Curse this house
If you thought your home was a haven from life’s hazards, think again. Rebecca Renner sneaks a look at the demons lurking in your carpet.

IT’S PLAYTIME at Emma’s house. Children in constant motion seem to be everywhere–under the dining room table, playing with toys, hugging the dog. Oops, Emma’s eating Cheerios off the carpet and Johnny’s licking the coffee table. Johnny, who is two, may put 76 things in his mouth in the course of an hour–toys, his fingers, someone else’s fingers –a recent study is covered. Emma, who is four, has more self-control, but she may still put 38 things in her mouth every hour. Their parents might not stop to think about it, but Emma and Johnny, like all kids, are little guinea pigs testing the toxicity of whatever pollutants are in their home.

And they are more common than you’d think. Our exposure to most toxic pollutants is between 10 and 50 times higher in indoor environments than it is outdoors, according to studies on adults in the late 1980s. For many contaminants, levels in house dust are so high that they would trigger a clean-up operation if they were found outside. A typical sample of household carpet dust sent to an environmental lab would ring regulatory alarm bells for high concentrations of heavy metals such as lead, cadmium and mercury, polycyclic aromatic hydrocarbons (PAHs), pesticides and polychlorinated biphenols (PCBs), says John Roberts, an environmental engineer in Seattle, Washington. Roberts is known as Dr Dust for his work and his obsession with vacuuming.

Children are more at risk than adults, because they have a higher metabolic rate and their organs are still developing. Kilogram for kilogram, for example, Emma and Johnny inhale 23 times as much air as their parents. And even relatively low levels of the poisons in dust could irritate their lungs, damage their developing nervous systems, retard their growth and hearing, or lead to cancer. For example, researchers estimate that every day the average infant under the age of two in urban America ingests 110 nanograms of the most toxic PAH, benzo(a)pyrene, which is found in tobacco smoke and cooking fumes. That’s the equivalent of smoking three cigarettes a day. But even though the problem may be far more extensive than people think, fortunately
there is an easy–if tedious–remedy close at hand.

Carpets are one of the biggest sources of toxic substances, the latest research shows. Normal vacuuming leaves in more dust than it picks up so that, over time, dust accumulates in carpets. “The carpet is the largest reservoir of dust in a house, so that a house with bare floors and a few area rugs will have about one-tenth of the dust found in a house with wall-to-wall carpet, all other things being equal,” says Roberts. That’s bad news for people living in cold climates, where most houses boast fitted carpets. Britain tops the charts with over 90 per cent of homes carpeted, compared with about 65 per cent for Germany and about 60 per cent for the US, according to 1997 figures compiled by the Healthy Flooring Network, a coalition of health and environmental groups based in London.

By now, most of the children are playing under the table. Johnny, who has been licking his hand, is rubbing it on the carpet. A rub like that transfers about 1 per cent of the surface contamination to the hand, said David Camann, a statistician at the Southwest Research Institute in San Antonio, Texas, at a meeting of the International Society of Exposure Analysis last October in Monterey, California. Many of these contaminants come from the vast array of indoor chemicals that Emma’s parents take for granted, such as cleaning products, solvents, deodorizers and air fresheners. Then there’s the residues left on dry-cleaned clothes. Even cooking fumes are loaded with toxins. When Emma’s mother made blackened catfish last night, for example, some of the PAHs in the smoke found their way into the living room carpet. Cigarette smoke, pet hair, dust mites and mould add to the load of indoor pollutants.

And there’s plenty of opportunity for busy little hands to pick all this up during the course of a day. Researchers at Stanford University videotaped 80 children at normal play for up to eight hours each, then painstakingly noted every move they made. The kids’ hands touched something 340 times per hour on average, and they were in contact with some surface 65 per cent of the time, or 61*2 hours out of a 10-hour day, the Stanford researchers reported at the Monterey meeting. Eventually the Stanford group hopes to combine its own data on children’s activities with information like Camann’s transfer coefficients to estimate the importance of various sources of contamination.

