What do popcorn bags, frying pans and mattresses have in common?
Chemicals contained in these and other common household items may affect maternal thyroid function and may lead to impaired fetal brain development, according to PhD candidate Glenys Webster, of UBC's School of Occupational and Environmental Hygiene.
Webster is leading an investigation into the effects of polybrominated diphenyl ethers (PBDEs), chemicals that are used as flame-retardants, and perfluroinated compounds (PFCs), used as stain or water repellents. The chemicals are found at low levels in all Canadians. They leach out of many products, can last for a long time in both indoor and outdoor environments, and accumulate in both animals and humans via dust, foods and air.
Called the Chemical, Health and Pregnancy study (CHirP), Webster believes it is one of the first such studies in the world. She is collaborating with investigators from BC Women's Hospital & Health Centre, Health Canada, and the University of Alberta.
Animal studies have shown that certain PBDEs interfere with the thyroid system, critical to fetal development. A butterfly-shaped gland in the lower front part of the neck, the thyroid controls metabolism and keeps basic functions such as body temperature, blood pressure and energy levels working properly.
It is known that thyroid disruption in early pregnancy can result in neurological damage in babies, but the mechanism -- including any negative environmental factors -- is not known. Although there are no known human health risks from common levels of PBDEs and PFCs, very few studies have been conducted in humans, says Webster, so at this point nothing is conclusive.
She suspects the chemicals may put additional stress on the thyroid system. Animal and laboratory studies have shown that certain PBDEs can mimic thyroid hormones and bind to a transport protein that sends the damaging "imposter" hormone from the mother to the fetus, possibly directly to the brain.
"Until recently, we didn't have the analytical methods we need to measure low levels of these chemicals and study effects on human health," says Webster, whose previous research focused on environmental toxicology and looking at how chemicals move through the environment. "There is considerable new interest among scientists to start looking at human health effects, and governments, including Canada's, are now making decisions about regulating these chemicals."
Researchers will enroll 150 pregnant women for the study, which was launched last month and will extend to September 2008. Participants will be asked, during in-home surveys, about exposures to PBDEs found in mattresses, furniture foam, plastic casing of electronic equipment such as TVs and computers, and other household goods. The women will also be asked about exposure to PFCs via products ranging from microwavable popcorn bags to non-stick cookware coatings and self-cleaning ovens.
Levels of PBDEs and PFCs will be measured in the air, dust and dryer lint in homes. Also, maternal blood samples will be collected in mid-pregnancy and a sample of umbilical cord blood will be collected at delivery. Levels of both groups of chemicals won't be analyzed until all 150 subjects have been recruited.
In humans, accumulation rates and toxicity relative to exposure levels are not well understood. It is known that PFCs are some of the most persistent compounds known, and the half-life of PBDEs in human tissues ranges from approximately 15 days to six years. However, fast-degrading PBDEs don't actually "clear" the body after two weeks. They transform into slower degrading chemicals and persist. A puzzling factor is that age doesn't necessarily affect PBDE accumulation.
In North America, PBDE levels in humans are approximately 10-100 times higher than levels found in Europe or Japan, according to a review of PBDE levels in humans conducted in 2004. Health Canada data showed PBDE levels in Vancouver mothers' breast milk increased approximately 15-fold from 1992-2002, but are still lower than levels found in certain areas of the US. Canada has this year prohibited the importation of certain chemicals that turn into PFCs.
Should expectant mothers be alarmed?
"We're not expecting to see dramatic changes here -- the effects, if any, will be subtle but may still be important, and show a trend that should be monitored," says Webster. "I think it's important to start looking at connections so we can take precautionary measures, if needed. Even if effects are subtle, because virtually everyone is exposed to these chemicals, any small effects may still represent a public health concern."
For more information about the study, visit www.cher.ubc.ca/chirp.
BC Women's Hospital & Health Centre is an agency of the Provincial Health Services Authority.
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