Animal Tests Overstate Cancer Fears: Part 3 of 3

Published August 1, 2003

Cancer scares created by environmental activist groups frequently focus on man-made chemicals. However, such chemicals play a very small role in human cancer rates and are far outweighed by the risks posed by natural chemicals, according to Misconceptions about the Causes of Cancer, a book published by the Fraser Institute and authored by leading cancer researchers Lois Swirsky Gold, Thomas H. Slone, Neela B. Manley, and Bruce N. Ames.

In this, the last of three articles culled from the new book, the authors explain why animal cancer tests tend to overstate human cancer fears, especially with respect to man-made chemicals.

part 1 * part 2

Comparative Index

“An analysis of synthetic chemicals against the vast array of natural chemicals shows that synthetic rodent carcinogens are a tiny fraction of the total. A comparison of potential hazards using a simple index can be helpful in efforts to communicate what might be important factors in cancer prevention. There is a need to identify what might be the important cancer hazards among the ubiquitous exposures to rodent carcinogens in everyday life.” (page 43)

“One reasonable strategy for setting priorities is to use a rough index to compare and rank possible carcinogenic hazards from a wide variety of chemical exposures at levels that humans typically receive and then to focus on those that rank highest. Ranking is thus a crucial first step. Our analyses are based on the Human Exposure/Rodent Potency Index (HERP), which indicates what percentage of the rodent carcinogenic potency a person receives from a given average daily dose when exposed over a lifetime.” (page 43)

Synthetic Chemicals Rank Low

“Overall, our HERP ranking has shown that synthetic pesticide residues rank low in possible carcinogenic hazard compared to many common exposures. HERP values for some historically high exposures in the workplace and some pharmaceuticals rank high, and there is an enormous background of naturally occurring rodent carcinogens in average consumption of common foods. This background of natural chemical results casts doubt on the relative importance of low-dose exposures to residues of synthetic chemicals such as pesticides. A committee of the National Research Council recently reached similar conclusions when they compared natural and synthetic chemicals in the diet and called for further research on natural chemicals.” (page 44)

“The ranking of possible hazards (HERP values in %) is for average exposures in the United States to all rodent carcinogens in the Carcinogenic Potency Database (CPDB), a widely used resource on the standardized results of chronic, long-term animal cancer tests. For pharmaceuticals, the doses are recommended doses, and for exposure in the workplace they are past averages for an industry or a high-exposure occupation. The 94 exposures in the ranking are ordered by possible carcinogenic hazard (HERP) and natural chemicals in the diet are reported in boldface. The median HERP value is 0.002% and the background HERP for the average chloroform level in a liter of United States tap water is 0.0008%. Chloroform is formed as a by-product of water chlorination and the HERP value reflects exposure to chloroform from both drinking water and breathing indoor air, for example, when showering. A HERP of 0.00001% is approximately equal to a regulatory risk level of 1-in-a-million based on a linear model, i.e. the Virtually Safe Dose (VSD).” (page 45)

“The rankings indicate that, if the same methodology were used for both naturally occurring and synthetic chemicals, most ordinary foods would not pass the default regulatory criteria that have been used for synthetic chemicals. For many natural chemicals, the HERP values are in the top half of the table, even though natural chemicals are markedly under-represented because so few have been tested in rodent bioassays. The ranking of HERP values maximizes possible hazards from synthetic chemicals because it includes historically high exposure values that are now much lower, for example, exposure to DDT and saccharin as well as to occupational chemicals.” (page 45)

For more information …

The full text of Misconceptions About the Causes of Cancer is available in Adobe Acrobat’s PDF format on the Fraser Institute’s Web site at The book can also be ordered from the Fraser Institute for $19.95 (CAN) plus $10.00 shipping and handling. Call 604/688-0221 or email your order to [email protected].

