The World of Nuclear Science

Food and Agriculture

Tracers like those used in medicine are also used in agriculture to study plants and their intake of fertilisers. The usage of tracers allows scientists and farmers to optimise the use of fertilising and weedkilling chemicals. Optimisation of these chemicals is desirable because it saves money, and reduces chemical pollution. When fertilisers are used in overly excessive amounts, the excess will run off and pollute rivers nearby, as well as possibly seeping through to the water table underground and polluting the water supply. To prevent this, studies are conducted to find out the optimal amount of chemical required, with fertilisers and weedkillers often tagged by nitrogen-15 or phosphorus-32 radioisotopes. These radioisotopes are analysed in the crops to see how much of the original chemical was actually consumed by the plants, compared to how much was given.

The ionising radiation from radioisotopes is also used to produce crops that are more drought and disease resistant, as well as crops with increased yield or shorter growing time. This practice has been in place for several decades, and has helped feed some third-world countries. The collection of crops that have been modified with radiation include wheat, sorghum, bananas and beans.

About 10% of the world's crops are destroyed by insects. In efforts to control insect plagues, authorities often release sterile laboratory-raised insects into the wild. These insects are made sterile using ionising radiation - they are irradiated with this radiation before they hatch. Female insects that mate with sterile male insects do not reproduce, and the population of the insect pests can be quickly curbed as a consequence. This technique of releasing sterile insects into the wild, called the sterile insect technique (SIT), is commonly used in protecting agricultural industries in many countries around the world.

The technique is considered to be safer and better than conventional chemical insecticides. Insects can develop resistance against these chemicals, and there are health concerns about crops treated with them.

The largest application of this technique so far was conducted in Mexico against Mediterranean fruit-fly and screwworm in 1981. It was highly successful, and over the next 10 years the eradication program yielded about US$3 billion in economic benefits to the country.

SIT is in use in several countries, with support from the UN Food and Agriculture Organisation (FAO) and the International Atomic Energy Agency (IAEA). Australia is a large producer of many fruits and sterilises up to 25 million fruit fly pupae per week.

Ionising radiation is used as an alternative to chemicals in the treatment and preservation of foods. A French scientist first discovered that radiation could be used to prolong food shelf life in the 1920s and it became more widely used in World War II. Today, astronauts often eat radiation-preserved food while on space missions.

In meats and other foods of animal origin, irradiation destroys the bacteria that causes spoilage as well as diseases and illneses such as salmonella poisoning. This allows for a more safer food supply, and meats that can be stored for longer before spoilage. Additionally, irradiation also inhibit tubers that cause fruits and vegetables to ripen. The result is fresh fruits and vegetables that can be stored for longer before ripening.

The irradiation technique is particularly important when exporting to countries with tropical climates, where foods can be spoiled easily due to the warm temperatures.

Irradiation of food is carried out using accelerated electrons (beta radiation), and ionising radiation from sources such as the radioisotopes cobalt-60 and cesium-137. X-rays are also sometimes used. None of these sources of radiation used have enough energy to make the exposed foods radioactive.

Inside the food treatment plant there is a conveyor belt or similar system that transports the food to the radiation source, so that workers do not have to move close to the radiation. The source is packaged in a pencil like device, about 1cm in diametre. The room where irradiation takes place is shielded by concrete walls to prevent radiation from escaping into the environment, although the radiation risk is considerably much less than that from a nuclear reactor. Where gamma radiation is used from a radioisotope source, the radioisotope is stored in a pool of water while not in use, to also help prevent radiation from escaping. However, the plant is in many ways similar to any other - refrigeration is still important. No process can make food completely spoil-proof.

Food treatment plants of this kind are monitored closely by government health and occupational safety authorities to ensure safe working conditions for employees, as well as safety to any nearby residents.

Food irradiation is a well-tested process. Scientists have performed numerous decades of research, and it has been shown that irradiation will not cause significant chemical changes in foods that may affect human health, nor will it cause losses that may affect the nutritional content of food. (Chemical residues left behind by irradiation are in concentrations equivilant to about 3 drops in a swimming pool. Chemical-based preservatives and treatments usually leave more residues.) Taste is usually unaffected. The World Health Organisation and food safety authorities in many countries have approved irradiation as a safe method of food treatment and preservation.

Radiation-treated food is still not very widely used today. Despite the scientific evidence and approvals, many activist organisations claim that irradiation is unsafe and exploit the lack of public awareness and concerns about food safety and nuclear issues. Some even say that irradiation is a way that governments can utilise nuclear wastes left over from weapons testing or power generation. (However, the wastes left cannot be used in food processing because they do not provide the right type of ionising radiation.) Consequently, these scare tactics deter the public and some food producers are reluctant to use irradiation for fear of consumer boycotts. However, a recent survey conducted in mid-1998 by the Food Marketing Institute (a United States organisation) revealed that less than one percent of all those surveyed identified irradiation as a concern. Most said that spoilage and microbial hazards were of great concern - they very problem that irradiation addresses. Another study by an academic revealed that about 99% of consumers were willing to buy irradiated food after they were shown scientific data and irradiated food samples. This compared to 50% before shown this data.

Irradiation poses less of a risk to human health than many chemical treatments that are used today, which include the addition of chemical preservatives. The use of radiation is sometimes favoured to using chemical preservatives, because no allergic side-effect results. It is also better than heat-sterilisation because irradiation does not destroy nutrients and vitamins, whereas heat treatment does.

Irradiation is inexpensive - typical costs are about 1-20 cents per kilogram of food irradiated.

About 40 countries worldwide allow irradiation of foods. Depending on the country, irradiated foods may need to be labelled.

Ionising radiation is used to rid goods of parasites and bugs before they are exported out of a country. The radiation kills these parasites that may be quarantine hazards in other countries.

The technique is used in Australia to clear primary produce materials such as raw wool and wood for export. It is also used worldwide in transporting archival and historical documents. This is beneficial in that any microorganisms existing in the paper that cause paper deterioration are destroyed.

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