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Radiation in the environment
In this section:
Depleted uranium
What is depleted uranium?
Naturally occurring uranium ores contain uranium in a mixture of isotopes. Natural uranium has about 99.3% 238U and 0.7% 235U, and a trace of 234U. The fuel used in light water reactors requires the proportion of 235U to be enriched to 3-4%. Some reactors such as fast reactors require considerably higher enrichment percentages. Uranium from which some 235U has been removed is termed depleted uranium and typically is made up of about 99.8% 238U and 0.2% 235U.
Why is depleted uranium used in weapons?
Uranium has a density of 19.05 g/cm3, which is almost twice that of lead. Its metallurgical properties are such that projectiles made from it are able to withstand the high firing velocities of modern weapons. Uranium-based shells fired from tanks and aircraft are able to penetrate and destroy heavily armed tanks at greater ranges than other types of anti-tank shells.
Other information can be found by following the link below:
The World Health Organisation has published a Fact Sheet on Depleted Uranium.
Environmental radioactivity monitoring programme
Atmospheric transport of materials from a distant source is a likely means by which remote countries such as New Zealand and the Pacific Islands could receive radioactive contamination. The NRL has monitored atmospheric radioactivity in the New Zealand and South Pacific regions since 1960, initially for radioactive fallout from nuclear weapons tests, though the present monitoring is intended to provide warning of any influx of radioactivity into the region from any source and to monitor trends in levels.
The Environmental Radioactivity Monitoring Programme has three monitoring components:
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Atmospheric radioactivity is monitored at stations located at Kaitaia and Chatham Islands, New Zealand and at Rarotonga, Cook Islands. These stations are part of the Comprehensive Nuclear Test-Ban Treaty International Monitoring Network.
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Radioactivity in deposition is monitored at a station located at Hokitika that consists of two different wet and dry deposition collection traps - a large area rain collector (1 m2) and a small area rain collector (0.2 m2).
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Radioactivity in milk is monitored in dairy milk powders from the Auckland, Taranaki and Westland regions.
The programme serves as the basis of consumer, government, and commercial advisory services concerning radioactivity, and is the basis of comparisons of the environmental radioactivity status of the South Pacific region with that of other regions.
Monitoring results are published each year in an Environmental radioactivity annual report. The latest report NRL-F/88 contains results for 2008 and can be viewed here (PDF - 170 kB). A hard copy (free-of-charge) is available by contacting the Publications Team.
Contact: the NRL's Environmental Laboratory.
Food irradiation
How does it work?
Food is irradiated by exposing it to a source of ionising radiation.
The ionising radiation usually is in the form of gamma rays from a source of 60Co (a radioactive isotope produced by irradiating cobalt in a reactor), or from a non-radioactive source (electron beam) generated from electricity. Electron beam technology does not require the use of radioactive source material, and can be "turned on and off".
As the radiation interacts with the food it causes changes in its biochemistry. With high doses, the radiation damages the genetic material of contaminating organisms (eg, microorganisms, insects) so that they can no longer survive or multiply. This is analogous to pasteurisation, where food is made safer to eat by bacteria being destroyed. However, unlike pasteurisation, it can be used on solids as well as liquids. Lower doses change the biochemistry of the food to inhibit sprouting and delay ripening.
Does irradiation cause the food to become radioactive?
The food does not become radioactive for two reasons:
First, the radiation used cannot make foods radioactive. Second, in the case of gamma radiation, the food never comes into direct contact with the source, so it is not possible for the food to become contaminated with the radioactive material.
Infrared radiation
IS 13 Infrared radiation contains information on sources, applications, biological effects, protection and recommended limits.
Natural radiation
Is natural radiation dangerous?
There is a wide range of sources of natural radiation to which we are being continuously exposed. Of these sources, the most familiar to us is the sun which produces infrared radiation that we feel as warmth, visible light, and ultraviolet light. The other sources are cosmic radiation which consists of high energy particles and rays that originate from outside our earth, terrestrial radiation which comes from naturally occurring radionuclides in the earth's crust, and internal radiation from radioactivity that is naturally present in our bodies.
Of these radiations, only one could be considered "dangerous", and that is the ultraviolet light from the sun. Over-exposure to the sun's ultraviolet light can prematurely age the skin, turning it hard and leathery, and can also cause sunburn which has in turn been linked to skin cancer. Unless we take precautions to cover up when outside it is easy to receive a fairly nasty sunburn. Although the nature of cosmic, terrestrial, and internal radiations is inherently hazardous and can cause cancer, these sources are not normally dangerous to us because the levels that are present naturally are sufficiently low that the risk of harm is negligible.
Cosmic radiation levels increases with altitude however, and some precautions may need to be taken for aircrew repeatedly flying on long distance flights to limit cosmic radiation doses. (More information can be found in IS 19 The exposure of New Zealand aircrew to cosmic radiation.)
Terrestrial radiation levels vary widely and while in some locations they are substantially higher than in other areas there is no clear evidence of increased incidence of cancer. New Zealand has a relatively low terrestrial radiation level.
More information can be found in IS 5 Sources, effects and risks of ionising radiation.
Power lines
Are the electric and magnetic fields around power lines dangerous?
It is not clear that there are any health effects caused by living near power lines. If there are effects, they must be rare because they have not shown up strongly or consistently.
A lot of research has been carried out over the past twenty years to investigate whether the electric and magnetic fields produced by the voltages and currents on power lines may be harmful. Such fields are present around any electrical wiring, electrical appliances or other equipment. The research has been reviewed several times by various national and international groups, with the conclusion that there is at worst only weak evidence suggesting that there might be any effects. Although some studies have suggested that there may be an association between living near power lines and a small increase in the incidence of childhood leukemia, other studies do not find such associations, and laboratory research does not support there being any link.
The field strengths around any particular line depend on a number of factors, such as the arrangement of the conductors, the current being carried, etc. The strength of the fields decreases quite rapidly with increasing distance from the line, and for many lines the field strengths 50 metres from the line are similar to those found in many houses and offices.
More information can be found in our free booklet:
Electric and magnetic fields and your health (PDF - 1325 kB).
The US National Institute of Environmental Health Sciences research programme on electric and magnetic fields can be found here. Amongst other items, you can download a booklet "Questions and Answers about EMF" published in June 2002, and an NIEHS report on health effects from exposure to power-line frequency electric and magnetic fields, released in 1999.
Research in this area is monitored in New Zealand by an interagency committee reporting to the Director-General of Health. Periodically this Committee prepares a report to Ministers. The most recent report, which covers both radiofrequency and extremely low frequency fields, was published in November 2004 and is available here (PDF 161 kB).
The WHO has a continuing project investigating possible health effects of electromagnetic fields, including the low frequency fields from power lines and other electrical equipment and cabling. The project's home page can be found here. A review of the research on low frequency electric and magnetic fields and health was published by the WHO in June 2007. The WHO has also prepared a Fact Sheet giving an overview of the findings.
UV radiation
Information on ultraviolet radiation can be found in the Information sheet:
IS 10 Ultraviolet radiation