Organic farmers are allowed to use a number of pesticides as long as they come from a natural source. Pyrethrum, an extract of chrysanthemum flowers, has long been used to control insects. The Environmental Protection Agency in the U.S. classifies it as a likely human carcinogen. There you go then, a “carcinogen” used on organic produce! Does it matter? Of course not. Just because huge doses of a chemical, be it natural or synthetic, cause cancer in test animals, does not mean that trace amounts in humans do the same. Furthermore, pyrethrum biodegrades quickly and residues are trivial. But that is the case for most modern synthetic pesticides as well! And how about rotenone? This compound was discovered in the 1800s in the extracts of the root of the derris plant. Primitive tribes had learned that the ground root spread over water would paralyze fish which then floated to the surface. Rotenone is highly toxic to humans and causes Parkinson’s disease in rats. It has been used by organic farmers to control aphids, thrips, and other insects on fruit although it is being phased out. Residues probably pose little risk to humans, but synthetic pesticides with the same sort of toxicological profile have been vilified.
Organic farmers are also free to spray their crops with spores of the Bacillus thuringiensis (Bt) bacterium which release an insecticidal protein. Yet, organic agriculture opposes the use of crops that are genetically modified to produce the same protein. Isn’t it curious that exposing the crop to the whole genome of the bacterium is perceived to be safe, whereas the production of one specific protein is looked at warily? The truth is that the protein is innocuous to humans, whether it comes from spores sprayed on an organic crop or from genetically modified crops. True, organic produce will have lower levels of pesticide residues but the significance of this is highly debatable.
A far bigger concern than pesticide residues is bacterial contamination, especially by potentially lethal E. coli 0157:H7. The source is manure used as a fertilizer. Composted manure reduces the risk, but anytime manure is used, as of course is common for organic produce, there is concern. That’s why produce should be thoroughly washed, whether conventional or organic. Insect damage to crops not protected by pesticides often leads to an invasion by fungi. Some fungi, like fusarium, produce compounds which are highly toxic. Two varieties of organic corn meal once had to be withdrawn in Britain because of unacceptable levels of fumonisin, a natural toxin.
Are organic foods more nutritious? Maybe, marginally. When they are not protected by pesticides, crops produce their own chemical weapons. Some of these, various flavonoids, are antioxidants which may contribute to human health. Organic pears and peaches are richer in these compounds and organic tomatoes have more vitamin C and lycopene. But again, this has little practical relevance. When subjects consumed organic tomato puree every day for three weeks, their plasma levels of lycopene and vitamin C were no different from that seen in subjects consuming conventional puree. In any case, we simply are not going to feed 7 billion people organically.