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Report: Safe levels of key toxins unknown

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.
/ Source: Reuters

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 Medicine.

“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, 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.”

The case against lead
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 paints.

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/dL) 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.

Chlorine in water concern
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/dL may increase the risk of bladder cancer. In the U.S., the maximum allowable THM level is 80 mcg/dL, and in Canada, it’s 100 mcg/dL.

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 exposure.