It is estimated that two million children have difficulties learning, and about 80 percent of them have trouble learning to read. Their brains find it hard to process the printed words they see on a page and turning those letters into language and meaning. Genetics can play a role, but exposure to flame retardants appears to be a major factor behind these numbers, a study by researchers at Columbia University Vagelos College of Physicians and Surgeons finds.

Flame retardants, also known as PBDEs or polybrominated diphenyl ethers, have been found to interfere with brain development for some time. They are now banned, but because these chemicals do not degrade easily and therefore linger in the environment — in air, sediment and food — the team suspected that pregnant mothers with PBDEs in their blood might be exposing their unborn babies in utero.

Children with greater exposure to PDBEs had a less efficient reading network in their brains.

Thirty-three five-year-olds who were learning to read were given a reading assessment to determine the nature of the reading difficulties they were struggling with. Then the team took a resting state functional MRI (fMRI) of each of their brains. They also analyzed blood samples taken from their mothers during pregnancy to check for the presence of PBDEs.

Kids who had a better-functioning reading network in their brains, as shown by the fMRIs, had fewer reading problems. At the same time, the researchers reported that children with greater exposure to PDBEs had a less efficient reading network in their brains.

What the study did not find is also worth noting: greater exposure to PBDEs did not appear to affect their brains' ability to process social information, such as is seen in autism spectrum disorders.

“Since social processing problems are not a common aspect of reading disorders, our findings suggest that exposure to PDBEs doesn't affect the whole brain — just the regions associated with reading,” explained Amy Margolis, an assistant professor of medical psychology in the Department of Psychiatry, in a statement.

The results also confirmed an earlier study that showed simple word recognition was not affected, but the ability to read strings of words and process them to understand the meaning of a sentence was. “Our findings suggest that the effects of exposure are present in the brain before we can detect changes in behavior,” Margolis added.

The study is published in Environment International.