IT鈥橲 playtime at Emma鈥檚 house. Children in constant motion seem to be
everywhere鈥攗nder the dining room table, playing with toys, hugging the
dog. Oops, Emma鈥檚 eating Cheerios off the carpet and Johnny鈥檚 licking the coffee
table. Johnny, who is two, may put 76 things in his mouth in the course of an
hour鈥攖oys, his fingers, someone else鈥檚 fingers鈥攁 recent study
discovered. 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鈥檇 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鈥檚
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鈥攊f tedious鈥攔emedy close at hand.
Advertisement
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. 鈥淭he 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,鈥� says Roberts. That鈥檚 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鈥檚 parents take for granted, such as cleaning
products, solvents, deodorisers and air fresheners. Then there鈥檚 the residues
left on dry-cleaned clothes. Even cooking fumes are loaded with toxins. When
Emma鈥檚 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鈥檚 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鈥� hands touched something 340 times per hour on
average, and they were in contact with some surface 65 per cent of the time, or
6陆 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鈥檚 activities with information like Camann鈥檚 transfer coefficients to
estimate the importance of various sources of contamination.
The back door flies open. Emma鈥檚 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鈥檚 dad sprayed on the lawn a few weeks ago. Cappy鈥檚 paws
also contribute鈥攑esticide residues on dog paws are between 55 and 250
times the background concentration, according to a recent study
(New 杏吧原创, 10 February, p 16).
Like 80 to 90 per cent of US households, Emma鈥檚 family uses three or four
different pesticide products, either indoors or outdoors, each year. Pesticides
that cling to shoes and pets鈥� 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鈥檛 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 鈥済rasshopper effect鈥� means that people who use
pesticides indoors may inadvertently expose small children to significant
contamination, even if they鈥檙e 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. 鈥淲e do this sampling with fuzzy
toys because they pick up the pesticides so well,鈥� he says. Many other
semi-volatile pesticides such as malathion and propoxur probably spread the same
way.
As if all that weren鈥檛 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鈥檚
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鈥攊n 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鈥檚 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鈥檛 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鈥檚
mother begins to get the little ones鈥� supper on the table. All seems well in
this healthy family. But in the US, Britain and other developed countries, the
incidence of children鈥檚 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.
The health risks for infants and toddlers posed by house dust in carpets are
high and the cost of control is low, says Dr Dust (environmental engineer John
Roberts). Here鈥檚 his prescription for ridding your house of dust.
- Become compulsive about vacuuming your carpets. Each week make 25 passes
over the area of the rug within four feet of the main entrance doors, 16 passes
over areas that receive a lot of foot traffic, and eight passes over the rest of
the carpet. After a few weeks, you鈥檒l be sick of vacuuming but you will have
removed a good portion of the deep dust in your carpets. From that time, careful
weekly vacuuming using half the passes mentioned above should keep carpet dust
levels low. - Use a vacuum with a power head, which picks up three to six times as much
dust as one without power brushes. A dirt-finder vacuum (which has a light that
turns from red to green when the carpet is clean) is even better. - Put a high-quality doormat at each of the entrances to your home and wipe
your feet twice before entering. Most doormats sold in retail stores are not
very effective at stopping tracked-in pollution. Buy the thickest mat you can
find. Better yet, have everyone leave their shoes at the door.
When Roberts鈥檚 daughter and her husband moved into an apartment that had old
carpets, they put his ideas to work. Before they began, Roberts measured lead
levels in the carpet of 7800 micrograms per square metre, far above the EPA鈥檚
safety threshold of 434 &mgr;g/m2.
To address the problem, the couple, who were planning to have children, put
in a high-quality doormat, began taking off their shoes at the door and used a
standard power-head vacuum cleaner twice a week. After six months, lead levels
were down to 160 &mgr;g/m2, and in 14 months had dwindled
to just 32 &mgr;g/m2.