Imágenes de páginas

certain substances and we are the only industrialized nation in the world without any decent paternity policy for women.

In the lead standard and the other things we have been arguing against the exclusion of women, I have always felt that what we have achieved is an equal right to be poisoned. I cannot push for allowing pregnant women to remain in the toxic work place.

On the other hand, I can also not generalize that the fact that one is pregnant, ipso facto, means there will be an adverse outcome. The relative weights and contribution of all this is not known.

The safest and surest thing to do would be to allow both future mothers and future fathers to have a prepregnancy planning time when they could avoid exposure to toxic substances and when they are pregnant, I don't see any reason why we, as a society, could not provide medical retention plans to allow them not to be exposed.

Mr. GORE. How long prior to a planned pregnancy would that period be?

Dr. STELLMAN. I think that depends on the substance. If it is a dibromochloropropane worker, it would be a very long time before prepregnancy for the male to plan that.

A 3-month cycle for spermatogenesis; 72 days. It is not clear how susceptible the ova are to different substances.

None of this work has been done. Some of the biomedical tests that Dr. Karrh alludes to in his testimony might be appropriate to determine the levels of chemicals that are present in a person's body prior to conception. I think it is a fruitless argument to engage in, which is the greatest. They are all potential risk factors and they must all be addressed if we are to provide for good reproductive health in our society.

Mr. GORE. Given the uncertainties are enormous, you would agree that the magnitude of the risk to the fetus and the magnitude of the risk to the offspring through the parent prior to conception are comparable.

Dr. STELLMAN. I think you can't generalize. I think it depends on the substance. For ionizing radiation, preconception is greater than in utero. There was just a study that came out to show that.

In animals, preconception exposure, particularly in the male, is of greater import. For heavy metals, it will depend on transport properties. For things like diethylstilbestoral or thalidamide-the thalidamide was only effective as a teratogen between the 19th and 35th day of pregnancy. Otherwise, it had no effect at all.

Pregnancy and reproduction is a dynamic process that can't be generalized about in that way. You are focusing on the host rather than the agency again, and that is where the problems arise.

Mr. GORE. Yesterday we heard about the use of pre-employment back X-rays in the railroad industry as part of an effort to find back problems that might enhance the risk of occupational injury.

Dr. STELLMAN. You should look into the reproductive health after all those back X-rays.

Mr. GORE. That, by coincidence, was going to be my question. What would the hazards to men and their future offspring be from such X-rays?

Dr. Hunt. I think relating this question to the last one, the real usefulness of ionizing radiation to scientists is that it is a hazard

which can be much better controlled in terms of observations of its effect than we can do with toxic substances, so it is indeed the model that we have which we can pin some of the comparisons between preconception for men and for women and the subsequent effect on the embryo, fetus.

We can't do this with anything else very much. Ionizing radiation, both from animals and from human observations, is for the same dose showing very, very much more marked effect on the male than it is on the female and also on the embryo fetus.

We are talking about fairly low doses and I must admit we have that as suggestive information but when you extrapolate from high doses, that statistical result that you get is a very specific number of cases of spontaneous abortion, of congenital anomalies that could be expected because of preconception exposure to the female.

That is, the impact on the ovum is so miniscule that it ends up in the charts, which are being developed by the United Nations Committee on Effects of Ionizing Radiation.

As little question marks for the female, because we will not accept in the radiation field that there is no damge from radiation.

There is a basic underlying philosophy that any dose presents a risk of some damage, however low. But that question mark acknowledges that if such a low risk is involved for the preconception female that you can only just put a question mark and not any specific numbers.

Then, when we come to the issue of the embryo fetus, most certainly in the dose range that we tend to be speaking of in a controlled situation, be it a well-monitored working environment in a reactor, well-monitored working environment in industry with Xray deffraction equipment, other methods or in a hospital, we do not have epidemiologically any case that I can think of, any case that we can absolutely attribute to an adverse effect on the child in terms of a congenital anomaly. We are talking about less than 5 rad per year to the mother and usually it is very much lower than in the work setting.

