Radioisotopes in Food & Agriculture

• The Food and Agriculture Organization of the United Nations estimates that about 735 million people (about one in ten) were suffering from chronic undernourishment in 2022.
• Radioisotopes and radiation used in food and agriculture are helping to reduce these figures.

The attributes of naturally decaying atoms, known as radioisotopes, give rise to their multiple applications across many aspects of modern day life (see also information page on The Many Uses of Nuclear Technology).

Food irradiation

Some 25-30% of food harvested is lost as a result of spoilage before it can be consumed. This problem is particularly prevalent in hot, humid countries.

Food irradiation is the process of exposing foodstuffs to gamma rays to kill bacteria that can cause food-borne disease, and to increase shelf-life. It has the same benefits as when food is heated, refrigerated, frozen, or treated with chemicals, but does not change the temperature or leave residues. In all parts of the world there is growing use of irradiation technology to preserve food. More than 60 countries worldwide have introduced regulations allowing the use of irradiation for food products including spices, grains, fruit, vegetables, and meat. It can replace potentially harmful chemical fumigants that are used to eliminate insects from dried fruit and grain, legumes, and spices.

Following three decades of testing, a worldwide standard was adopted in 1983 by a joint committee of the World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO), and the International Atomic Energy Agency (IAEA). In 1997 another such joint committee said there was no need for the earlier-recommended upper limit on radiation dose to foods. The IAEA and FAO are working together with the International Plant Protection Convention (IPPC) and the Codex Alimentarius Commission to standardize worldwide use of irradiation for foodstuffs.

In addition to inhibiting spoilage, irradiation can delay ripening of fruits and vegetables to give them greater shelf-life. Its ability to control pests and reduce required quarantine periods has been the principal factor behind many countries adopting food irradiation practices.

As well as reducing spoilage after harvesting, increased use of food irradiation is driven by concerns about food-borne diseases as well as growing international trade in foodstuffs which must meet stringent standards of quality. On their trips into space, astronauts eat foods preserved by irradiation.

Whilst food irradiation has consistently been shown to be safe in clinical studies, consumer concerns have largely limited its use to imported spices and fruits in the USA and Europe. The relevant bodies in each jurisdiction stipulate that foods that have undergone irradiation must be labelled accordingly.

Food irradiation applications

Radiation is also used to sterilise food packaging. In the Netherlands, for example, milk cartons are freed from bacteria by irradiation.

Fertilisers

Fertilisers are expensive and if not properly used can cause water pollution. Efficient use of fertilisers is therefore of concern to both developing and developed countries. It is important that as much of the fertiliser as possible finds its way into plants and that a minimum is lost to the environment. Fertilisers 'labelled' with a particular isotope, such as nitrogen-15 or phosphorus-32, provide a means of finding out how much is taken up by the plant and how much is lost, allowing better management of fertiliser application. Using N-15 also enables assessment of how much nitrogen is fixed from the air by soil and by root bacteria in legumes.

Insect control

Estimates of crop losses to insects vary, but are usually significant. Despite widespread use of insecticides, losses are likely to be of the order of 10% globally and often notably higher in developing countries. One approach to reducing insect depredation in agriculture is to use genetically-modified crops, so that much less insecticide is needed. Another approach is to disable the insects.

Increased awareness of the adverse effects of significant pesticide use on public health and the environment has led to efforts to control insects and pests via alternative methods. Radiation is used to control insect populations via the Sterile Insect Technique (SIT). This involves rearing large populations of insects that are sterilised through irradiation (gamma or X-rays), and introducing them into natural populations. The sterile insects remain sexually competitive, but cannot produce offspring. The SIT technique is environmentally-friendly, and has proved an effective means of pest management even where mass application of pesticides had failed. The IPPC recognizes the benefits of SIT, and categorizes the insects as beneficial organisms. SIT is distinct from classical biological control (e.g. augmentation), offering a series of desirable differences:

• Introduced insects are not self-replicating, and so cannot become established in the natural environment.
• SIT impacts only the targeted pest’s reproductive cycle, and so is species-specific.
• SIT does not involve the introduction of non-native species to an ecosystem.

