Now, reproductive toxicity, like cancer or carcinogenicity, is a complicated process.
The reason is that reproduction itself is a complicated process with
many different steps.
I already mentioned, for example, that you can cause damage to the DNA even before
the egg and the sperm combined, and that can cause a mutation and a birth defect.
In addition, once the fetus is developing, there are certain critically
important developmental processes that can be affected by chemicals or drugs.
Some examples of this that you may be familiar with,
for example, are thalidomide, which can cause damage to the developing limb buds,
resulting in small or malformed limbs.
Also, DES, diethylstilbestrol, which is a chemical that was used many years ago for
women and it caused problems in girls who were born to mothers who had taken DES.
And it caused problems with the formation of the cervix and
the development of the cervix.
There are also chemicals such as lead, which can cause, at many different points
along development, problems with the developing central nervous system.
So there are many different points where you could interrupt or
damage the process of reproduction.
And at that same time, again, in most cases, when we look at birth defects,
they are, like cancer, very complex to disentangle a particular cause.
So, in many cases, unless we are relatively confident of the exposure and
relatively confident that we can link a particular agent, when we
have a child who has a birth defect, it's sometimes difficult to go back and
figure out exactly what the exposure was that contributed to the birth effect.
Now, many of you may have heard the term endocrine disruption.
This is a term that's been relatively recent in the literature and it refers to
the idea that we have hormones, chemicals that are chemical messengers in the body.
Sometimes they are sex hormones like estrogen or testosterone.
There are other kinds of hormones as well.
These hormones can be, in some cases, chemically similar to or similar enough
in structure to chemicals that are in the environment that the body sometimes is
fooled and thinks that the chemical in the environment, once it's in the body,
is similar to or acts the same as a naturally occurring hormone like estrogen.
When that happens, these estrogen mimics, or these endocrine mimics, or
endocrine disruptors can either block or exaggerate or somehow interfere
with the normal signaling in the body that is what the chemicals are used for.
That can cause a number of problems that we usually see or
can see in terms of growth and development.
Sometimes it's development or sexual differentiation.
Sometimes it's a difference in terms of the way the hormones behave.
And it's an emerging field which has caused a great deal of
interest in the scientific community because there are many concerns that these
persistent chemicals in the environment may be leading to these effects not
only in people, but in various animals throughout the ecosystem.
So, endocrine disruption is a concept that you'll see more of in years to come.