ADHD and pollution: MRI shows possible PAH link

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  • Published: Apr 1, 2015
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: ADHD and pollution: MRI shows possible PAH link

White matter

Magnetic resonance imaging (MRI) reveals differences in parts of the brain that support information processing and behavioural control depending on whether or not a child was exposed to polycyclic aromatic hydrocarbons (PAHs) before they were born. The study thus hints at a possible link between pollution and attention deficit hyperactivity disorder (ADHD).

Magnetic resonance imaging (MRI) reveals differences in parts of the brain that support information processing and behavioural control depending on whether or not a child was exposed to polycyclic aromatic hydrocarbons (PAH) before they were born. The study thus hints at a possible link between pollution and attention deficit hyperactivity disorder (ADHD).

A collaboration between teams at the Institute for the Developing Mind at the Children’s Hospital Los Angeles (CHLA) and Columbia University’s Center for Children’s Environmental Health have investigated a possible link between antenatal exposure to PAH and "disturbances" in the brain. Their study of 40 children tracked from before birth until age 7 to 9 years was part of the Center’s large community-based cohort and details were reported online in JAMA Psychiatry at the end of March.

PAH are ubiquitous in the environment, the home and the workplace and are commonly generated by the incomplete combustion of fossil fuels in motor vehicle engines, oil and coal fired power stations and heaters, through industrial waste incineration, tobacco smoke and natural sources such as wildfires. They are known neurotoxic substances and carcinogens and have been shown to cross from the expectant mother's blood, across the placenta to the unborn child. Earlier animal studies had already shown that antenatal exposure to PAH can lead to impaired behavioural development and problems with learning and memory.

PAH exposure

Now, Bradley Peterson of CHLA together with Virginia Rauh and and Frederica Perera at Columbia have looked at the effects of PAH on brain structure during the final trimester of pregnancy using MRI for 40 mother-children pairs from a much larger cohort of more than 600 pairs from minority communities in New York City. The Columbia team had already published data showing exposure to airborne PAH during gestation in this group was associated with various neurodevelopmental problems, such as developmental delay to age 3, reduced verbal IQ at age 5 and symptoms of anxiety and depression at age 7.

Specifically, antenatal exposure to PAH correlated with a reduction in almost the entire white matter surface of the brain's left hemisphere and this was associated with slower processing of information during intelligence testing and more severe behavioural problems, including ADHD and aggression. “This is the largest MRI study to date of how early life exposure to air pollutants, specifically PAH, affect the developing mind,” explains Peterson. “Our findings suggest that PAH are contributors to ADHD and other behavioural problems due to the pollutants’ disruptive effects on early brain development.” The team also found that postnatal PAH exposure as measured at age 5 was a contributing factor in additional developmental disturbances in the dorsal prefrontal region of the brain; a region associated with concentration, reasoning, judgement, and problem solving.

Attention

Peterson explains that the morphological changes associated with ADHD symptoms in this sample are different from those reported in youth with the disorder, which suggests that exposure to high levels of PAH may be a factors in the development of a specific form of ADHD. However, the study was limited to a minority population where a high level of poverty and low educational attainment were prevalent in general and so the findings may not extrapolate to other demographics. That said, the researchers point out that impoverished urban minority populations are disproportionately exposed to air pollutants. The team suggests that a much wider study will help them to generalise the findings.

“Our findings raise important concerns about the effects of air pollutants on brain development in children, and the consequences of those brain effects on cognition and behaviour,” concludes Peterson. “If confirmed, our findings have important public health implications, given the ubiquity of PAH in air pollutants in the general population.”

"This report describes research that was conducted as a pilot study," Rauh told SpectroscopyNOW. "The larger study, using five different neuroimaging modalities, is being conducted on 350 inner-city children and will investigate the effects of multiple pollutants on brain function and structure.  I am the principal investigator and Brad Peterson is the co-principal investigator.  The results of that work will be available in the fall of 2015.  We are very hopeful that the larger study will further inform public health policy and decision-making around safety standards for exposure to several other pollutants, including organophosphate pesticides and secondhand smoke." 

Related Links

JAMA Psychiatr 2015, online: "Effects of Prenatal Exposure to Air Pollutants (Polycyclic Aromatic Hydrocarbons) on the Development of Brain White Matter, Cognition, and Behavior in Later Childhood"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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