Dr. Philip Landrigan, a pediatrician who is director of the Children's Environmental Health Center at Mount Sinai School of Medicine, called the results "intriguing, but in my mind preliminary because they are based on very small numbers." Landrigan said he has "no doubt that environmental exposures are involved in causation of autism," but he suspects the most significant exposures occur not in childhood, but early in pregnancy, "when the basic architecture of the brain is still being established."
The researchers relied on questionnaires and did not measure any chemicals in the homes, which limits the reliability of the findings because they do not know for certain that the children were exposed to phthalates. Previous studies have found that phthalates are common in household dust.
Phthalates are used as softeners in plastic for vinyl flooring as well as other building materials, toys and medical equipment. The chemicals have become increasing controversial in recent years, with Congress last year banning their use in children's products.
The American Chemistry Council, representing chemical companies producing phthalates, said in a statement Monday that the new study does not prove a link between the chemicals and autism. "No other means for assessing these children existed except for the questionnaire and the parent's responses, making this finding rather insignificant," said Chris Bryant, the group's managing director. Autism, he said, "was not systematically analyzed, but just happened to be a question asked five years into the study."
The industry group has said flooring emits "extremely low" levels of phthalates. Because the compounds are heavy molecules with low volatility, they do not tend to evaporate, and wear and tear that might release particles into dust is slight, they said.
Vinyl flooring is commonplace in Sweden, where only about 1 percent of homes have carpeted floors. But it is uncommon in U.S. bedrooms, so it may not be related to autism among American children. However, carpeting contains other contaminants, including pesticides and brominated flame retardants, which have been found to harm brain development in animal tests.
The scientists said their new finding "suggests that studies of other chemical contaminants with endocrine disruptor properties might yield useful insights into the genesis of" autism.
Previously, three studies in California have found a connection between children's exposure to household or agricultural pesticides and autism.
Rates of autism in California have increased seven-fold since 1990, a recent study found. Because genetics do not change that quickly, scientists suspect that chemical pollutants are probably playing a role. But there have been few studies attempting to pinpoint which chemicals, or combination of chemicals.
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.