FEW ISSUES excite such intense argument as the use of irradiation to clean and preserve food. Supporters of the technique say that irradiated food is as safe and nutritious as food prepared and preserved by more conventional methods, such as cooking, freezing or smoking. They also say that the technique offers better opportunities for cleaning and preserving produce such as spices and fruit from tropical countries, and it can prolong the shelf life of a wide variety of food stuffs.
Opponents, however, say that irradiation is a technology ‘looking for a use’. They criticise the way it has been promoted by international bodies such as the World 91É«ÇéƬ Organization (WHO) and the UN’s Food and Agricultural Organization (FAO). These critics claim that irradiation can be used to disguise food that would otherwise be unfit for sale. They believe that the joint expert committees evaluating irradiation for the WHO, for example, have distorted their results to make the method seem safer than it really is.
Whatever the merits of the conflicting arguments, few methods of handling food have undergone such detailed scientific scrutiny. Irradiation techniques involve bombarding batches of food with gamma radiation, X-rays or accelerated electrons. The bombardment causes subtle chemical changes in the food that halt spoilage and kill contaminants such as bacteria.
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These changes arise from the creation and subsequent activity of short-lived and extremely reactive chemical agents, called free radicals. These are soaked up in food tissue almost as soon as they are created, but exist for long enough to kill bacteria and prevent food from rotting.
Exhaustive studies
Supporters of irradiation include the British government’s Advisory Committee on Irradiated and Novel Foods. They claim that exhaustive studies of irradiation carried out over the past four decades provide compelling evidence that food subject to less than the internationally recommended limit of 10 kilograys of radiation is safe to eat. They say that food which can be irradiated safely without spoiling its taste or smell includes poultry, seafood, fruit, vegetables and spices.
Since 1970, much of the research into irradiation has been managed jointly by the FAO, the WHO and the International Atomic Energy Agency (IAEA). The results are summarised in the reports of two expert committees which published their findings in 1976 and 1980. The second of these reports contained the recommendation that 10 kilograys be adopted as an international limit. It stated that, up to this level, irra diation could be considered a safe method of food preservation ‘which presents no toxicological hazard and no special nutritional or microbiological problems’.
Yet despite such assurances, and despite the WHO’s estimate that no more than 5 per cent of our food is ever likely to be irradiated, consumer organisations throughout the world continue to express reservations about the safety and the desirability of food prepared by the technique.
Their concerns, amplified through the mass media, have had a major impact on consumers, who have been demonstrating rising hostility to irradiation. For example, a recent survey in Britain carried out by Nielsen Marketing Research of Oxford in conjunction with the Henley Centre for Forecasting, showed that of 7000 respondents, 51 per cent felt that irradiated food would be ‘bad for them’, 6 per cent more than in a similar survey last summer. Only 8 per cent considered that irradiated food would be good for them.
One of the strongest critics has been the Consumers’ Association. Members of the association say that, even before the government begins to consider the legalisation of irradiation, it should force the food industry to observe stricter safety standards across the board.
‘Our biggest concern is that (irradiation) might let food producers off the hook,’ says Margaret Rogers, a researcher with the association. ‘We need to redress problems arising from lax food hygiene and standards before we even think about food irradiation.’
One thing, however, is clear. Many radical consumer groups oppose the irradiation of food uncompromisingly. They accuse both the food industry and national and international health authorities of promoting irradiation through claims that are misleading, taken out of context and illogical.
The misgivings voiced by such consumer organisations are summarised in the views of the International Organisation of Consumers’ Unions, which represents 170 consumer bodies in 70 countries. The IOCU says it fears that some food producers may use irradiation to make unwholesome food appear fit for sale. It is demanding a worldwide moratorium on the further use and development of the technique until methods of labelling irradiated food and distingushing it from non-irradiated food are available.
