File photo. Di-n-butyl phthalate (DnBP) is often found in seafood. (AP Photo/J. Scott Applewhite)

Chemicals found in food and common household products have been linked to lower IQ in kids exposed to high levels during pregnancy.

Previous research linked higher exposure to chemicals called "phthalates" to poor mental and motor development in preschoolers. This study was said to be the first to report a link between prenatal exposure to the chemicals and childhood development.

Researchers from Columbia University’s Mailman School of Public Health studied exposure to five types of phthalates, which are sometimes referred to as “hormone disruptors” or “endocrine disruptors.” Among these, di-n-butyl phthalate (DnBP) is used in shower curtains, raincoats, hairspray, food wraps, vinyl and pill coating, among other things — but according to the EPA, the largest source of exposure may be seafood. Di-isobutyl phthalate (DiBP) and Butylbenzyl phthalate (BBzP) are added to plastics to make them flexible. These chemicals may also used in makeup, nail polish, lacquer and explosives.

The researchers linked prenatal exposure to phthalates to a more than six-point drop in IQ score compared with kids with less exposure.

The study, “Persistent Associations between Maternal Prenatal Exposure to Phthalates on Child IQ at Age 7 Years," was published Wednesday in the journal PLOS One.

"The magnitude of these IQ differences is troubling," one of the study’s authors, Robin Whyatt, said in a press release. "A six- or seven-point decline in IQ may have substantial consequences for academic achievement and occupational potential."

While phthalates are banned from use in children’s toys and child-care products, they may be present in other products that do not list them as an ingredient.

The participants in the study were 328 low-income mothers from the New York City area and their children. To determine the level of phthalate exposure, researchers looked at urine samples collected from the mothers during their third trimester of pregnancy. Then they gave the children, all aged seven, the Wechsler Intelligence Scale for Children, an IQ test.

They compared children of mothers with the highest 25 percent of exposure to the chemicals to children of mothers with the 25 percent lowest exposure while controlling for other factors known to affect IQ, including maternal IQ and education and quality of home environment.

They found the children of mothers exposed to more DnBP and DiBP had IQ’s that were 6.7 and 7.6 points lower, respectively, than the children of others. They found a link between those chemicals and certain aspects of IQ, including the children's processing speed, perceptual reasoning and working memory. They found that BBzP also affected child perceptual reasoning.

The mothers’ level of exposure to the chemical was not unusual compared to a national sample from the Centers for Disease Control and Prevention. “Because phthalate exposures are ubiquitous and concentrations seen here within the range previously observed among general populations, results are of public health significance,” the researchers wrote.

"While there has been some regulation to ban phthalates from toys of young children," lead author Pam Factor-Litvak said in a press release, "there is no legislation governing exposure during pregnancy, which is likely the most sensitive period for brain development. Indeed, phthalates are not required to be on product labeling."

Avoiding phthalates is impossible, but the researchers suggest pregnant woman reduce exposure by not microwaving food in plastics, avoided scented products like dryer sheets and avoiding plastics labeled 3, 6, and 7.