It's interesting that you claim there is absolutely nothing to back up the belief that it is our exposure to chemical toxins in the environment, caused by industry and nonorganic farming, which is to blame for the soaring rates of cancer over the past 30–40 years.1 How can you say in one fell swoop that our food is safe if you haven't conducted extensive research to establish that significant levels of various chemicals are never inserted into the food supply system? You can't, but you choose to anyway, at risk to us all.

And then there is the effect of antibiotic resistance – no small issue – and the pollution of our environment, which again comes back to human beings via the water supply and other chemical exposures. It's easy to dismiss the whole organic movement with one or two sentences, but your argument is not good science. In...

The three letters on organic food1 reiterate misunderstandings about organic food and farming that would require a lengthy article to rebut. However, two issues stand out. First, natural pesticides are found in all fruits and vegetables and are made by plants to efficiently kill herbivores. What we eat every day contains natural carcinogens, teratogens, chromosome breakers, estrogen mimics, sterility-inducing chemicals, nerve toxins, blood-disorder agents, and goitrogens in gram quantities. These represent, by a factor in the thousands fold, the major chemical exposure of all human beings.

Second, when food is sold off-farm, the minerals it contains must be replaced or the soil becomes deficient. Current sources of minerals used by organic farmers are manure and straw produced on conventional farms, nonrenew-able mined sources (such as rock phosphate), and rock weathering, which has reduced African soils to the seriously depleted state many currently experience.

Organic farming, in its reliance ultimately on nonrenewable materials (or conventional manure), is no more sustainable than conventional farming. It is a niche ideological agriculture that can exist only within the framework of rich countries that can tolerate agricultural variability because most of the population relies on conventional, cheap, and abundant food.2

Anthony TrewavasUniversity of Edinburgh

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