The international body also wants a ban imposed on the use of irradiation until what it sees as various outstanding safety and nutrition issues are resolved. It has expressed fears about the effects of irradiation on pesticide residues in food and on the chemicals within plastic packaging materials.
The London Food Commission is one group that has campaigned against irradiation for five years. Its criticisms are harsh. Two commission members, Tim Lang and Tony Webb, say in their book Food Irradiation – The Myth and the Reality: ‘There are serious questions about the objectivity and integrity of those in the food, nuclear and irradiation industries who promote food irradiation – questions that need to be put to those in government and science who have decided to approve its use.’
Webb accuses the expert committee set up by WHO, FAO and the IAEA of an ‘appalling misrepresentation of evidence’, and of systematic bias in its interpretation of the results. He says that 60 per cent of the research on which the evaluations are based has not been published in the open literature, and that much of it has not been subject to peer review.
Lang and Webb attach much significance to an investigation carried out in India 15 years ago. This examined what happened to five severely malnourished children who were deliberately given chapatis made with freshly irradiated wheat. It found that they subsequently developed increased levels of polyploidy, a naturally occurring syndrome caused by the presence of cells containing abnormally high numbers of chromosomes.
The organisers of the study, from the National Institute of Nutrition in Hyderabad in India, halted the trial when these effects became evident. Polyploidy returned to normal levels in all the children after about eight months.
However, the organisers continued with similar experiments on laboratory animals. Their results showed that polyploidy recurred, in addition to other health effects, such as damage to sperm, an increased incidence of miscarriages, and a reduced immune response.
Lang and Webb say in their book that when the IAEA repeated the experiment on animals, it fed the subjects with oils that supplemented the vitamin content of their diet, and so distorted and ameliorated the results. The WHO has since answered this allegation, and many others about irradiation, in a reply to concerns raised by the IOCU.
The WHO acknowledges that irradiation does destroy some vitamins. It says that in many feeding studies aimed at discovering what other damage irradiation might do, animals received vitamin supplementation. The effects of eating highly irradiated food would otherwise have been indistinguishable from the expected effects of vitamin loss.
‘Half truth’
Johannes Friedrich Diehl, director of the Institute of Nutrition and Physiology at the Federal Research Centre for Nutrition in Karlsruhe, West Germany, describes the criticisms of the London Food Commission as ‘a lot of half truth and exaggeration’.
Diehl is a member of the WHO’s expert advisory panel on food safety, and has personally studied the effects of irradiation on the chemical composition of food. He says that ‘the whole thing has been blown up out of proportion because the num ber of foods listed (for irradiation) is very small’. He estimates that by the year 2000, no more than 5 per cent of our food will be irradiated.
Diehl also dismisses the contention that irradiation can mask stale produce. ‘The spoiling of food cannot be reversed. If it smells, irradiation will make it smell worse,’ he says. Moreover, he says, critics of irradiation have paid too little attention to the effects that rival processes have on food. Indeed, Lang and Webb’s book devotes little space to such comparisons – which, according to supporters of irradiation, are the best context in which to judge the technique.
Geoffrey Campbell-Platt, professor of food technology at the University of Reading, and another supporter of irradiation, says that vitamin losses occur more during home cooking than in irradiation, particularly in the case of potatoes and vegetables boiled in water. He adds that the known chemical products generated by irradiation are found in ordinary stored or cooked food anyway.
Similar views are expressed by Alan Holmes, the director of the Leatherhead Food Research Association. ‘The biggest proof that it (irradiation) is safe is that you can’t detect it,’ he says.
Other scientists who back irradiation take the same line, but are desperately seeking analytical methods with which food inspectors can distinguish irradiated from non-irradiated food. The British government is determined to legalise irradiation, irrespective of whether such a test is available, according to David Maclean, junior minister at the Ministry of Agriculture, Fisheries and Food with responsibility for overseeing aspects of irradiation. Like other governments, however, it is funding work which will, it hopes, eventually lead to the development of satisfactory assays .