Ranking Possible Carcinogenic Hazards
(Chemicals that occur naturally are in bold)
HERP (%) Average Daily US human exposure Rodent carcinogen
140 EDB; production workers (before 1977) Ethylene dibromide
17 Clofibrate Clofibrate
12 Phenobarbital, 1 sleeping pill Phenobarbital
6.9 Gemfibrozil Gemfibrozil
6.8 Styrene-butadiene rubber industry workers (1978-86) Butadiene
6.2 Comfrey-pepsin tablets, 9 daily (no longer recommended) Comfrey root
6.1 Tetrachloroethylene; dry cleaners with dry-to-dry units (1980-90) Tetrachloroethylene
4.0 Formaldehyde: production workers (1979) Formaldehyde
3.6 Alcoholic beverages, all types Ethyl alcohol
2.4 Acrylonitrile: production workers (1979) Acrylonitrile
2.2 Trichloroethylene: vapor degreasing (before 1977) Trichloroethylene
1.8 Beer, 229 g Ethyl alcohol
1.4 Mobile home air (14 hours/day) Formaldehyde
1.3 Comfrey-pepsin tablets, 9 daily (no longer recommended) Symphytine
0.9 Methylene chloride: workers, industry average (1940s-80s) Methylene chloride
0.6 Wine, 20.8 g Ethyl alcohol
0.5 Dehydroepieandrosterone (DHEA) DHEA supplement
0.4 Conventional home air (14 hours/day) Formaldehyde
0.2 Fluvastatin Fluvastatin
0.1 Limonene in food Limonene
0.1 Coffee Caffeic acid
0.06 Lovastatin Lovastatin
0.04 Lettuce, 14.9 g Caffeic acid
0.03 Safrole in spices Safrole
0.03 Orange juice Limonene
0.03 Comfrey herb tea, 1 cup (1.5 g root) (no longer recommended) Sympnytine
0.03 Tomato, 88.7g Caffeic acid
0.03 Furfural in food Furfural
0.02 Coffee, 11.6 g Catechol
0.02 Mushroom 9Agaricus bisporus 2.55 g) Mixture of hydrazines, etc.
0.02 Apple, 32.0 g Caffeic acid
0.01 BHA: daily US avg (1975) BHA
0.01 Beer (before 1979), 229 g Dimethylnitrosamine
0.008 Aflaoxin: daily US avg (1984-1989) Aflatoxin
0.007 Celery, 14 g Caffeic acid
0.007 Limonene Food additive
0.007 Cinnamon, 21.9 mg Coumarin
0.006 Coffee, 11.6 g Furfural
0.005 Coffee, 11.6 g Hydroquinone
0.005 Saccharin: daily US avg (1977) Saccharin
0.005 Carrot, 12.1 g Aniline
0.004 Bread, 79 g Furfural
0.004 Potato, 54.9 g Caffeic acid
0.004 Methyl eugenol in food Methyl eugenol
0.003 Conventional home air (14 hour/day) Benzene
0.002 Coffee, 11.6 g Methylcatechol
0.002 Nutmeg, 17.6 mg Limonene
0.002 Carrot, 12.1 g Caffeic acid
0.002 Ethylene thiourea: daily US avg (1990) Ethylene thiourea
0.002 BHA: daily US avg (1987) BHA
0.002 DDT: dialy US avg (before 1972 ban) DDT
0.001 Estragole in spices Estragole
0.001 Pear, 3.7 g Caffeic acid
0.001 Toxaphene: daily US avg (before 1982 ban) Toxaphene
0.001 Mushroom (Agaricus bisporus 5.34 g) Glutamyl-hydrazino-benzoate
0.001 Plum, 1.7 g Caffeic acid
0.001 [UDMH: dialy US avg (1988)] [UDMH (from alar)]
0.001 Bacon, 19 g Diethylnitrosamine
0.0008 Bacon, 19 g Dimethylnitrosamine
0.0008 Tap water, 1 liter (1987-92) Chloroform
0.0008 DDE: daily US avg (before 1972 ban) DDE
0.0007 Bacon, 19 g Nitrosopyrrolidine
0.0006 Methyl eugenol Food additive
0.0004 EDB: Daily US avg (before 1984 ban) EDB
0.0004 Tap water, 1 liter (1987-92) Bromodichloromethane
0.0004 Celery, 14 g Methoxypsoralen
0.0003 Mango, 1.0 g Limonene
0.0003 TCDD: daily US avg (1994) TCDD
0.0003 Furfural Food additive
0.0003 Carbaryl: daily US avg (1990) Carbaryl
0.0003 Mustard, 18.9 mg Allyl isothiocyanate
0.0002 Beer (1994-95), 229 g Dimethylnitrosamine
0.0002 Mushroom (Agaricus bisporus, 5.34 g) Hydrazinobenzoate
0.0002 Estragole Food additive
0.0002 Allyl isothiocyanate Food additive
0.0002 Hamburger, pan fried, 85 g PhIP
0.0001 Toxaphene: daily US avg (1990) Toxaphene
0.00008 PCBs: daily US avg (1984-86) PCBs
0.00008 Toast, 79 g Urethane
0.00008 DDE/DDT: daily US avg (1990) DDE
0.00007 Beer, 229 g Furfural
0.00006 Parsnip, 48.8 mg Methoxypsoralen
0.00004 Parsley, fresh, 257 mg Methoxypsoralen
0.00003 Hamburger, pan fried, 85 g MeIQx
0.00002 Dicofol: US avg (1990) Dicofol
0.00001 Hamburger, pan fried, 85 g IQ
0.000009 Beer, 229 g Urethane
0.000005 Hexachlorobenzene: daily US avg (1990) Hexachlorobenzene
0.000001 Lindane: daily US avg (1990) Lindane
0.0000004 PCNB: daily US avg (1990) PCNB
0.0000001 Chlorobenzilate: daily US avg (1989) Chlorobenzilate
0.00000008 Captan: daily US avg (1990) Captan
0.00000001 Folpet: daily US avg (1990) Folpet
<0.00000001 Chlorothanlonil: daily US avg (1990) Chlorothalonil