How safe is x-ray inspection?
A question we are often asked, especially by food manufacturers and processors, is “how safe is x-ray inspection of food?”
Here we explain the difference between x-ray radiation and radioactivity and provide some of the evidence to show that the level of x-ray radiation used in our inspection procedures is not harmful to food and other products.
What are X-Rays?
X-rays are invisible as they are a form of electromagnetic radiation, like light or radio waves. All types of electromagnetic radiation are part of a single continuum known as the electromagnetic spectrum. The spectrum runs from long-wave radio at one end to short wave gamma rays at the other.
The wavelength of x-rays enables them to pass through materials that are opaque to visible light. The transparency of a material to x-rays is broadly related to its density and that’s why x-ray inspection is so useful as a quality tool. The denser the material, the fewer x-rays that pass through. Hidden contaminants, like glass and metal, show up under x-ray inspection because they attenuate more x-rays than the surrounding food.
X-ray inspection systems should not be associated with radioactive materials such as uranium. Radioactive materials are physical sources of radiation. They emit radiation in the form of alpha particles, beta particles, and gamma rays– and they do it continuously, which is why they cannot be switched off. The only way to contain radiation from a radioactive material is to encase it in a substance that absorbs radiation.
X-rays used for inspection are different. Like light from a bulb, they can be turned on and off at will. Switch off the electricity supply to the x-ray system, and the flow of x-rays ceases instantaneously.
Radiation in Everyday Life
X-rays are just one of several naturally occurring sources of radiation. The combined effect of all these sources is known as background radiation – and humans have been exposed to it since the beginning of time. Our modern daily dosage is higher than for previous generations because the radiation used in medical science has contributed to an increase of background radiation received by about 18%. That might sound like a big increase, but the overall levels are so small that the increase is negligible.
The chart below shows the four major sources of radiation that add up to the background radiation received by a typical person.
Putting Radiation Doses into Context*
From the point of view of occupational exposure, the accrued radiation dose is the most important measure. Occupational exposure limits are given in terms of the permitted maximum dose. The SI unit of radiation dose is the sievert (Sv). As occupational exposure levels are normally low, smaller units – millisievert (mSv: a thousandth of a sievert) or microsievert (μSv: a millionth of a sievert) – are more commonly used. The radiation dose rate measures the rate at which radiation is absorbed over time. This is expressed in μSv/h (Dose Rate = Dose (μSv) ÷ Time (hours)).
For the average human, natural background radiation contributes about 2,400 μSv (2.4 mSv) of radiation in a year from natural sources. This typically far exceeds the radiation exposure received from an x-ray inspection system in industry. The typical maximum dose rate immediately adjacent to an x-ray inspection system is <1 μSv (0.001 mSv) per hour. Which means an operator would receive 2,000 μSv (2 mSv) per year when working 50 weeks a year and 40 hours each week in direct contact with an x-ray system.
Naturally occurring radiation comes from outer space. Our daily dose is small because the atmosphere filters most of it out. The filtering effect declines with altitude. Those who fly absorb more x-rays than those who stay on the ground.
A frequent flyer, for example, absorbs around 8% more radiation 200 μSv (0.2 mSv) than a non-flyer. The frequent flyer’s typical annual dose is about 2,600 μSv (2.6 mSv) a year. Pilots and cabin crew absorb more still: about 4,400 μSv (4.4 mSv) a year, depending on routes flown and total flying time. Their annual dose of radiation is typically greater than workers at a nuclear plant – and almost twice as high as those who spend their lives at ground level. Even so, the frequent flyer’s additional dose of radiation is extraordinarily low.
Although it is of little concern the effect of x-ray inspecting a road wheel or a suitcase there is naturally reason to be cautious when inspecting items which may be ingested such as food or pharmaceutical products.
Food processors use x-rays in two ways:
(1) to inspect food for contaminants or quality control, and
(2) to irradiate food (a process that destroys bacteria)
The technologies have one similarity – both processes involve radiation – but that is where the similarity ends. Dose levels equivalent to several orders of magnitude* separate food irradiation from food inspection.
X-ray inspection of food, pharmaceuticals or any other product does not cause it to become radioactive, just as a person does not become radioactive after having a chest x-ray.
There is scientific evidence to show that x-rays do not harm food. A 1997 study by the World Health Organisation (WHO) confirmed that food radiation levels up to 10,000 Gy does not affect food safety or nutritional value. That means the food was subject to radiation doses around ten million times as great as those used in x-ray inspection. It proved that the food remains safe to eat and that it loses none of its nutritional value. This view is supported by the experience of leading brands across the world. Those that have already switched to x-ray inspection find that consumers experience no change in the quality other than the improvement by the removal of undesirable contamination.
The dose levels used in x-ray inspection are less than one ten millionth of those used in the WHO study. Food that passes through an x-ray inspection system spends about 250 milliseconds in the x-ray beam. During that short time it receives a radiation dose of around 200 ?Gy (0.2 mGy). The levels are so low that organic food can be subject to x-ray inspection with no diminution of its organic status.
In comparison to x-ray inspection the dose levels for food irradiation are much higher and range from 500 Gy up to 10,000 Gy in approved protocols for food items. (Source: Radiation Threats and Your Safety, Armin Ansari, 2010, page 311)
Whichever way you look at it, food that has passed through an x-ray inspection system is as good and tasty to eat as it was before it was scanned. There are no measurable changes to flavours, textures, or nutritional values: food that has been x-rayed is indistinguishable in every respect from food that hasn’t.
Please also read this article, ‘The use of X-rays in food inspection‘, by the European Food Information Council (EUFIC).