Children exposed to chemical flame retardants while still in their mother's womb face an elevated risk of developmental problems, a new study suggests.
Previous research has shown that prenatal exposure to polybrominated diphenyl ethers, or PBDEs, is associated with lower intelligence and hyperactivity in laboratory mice.
But the new study, by a team of Canadian and U.S. scientists, provides additional evidence that these ubiquitous chemicals are also harmful to human fetal development.
Some of these chemicals have already been banned. However, exposure to them continues because they are in so many products, ranging from furniture to electronic equipment.
"Most PBDEs are long-lived and persist in the environment and in people for years," one of the study authors, Glenys Webster of Simon Fraser University, said in an e-mail.
"A typical Canadian may already have a kilogram or more of PBDEs in their home or offices, in older foam furniture, carpet underlay and electronic items. Some of these items won't be replaced for many years. These reservoirs of indoor PBDEs mean that human exposures will continue long after PBDEs have been banned."
For the study, the researchers measured PBDE levels in blood samples collected from 309 pregnant women at Cincinnati Children's Hospital Medical Center. Over the next five years, the women's children were given annual intelligence and behavioural tests.
The findings showed that the risk of hyperactivity and cognitive deficits increased in the kids with higher levels of PBDEs in the mother's bloodstream. For instance, a 10-fold increase in maternal PBDEs was associated with an average four-point lower score on an IQ test at the age of five, said the study's lead author, Dr. Aimin Chen of the University of Cincinnati College of Medicine.
Problems of hyperactivity became evident as early as two years of age. "If the mothers were exposed to higher levels of PBDEs, then the children were more likely to have a higher hyperactive score," Chen said.
The study was presented Monday at the annual meeting of the Pediatric Academic Societies in Washington.
Animal studies suggest that PBDEs can disrupt the production of thyroid hormone, which helps regulate metabolic activities. That can be a significant problem for any individual. But it is especially worrisome during pregnancy because the hormone plays a key role in fetal development. In the first few months of a pregnancy, the fetus depends on a proper amount of thyroid being supplied by the mother.
"The baby relies on the mother's thyroid hormone to regulate the growth of cells. So if the thyroid hormone is disturbed, the baby's neuro-development can be affected," Chen said.
"In our study, we observed consistent behaviour problems – especially in hyperactivity and disruptive behaviours such as aggression."
Chen noted that almost everyone is exposed to PBDEs. The chemicals were added to a wide range of plastic products to reduce the chance they would catch fire, or at least hinder their combustion. There are three main mixtures of PBDEs – Penta, Octa and Deca. Penta was mainly added to polyurethane foam used in couches, office chairs and carpet underlay. Octa was primarily used in the plastic parts of electronic devices such as TVs and computers.
Canada banned Penta and Octa in 2008, and there are plans to phase out the use of Deca. In the meantime, Deca "is still used in Canada, mainly in electrical and electronic equipment such as TVs, computers, hair dryers and cables. It is also used in treated upholstery and drapery," Webster noted.
One of the big problems with PBDEs is that they don't remain bound in plastics. Instead, they gradually leach out over time. Once they are in the environment, they don't easily biodegrade. To make matters worse, they accumulate in fat tissues. The main routes into the human body tend to be through the ingestion of dust and the consumption of fatty foods, Webster noted.
"The evidence for human health effects from PBDEs is growing," Webster said. "Pregnant women and young children are at the greatest risk. Several studies now point to altered neuro-development in children. Our study confirms this trend in a representative population of Cincinnati children."
Webster offers the following tips that may help reduce exposure to PBDE flame retardants:
• Wash your hands before eating or cooking.
• Reduce exposure to indoor dust.
• Clean with a damp cloth to avoid stirring up dust.
• Use a vacuum with a HEPA filter.
• Avoid foam products with a California Technical Bulletin 117 (TB117) label. These products contain flame retardants.
• Seek alternatives to foam mattresses, pillows and bedding.
• Repair or replace exposed foam.
• Minimize children's contact with electronics (e.g. mouthing remote controls or phones).
• Choose wool or snug-fitting cotton fabrics for children's sleepwear.
• Ask about flame retardants when buying new furniture and electronics.
• Consider wool carpets or no carpets during renovations.
• Use proper ventilation during cleaning and construction projects.
• Never burn plastic.
• Air out your car before entering on a hot day. Flame retardants are used in the seats and plastic interior parts.
• Minimize contact with dryer lint.
• Avoid foam pits at gymnastics classes.