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Name: M. R.
Status:  student
Age: 13
Location: N/A
Country: N/A
Date: 3/26/2004


Question:
I am doing a science fair experiment on "the mutations of small animals caused by different types of radiation" and I was hoping you could be a source. We were not sure if our Fruit Flies were mutating because of inter-breeding or because of the radiation we were applying to them. So can microwave radiation cause minor mutations in plants and/or animals? and can it affect the heart rate of small creatures such as goldfish?


Replies:


The NEWTON BBS staff needs to point out that this student's experiement is misconceived and we are posting this question to deter other students from following the same design. Parental or teacher infput is necessary for this type of activity.

M.R.

Not all radiation is the same. The kind that may cause mutations is of high frequency and short wavelength -- ionizing radiation. Microwaves are much lower in frequency and longer in wavelength than visible light. If a microwave oven is your source of "radiation" all you can be certain of is that you're exposing the fruit flies to a potentially agonizing death because microwaves simply boil the water in the tissue of the flies.

Indeed, microwaves can alter the heart rate of goldfish because the heating process affects their comfort level. Bear in mind: microwaves are absorbed by water. If the goldfish is in water while in the oven, you're simply cooking the fish alive. I don't think you intend to be cruel to the creatures in your experiment. It is neither wise nor compassionate to place any living critter in an operating microwave oven.

I suggest you read quite a lot more on the subject of ionizing radiation and the electromagnetic spectrum in general. I doubt if you can find a legal source of ionizing radiation that you could safely use in your proposed experiment.

Regards,
ProfHoff 836


Hmmm...I am not sure you understand what "mutations" are. A mutation...in simple terms ...is a change in the DNA base code. Mating of fruit flies and observing the physical traits of the offspring will often produce (depending on the genetic makeup of the parent flies) a large array of new traits in the offspring, sometimes because of recessive genes and sometimes from more complex reasons but NOT necessarily from mutations. Consider breeding a chocolate lab retriever with a bloodhound...the offspring would look quite different and we would not say the offspring looked different from the parents because of mutations.

Investigations on the genetic effects of microwaves on bacteria, fruit flies, plants and mammalian cells in tissue cultures to my knowledge have not produced any reliable evidence that microwaves induce mutations other than through the heat it imparts to the system. Mutations increase with increased temperature. A good control, in this case would be to cause a similar rise in temperature in a "warm room" and look for any differences in mutations. The problem in your system is discerning a mutation from a recessive trait that just shows up in breeding your flies.

pf


Your first name, please?

Your experiment causes me some concern. I would need to know more about it.

What is the frequency of your microwave radiation?

What level of microwave radiation are you applying to your goldfish?

How were you going to measure the goldfish's heart rate?

How will you make the microwave radiation intensity small, and how will you measure it's strength, so you know how much "stimulus" you are applying, to cause the (heartbeat) effect?

Honestly, is this a prank letter?

Sounds like you are walking right on the border between "scientist" and "Mad Scientist". No insult intended; please just notice the difference. I'll explain.

I gotta tell you, if you are merely nuking your goldfish in a plastic cup full of water, no matter how short, this experiment seems verging on cruel to me, and is against the rules in the science fair I have worked for. Your project likely will not be admitted. Applying enough radiation to heat the flesh of the animal, one must presume the animal can feel this, and it likely doesn't feel good. Besides, it's kind of no scientific surprise that being cooked in a pot induces mutated offspring, or makes a heartbeat speed up. In addition to thermal effects, there may be nerve effects, such as numbing, possibly permanent, or a sensation of sound resembling whatever modulation your microwaves have, lasting only while the microwaves are on.

To treat this like a scientist, you need to clearly distinguish between "direct" effects of radiation, and indirect effects due to heating by the radiation. Reducing the intensity to where it causes no noticeable heating is the main way to do that.

Years ago, the relatively lax U.S. microwave radiation limit for people once was 10mW/cm2 (0.01 Watt per square centimeter), or the start of perceptible body-warming. Other countries decided to be afraid of sneakier things like cancer and mutations, and they set their legal limit to 0.1mW/cm2. Your legitimate range of microwave intensity for a mutation experiment would be in between these two numbers.

To do those lower intensities, the power of a microwave oven is just too high. In a typical microwave oven, the total power is 1000 Watts at 2.45 GHz (2,450,000,000 cycles per second). The biggest pot of water that fits inside is approximately a 20 cm cube, which would have a surface area of 2400 cm2. (1000 W) / (2400 cm2) = 0.4 W/cm2, or 40x times the maximum humane intensity. For intuitive comparison, the power intensity of sunlight on the warmest day is 1000 Watts per square meter, or 0.1 Watt/meter2.

You may say, what about running the oven at 10% power? Unfortunately, most ovens never really do 10% power, they do 100% power for 10% of the time. Typically it does ON for 3 seconds, then off for the remainder of 30 seconds. 3 seconds at 100% power is too much to apply to a live fish, in principle.

There are probably ways to modify the use of normal microwave oven, which will let in only a little power, and you can change how much. On the bad side, inventing this method would be a science fair project all by itself, because you would have to learn about radio waves and heat and metal and absorbtion rates, and find a way to measure your reduced power intensity. On the good side, I bet nobody ever did it before, and if you put it on the internet when you were done, other people would do it your way for years later, and it might get into some science experiment books. I am willing to give you advice on that.

If you still want to do "microwave effects" studies, we need to talk more. Sounds like you don't entirely understand mutations, for example. So please reply directly to my e-mail address, and answer the questions in the first two paragraphs.

Jim Swenson



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