The back door flies open. Emma’s older brother and sister burst in with Cappy, their dog. Cappy is a big, lively golden retriever who loves to run and play with the children in the yard. The kids grab some food and all three go into the living room to watch some TV. In the process, they bring in some of the pesticides that Emma’s dad sprayed on the lawn a few weeks ago. Cappy’s paws also contribute–pesticide residues on dog paws are between 55 and 250 times the background concentration, according to a recent study (New Scientist, 10 February, p 16).

Like 80 to 90 per cent of US households, Emma’s family uses three or four different pesticide products, either indoors or outdoors, each year. Pesticides that cling to shoes and pets’ paws get rubbed off on carpeting inside the home and can raise indoor pesticide levels far above background levels. An earlier study conducted for the US Environmental Protection Agency by the Battelle Memorial Institute in Columbus, Ohio, found that shoes and paws increased the pesticide loads in carpet dust as much as 400-fold. Families with energetic children and energetic dogs racked up the biggest increase.

Even worse , pesticides, PAHs and other semi-volatile compounds don’t stay put once they are in the carpet. They evaporate, drift from place to place and then precipitate back onto the carpet, toys or other household objects, where the cycle starts again. This “grasshopper effect” means that people who use pesticides indoors may inadvertently expose small children to significant contamination, even if they’re careful to keep kids and chemicals apart, says Paul Lioy, deputy director of the Environmental and Occupational Health Sciences Institute, an academic research institute in Piscataway, New Jersey.

His comments are based on a 1998 experiment in which researchers from the institute treated two apartments with chlorpyrifos, a pesticide widely used for flea control, and then opened the windows to ventilate the rooms for the recommended four hours. An hour after the ventilation was finished, they placed plastic and plush toys on the living room floor. When they removed the toys days later they found that chlorpyrifos had collected on them (Environmental Health Perspectives, vol 106, p 9).

The results suggest that for children mouthing the toys, or touching the toys and then mouthing their hands, the dose could be significant and the potential for exposure would persist for many days after the application, says Lioy. Toys, he says, are ideal for accumulating pesticides. “We do this sampling with fuzzy toys because they pick up the pesticides so well,” he says. Many other semi-volatile pesticides such as malathion and propoxur probably spread the same way.

As if all that weren’t enough, pesticides persist for years indoors because they are sheltered from sun, rain and other forces that quickly degrade them outdoors. This is why long-banned pesticides such as DDT are often present in carpet dust, says Robert Lewis, who heads indoor air research at the EPA’s facility in Research Triangle Park, North Carolina.

Last year, Lewis commissioned a study designed to find out just how much pesticide lurks in fitted carpets . Researchers took old plush carpets, between 10 and 33 years old, and cut them up. They found plenty of pesticide deep within the carpets–in one case, a square metre of carpet contained more than a gram of permethrin, an ingredient in some household insect sprays. It was also not uncommon to find two to five different pesticides at concentrations of between 10 and 100 milligrams per square metre, or many times the amount applied in a single application, Lewis told last October’s meeting.

It is not clear what the high levels of pesticides in these carpets portend, says Lewis. Most of the residues were not at the surface of the carpet, but deep among the fibres and the backing, and in the foam padding underneath. The residues can’t be vacuumed up , so they are largely unavailable for human exposure. However, as carpets age, their fibres break down and may release some of these pesticide residues back into the air.

Playtime is almost over. The big kids rush off to the back yard, and Emma’s mother begins to get the little ones’ supper on the table. All seems well in this healthy family. But in the US, Britain and other developed countries, the incidence of children’s diseases that have a significant environmental component, including asthma, allergies and even cancer, continues to rise. And
according to Roberts and his colleagues, dirty carpets may be one of the major causes.

Rebecca Renner is a science writer based in Williamsport, Pennsylvania From New Scientist magazine, 05 May 2001.
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