|MadSci Network: Medicine|
Jeff, you ask:
How is harmfulness of radiation measured? [and] Is there is a flat line that defines harmfulness?
Further you write:
I wanted to do a project on how radiation affects living things. I didn't choose a specific type of radiation, but will probably use several sources of electromagnetic radiation around the house (such as the microwave oven, cell phone). I wasn't sure of how to measure the effects of radiation. My teacher suggested exposing planarian worms to these types of radiation and see if it affects their reproduction rate... I wasn't very sure if the worm reproduction idea was a very accurate way to measure the effects of radiation...the radiation from the cell phone is not strong enough to have measurable effects on the worms...I have also heard somewhere about a liquid that simulates the electrical properties of human tissue and is used to determine the SAR of cell phones. Are you familiar with this material and if it is possible to make a similar material at home?
There are a lot of different issues here.
It seems that you are interested in a specific kind of radiation, since you mention microwave ovens and cell (mobile) phones. The type of radiation they produce is called radiofrequency (RF) radiation or microwaves (MW).
You are correct to suspect that the level of radiation from a mobile phone or leaking from a microwave oven will be too low to affect Planaria. In fact, this level of RF radiation is not high enough to affect any known biological systems. The RF radiation levels inside a microwave oven are high enough to cause biological effects, but those effects are due to the heating and are not very different from the effects caused by other kinds of heat..
For exposure to RF radiation, the things we measure are the exposure (called power density and measured in milliwatts per square centimeter, mW/cm-sq) or the absorption rate (called SAR and measured in watts per kilogram, W/kg). Neither of these things can be measured without some very specialized and expensive equipment.
The hazard (harmfulness) of exposure to RF radiation depends on the SAR. For whole body exposures below about 4 W/kg, no biological effects of RF radiation have been proven to exist. Since the laws in the US limit the maximum SAR from a mobile phone to a peak of 1.6 W/kg in any one gram of tissues, the whole body exposure is far to low to cause any biological effects. For whole body exposures above 4 W/kg, the chance and the potential seriousness of injury increases; but there is no exact "line" that separates "safe" and "unsafe".
You are also correct that there is a special liquid that is used to measure
SAR in models of humans, but for most purposes plain water would also do
okay. And just having this liquid would not help you measure SAR, you
would still need the meausrement equipment. For a photo of this equipment
and a longer discussion of how SAR measurements for mobile phones are done
KR Foster and JE Moulder: Are mobile phones safe? IEEE Spectrum, August 2000, pp 23-28. which is on line at:
The bottom line is that there are probably no consumer sources of RF radiation that are powerful enough to cause reproducible biological effects unless you do it by cooking in a microwave oven. This would also be true of power-frequency electromagnetic fields and static electromagnetic fields. The only common source of non-ionizing radiation that I can think of that would be powerful enough to cause biological effects would be visible light (particularly sunlight).
Medical College of Wisconsin
Electromagnetic Fields and Human Health
Some source material available on the net:
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