene) for just 10 days had babies with birth defects. Mice exposed through their food to 923 ppm of that same PAH for months had liver and blood problems. Although animal studies indicate pretty conclusively the harm of PAHs, there are fewer and apparently less precise human studies. Nevertheless, the Mailman School of Public Health found that babies exposed to high levels of PAHs in the womb and secondhand smoke after birth coughed and wheezed more when 1 years old. These same overexposed children also developed breathing problems and were more likely to be diagnosed with asthma when 2 years old.

Such observations naturally lead to other questions. What about exposure levels to PAHs and the potential effects on a child’s neurobehavioral development? As a scientist would never intentionally expose a mother or child to a potentially harmful pollutant, properly investigating this matter required a search far and wide. Soon, though, the researchers found an environment in which they could pursue their study of these chemicals.

Maternal Stress

In fact, the researchers ended up in the coal-burning region of Krakow, Poland. There, they conducted a longitudinal birth cohort study of babies born to nonsmoking women, with the researchers following a total of 248 children from in utero until the age of 9. Among various assessments made throughout the study period, the researchers focused on three measures for this particular investigation of PAHs. They studied prenatal PAH exposure by monitoring air in the mothers’ homes during pregnancy. They also studied maternal ‘demoralization’ — a measure of psychological distress capable of affecting a woman's ability to cope with anxiety-producing or stressful situations — during pregnancy by utilizing the Psychiatric Epidemiology Research Instrument–Demoralization. Finally, once the infants were born, the researchers examined and contrasted each child's behavior with the Child Behavior Checklist.

What they discovered was disheartening: maternal demoralization combined with PAH exposure amounted to a pretty toxic interaction. The children identified as having been prenatally exposed to high levels of both stress and PAHs exhibited behavior problems, including anxiety, depression, attention problems, rule-breaking, externalizing problems, and aggressive behavior. Yet these effects were only seen when children were exposed to maternal demoralization in conjunction with high PAH exposure. In the low-PAH-exposure group, children showed fewer negative behaviors.

“The results provide the first evidence of an interaction between prenatal exposure to maternal demoralization and air pollution on child neurobehavioral development, indicating the need for a multifaceted approach to the prevention of developmental problems in children,” wrote the authors in their study.

"Air pollution exposure is ubiquitous and often co-occurs with socioeconomic disadvantage and maternal psychological distress," lead author Frederica Perera, Ph.D., director of the Columbia Center, told Psychology Today.

Source: Perera FP, Wang S, Rauh V, et al. Prenatal Exposure to Air Pollution, Maternal Psychological Distress, and Child Behavior. Pediatrics. 2013.