Exposure to chemicals found in household objects such as furniture, carpets and electronic equipment increases the time taken to become pregnant, according to a study published online in the journal Environmental Health Perspectives. Professor Kim Harley and colleagues at the University of California, Berkeley (UCB) School of Public Health found that women with a higher blood concentration of polybrominated diphenyl ethers (PBDEs), which have been used as flame retardants since the 1970s, took 'significantly' longer to conceive. It is the first study in humans to examine the association between PBDEs and fertility.

The researchers interviewed 223 pregnant women living in a predominantly Mexican-immigrant, low-income community in northern California. They were asked how long it had taken for them to conceive and blood samples were collected. 'For every tenfold increase in PBDEs in the blood, we saw a 30 per cent to 50 per cent decrease in the odds of becoming pregnant in any given month,' said Professor Harley. The researchers controlled for other factors, such as pesticide exposure, which could potentially affect fertility.

PBDEs were commonly used in the US after the implementation of new fire safety standards four decades ago. Production of certain types of PBDE ceased in 2004, but the chemicals are still found in older products. Previous studies showed that 97 per cent of Americans have detectable levels of these chemicals in their blood, with Californians having higher than average levels due to strict flammability laws. Overall, the levels found in the new study were below the national average.

Household items are considered a major source of PDBE exposure. After leaching out, the chemicals can be inhaled with house dust and stored in the body's fat cells. The chemicals are also found in some foods, such as dairy products and high-fat meat. It is unclear how PDBEs may impair fertility, but one possibility is that they alter the level of the thyroid hormone, which is believed to play an important role in fertility. They have previously been associated with reproductive and hormonal defects in animals.

Industry spokesman John Kyte responded to the study by saying that the findings are limited to PBDEs no longer in use, the environmental levels of which are expected to decline over time. However, Professor Harley maintained that although several PDBEs are banned, exposure is likely to continue for many years. She also described the need for research into newer flame retardants: 'We know less about the health effects of these new chemicals than we do about PBDEs'. This is not the first time that chemicals found in household materials have been linked to reproductive problems. In January 2009 scientists found a link between perfluorinated chemicals (PFCs) and fertility, and in May last year household chemicals were reported to disrupt the sexual development of male fetuses.