P2.2 Which types of electromagnetic radiation harm living tissue and why?
When living cells absorb radiation, damage can occur in different ways:
- The heating effect can cause damage
- Ionising radiation, such as ultraviolet radiation, can damage cells, causing ageing of the skin
- Ionising radiation can cause mutations in the nucleus of a cell, which can lead to cancer
- Different amounts of exposure can cause different effects, e.g. high-intensity ionising radiation can kill cells leading to radiation poisoning
MICROWAVES are strongly absorbed by water molecules, which means microwaves, can be used to heat objects containing water – there is water in all food substances.
Microwave ovens have a metal case and a wire screen door – this reflects the microwaves and protects users by preventing too much radiation from escaping. The door screen also absorbs microwaves, protecting users from the radiation.
There may be a health risk from the low-intensity microwaves of mobile phone handsets and masts, though evidence for this is disputed because the intensity of the microwaves is too low to damage tissues and microwaves are not ionising.
One health risk which is definitely present in our environment is ultraviolet, in sunlight. Not much of the ultraviolet reaching the Earth gets to us because the OZONE LAYER (a thin layer of gas in the Earth’s upper atmosphere) absorbs most of it.
The energy from the ultraviolet radiation causes CHEMICAL CHANGES in the upper atmosphere when it is absorbed by the ozone layer, but these changes are REVERSIBLE.
Without the ozone layer, the amount of ultraviolet radiation reaching Earth would be very harmful to living organisms, especially animals due to cell damage.
Other physical barriers are used to protect people from ionising radiations:
- Sun-screens
- Clothing can absorb most of the UV radiation – preventing skin cancer
- X-rays are absorbed by dense materials so they can be used to produce shadow pictures of our bones or of objects in aircraft passengers’ luggage
- Radiographers are protected from radiation by dense materials such as lead and concrete