Calming Parents; Fears About Environmental Hazards
July 13, 2004
By JANE E. BRODY
Dr. Robert L. Brent has been studying environmental
toxicology for nearly half a century.
A distinguished professor at Thomas Jefferson Medical
College in Philadelphia, he specializes in the effects of
environmental factors like radiation, drugs and chemicals
on the developing embryo and child.
But Dr. Brent, who is also the head of a birth defects
research laboratory at the Alfred I. duPont Hospital for
Children in Wilmington, Del., said he often found himself
defending the safety of such environmental agents in the
face of misinformation that ignites the fears of parents
and causes confusion.
Too often, Dr. Brent says, many millions of dollars are
spent to clean up substances that actually present little
or no risk to anyone's health.
To clarify what is known and what is not about
environmental hazards, Dr. Brent, whose research has been
financed by the National Institutes of Health and the
Department of Energy, was a co-author of a printed
symposium that appeared as a supplement to a recent issue
of the journal Pediatrics.
In a telephone interview, he discussed the current state of
Q. Claims of harm from environmental exposures attract a
lot of media attention and arouse intense parental concern.
How justified are they?
A. There's a lot of misinformation out there scaring
parents. Just because you have trichloroethylene in your
well doesn't tell you what your exposure is and whether
there's any risk. I wish there wasn't one chemical in the
environment. But they're there, and we have to deal with
them scientifically - find out if they're at a dangerous
Q. You and your co-authors say our knowledge of toxic
effects - particularly for low-level exposures experienced
by embryos and fetuses - is very limited, which in itself
can be a source of anxiety for parents. Can you offer any
A. We know the threshold dose - the level above which harm
can be done - for most of these substances from animal
studies. We also know that their mechanisms of action are
not the same in every species. We can use animal data to
allay anxiety in certain instances. When the levels in
humans are close to what we see causes harm in animals,
then we're concerned.
This is easy to do with drugs: if you take a drug I know
what your exposure is. But I can't say the same for
Q. What has to be done to clarify the potential harm of
A. You have to know what levels of chemicals are in the
population, their range of exposure, and whether children
have higher or lower levels at different stages of
development. Children's behavior can change their exposure.
An infant who crawls on the floor or who eats dirt will
have a different level than an older child. You can't
guess, you have to know what's in the person's blood. Then
you can do quality animal studies to determine the
threshold dose for toxic or embryonic effects. If what's
present in the environment is one-hundredth or
one-thousandth the level that produces any effect in
animals, that gives you a safety valve. But if you find the
levels are equal, that's a concern.
Q. You say that the dose often makes the poison. Is it
reasonable, then, for people to become alarmed when exposed
to any level of a toxic substance?
A. Toxicological agents all have a threshold below
they will have no effect. There are only two mechanisms in
which there is no threshold - no dose without a risk. These
are chromosomal changes that cause a genetic disease or
cancer, which can result from a change in a single cell.
There's more data to support cancer risks. But for many of
the genetic abnormalities, the damaged embryo is lost even
before a woman knows she's pregnant.
Q. What limits scientists' ability to determine the
specific effects of various agents on the developing fetus
or young child?
A. We don't have good animal models for attention deficit
disorder, convulsive disorders, autism or lowered I.Q. It's
pretty hard to determine whether subtle changes in an
animal will be reflected in the human.
Q. In the meantime, how can parents best protect their
children from possible harm from environmental agents,
short of raising them in a bubble?
A. Many women do limit the medications they take during
pregnancy to only what is necessary. They should stay away
from all herbal medications, which are not well controlled.
A pregnant woman shouldn't put anything in her body that is
not approved by the Food and Drug Administration. As for
environmental agents, city water is as safe if not safer
than what most people drink. Wells can get contaminated.
For city water supplied from a large reservoir, dilution is
the best safety factor.
We don't always know what's in bottled water. Perrier had
benzene in its water a couple of years ago. And you've got
to be sensible about foods you eat. I don't know what's in
food made in a restaurant. I do know what's in food my wife
makes. You're better off eating at home, especially if
you're raising children.
Q. Can you give any examples of false claims from animal
studies of potential toxins?
A. Most agents that cause birth defects have not been
discovered through animal studies, which are helpful
primarily to corroborate risks. There was a claim that
trichloroethylene produces cardiac malformations in the
fetus, but scores of studies say it doesn't. There was
another claim that Retin-A, used to treat acne and
wrinkles, caused birth defects. But you don't get enough
into the body when it's put on skin to affect the embryo.
Q. Some advocates insist that the environment be cleansed
of suspect agents even when clear evidence of harm is
lacking and regardless of the cost of such cleanup. Is this
reasonable or necessary to protect our young?
A. Love Canal was an example of a terrible environmental
problem that should be cleaned up, but there was no
evidence of risk to the people who lived there.
are irrational. Each instance has to be evaluated it on its
own merits. They wanted to tear down a group of houses in
Philadelphia in which the level of radon was just a little
above background. All that was needed was to put a fan in
the basement to blow the stuff out.
Q. Once a substance has been shown to cause birth defects,
pregnant women often become alarmed when they realize
they've been exposed to it. But dose and timing make a
difference. When should women worry?
A. Timing is important. If ACE inhibitors, used
blood pressure, are given in the first trimester, nothing
happens because it doesn't interfere with organogenesis.
But in the second and third trimester, it produces fetal
hypotension and babies are born severely growth-retarded -
with hypoplastic lungs and damaged kidneys - and die. The
same is true for dosage: if you give cortisone at a high
enough dose, you could cause birth defects. But at
therapeutic doses it's innocuous during pregnancy. Health
care workers often misinform pregnant women. There are
probably 1,200 babies in this country alive today because I
stopped their mothers from having an abortion once I knew
the timing or dose of their exposure.