Society has been “blindsided by product decisions that were made before this new science started to come out,” said Pete Myers, co-author of Our Stolen Future, a book that describes how many everyday chemicals behave like hormones.
Researchers are finding that flame retardants don't obey traditional rules of toxicology, shedding light on the novel ways that some chemicals may still hold dangers, even though they aren't outright poisonous or don't trigger cancer.
The traditional mantra of toxicologists has been that the dose makes the poison, or that exposures have to be large to have an effect, with larger exposures packing more punch than smaller ones.
In experiments with rodents, effects have been noted on the offspring of rats given only one exposure of 60 parts per billion, an amount that a few decades ago scientists would have dismissed as too low to have an impact. To get an idea of the amount involved, a part per billion equals a single drop of water in a gasoline tanker truck.
The pups born to exposed rats were found by motion sensors to be 24 per cent more active in their cages than unexposed control animals.
When researchers upped the dose to 300 ppb, there was hardly any increase in activity; it went up only 27 per cent compared with the controls, despite the fivefold increase in exposure.
The amounts used in the rat experiment, the lowest seen to produce effects, are approaching levels seen in some people in North America, and were thousands of times smaller than the amounts found to kill test animals.
“There was a lot of surprise that these compounds could produce some effect at concentrations like that,” said Dr. Thomas Zoeller, a biologist at the University of Massachusetts who is studying flame retardants for the U.S. Environmental Protection Agency.
What is more, the behaviour effects persisted as the animals aged, indicating that whatever the chemicals did was permanent. “It means that you can't go back and fix it,” Dr. Zoeller said. “You either prevent these [effects] or you cope with them.”
In another experiment, using newborn mice, researchers found another unusual property. Sometimes it isn't the size of the dose that makes flame retardants harmful, but the point in an animal's life when the exposure was given.
Young male mice given traces of the chemicals four and 10 days after birth exhibited behavioural abnormalities, but the same dose given to 19-day-olds caused no changes at all, compared with control animals.
Scientists theorize that the flame retardants had their effect by interfering with hormones during the period of rapid brain growth in the rodents in the first two weeks of life. In humans, this brain growth spurt lasts from the final part of pregnancy through the first two years of life.
The amounts of flame retardants given to the mice was low, in the parts per million range, but what is more remarkable is that the quantity that made its way into brain tissue was the scientific equivalent of almost nothing, only 10 parts per trillion. A part per trillion is the equivalent of a grain of salt in an Olympic-size swimming pool.
Researchers are finding that flame retardants don't obey traditional rules of toxicology, shedding light on the novel ways that some chemicals may still hold dangers, even though they aren't outright poisonous or don't trigger cancer.
The traditional mantra of toxicologists has been that the dose makes the poison, or that exposures have to be large to have an effect, with larger exposures packing more punch than smaller ones.
In experiments with rodents, effects have been noted on the offspring of rats given only one exposure of 60 parts per billion, an amount that a few decades ago scientists would have dismissed as too low to have an impact. To get an idea of the amount involved, a part per billion equals a single drop of water in a gasoline tanker truck.
The pups born to exposed rats were found by motion sensors to be 24 per cent more active in their cages than unexposed control animals.
When researchers upped the dose to 300 ppb, there was hardly any increase in activity; it went up only 27 per cent compared with the controls, despite the fivefold increase in exposure.
The amounts used in the rat experiment, the lowest seen to produce effects, are approaching levels seen in some people in North America, and were thousands of times smaller than the amounts found to kill test animals.
“There was a lot of surprise that these compounds could produce some effect at concentrations like that,” said Dr. Thomas Zoeller, a biologist at the University of Massachusetts who is studying flame retardants for the U.S. Environmental Protection Agency.
What is more, the behaviour effects persisted as the animals aged, indicating that whatever the chemicals did was permanent. “It means that you can't go back and fix it,” Dr. Zoeller said. “You either prevent these [effects] or you cope with them.”
In another experiment, using newborn mice, researchers found another unusual property. Sometimes it isn't the size of the dose that makes flame retardants harmful, but the point in an animal's life when the exposure was given.
