October 25, 2005


By Amy Norton

NEW YORK (Reuters Health) -- There is no clearly safe level of
exposure to four of the most common environmental toxins in the world,
and more should be done to protect the public, researchers argue in a
new report.

The toxins in question -- lead, radon, tobacco smoke and byproducts of
drinking-water disinfection -- are ubiquitous, and there is growing
evidence that even low-level exposure can have health consequences,
according to the report, published in the medical journal PloS

"Emerging evidence indicates that exposures must be virtually
eliminated to protect human health," conclude Dr. Donald Wigle, of the
University of Ottawa in Canada, and Dr. Bruce Lanphear, of Cincinnati
Children's Hospital Medical Center in Ohio.

The problem, Wigle told Reuters Health, is that there are no known
safe levels of exposure to these toxins, yet people are persistently
in contact with them.

"These are widespread exposures," he said. "They're not rare."

Lead, for instance, is present in the air, soil and water, and it has
become clear that even relatively low-level exposure can damage the
developing brain in young children and fetuses, leading to learning
and behavioral problems. In adults, lead exposure may raise blood
pressure and damage the kidneys, brain and nerves.

In developed nations, much progress has been made in recent decades to
reduce people's lead exposure, Wigle pointed out. Lead has been
removed from gasoline, for instance, and it is no longer used in

However, people in developing nations continue to be exposed to lead
from these and other sources, Wigle noted. And in places like the U.S.
and Canada, dust and chips from lead-based paints in older homes are
still a prime source of exposure. Drinking water can also contain low
levels of lead, especially if a home has old lead pipes.

In the U.S., the "level of concern" for blood lead levels is 10
micrograms of lead per deciliter (mcg/deciliter) of blood. However,
Wigle and Lanphear point out, a number of studies in several countries
have linked lead levels below that threshold to lower IQ scores.

Health officials, Wigle noted, have never dubbed the 10-microgram
level as "safe." Conversely, "The science suggests (the level) is too
high, and should be moved down," he said.

One way to curb lead levels in tap water is to use a carbon-based
water filter -- a tactic that also reduces disinfection byproducts,
Wigle noted.

Disinfection byproducts form when drinking water is treated with
chlorine to kill disease-causing microbes. The chlorine reacts with
organic materials in the water to create a range of chemicals,
including a group known as trihalomethanes (THMs). THMs are known to
cause cancer in animals, and some studies have linked them to
miscarriage and other pregnancy risks. There is also evidence tying
them to bladder cancer in humans.

Wigle and Lanphear point to a recent analysis of several studies that
found that exposure to water with THM levels of 1 mcg/deciliter may
increase the risk of bladder cancer. In the U.S., the maximum
allowable THM level is 80 mcg/deciliter, and in Canada, it's 100

Again, Wigle said, these levels may be "much too high."

The two remaining toxins he and Lanphear highlight -- secondhand smoke
and radon -- also have no apparently safe level of exposure. Radon is
a natural radioactive gas found in soil, air and ground water that is
known to cause lung cancer.

Radon levels in homes and other buildings vary widely, and health
officials recommend that people whose homes have radon levels
exceeding 4 picoCuries per liter of air take action -- such as
increasing ventilation. But again, Wigle and Lanphear note, there are
studies suggesting that radon exposure below this level increases the
risk of lung cancer.

When it comes to tobacco smoke, the researchers say, growing evidence
suggests that low-level, secondhand exposure during pregnancy can
impair fetal growth -- a long-recognized danger of active smoking.

Though personal behavior is a big factor in exposure to tobacco smoke,
Wigle said, workplace laws -- including recent local bans on smoking
in restaurants and bars -- can also protect people from unwanted

SOURCE: PloS Medicine, December 2005.

Copyright Reuters 2005.