Changes in Toxicological Dogma
If you haven't yet heard of “hormesis” you probably soon will. A revolution is taking place in toxicology which will eventually change perspectives radically about the hazards or otherwise of pesticide traces in food. Hormesis is described as the paradoxical effect of toxins at low concentrations. The paradox is that although most chemicals are toxic at high concentrations (or dose), the majority are likely beneficial at low concentrations (or dose). The common regulatory assumption is that if a chemical is toxic at high dose it continues to be toxic but with diminishing toxicity as the dose is lowered. In contrast, hormesis indicates that many chemicals have the opposite effect at low doses to those at high doses. There are a number of common examples that are in the hormetic category. A tablet of aspirin a day is recommended to improve the circulation; 50 tablets a day will not improve the circulation 50 fold, but likely see its complete cessation. This activity in not unlike most pharmaceuticals. The recommended daily intake of vitamin A is 1-3 mg/day; teratogenic effects appear at 9-10mg/day. Fluoride at 1 part per million in drinking water strengthens teeth against decay; 100 ppm is definitely poisonous. Copper is essential for plant growth but rapidly becomes toxic as the concentration in the soil increases.
It is unlikely that just one mechanism is responsible for the hormetic response. A good example is sunshine/UV-exposure. At low concentrations sunshine beneficially induces the formation of vitamin D. At higher levels, protective melanin formation ensures that potentially higher and future UV stress can be tolerated. But exposure to large doses of UV without protection causes oxidative damage to the skin, overwhelms protective mechanisms, and potentially initiates skin cancer. This sequence is a fair analogy to the response to many chemicals. Hormetic protective mechanisms were probably essential for hunter-gatherers who ate a varied diet containing many potentially toxic chemicals in fruit and vegetables. The large number of natural pesticides in fruit and vegetables may exert the known protective effects against cancer that result from a diet high in fruit and vegetables. Possible conclusions include the idea that there are safe doses for many chemicals and that the effects of low concentrations of toxins such as pesticides can be directly beneficial by decreasing cancer incidence or increasing growth. For more information see http://www.belleonline.com. (Anthony Trewavas FRS, University of Edinburgh, UK, via AgBioView via AgNet, 1/7/03).