So that is the only complete set of data that is comparing those three situations of biological, chemical, and phsical hazards that you are interested in and it seems to me, that we must get comparable information on, the body burden of pesticides; for example, in either a work population or in the environment at large, and run through that same relationship. The Atomic Energy Commission poured millions of dollars into their studies through the late 1950's and early 1960's. We are still standing on that base to develop our assessment of the relative importance of these three kinds of hazards.

We have it only for ionizing radiation. We have very little for any other environmental hazard.

Dr. STELLMAN. I think I would like to point out that the EPA recently proposed regulations on ionizing radiation in which they assumed that male risk and whole-body risk for radiation were equivalent and were seeking to set up special rules for the fetus in the workplace.

It is just again a presumption based on no excess male risk, so here we have a new regulation being proposed by the Government in this very area, if in the only area we have data, too.

Dr. Hunt. The only area we have fix on data, is on the reproduction of the whale.

Mr. GORE. In summary, then, all three of you believe that given the current state of knowledge, it is irrational to assume or conclude that the risk to the fetus directly through exposure to the pregnant woman is greater than the risk to the fetus through exposure to either parent prior to pregnancy; that such an assumption is currently irrational.

Dr. HUNT. Yes.
Dr. STELLMAN. I don't agree with that.
Dr. HUNT. You want to caveat that?

Dr. STELLMAN. The only thing I agree to is that we are talking about an extremely dynamic process and that that is the trouble with the whole field of reproductive toxicology; people have tried to make generalizations, none of which are true.

We have policies based on placental transfer, in the first 3 months, when all the organs are being formed, placental transfer is irrelevant before the placenta is not fully functioning.

Mr. GORE. Isn't there some comparable avenue of exposure from the mother to the developing fetus during the first 3 months?

Mr. GORE. Do they not share the same bloodstream?

Dr. STELLMAN. To some extent they do. In the very earliest part, it is what is called histiotrophic nutrition and the embryo draws its nutrition from stored blood. That is what menstruation is, the shedding of stored food supplies.

There is not a dynamic process of transfer between the maternal and embryonic bloodstreams at the outset of pregnancy. In fact, studies on cadmium transfer in rabbits, for example, have shown that the amount of cadmium that is transferred from the mother's blood to the rabbit is a function of the age of the embryo or the fetus and not how much is in the mother's blood.

We have gone full circle in imagery of reproduction. I also disagree, it used to be women were not considered part of the conception process. There was a model called the homunculus man in which it was felt that the fully formed offspring was actually contained in the male sperm and the mother simply served as a vessel.

Then we went to, along with the Victorian era, in which women were with the guardians of the home and art to imagery in which the placenta and the womb was the all-embracing "Garden of Eden" environment for the child and which, until thalidomide, was called the placental barrier.

It wasn't until the 1960's, after the thalidomide tragedy that the whole field of reproductive toxicology, teratology was born and we have now come to a model in which the placenta performs no function at all, in which the womb is simply a sieve, in which everything in the outside world is passed to the embryo or to the fetus. None of these models is correct. The mother and the womb do serve as a protective function; in fact, if you take a child whose father is a leadworker, that child probably stands a better chance of being less exposed to lead, who works in a dirty place, brings the lead home, but probably have less lead exposure in utero than after



being born because it is very well-documented that children of smelterworkers have high lead.

The mother protects the child from that. So all of these models are really mirrors of our social imagery of the role of the female.

They can't be generalized like that.

Dr. HUNT. I wonder if the caption of your summary might better include a probability concept in it, that it is not so much the fact that one avenue is greater or less than another, as it is that the probability of an effect is quite wide in all three instances of physical, chemical, and biological hazards.

But I would almost say that the probability of effect on the male for a given dose is going to be much higher, much narrower probability band than is the case for the same dose for the fetus; that indeed the fetus still can be damaged and that damage might turn out to be quite severe, but the variation, that variation band is going to be very, very widespread for that fetus.