But the lack of an adequate test at the present time is one of the main reservations that consumer organisations have about irradiation. Their fear is that inspectors will have no way of checking whether shops are selling irradiated food illegally without labelling it.
The London Food Commission has produced evidence of cases where, it says, abuses of the technique have already taken place. The authors call the practice ‘Dutching’, because the cases they have documented have all taken place in Holland, where irradiation is already permitted. France and Belgium also permit irradiation.
Maclean says that when irradiated produce is finally permitted on supermarket shelves in Britain – perhaps early next year – strict policing will be in operation to stamp out such abuses, and to catch and punish offenders. ‘We’re working to clean up food throughout the chain,’ he says.
The UN agencies are also keen to rebut consumer allegations about the integrity of their research. ‘It’s part of a normal and useful venture that we selected scientists and experience from the best of the scientific community, just as we have done in the past 40 years of scientific endeavour at the WHO,’ said Friedrich Kaferstein of the Food Safety Unit of the WHO.
‘Even if there was just one member of the committee ‘bought off’ by commercial interests, his opinions would be outweighed by the other members,’ he says.
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How DNA can help to detect the telltale signs
IRRADIATED food is so similar chemically to unirradiated food that analysts have faced considerable difficulties in developing tests that food inspectors can use to distingush the two. However, they have recently been making steady progress towards this goal.
The best-documented technique for distinguishing irradiated products is electron spin resonance (ESR). The method not only shows if food has been irradiated, but can also indicate the amount of irradiation that has been applied to it.
ESR is mainly useful for food that contains bone, fragments of bone, or shell. When food is irradiated, reactive chemical agents called free radicals are generated. The bulk of these are so-called hydroxyl radicals, which originate from the water contained in meat, fruit and vegetables.
The free radicals decay instantly into stable radiolytic products, except for those which get trapped in hard tissue, such as bone, where they can remain for at least 10 years – and can even survive cooking. It is these surviving radicals that ESR is capable of detecting.
The technique of ESR is not new. It was first used in 1958 to measure dosage of radiation in radiation accidents. However, researchers in Berlin abandoned attempts to use ESR for detecting irradiated food in 1970, after failing to make the technique work successfully.
John Swallow and Nick Dodd of the Cancer Research Campaign’s Paterson Institute for Cancer Research in Manchester, revived the technique in the mid-1980s, and in 1985 published the first of several papers outlining its potential for use in the analysis of irradiated foods.
The drawback of ESR, as Dodd and other researchers point out, is the cost of the analytical equipment. An ESR spectrometer costs between Pounds sterling 50 000 and Pounds sterling 200 000, which is too expensive for many public health laboratories.
Two other techniques, also relying on the detection of free radicals, could reveal whether consignments of spices have been irradiated. The techniques, called chemiluminescence and thermoluminescence, both detect the radicals by stimulating them in different ways to discharge detectable levels of light. These techniques are currently being studied at the Scottish Universities’ Reactor Centre at East Kilbride in Scotland.
But perhaps the most novel technique currently being developed is one funded by the Ministry of Agriculture, Fisheries and Food. This technique identifies changes in the DNA of irradiated food. Brigid Hoey and her colleagues at the Paterson Institute in Manchester have already applied the procedure to samples of prawn and chicken with some success, and they plan to evaluate its application to a wider range of foodstuffs in the near future.
The Manchester researchers have found a way of singling out abnormal bases created in the DNA of the food which has been irradiated. They use enzymes to label the abnormal DNA with phosphorus-32, a radioactive isotope. After processing the sample to reduce the abundance of normal bases, the analysts manipulate what remains to isolate and detect the tagged bases through high performance liquid chroma tography.
‘Vegetables might pose some problems,’ says Hoey, ‘because it’s more difficult to extract the DNA.’ However she adds that she expects to have evolved a practical method for analysing food routinely within 18 months.