SIT was first developed in the USA and has been used successfully for more than 60 years. At present, SIT is applied across six continents. Since its introduction, SIT has successfully controlled the populations of a number of high profile insects, including: mosquitoes, moths, screwworm, tsetse fly, and various fruit flies (Mediterranean fruit fly, Mexican fruit fly, oriental fruit fly, and melon fly). Three UN organizations – IAEA, FAO, WHO – along with the governments concerned, are promoting new SIT programs in many countries.

SIT was used very successfully in the eradication of the screwworm in southern USA, Mexico, and Central America and Panama. Screwworms are parasitic insects that are potentially fatal pests to all warm-blooded animals. Females lay eggs into soft tissues (open wounds or orifices). The larvae, when hatched, burrow through the host flesh creating infections that attract more females.

In 1998 screwworm was discovered in Libya. A major national and international response utilising SIT prevented its spread to the rest of Africa and the Mediterranean Basin. The campaign successfully eradicated the infestation.

Major SIT operations have been conducted in Mexico, Argentina, and northern Chile against the Medfly (Mediterranean fruit fly), and in 1981 this was declared a complete success in Mexico. In 1994-95 eradication was achieved in two fruit-growing areas of Argentina, and 95% success achieved in another, as well as in Chile. The program has been extended to all of southern South America and to Africa.

SIT has been effective on the Medfly in southern Africa and is now being applied to codling moths which damage citrus crops. The IAEA and FAO are assessing the potential of using SIT against sugarcane borers, as well as consolidating codling moth management to support the apple and pear export industries.

A number of the most fertile parts of Africa cannot be farmed because of the tsetse fly, which carries the parasite trypanosome that causes African trypanosomiasis (sleeping sickness) and nagana (cattle disease). According to the IAEA, the presence of the tsetse fly prevents profitable livestock farming in almost two-thirds of sub-Saharan Africa, resulting in economic losses of $4 billion per year. However, SIT, in conjunction with conventional pest controls, is starting to change all this. Zanzibar was declared tsetse-free in 1997 and Nigeria has also benefited. With the support of the IAEA, Ethiopia has established the largest tsetse fly mass rearing facility in the world.

The most recent high-profile application of SIT has been in the fight against the deadly Zika virus in Brazil and the broader Latin America and Caribbean region.

Plant mutation breeding

Plant mutation breeding is the process of exposing the seeds or cuttings of a given plant to radiation, such as gamma rays, to cause mutations. The irradiated material is then cultivated to generate a plantlet, which is selected and multiplied if it shows desired traits. A process of marker-assisted selection (or molecular-marker assisted breeding) is used to identify desirable traits more quickly based on genes. The use of radiation essentially enhances the natural process of spontaneous genetic mutation, significantly shortening the time it takes.

The IAEA, jointly with the FAO, assists its member states in the development and implementation of plant mutation breeding. The technique has a number of important advantages: it is proven, quick, cost-effective, non-hazardous, and environmentally friendly.

Ionising radiation to induce mutations in plant breeding has been used for several decades, and some 3200 new crop varieties have been developed in this way. Gamma or neutron irradiation is often used in conjunction with other techniques to produce new genetic lines of root and tuber crops, cereals, and oil seed crops. New kinds of sorghum, garlic, wheat, bananas, beans, and peppers have been developed that are more resistant to pests and more adaptable to harsh climatic conditions. Countries that have used plant mutation breeding have frequently realized great socio-economic benefits:

• In Mali, irradiation of sorghum and rice seeds has produced more productive and marketable varieties.
• In Bangladesh, new varieties of rice produced through mutation breeding have increased crops three-fold in the last few decades. During a period of rapid population growth, the use of nuclear techniques has enabled Bangladesh, and large parts of Asia in general, to achieve comparative food security and improved nutrition.
• In Namibia, mutation breeding has produced seeds of the country’s most important crops – cowpea, sorghum, and pearl millet – that have yields increased by 10-20%. The new varieties are more resistant to drought, temperature stress, and pests – essential attributes in Namibia’s difficult growing environment.
• Across many IAEA member states, coffee plants are threatened by a fungal disease known as coffee leaf rust. The IAEA, together with the FAO and the OPEC Fund for International Development (OFID), is training scientists from the plant’s principal growing region, South America, to implement plant mutation breeding.