It is far less likely to be affected for the same dose when compared with what might happen to the sperm along the way.

Mr. GORE. OK, I guess the root of my assumption was the belief that the process of development the fetus has under way carries with it a vulnerability that exceeds the vulnerability of the antecedent sperm

and ovum. Dr. HUNT. Yes; I don't think we can always say that.

Mr. GORE. I began the questions for this panel with questions of you, Dr. Hunt, on research priorities. Coming back to that briefly, in light of the discussion that we have just had, how would you characterize the current allocation of research effort as between preconception hazards and postconception hazards?

Dr. HUNT. I would say that the few studies that are being done on preconception are being done by the National Institute of Occupational Safety and Health for the male. That is about the sole location, I think, of studies in this area: The basic research being done in the National Institute for Child Health and Human Development has been primarily emphasizing the female preconception, the whole area of oocyte toxicity.

There are just very few people involved in both and not a large budget.

The second component which is more the area of developing tests and validating those tests, I see only in the area of a few epidemiologic studies, again by the National Institute of Occupational Safety and Health, in workplace epidemiology: The effort for test development is going along at a much faster pace in EPA now than it was a few years ago.

But, again, I suspect that the availability of funds for this very expensive component of validation which means human studies, we are going to have to rely perhaps on the Europeans and others to do this.

Mr. GORE. But the Science and Technology Committee is having hearings shortly on the research and development funds at EPĂ and what I regard as a mindless elimination of R. & D. effort.

But that is a matter of some controversy.

Dr. HUNT. I think it is the critical component of who is going to be responsible for validation; and whatever happens, who will do it and see that it is done.

Mr. GORE. Yes; another conclusion which I gathered from this panel's testimony was that the current examples of genetic screening or screening of people supposed to have enhanced risk in the workplace don't really reflect a rational, comprehensive view of what the most avoidable hazards really are, where we can really have the best effect on outcomes but exhibit instead an apparently irrational pattern that reflect other factors at work in addition to a legitimate concern for protecting the health of workers.

We had a very candid statement yesterday from representatives of the railroad industry about the impact of a particular statute that imposes a strict negligence standard on preemployment screening efforts, that leads to an irrational outcome, in my view, if you carry the outcome to what you would get if you sat down and said, “What are the worst risks and how can we avoid them?

And you have cited several examples of risks that are arguably much greater than the risks that we now selectively try to avoid and argue for more and more reasoned, rational approaches to screening if we are going to have such screening.

Any of you wish to comment on that? Is that a fair summary of that particular point?

Dr. HUNT. Yes.

Ms. BERTIN. Let me just make one comment here. I think the lack of rationality is very troublesome because it suggests that other motives are at play in creating some of these policies.

I did want to clarify something because of a comment Jeanne made. None of us is arguing that real risks should be ignored. What we are arguing is that everyone should be protected. In particular real people require the same level of care and attention as those potential future children of some workers who may not intend to have any future children.

We are not trying to say that people should be equally poisoned. We are trying to say that if an industry is using toxins or producing toxins, look at all of the effects and start attacking the worst ones.

First, do it in a nondiscriminatory fashion, don't do it because of assumptions that you have about homunculus man or earth-mother or whatever, but based on some sort of a rational scientific approach.

Dr. STELLMAN. I think the model that should be looked at, I am very much concerned at the Cancer Center at Columbia, with early detection and screening for cancer itself, not of any necessity origin.

And there, even when looking for early signs of a frank disease, the ability to detect, to detect a significant number of those who are at risk are very limited. In fact, even the very popular ones that are tested that are out there are of limited usefulness.

Perhaps it is a good example for the Congress to bear in mind, the recent reexamination of tests that the American Cancer Society went through. They have just changed their recommendation for cervical pap smears from annually to every 3 years.

The kind of exercise and thoughtfulness that people like David Eddy at Stanford go through in calculating the utility of screening must, at the very least, be applied in this area, where the effects of

« AnteriorContinuar »