The most commonly stated reason people buy organic food is avoidance of pesticide residues. Indeed, organic producers cannot use conventional synthetic pesticides, but that does not mean no pesticides are used. Soap-based herbicides and insecticides such as boric acid, lime sulfur, elemental sulfur and various oils are allowed. So is copper sulphate since it occurs in nature, although for agricultural use it is synthetic, made by reacting copper oxide with sulphuric acid. Curiously, the bacterium, Bacillus thuringiensis (Bt) is allowed for caterpillar control, but crops that have been genetically engineered to produce the toxin the bacterium uses to kill caterpillars are not allowed.

A variety of chrysanthemum grown mainly in Africa contains pyrethrins, chemicals the plant uses as protection against insects. A bug that dines on the flower’s leaves learns what indigestion is all about and looks elsewhere for its next meal. Organic farmers make use of this repellant effect by spraying crops with commercially available natural pyrethrins. But does the fact these substances are natural absolve them of potentially harmful effects? Not at all. Natural compounds can be every bit as dangerous as synthetics. Exposure to high doses of pyrethrins can cause neurological symptoms and has also been linked to liver tumours in mice and rats.

Now here is the kicker to this little story. Chemists have been able to improve upon natural pyrethrins. The molecular structures of these compounds have been determined and analogues that differ only slightly in structure have been synthesized. These are more powerful........

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