Science: Is organic food safe?

It is certainly more popular than ever, with supermarkets competing fiercely to offer more lines. But shunning modern methods of agriculture brings its own risks.

Among the distinctly unpleasant odours emanating from the controversy surrounding food safety, one area of agriculture has come up smelling sweet. In the welter of adverse publicity concerning BSE, E coli poisoning and genetically modified (GM) food, organic produce has acquired the mantle of purity and healthiness.

In fact organic food has never been more popular. People assume that it is natural, non-industrialised and therefore problem-free. But just how safe is organic farming?

Investigations both in Europe and in the US have failed to find any difference between organic food and other food in terms of all the major constituents, minerals and vitamins. Every day, each of us eats a quarter of a teaspoonful of carcinogens; 99.99 per cent of these are made naturally by all plants - whether organic, GM or intensively farmed - to inhibit disease organisms and deter consumption by animals and insects.

The remaining 0.01 per cent comes from food preparation and agricultural activities; in part these are carcinogens derived from the frying and smoking of food. Government regulations set this 0.01 per cent level at a concentration between 10,000th and 100,000th of the recommended safe dose.

Pesticide residues are lower in organic food - but not absent. Organic farmers are allowed to use pesticides, but apply them more sparingly and tend not to use the broad-spectrum pesticides - although pyrethrum (a common fly-killer spray) is permitted, because it is found naturally in some plants. Regulations vary from country to country, but antibiotics such as streptomycin are acceptable if they are derived from fermentation.

Organic enthusiasts believe that they are eating the diet of our grandparents; but food safety regulations were not common a century ago, and food contamination by micro-organisms producing mycotoxins - fungal poisons - was much more extensive then. Regulations have changed the situation in only a limited way.

The use of effective fungicides has reduced the risk from mycotoxins in normal food, but not necessarily in organic food. Health-store nuts, for example, may contain aflatoxin (made by the fungus aspergillus), the most potent known carcinogen.

For this reason, microbiological spoilage of organic food is a recognised problem, and most organic produce is rushed more quickly into market; the benefit is that it often tastes fresher. But constant exposure to mycotoxin carcinogens can be expected to have long-term effects, detectable only by continual monitoring. However, there are no current plans to carry out this monitoring.

Such data is hard to find. Alongside the introduction of intensive but strictly regulated agriculture during the last 50 years, human longevity in Britain has increased by five to six years, to its probable biological maximum. Can we claim the same for organic food? No long-term data of comparable present-day organic consumption is available, except with small farming communities such as the Amish in the US. However, consumption by these people of their own completely fresh produce negates direct assessment of the effects of transport and storage on the safety of micro-organisms.

Organic farmers can and do use modern crop varieties, since they have disease resistance and good yields. However these varieties (of, for example, wheat, barley, oats, tomatoes, turnips, sugar beet, blackcurrants, potatoes) acquired their genes from different species by difficult laboratory procedures; for example, rice obtained genes from sorghum wheat. These are not natural plants and they don't survive in fields unless continually cultivated.

These genetically manipulated plants have been used in agriculture for 50 years, starting with triticale (1 million hectares planted world- wide). There has been no noticeable impact on the environment or health of communities, or distrust of organic food, from the incorporation of these foreign genes. More generally, no crop plant can be seriously regarded as completely "natural"; the first act of domestication is to select desirable individuals from the available gene pool and thereby to diminish genetic variability.

There are four concerns about whether organic food is safe. Organic farmers preferably apply cow or pig manure when this is available. It can be infected with the dangerous bacterium E coli 0157 disease organism that lives happily in the guts of cattle. Infection in human beings kills, or leaves victims without functioning kidneys.

Citrobacter freundii lives in pigs' guts and is also potentially lethal. If manure is pasteurised, or if you properly cook contaminated food, then the organism is killed. The problem is to guarantee that this is done.

Oversights do occur. Two outbreaks of E coli 0157 in the US were traced to organic strawberries and lettuce. In Aberdeen, home-made organic goats' cheese initiated an E coli outbreak among children; in Germany an outbreak of Citrobacter that killed one child and damaged nine others was traced to organic parsley treated with pig manure.

Organic farmers use sulphur as a weak pesticide. But sulphur contains lead, a known danger. What is not known is how much of the lead is transferred to the food we eat.

Similarly, organic farmers are allowed to spray crops with bacterial spores to act as a general-purpose insecticide. But earlier this year these spores were found to cause serious, often fatal, lung infections in mice, and to infect wounds and damage human cells in culture. Some people suggest that this technique should be curtailed until further investigations are carried out. And while many organic farmers do use the spores sparingly, serious insect infestations still have to be treated. The image of an organic farmer with spray gun, mask and protective suit does not create a feeling of a natural technology.

Finally, plants react vigorously when attacked by disease organisms and synthesise many chemicals that are carcinogenic. Thus organic cider from apples has much higher patulin levels, and celery has higher levels of psoralen which, without careful harvesting, can cause serious skin burns. Much more investigation is needed into the carcinogen content of organic food as it is sold.

The list goes on. Organic foods cost more, because the farming is more labour-intensive and suffers greater losses to weeds and insects. Organic manures are less effective than chemical fertilisers. To institute organic farming countrywide would mean ploughing up wilderness, hedges and woodland to make up the shortfall compared to intensive farming, and putting people back into farm labour - generally associated with poor pay and long hours. Efficient farming releases land for animals and plants that cannot easily co-exist with any form of agriculture.

But exciting possibilities do exist. To combine the power of genetic modification with an efficient, sustainable agriculture free of requirements for crop sprays. The philosophy of minimal impact upon the world ecosystem is the right one to safeguard the future. You might call it a "third way" of agricultural technology - employing the best of the organic ethos and GM procedures. I, for one, would welcome it.

Professor Anthony Trewavas is a research scientist at the Institute of Cell and Molecular Biology at the University of Edinburgh

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