Science Buddies: "Ask an Expert"

Background Information
I am doing a science fair project for school. I am testing chemical v. physical sunscreen using titanium dioxide and zinc oxide on _____ breeding rates. Should I test this on drosophila or an earth worm? The earth worm experiment would take longer to do, but I think it would be easier to apply the sunscreen. I would put the chemical sunscreen in the food because human skin would also absorb the chemical sunscreen. I would just rub the physical sunscreen on the worms outside body. The drosophila would take shorter time, but how can I apply the sunscreen to the flies?
Independent variables = oxybenzone, homosalate, titanium dioxide and zinc oxide
Dependent variables = breeding rates

Question list
1. Should I use worms or flies?
2. How would I apply the sunscreen to either?
3. How would I measure the breeding rates? Can I just count and see if there is another egg or worm
4. Is this a good project idea?

Thanks!

Hello!

This sounds like an interesting project idea! As you said, using fruit flies would take less time since they breed faster than worms. That would give you more of an opportunity to observe multiple generations of flies and see if the sunscreen causes any changes in their physical appearance or the number of new flies that are born. The problem is that you probably wouldn’t be able to apply sunscreen to the flies because they’re too small. Since humans rub both physical and chemical sunscreens on the outside of their skin, having the animals eat the chemicals in their food wouldn’t be the same as having it on their bodies.

If time is not an issue for you, worms would probably be the easier and cheaper option. Red worms might be a better choice than earth worms because they can survive at room temperature. Earth worms can only live at cooler temperatures, so if you leave them at room temperature for more than a day they probably won’t survive. Worms are still pretty small, so you still might have some trouble rubbing the sunscreen on their bodies. Maybe you could try using a cotton swab to very gently rub it on. You should be able to measure the breeding rate by counting the number of new worms that appear in the habitat.

If applying the sunscreen to the worms ends up being too hard, you might want to try adding it into the soil instead. Since the sunscreen we wear gets washed off while we're outside, this experiment could be a model for how sunscreens could impact the soil and the health and behavior of the animals that live in it.

I hope this helps! Let me know if you have more questions.

Just a thought, it might work to dilute your sunscreens down with a bit of water and apply them with a spray bottle. I also like the idea of applying it to the soil, though!

Seems like a cool project, let us know how it goes.

Hello,

Very interesting and important project idea! Sunscreen pollution especially in soil and water can be harmful to ecosystems and marine life, so testing the breeding rates of organisms in relation to the presence of sunscreen on/in organisms is so important.

To build on your project to test the effects of sunscreen on the environment (including earthworms and fruit flies), you could create a small ecosystem or habitat for your organisms to test this effect. Your experiment could include creating a habitat for either the earthworms or fruit flies, including soil. For this experiment, you could collect data pertaining to the nutrient content in soil using test strips. For example, here are some test strips that would allow you to measure nitrogen, phosphorus, and potassium levels in soil that you can purchase: https://www.carolina.com/environmental- ... /181875.pr

(Note that it would be a good idea to test for oxygen content in the soil too for this project, and this kit does not include oxygen tests)

For this experiment idea after you add soil to your ecosystem/habitat, the next step would be to measure the soil nutrient levels (using test strips) before you add the sunscreen into the habitat through the organisms. I recommend a method similar to what my fellow intern suggested to apply the sunscreen to these organisms: create a mixture of about 2/3 sunscreen and 1/3 distilled water in any clean spray bottle and use a light spray to apply the sunscreen to your organisms (if the sunscreen mixture is too thick to spray out of the bottle, just add more distilled water). After you find and count your next generation of organisms, test the soil nutrient content again. For this experiment, you will also need a "control" which essentially means a non-manipulated ecosystem or habitat, in this case, to compare to. In other words, allow another group of the same organisms you use for the project to live and breed in a separate habitat without adding the sunscreen so you can compare the results of your addition of sunscreen to the habitat containing the organisms you sprayed the sunscreen on. This will help you to measure the effects of sunscreen on breeding rates by looking at the numbers of organisms in each habitat at the end of your experiment.

In addition to the spray bottle method, I also recommend using your idea of adding sunscreen to the organisms' food along with applying the sunscreen to the outside of organisms.

To measure breeding rates, your idea of counting the number of new organisms should work for this project. Make sure to record all your data in a notebook, such as the number of organisms, so that it is easy to monitor any changes in this number. You can also use the idea above to monitor the effect of sunscreen on breeding rates (by comparing sunscreen effects in one habit to the control habitat) while including the soil component in the project if you would like.

Fruit flies do multiply very quickly and are used in many science experiments, so this may be a better choice than earthworms for your project if you don't have a lot of time.

Hope this helps and feel free to reach out with more questions!
-cnoonan180