Young male mice given traces of the chemicals four and 10 days after birth exhibited behavioural abnormalities, but the same dose given to 19-day-olds caused no changes at all, compared with control animals.
Scientists theorize that the flame retardants had their effect by interfering with hormones during the period of rapid brain growth in the rodents in the first two weeks of life. In humans, this brain growth spurt lasts from the final part of pregnancy through the first two years of life.
The amounts of flame retardants given to the mice was low, in the parts per million range, but what is more remarkable is that the quantity that made its way into brain tissue was the scientific equivalent of almost nothing, only 10 parts per trillion. A part per trillion is the equivalent of a grain of salt in an Olympic-size swimming pool.
MARTIN MITTELSTAEDT
Published by Ceser.
For the past 30 years, flame retardants have been found in every Canadian home, added liberally as a safety precaution to everything from mattresses and carpets to stereos, televisions and computers.
Now Canada is poised to add flame retardants — or polybrominated diphenyl ethers (PBDEs) — to its toxic-substances list.
If a draft proposal it is circulating is any guide, the federal government is expected to virtually eliminate some varieties of the chemical and place tight controls on others.
Regulators are considering drastic action because laboratory studies using animals have linked the chemicals to behaviour changes that bear an uncanny similarity to attention-deficit and hyperactivity disorders common in children. Some researchers believe PBDEs could offer a clue for the sudden rise of these childhood disorders in recent years.
The animal findings on their own would not be a major concern, except for a second disturbing discovery: Flame retardants are not staying put in consumer products. They have been migrating from mattresses and computers, in ways that are not completely understood, into the environment and into people.
It's been a strange odyssey for flame retardants — from lifesaver to possible health hazard.
When the chemicals, known as polybrominated diphenyl ethers, were tested in the 1980s, they seemed to have few drawbacks. They weren't excessively toxic because huge exposures were needed to kill test animals. They also didn't appear to be a cancer risk and were given a clean bill of health for such uses as preventing TV sets, computers and mattresses from catching fire.
It took nearly two decades of their widespread use before scientists began conducting new tests on chemicals, checking whether they had hormone-like properties — a field of science that only started to develop in the mid-1990s after discoveries that many industrial compounds once deemed safe exhibited this unusual attribute.
This new research has found that flame retardants have an ability to mimic thyroid hormones; it is thought that by following that hormonal route, the chemical plays havoc in laboratory animals, where exposures have been linked to hyperactivity, impaired learning and decreased sperm counts.
Now Canada is poised to add flame retardants — or polybrominated diphenyl ethers (PBDEs) — to its toxic-substances list.
If a draft proposal it is circulating is any guide, the federal government is expected to virtually eliminate some varieties of the chemical and place tight controls on others.
Regulators are considering drastic action because laboratory studies using animals have linked the chemicals to behaviour changes that bear an uncanny similarity to attention-deficit and hyperactivity disorders common in children. Some researchers believe PBDEs could offer a clue for the sudden rise of these childhood disorders in recent years.
The animal findings on their own would not be a major concern, except for a second disturbing discovery: Flame retardants are not staying put in consumer products. They have been migrating from mattresses and computers, in ways that are not completely understood, into the environment and into people.
It's been a strange odyssey for flame retardants — from lifesaver to possible health hazard.
When the chemicals, known as polybrominated diphenyl ethers, were tested in the 1980s, they seemed to have few drawbacks. They weren't excessively toxic because huge exposures were needed to kill test animals. They also didn't appear to be a cancer risk and were given a clean bill of health for such uses as preventing TV sets, computers and mattresses from catching fire.
It took nearly two decades of their widespread use before scientists began conducting new tests on chemicals, checking whether they had hormone-like properties — a field of science that only started to develop in the mid-1990s after discoveries that many industrial compounds once deemed safe exhibited this unusual attribute.
This new research has found that flame retardants have an ability to mimic thyroid hormones; it is thought that by following that hormonal route, the chemical plays havoc in laboratory animals, where exposures have been linked to hyperactivity, impaired learning and decreased sperm counts.
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