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Toxic air linked to alterations in brain structure of children

Exposure to fine particulate matter, especially during the first two years of life, increased the part of the brain associated with psychiatric disorders including autism and schizophrenia.

(CN) — Exposure to air pollution in the womb and in early childhood has been linked to alterations in the white matter structural connectivity in children's brains, according to a study published Thursday.

To understand the full effects, however, researchers from the Barcelona Institute for Global Health (ISGlobal) first had to look at how the brain worked. Co-led by ISGlobal researcher and first author Anne-Claire Binter, the team found a connection to the effects of air pollution on white matter microstructure — the stuff that interconnects the various parts of the brain and is a marker of typical brain development.

They published their findings Thursday in the journal Environmental Pollution.

“We know from previous animal and epidemiological studies that air pollutants may affect the brain through neuroinflammation and oxidative stress processes. Our hypothesis is that these processes may affect the microstructure of the white matter tracts,” Binter said in an email.

Researchers found that greater exposure to fine particulate matter (PM2.5), especially during the first two years of life, increased putamen, a brain structure involved in motor function and learning processes. "A larger putamen has been associated with certain psychiatric disorders (schizophrenia, autism spectrum disorders, and obsessive-compulsive spectrum disorders)," Binter said.

To test their hypothesis, the researchers studied 3,515 children enrolled in the Generation R Study in Rotterdam, the Netherlands, which Binter said provided the researchers a “unique opportunity for studying the effect of air pollution on the neurodevelopment, and to have insights on the possible mechanisms.”

To determine each child’s exposure to air pollution during the study period, the researchers estimated the daily levels of nitrogen dioxide (NO2) and PM2.5. The researchers set their time frame between the mother’s pregnancy and 8.5 years of age, and took the extra step to study specific periods.

“The novel aspect of the present study is that it identified periods of susceptibility to air pollution,” said Binter. “We measured exposure using a finer time scale by analyzing the data on a month-by-month basis, unlike previous studies in which data was analyzed for trimesters of pregnancy or childhood years.”

Between the ages of 9 to 12, the children underwent brain MRIs to examine the structural connectivity and the volumes of various brain structures at the time. Binter said the researchers repeated the MRI assessments on the children from ages 13 to 17, so “it would be possible to extend the period into adolescence in future research.”

Researchers found greater air pollution exposure before the age of five led to greater brain structure alteration observed in preadolescence. Also, they recorded levels of NO2 and PM2.5 that exceeded the World Health Organization’s guidelines for the annual threshold limits.

Surprisingly, however, these levels met European Union standards.

“We should follow up and continue to measure the same parameters in this cohort to investigate the possible long-term effects on the brain of exposure to air pollution,” said ISGlobal researcher and study co-author Mònica Guxens.

When asked on how we can mitigate the effects of air pollution on children’s brains, Binter emphasized the importance of reducing the levels of air pollution. “We need public health policies and urban planning to support the reduction of motorized traffic, the promotion of active and public transport and of green infrastructure," she said.

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