Actually, NRC did an evaluation of this as part
of the early talks with EPA on risk harmonization. It is attachment 3 of
SECY-96-110 dated May 17, 1996 - from James M. Taylor called "Completion
of response to the staff requirements memorandum, for SECY-95-249, on Risk
harmonization white paper and recommendations by the Interagency Steering
Committee on Radiation Standards".
It is a VERY interesting read. Among other
gems, they conclude,
"99.99% of of the chems to which people are exposed
are naturally occurring"
"as is the case with synthetic chemicals, about half
the natural chemicals that have been tested have been classified as possible
or probable human carcinogens because they cause cancer in lab rodents at very
high doses"
"If one assumes that the positivity rate for untested
synthetic chemicals is the same as that for untested naturally occurring
chemicals, natural chemical carcinogens make up the majority of the chemical
carcinogens to which humans are exposed".
My personal favorite:
"Gold et al. hazard rankings indicate that if you eat
one apple a day, the calculated lifetime cancer risk form the caffeic acid in
the apple would be equivalent to 3 x 10^-3. One eighth of a head of
lettuce perday would yield a lifetime risk of 1e-2 (also from caffeic acid);
the risk of one mushroom per day would be equivalent to 1e-2 (from
hydrazines). A cup of coffee per day would imply a lifeitme risk of 1e-3
of cancer from caffeic acid (Coffee contains 1000 natural chemicals, and only
26 have been tested. Of those that have been tested. 19 have produced cancer
in lab animals." (For what it is worth, the only way you are going to get the
coffee cup out of MY hands is by prying it from my cold dead fingers
...)
They do, point out, however, that "one should
probably not pay much attention to these absolute numbers because, despite the
fact that fruit and vegetables are full of rodent carcinogens, it is fairly
clear from epi studies that fruit and vegetable consumption actually reduces
risk of cancer." (A very depressing conclusion for a risk
assessor).
They
conclude:
"If the
fraction of natural chemicals that are carcinogenic is the same as the
fraction of synthetic chemicals that are carcinogenic, then the calculated
chemical background risk is actually much larger relative to calculated
man-made chemical risk than radiation background risk is relative to man-made
radiation."
Anyway, it
is a great read. But also to answer part of your question, some of the
naturally occurring chemical carcinogens include aflatoxin, arsenic (in
groundwater for example), criminy - I mean dioxin can be produced in forest
fires. Tobacco is naturally occurring!
Unfortunately, I don't have a software version, or
know where it is posted. But I'm sure someone has posted it
somewhere.
-Eric
Eric Frohmberg
Toxicologist
Key Plaza, 8th Floor
11 State House Station
Augusta, ME 04333-0011
Tel: (207) 287-8141
FAX: (207) 287-3981
TTY: (207) 287-8066
eric.frohmberg@state.me.us
-----Original
Message-----
From: BLHamrick@AOL.COM
[mailto:BLHamrick@AOL.COM]
Sent: Sunday, March 09, 2003 4:37
PM
To: radsafe@list.vanderbilt.edu
Subject: Hazardous vs.
Radioactive Materials
This may be slightly off-topic for this list, but I was
wondering if anyone knew of any specific hazardous materials (carcinogens)
that are present in the natural background, as radioactive material is, and
what the "background" risk levels might be for those hazardous
materials.
Barbara