By Jane E. Brody for the NY Times
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 knowledge.
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 level.
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 reassurances? 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 environmental chemicals.
Q. What has to be done to clarify the potential harm of environmental exposures?
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 which 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. Many fears 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 to control 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.