DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
PUBLIC HEALTH SERVICE

NATIONAL INSTITUTES OF HEALTH
BETHESDA, MARYLAND 20014

DEC i 5 1969

December 10, 1969

Dr. Joshua Lederberg

Professor of Genetics

Stanford University
Medical Center

Stanford, California 94305

Dear Dr. Lederberg:

I was delighted to read your editorial "Pretesting chemical
additives” in C and E News of December 8, 1969, as well as
similar comments expressed in one of your weekly newspaper
columns.

We have been concerned with this problem of evaluating materials
in our environment for carcinogenicity or indeed any other
untoward toxic effect for many years. We believe that we need
to safeguard the future health of our people. In our view many
cases of cancer seen at this time are due to exposure to
environmental factors many years ago. I personally believe
that many such factors were "naturally occurring" rather than
synthetic materials. Cancers of the type seen in our
industrialized civilization are also seen in more primitive
environments where the products of industry cannot be possibly
responsible. However, superimposed on this natural background
of carcinogen we now have the additional possible contamination
by synthetics.

Our concern is to reduce as much as possible the carcinogen
loads from all sources, synthetic or naturally occurring. You
express this idea very well in the editorial. We have discussed
this very same problem in a recent paper in Food and Cosmetics
Toxicology. J am pleased to send you a reprint.

Sincerely yours,

Vl Weivher —_—

Jouh He Weisburger, Ph.D.
Head, Carcinogen Screening Section
Biology Branch, Etiology
National Cancer Institute