It’s almost impossible to escape exposure to the pollution that surrounds us, but for pregnant women, high levels of air pollution may have a long term impact on their unborn baby.

Researchers have found a link between moms-to-be who were exposed to high levels of polycyclic aromatic hydrocarbons (PAHs) and an increased risk of their children developing anxiety, depression and attention problems.

The new study was published in the journal Environmental Health Perspectives.

What are PAHs? They are the byproduct of burning fossil fuels, tobacco, charcoal-broiled foods - especially meats- auto emissions or industrial exhausts. They are also found, in low concentrations, in some skin creams and anti-dandruff shampoos that contain coal tars.

The researchers, led by Dr. Frederica Perera at Columbia University, showed for the first time that expectant women exposed to higher levels of air pollution, and those with the highest levels of PAH in their blood, were more likely to have children who developed anxiety, depression and attention problems by age 6 or 7.

Here’s how the trial worked. Scientists monitored 253 non-smoking inner-city women who gave birth between 1999 and 2006. Those with the highest levels of PAH in their homes during the mothers’ third trimester of pregnancy, were 4.5 times more likely to have children with anxiety problems that might qualify for a clinical diagnosis.

Perera and her colleagues also measured levels of compounds that PAH form in the blood, to get a sense of how much of the toxin that both the mothers and their babies actually absorbed in their bodies. Women with higher levels of PAH residues in their blood at the time of delivery were 23% more likely to have children scoring higher on the anxiety and depression measures than those with lower levels, and babies who had elevated amounts of PAH in their cord blood were 46% more likely to be anxious or depressed than those with the lowest amounts. The results were similar for attention disorders measured in the children as well.

“Our study provides new evidence that prenatal exposures to these air pollutants, at levels commonly encountered in New York City and other urban areas, may adversely affect child behavior,” says Perera.

This study is a continuation of Perera’s work in investigating factors that can influence fetal development. In the first stage of this research, Perera reported in 2011 that higher levels of PAH in cord blood was linked to more symptoms of anxiety, depression and attention disorders in children at ages 3 and 5; her current findings extend that effect out to older children.

Perera’s biggest challenge was to account for the effect of the many other environmental factors, beyond pollution, that can affect human behavior, and try to ensure that she was zeroing in just on the relationship between a mother’s exposure to PAHs and her child’s later behavioral outcomes. So she measured and then controlled for the effect of secondhand smoke, lead, bisphenol A (BPA) and other known neurotoxins that are also thought to contribute to anxiety, depression and attention disorders in children. “There is always the possibility of unmeasured factors that could have also played a role,” Perera says. “But we have taken practical steps to control for as many factors as we could.”

Even after the adjustments, the correlation between PAH exposure and behavioral problems remained strong. Which leaves the worrisome question of what parents, particularly expectant mothers, should do to minimize the risks from PAH.

While heavy traffic areas are difficult to avoid, there are some things pregnant women can do to help minimize their exposure to PAHs such as;

- Don’t smoke and eliminate exposure to second hand smoke.

- Avoid direct exposure to meat on an open flame.

- When cooking indoors - don’t burn, char, or blacken food. Use a kitchen fan while cooking.

- Eat plenty of fruits and vegetables that are high in antioxidants, which can counteract some of the harmful effects of PAHs on the genetic integrity of cells.

- Decrease the use of coal-tar-based cosmetics and shampoos.

- Substitute cedar shavings or aromatic herbs for mothballs, moth flakes, and deodorant cakes.

- Limit the use of candles and incense in your home.

 “You can’t draw conclusions from our results about any single child, or conclude that exposure to PAH causes behavioral symptoms later,” says Perera. “But the results do add to existing evidence that these exposures could have deleterious effects in children.”

Air pollution isn’t only found outside the home, The Columbia Center for Children’s Environmental Health notes on its website that their studies showed more tiny particles of PAHs were found inside the home than outdoors.  “They can be very dangerous to children’s health, increasing risk of asthma and cancer. PAHs get into the air when fuel is burned. Indoor sources of PAHs add to the pollution coming in from outside. Common indoor sources are home heating fuels, tobacco smoke, cooking blackened foods, and burning candles and incense.”

Again, it’s not possible to avoid all dangerous pollutants, but you can cut down on your contact by being aware of what produces them and taking action to limit your exposure.